FINAL – 26/09/10 IF0124 - Development of an integrated ...randd.defra.gov.uk/Document.aspx?Document=9846... · FINAL – 26/09/10 . IF0124 - Development of an integrated farm management

FINAL – 26/09/10

IF0124 - Development of an integrated farm management framework and approaches for livestock farming systems.

WP3. To quantify, where appropriate, the potential of Integrated Farm Management (IFM) approaches to reduce the environmental impact of livestock farming.

Dr Dave Chadwick and Dr. Tom Misselbrook (Rothamsted Research - North Wyke, Okehampton, Devon EX20 2SB, UK)

Dr. Agustin del Prado

(Basque Centre for Climate Change, Bilbao, Spain) AIM To use modelling to quantify the potential impact of selected potential Integrated Farm Management (IFM) practices on the environment: including gaseous emissions; nitrous oxide, nitric oxide, methane and ammonia emissions; and water pollution – nitrate losses for a number of different livestock farming systems (dairy, beef, sheep, pig and poultry). APPROACHES Work packages 1 and 2 established a list of >90 management practices that would support Integrated Farm Management (IFM). A number of these management practices were selected to determine their impacts on production and environmental losses. The criteria for the selection of management practices that were followed in this modelling phase were based on whether the models available could be used to investigate the specific practice. For example, none of the models could investigate the effects of animal breed on production and environmental losses, since this component is not currently reflected in model structures and output. However, where possible management practices within each of the IFM management categories were included in the modelling. The list of IFM practices that were applied to the model dairy, beef & sheep farm typologies are shown in Table 1, whilst Table 2 summarises the IFM practices applied to the model pig and poultry farm systems.

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Table 1. Management practices investigated using models to determine their effect on productivity and the environment on Dairy and Beef & Sheep farm typologies. Management practice Typology

1. Animal Health

2. Animal Nutrition Use of higher quality feeds for better efficiency, e.g. increased use of maize silage in the diet

Dairy

Use of low crude protein diets Dairy 3. Nutrient management

Reduce fertiliser N use, e.g. reduce by 20% Dairy, Beef, Sheep Methods of manure application to land; shallow injection

Dairy, Beef*, Sheep*

Methods of manure application to land; rapid incorporation

Dairy

Covering slurry stores Dairy Use of nitrification inhibitors Dairy Use of anaerobic digestion on farm Dairy 4. Housing and Environmental Control Bedding type; a move from slurry to FYM system

Dairy, Beef, Sheep

Use of lower stocking density systems, e.g. reduce stocking rate by 10-20%

Dairy, Beef, Sheep

5. Land and Soil Management

6. Enterprise type Extended grazing Dairy, Beef , Sheep *combined with IFM practice to switch from FYM to slurry

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Table 2. Management practices investigated using models to determine their effect on environmental losses on the pig and poultry farm typologies. Management practice Typology

1. Animal Health

2. Animal Nutrition Use of phase feeding Indoor pigs

3. Nutrient management Frequent removal of manure from house Indoor pigs, Poultry Frequent removal of manure from house via converting deep pit laying hen system to belt manure removal

Indoor pigs, Poultry

Use of mechanical separation of manures and slurries

Indoor pigs

Solid manure storage: composting Indoor pigs, Poultry Solid manure storage: covering heaps Indoor pigs, Poultry Method of manure applications; band spreading Indoor pigs Method of manure applications; rapid incorporation


4. Housing and Environmental Control Bedding type: Change from slurry to solid manure system

Indoor pigs

Bedding type: Changes from solid manure to slurry system

Indoor pigs

Use of lower stocking density systems, e.g. reduce stocking rate by 10-20%

Indoor pigs, Outdoor pigs, Poultry

Use of powered ventilation systems e.g. install air scrubbers to buildings

Indoor pigs

Use of renewable energy sources; grow biomass crops

Outdoor pigs

Use of renewable energy sources; incinerate poultry manure

Poultry

5. Land and Soil Management Establish areas of vegetation on site for conservation purposes; permanent woodlands

Outdoor pigs

Establish areas of vegetation on site for conservation purposes; establish new hedges

Outdoor pigs

Establish areas of vegetation on site for conservation purposes; establish tree shelter belts around buildings and manure stores


Establish buffer strips Outdoor pigs 6. Enterprise type

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Models In order to simulate the effect of different IFM practices on emissions of nitrous oxide (N2O), methane (CH4), ammonia (NH3), other oxides of nitrogen (NOx), and nitrate (NO3

-) losses to waters, model runs were carried out using existing modelling approaches. SIMSDAIRY (del Prado et al., 2006; del Prado and Scholefield, 2006) was used for modelling effects of farming practices on productivity, losses of nitrogen to air and water, and indices of other farm benefits on dairy systems. NGAUGE (Brown et al., 2005) was used to investigate nitrogen losses from beef and sheep systems, whilst NARSES (Webb and Misselbrook, 2004; Webb et al., 2006) was used to investigate management practices on NH3 emissions from pig and poultry systems. Table 3 summarises the environmental and production outputs that each model generated for the different farming systems. Table 3. Environmental and production outputs from the models used. Dairy Upland beef and

sheep Lowland beef and sheep

Indoor and outdoor Pigs

Poultry

SIMSDAIRY N2O, CH4, CO2, GHG, NOx, NH3, NO3, C sequestration, Milk yield Milk composition Biodiversity index Landscape index Animal welfare index Soil quality index

- - - -

NGAUGE - N2O, NO, NH3, NO3, CH4, C storage, GHG

N2O, NO, NH3, NO3, CH4, C storage, GHG

- -

NARSES - - - NH3 NH3 SIMSDAIRY For dairy systems, the SIMSDAIRY (Sustainable and Integrated Management Systems for Dairy Production) is a modelling framework which integrates existing models for N cycling (NGAUGE: Brown et al., 2005; NARSES: Webb and Misselbrook, 2004), P cycling (PSYCHIC: Davison, in press), equations to simulate NH3 losses from manure application (Chambers et al., 1999), prediction of CH4 losses (Chadwick and Pain, 1997; Giger-Reverdin et al., 2003), cows’ nutrient requirements [Feed into Milk (FiM) system (Thomas, 2004)] and ‘score sustainability matrices’ for measuring attributes of biodiversity, landscape, milk quality, soil quality and animal welfare and an economic model (A. Butler, pers. comm). SIMSDAIRY is capable of simulating the effect of a wide range of farm management, soil and climatic factors on: (i) internal and external N and P flows, (ii) environmental losses (N2O, CH4, NH3, NOx, NO3 and P) and (iii) other aspects that affect the farm sustainability (e.g. net income, milk quality). Some sustainability matrices are scored by the submodel SIMSSCORE, which simulates the effect of both nutrient management variables (e.g. effect of unsaturation of fatty acids in the diet on milk yield) and non-nutrient management variables (e.g. available surface per cow during housing) on the sustainability of the farm in terms of biodiversity, landscape, milk quality, soil quality and animal welfare. The scores assigned reflect poor (0) to very satisfactory (6) sustainability. The main assumption of land use in the farm is that on-farm forage is assumed to be grass and/or maize. Within grasslands three types of land subtypes are allowed: grass for cutting-only, grass for dairy grazing (and cutting if required) and grass for young cattle grazing. SIMSDAIRY´s typical inputs include: average milk yield and concentration (N and butterfat) target per dairy cow, numbers of dairy and young cattle, mineral fertiliser N and P application

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rate in each land subtype, housing period, % of manure applied to each land subtype and timing and site conditions (soil type, history of the field, sward age, climatology). In the SIMSDAIRY modelling, the following assumptions were taken into account: (i) maize was always grown on-farm (i.e. when the requirement for forage maize is increased, the surface to grow maize is also increased proportionally), (ii) followers were not assumed to either incorporate maize in the diet or decrease their CP intake, (iii) CP intake was restricted by decreasing CP content in the concentrates and increasing the maize intake and (iv) whereas forage maize was increased about 50% in extended and medium dairy systems, maize intake remained the same in the housed/fully scenario (as there was already a high maize intake content) and (v) thereby, the housed/fully scenario decreased the CP content of the diet by only altering CP content of the concentrates profile. NGAUGE For modelling beef-sheep systems, we used a modified version of NGAUGE that is capable of simulating white clover-grass swards and is adjusted to beef and sheep animals. NGAUGE is an empirically-based mass-balance model which simulates monthly N flows within and between the main components of grazed or cut grassland system according to user inputs describing site conditions and farm management characteristics (i.e. monthly fertiliser and manure application) (Brown et al., 2005). NGAUGE is an improvement on existing N fertiliser recommendation systems in that it relates production to environmental impact and is therefore potentially valuable to policy makers and researchers for identifying pollution mitigation strategies. Main losses and flows simulated are as follows: Losses of N per ha in different forms: N2O (both from nitrification and nitrification), NH3, NOx, N2, NO3 leaching. Concentrations of N in the water-associated losses (average and peak NO3-N in the leachate). Grass offtake/uptake and total N and DM per ha (hence %N content in herbage). Methane losses from manure storage and application, and excreted dung during grazing were calculated according to emission factors for each potential source based on literature values (see: Schils et al., 2007). Emissions and N flows during housing were simulated following the approach by Webb and Misselbrook (2004). NARSES For pig and poultry systems, NARSES is a model that estimates the magnitude, spatial distribution and time course of agricultural NH3 emissions, together with the potential applicability of abatement measures and their associated costs (Webb and Misselbrook, 2004; Webb et al., 2006). Farm systems Information about typical livestock systems in the UK were taken from existing studies (e.g. DEFRA project: AC0209 for Dairy, Beef and Sheep, and WQ0106 for Pig and Poultry) and used to establish typical livestock scenarios in different UK regions for each sector. This information was used as input-data for SIMSDAIRY (dairy), NGAUGE (beef and sheep) and NARSES (pigs and poultry) and the outputs of environmental losses were expressed per hectare (for all farm typologies) and per kg of product (for dairy typologies only). SIMSDAIRY and NGAUGE are sensitive not only to management but also weather, topography and soil characteristics, so farming typologies were located on soils and climates typical for the sector. Tables 4 summarises some of the main characteristics of the farm typologies. The pig and poultry model runs were for NH3 emissions only (using NARSES), which is currently not sensitive to geographical location and soil type.

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Table 4. Site characteristics for the Dairy, Beef and Sheep model farm typologies. Farming typology

Intensity of

production

Location Soil texture

Drainage class

Annual drainage (mm/year)

Average annual air temperature

(oC) Dairy Intensive Wilts. Sandy loam Good 300-350 11.5 Dairy Medium Lancs. Loam Moderate >500 10.0 Dairy Extended Leicts. Clay loam Poor 300-350 11.5 Beef Lowland Devon Loam Moderate >500 11.0 Beef Upland Wales Loam Moderate 450-500 9.0 Sheep Lowland Devon Loam Moderate >500 11.0 Sheep Upland Wales Loam Moderate 450-500 9.0 The dairy, beef and sheep baseline typologies are similar to those used in project AC0209 (see Tables 5 and 6 for summary descriptions). The pig and poultry farms are based on the robust farm typologies (RFT) for specialist pig and poultry farms with no land base coupled to arable farms where pig manure is applied to combinable crops, and poultry manure is applied to root crops. The RFT sizes were all based on the 2006 Farm Business Survey, whilst the proportions of the land area occupied by each crop type and the stocking densities of each livestock type were derived from the Defra June Agricultural Census for 2004 for each farm type. Project WQ0106 details the adjustments required so that the England totals across all farm types agreed with the published census data. Table 7 summarises the key pig and poultry information. Table 5. Indicative characteristics of the dairy systems used in the modelling of production and environmental impacts of IFM practices Dairy – Wiltshire

Intensive (Indoors) Dairy - Lancaster Medium

Dairy - Leicestershire Extended grazing

Livestock numbers

500 lactating 137 followers



Milk yield (L/cow)

8625 7125 5700

Stocking rate (cows/ha forage)

2.7 1.8 2.1

Grazing days 60 192 290 Diet % grass silage % maize silage % concentrates

20 40 40

50 25 25

85 0 15

Fertiliser N rate* Cut grass Grazed grass Maize

300 NA** 40

300 210 40

310 230 --

% slurry applied to land Cut grass Grazed grass Maize

35 0 65

50 25 25

50 50 0

*Based on revised RB209, ‘Good’ Grass Growth Class, moderate SNS. ** High intensity/indoor systems are assumed to have grazed and cut (1 cut) grassland areas. Forage areas are calculated depending on animal requirements and diet by the SIMSDAIRY. Manure on the Dairy farm typologies is managed as slurry, 50% of the slurry generated is spread on cut grass on the medium and extended grazing systems, whilst 65% of the slurry

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is applied to maize and 35% to the grazing land on the intensive dairy system. Slurry is applied to grazed grass in approximately equal splits in April, June and September. The rates of fertiliser N used and timings of split applications on the dairy, beef and sheep farms were based on the revised RB209 (Anon, 2010). Table 6. Indicative characteristics of the beef/sheep systems used in the modelling of production and environmental impacts of IFM practices. Intensity

of system

Livestock numbers

Grazing days

Concentrate use (kg

DM/anima/yr)

Forage area

(ha)

Average N fertiliser

application rate

(kg N / ha)

% clover

in sward

Beef – Devon

Lowland

45 adults 76 young

200 170

600 200

75 grazed 15 cut

47 90

10

Beef – Wales

Upland 38 adults 34 lambs

200 170

50 0

85 grazed 60 cut

47 90

25

Sheep – Devon

Lowland 184 adults 170 young

330 180

125 0

75 grazed 15 cut

47 90

10

Sheep - Wales

Upland 360 adults 340 lambs

330 180

100 0

85 grazed 60 cut

47 90

25

Manure on the Lowland Beef and Sheep farming typologies is managed as solid manure (Farm Yard Manure – FYM). Approx 80% of the FYM is applied to grazing land, the remaining FYM is applied to cut grass. 40% of the FYM is applied in Feb-Apr, 15% May-Jul, 20% Aug-Oct and 25% Nov-Jan. In the upland Beef and Sheep systems, all the FYM is applied to cut grass with 40% applied in spring, 15% in June, 20% in September and 25% in December. Table 7. Indicative characteristics of the pig and poultry systems used in the modelling of production and environmental impacts of IFM practices (further detailed information about these model farm types and the arable cropping farms they are associated with can be found in Appendix 1). Intensity of

production Livestock numbers

Excreta (m3/yr)

% managed as manure

Land area

(ha)

Average N fertiliser

application rate (kg N / ha)

Pigs* Indoor 3,524 4,390 100 172 170 Pigs Outdoor 440 1,457 0 57 153 Poultry** Indoor 81,351 2,157 80*** 180 135 *the livestock rearing farm for indoor pigs is coupled with a combinable crops arable farm for this modelling exercise in order to reflect IFM management practices that can be introduced in the animal house, for manure management during storage and following manure applications to land. ** the livestock rearing farm for poultry is coupled with an arable farm growing root crops for this modelling exercise in order to reflect IFM management practices that can be introduced in the animal house, for manure management during storage and following manure applications to land. *** the remainder is sent for incineration. Before determining the potential effect of different IFM practices on environmental losses, model runs were conducted for the baseline scenarios for each farming typology. IFM practices were then run for each model farm and the percentage reductions from those

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baselines as a result of the IFM practices (listed in Tables 1 and 2) were then estimated following the modification of model inputs. Note: whilst it is tempting to take exact values provided by the model runs at face value, by their nature deterministic models are based on generic relationships, limited experimental data and several assumptions. Individual components have been validated, but it is rare that validation has been conducted on multiple N loss forms. Therefore importance should not be attached to the precise numbers. It is the relative magnitude of losses between systems and between different forms of N loss within a system that are more important, as well as the direction of change following the introduction of an IFM practice.

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RESULTS Results of the model runs to investigate the effects of IFM practices on production and environmental losses are discussed in turn for the dairy, beef, sheep, pig and poultry systems. DAIRY Baseline Losses Baseline losses of gaseous emissions, losses to water and C sequestration in soils are shown in Table 8, where units are expressed on a per ha basis. Table 9 summarises the same information on a per litre of milk basis. It is clear that the dairy farms are significant sources of NH3, N2O and CH4 as well as NO3 leaching. Table 8. Baseline losses of pollutants (expressed in kg/ha) from the model dairy farms in different geographical regions. kg/ha Milk

prodctn (litres)

NH3-N

N2O-N CH4 CO2 NOx C seqstn.

NO3 –N loss

Area of land

required (ha)

Wiltshire 11700 43 0.5 216 4808 0.46 301 37 356 Lancashire 11000 21 1.8 221 3287 3.12 355 27 77 Leicestershire 8800 30 4.3 195 2954 2.31 812 3 157 Table 9. Baseline losses of pollutants (expressed as g per litre of milk) from the model dairy farms in different geographical regions. g/litre of milk NH3-N

N2O-N CH4 CO2 NOx C seqstn NO3-N

Wiltshire 3.7 0.0 18.5 412 0.04 26 3.2 Lancashire 4.2 0.2 20.1 296 0.28 33 2.4 Leicestershire 3.5 0.5 22.2 330 0.26 59 0.4 Table 10 summarises the score indices for other on-farm benefits; milk composition, above ground biodiversity, animal welfare and soil quality. Sustainability scores range from 0 (poor) to 6 (very satisfactory). The net margin of the farming system is also indicated. Table 10. Baseline scores for other on-farm benefits. Score indices Milk

composition Biodiversity Animal

welfareLandscape Soil

qualityNet margin (£ per farm)

Wiltshire 1.9 1.5 1.8 3.0 2.8 389,600 Lancashire 2.5 2.1 1.6 3.0 1.2 47,700 Leicestershire 2.9 1.4 2.0 3.0 1.9 135,800 IFM Practices The SIMSDAIRY model management inputs were modified to reflect the different IFM management practices and the changes from the baseline milk production, nitrogen losses, carbon sequestration and sustainability scores were recorded. Table 11 summarises the changes from baseline for production, N and C losses and C sequestration on a per ha basis; whilst Table 12 summarises these changes from baseline on a per litre of milk basis. Table 13 summarises the changes from baseline for the sustainability scores and farm margin.

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Table 11. Effect of IFM practices on environmental losses from dairy farm systems (% change from baseline) (losses expressed per ha)

IFM practice Site and system applicability

Litres milk

N2O-N NH3-N CH4 CO2 NOx GHG C seq NO3-N

Use of higher quality feeds for better efficiency, e.g. increased use of maize silage in the diet

Lancs. (med) Leic. (ext)

1 1

6 5

-1 0

0 1

-1 -1

-11 -11

2 2

-6 -6

18 19

Use of low crude protein diets

Wilts. (int) 3 0 1 3 17 2 4 30 -6

Reduce fertiliser N use, e.g. reduce by 20%

All -7 -23 -11 -7 -12 -9 -13 2 -12

Methods of manure application to land; shallow injection

All 0 3 -13 1 0 -13 1 0 4


All 0 2 -9 0 0 -9 1

0 5

Covering slurry stores

All 0 0 -9 0 0 -9 0 0 2

Use of nitrification inhibitors

Leic. (ext) Wilts. (int)

2 1

-44 -63

8 1

2 2

2 2

-2 0

-12 -14

-5 4

-43 -45

Use of anaerobic digestion on farm

All 1 -9 -9 0* 1 -9 -76 0 15

Bedding type; change from a slurry to an FYM system 1000 kg straw/head 1500 kg straw/head 2000 kg straw/head

Lanc. (med) Wilts. (int)

0 0 0

57 51 45

0 -3 -4

10 10 10

0 0 0

1 1 1

23 21 20

1 1 1

-17 -17 -16

Use lower stocking density systems; reduce stocking rate by 10-20%

Wilts. (int) Leic. (ext)

-4 -14

-31 -33

-7 -15

-4 -12

-7 -19

-8 -14

-11 -19

3 12

-9 -17

Extended grazing; increase number of grazing days by 20%

Lanc. (med) Wilts. (ext).

0 -5

2 11

-3 1

0 -5

-2 -3

-1 69

-1 -4

5 -10

0 0

*SIMSDAIRY simulations do not currently assume a reduction in CH4 emissions from the stored slurry as a result of biogas production. This could be changed for future simulations, but it is worth noting that since 85-90% of all CH4 emissions form the farm are from the rumen of the dairy stock, even if AD can reduce CH4 emissions by 50% from this stored manure, then the overall percentage loss (per ha) would be relatively small.

Use of higher quality feeds for better efficiency, e.g. increased use of maize silage in the diet The amount of N excreted can be reduced by changing the composition of the diet to increase the proportion of dietary N utilised by the animal. For example, by optimising the balance of N to carbohydrate in ruminant diets. If the diet contains too little carbohydrate to provide the energy for rumen micro-organisms to utilise all the N present, the surplus N will be excreted in urine. Additional energy (carbohydrate) can be supplied by increasing the proportion of maize silage within the diet.

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Nitrous oxide emissions and NO3 leaching losses increased, and may be due to maize being less responsive to N fertiliser than grass. Reductions in fertiliser N and manures on maize land could improve N efficiency on maize land. Use of low Crude Protein diets Livestock are often fed diets containing N above recommended levels as a safeguard against a loss of production from feeding too little. Nitrogen in forage and feed is generally provided via the crude protein content. However, surplus N not utilised by the animal is excreted in dung and urine without providing any benefits to animal performance. Avoiding rations that contain more than the recommended content of N will reduce the amounts excreted without affecting growth or milk production. Nitrogen utilisation can also be improved by reducing the proportion of rumen-degradable protein in the diet. In non-ruminants the amount of N excreted can be reduced by increasing the digestibility of the ration. Utilisation can be increased in ruminants and non-ruminants by feeding a ration that supplies amino acids in the correct proportions required for protein synthesis. If supplies of one or two essential amino acids, such as methionine or lysine, are inadequate, they will limit the amount of protein synthesised and leave a surplus of other amino acids that will be excreted. The modelling illustrates a potential reduction in nitrate leaching as a result of the introducing this IFM practice. Reduce fertiliser N use, e.g. reduce by 20% A reduction in fertiliser N resulted in a decrease in milk production in this simulation. Although, a reduction in fertiliser use can be possible without affecting crop yield or quality, depending on the baseline current M fertiliser rate. Use of a good fertiliser recommendation system would ensure that the necessary quantities of essential crop nutrients are only available when required for uptake by the crop. Nitrogen would only be applied as mineral fertiliser when the supply of nutrients from all other sources was insufficient to meet crop requirements. As a result, the amount of excess nutrients in the soil is reduced to a minimum. Ensuring that other macro nutrients were present in the soil to ensure efficient plant N uptake an reduce losses would also be essential. The method would perhaps require investment in education and guidance Reductions in N fertiliser could have an immediate impact on all crops other than legumes. For most crops, any reduction in fertiliser N would cause a small but economically significant reduction in yield. For example, for winter wheat, a 10% reduction in fertiliser N (from the economic optimum) would result in a 1 - 3% reduction in yield. It is important that any reduction in fertiliser use should take account of the interactions between nutrients and not create an imbalance in the soil. A shortage of one nutrient may limit uptake of another and potentially increase losses of this second nutrient. There would be considerable resistance to the method, due to the impacts on crop yields and the inability to maintain a productive system. All environmental losses were reduced through introducing this IFM practice. Methods of manure application to land; shallow injection

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Ammonia volatilisation occurs from the surface of applied slurry, therefore reducing (for open slot shallow injection) or eliminating (for closed slot deep injection) the overall surface area of applied slurry will greatly reduce ammonia emissions. Slurry is delivered to the soil, either into shallow slots (5-10 cm depth, at 25-30 cm spacing) which are cut by preceding discs, or much deeper into the soil (about 25 cm depth) where slurry is placed behind a tine. Placing slurry into narrow open slots, via shallow injection, greatly reduces the exposed slurry surface area. Placing slurry deeper into the soil behind cultivation tines, as with deep injection, essentially eliminates the exposed slurry surface area. Diffusion of any NH3 present within the soil pore spaces to the surface is very much slower than emission directly from the soil surface. The ‘free’ ammonium content of the slurry placed within the soil will also be reduced through direct adsorption to clay particles and through the action of nitrifying bacteria, further reducing the potential for ammonia emission. Shallow injection is suitable for grassland where field slopes or stoniness are not limiting (estimated to rule out approximately 30% of agricultural land) and for arable land prior to crop establishment. Deep injection is suitable for arable land prior to crop establishment. Current deep injector designs are generally not suited to application to growing crops, where crop damage can be great. Slurry injection will be a slower operation, with lower application rates than conventional surface broadcast application. It will also require higher draught forces, so larger tractors will be required, particularly for deep injection. This may limit the application window, particularly early in the season to grassland. Additionally, injection to grassland under hot and dry conditions can result in significant sward damage and may not be that successful. Deep injection will generally achieve >90% reduction in NH3 emissions compared with surface broadcast application. The effectiveness of shallow injection depends on a number of factors including the application rate of slurry (injection slots can be overfilled at high rates) and soil conditions. The mean shallow injection reduction efficiency is estimated as about 70% (Smith et al., 2000; Misselbrook et al., 2002). Slurry injection will also greatly reduce odour emissions arising from application. Also, slurry will be applied much more uniformly across the entire application width in comparison with conventional broadcast application. Applying shallow injection (particularly of dilute slurries) on sloping land can result in run-off along the injection slots. With deep injection it is important to avoid slurry application directly into gravel backfill over field drains. Slurry placement into the soil will reduce crop contamination and can to some extent increase the window of spreading opportunity compared with surface broadcast application. Reducing ammonia emissions from the applied slurry increases the potential for nitrogen losses via nitrate leaching or nitrous oxide emissions, depending on time and rate of application Generally, if slurry is applied at an agronomically suitable time (e.g. spring/summer) and rate, the risk of pollution swapping will be minimal, although there is a small increase in NO3 leaching in this simulation. When slurries are injected, microbial pathogen are protected from ultra-violet radiation and can survive for longer as a result. Methods of manure application to land; rapid incorporation Applied slurries or solid manures are rapidly (within 4 hours, the sooner the better) incorporated into the soil by ploughing or with disc or tine cultivation. Incorporation into the soil greatly reduces the exposed surface are of the manure from which ammonia emissions can occur. Diffusion of any NH3 present within the soil pore spaces to the surface is very much slower than emission directly from the soil surface. Hence the modelling indicates a 9% reduction in NH3 emission from the dairy farms. The ‘free’ ammonium content of the slurry placed within the soil will also be reduced through direct adsorption to clay particles and through the action of nitrifying bacteria, further reducing the potential for ammonia emission.

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This method is applicable to manure applications to arable land prior to crop establishment, which accounts for approximately 50, 70 and 90% of applications of slurry (pig and cattle), poultry manure and pig/cattle FYM to arable land, respectively. The method could also be applied to grassland reseeds. Immediate incorporation (within 4 h) reduces emissions to a greater extent than leaving the manure on the surface for longer, e.g. 24 h (Webb et al., 2004), but may be impractical due to different work-rates of the manure application and cultivation operations. Rapid incorporation may require additional resources (machinery and labour) or the use of a contractor. This method will greatly reduce odour emissions following manure application. It will also reduce the risk of mobilisation of manure nutrients and pathogens in surface run-off waters. Reducing ammonia emissions from the applied manure increases the potential for nitrogen losses via nitrate leaching or nitrous oxide emissions, depending on the manure type (risks are greater for slurries and poultry manures), time and rate of application. If the rapid cultivation policy damages soil structure, this may compromise crop yields and result in applied inorganic fertiliser and organic manure N being poorly utilised by crops and at risk of leaching over the next winter drainage period. When manures are incorporated, microbial pathogens are protected from ultra-violet radiation and may survive for longer in the soil. However, as they are mixed throughout the soil matrix, they are less likely to be lost in surface run-off and via drain flow. Covering slurry stores Excluding rainwater from the store reduces the total volume produced and increases the number of days of storage capacity. This reduces the risk of losses from fields by providing greater flexibility about when to apply slurry to fields and by allowing lower application rates. Covering the slurry store also reduces emissions of ammonia and methane. Reducing the total volume of slurry produced is an alternative to providing additional storage volume. Both increase the number of days of storage capacity available. Farms are less likely to run out of storage in mid-winter and be forced to apply slurry when there is a high risk of losses occurring. Applications can be timed to avoid ground conditions when there is a high risk of run-off, which would transport N, P and FIOs to watercourses. Reducing application rates also lessens the risk of run-off. Spreading can be timed to coincide with periods when crops are actively growing and can utilise the nutrients in the slurry. Greater uptake from the soil reduces the amount of residual N available for leaching and loss as N2O. Fitting a cover will reduce ammonia losses during storage (as shown by the modelling) and, hence, produce a slurry with a higher N content. Most covers include some vents (to prevent a build up of methane), so emission will not stop entirely, but will be greatly reduced compared with a situation of free air movement above the slurry store. This method could be applied to all open slurry stores. There may be little benefit in applying the method to cattle slurry stores, where natural crusts often develop and give effective ammonia emission reduction. Therefore the method is most relevant to the pig sector (Portejoie et al., 2003). Little benefit will be gained from covering of very dilute slurry stores, so separate storage of slurry and dirty water is recommended with the slurry store being covered. Rigid covers are applicable to concrete or steel tanks, but may not be suitable for all existing stores (e.g. where the existing store has insufficient structural support for a rigid cover). Plastic floating covers are effective (Scotford and Williams (2001) and applicable to tanks and small earth-banked lagoons, but become increasingly difficult to fit and manage on

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larger lagoons. ‘Low technology’ floating covers (e.g. oil-based liquids, chopped straw, peat, bark, LECA balls) may be applicable to concrete or steel tanks, but the solid-based materials are probably not suitable on earth-banked lagoons, where wind drift can cause problems with retaining a complete surface cover. Consideration needs to be given as to how the cover impacts on store filling, mixing and emptying. A cover may increase the amount of N potentially available for leaching but will only be significant where measures are taken to reduce ammonia losses at spreading. If not, the ammonia that was saved during storage is likely to be lost anyway when the slurry is applied to the field. Preventing entry of rain into the store also increases the dry matter content of the slurry. This may increase ammonia volatilisation as there will be less infiltration of slurry into the ground. Nitrification inhibitors Adding a nitrification inhibitor to fertiliser N, liquid manures with a high ammonium content prior to spreading or direct to the pasture to effect applied fertiliser N, manure applications or urine deposition slows the rate of conversion of ammonium to nitrate at a rate that the crop can use (i.e. slow release), increasing N efficiency and reduces the risk of nitrate leaching and N2O emissions. The method works by reducing the amount of nitrate available for leaching or loss via denitrification. Nitrification inhibitors can potentially reduce nitrate leaching and N2O emissions markedly, as shown via the modelling. However, degradation of the inhibitor in the soil limits the duration of its effectiveness. Compounds such as nitrapyrin, dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) have been demonstrated to be effective in reducing N2O emissions from fertiliser and animal slurries. Chemicals such as DCD have been evaluated for reducing N losses from autumn applied slurries for many years, but have generally failed to gain acceptance with the farming community due to their poor cost-effectiveness in terms of giving yield benefits and reduced NO3 leaching losses (Chambers et al., 2000). However, Dittert et al. (2001) showed that inhibitors reduced N2O emissions by about 30% when they were mixed with slurry and injected into grassland in late summer. More recent research conducted in New Zealand, has shown that nitrification inhibitors can be extremely effective when added to mineral fertiliser or used with urine patches (Di et al., 2007; Moir et al., 2007), manures and even dosed to animals in reducing N2O emissions. In the laboratory, such inhibition has been shown to be potentially close to 100% efficient, while reducing to about 30% typically under field conditions (Hatch et al., 2005). Use of anaerobic digestion (AD) on farm Methane produced from slurries and manures has valuable potential to replace fossil fuel use. Processing in digesters that capture the CH4 for burning enables this energy to be used and at the same time reduces the global warming potential of the gas released into the atmosphere (CO2 instead of CH4). To increase CH4 yield, food ‘wastes’ are commonly added to the digestion process, although in this scenario digestate is digested slurry only. Additionally, the food ‘wastes’ provide a valuable source of income via gate-fees. *SIMSDAIRY simulations do not currently assume a reduction in CH4 emissions from the stored slurry as a result of biogas production. Therefore, there is a ‘0’ percentage change in Table 11. This could be changed for future simulations, but it is worth noting that since 85-90% of all CH4 emissions form the farm are from the rumen of the dairy stock, even if AD can reduce CH4 emissions by 50% from this stored manure, then the overall percentage loss (per ha) would be relatively small. Anaerobic digestion of organic materials by microbial populations in a sealed container results in the formation of CH4 and digestate. Methane produced by these processes can be

14

used for heating and power, and the digestate returned to the land as a soil conditioner and fertiliser. Methane emissions are not reduced by much on these farms, recognising that this is slurry only and biogas yields are low, and that the vast majority of CH4 arises from enteric sources. In order to fully realise the benefits of AD it is important that the system is operated well and that the digestate is correctly applied to land (particularly in terms of application timing, rate and method) so that the nutrients can be used effectively. During AD, organic N is mineralised to ammonium (NH4) N. Furthermore, N can be added by the inclusion of other (e.g. food ‘waste’) materials. Hence, the N content of the digestate can be greater than that of the original ’raw’ manure. This could potentially result in greater NH3 (during both storage and following land spreading) and N2O emissions, and NO3 leaching losses following land spreading (as shown by the modelling – but depends upon application timing). However, digestate tends to have a lower dry matter content and is likely to more rapidly infiltrate into soil, thus potentially reducing NH3 emissions compared with the ‘raw’ manure but also potentially increasing NO3 leaching losses when applied in the autumn (as indicated by the modelling). If the crop/grass is not able to utilise this conserved N, then it is potentially at risk of loss as NO3 or N2O. Also, AD uses up readily available carbon in the production of biogas, hence, when digestate is spread on land there is less carbon to fuel nitrification and denitrification, hence N2O emissions might be expected to be lower compared with the original ’raw’ manure (as indicated by the modelling). Bedding type; change from slurry to FYM (different straw use scenarios) Sufficient bedding is provided in animal houses to soak up the liquid portion of the excreta to produce a solid manure that can be stacked and does not flow under gravity. As a result, there are fewer storage problems than with slurry. Manure in cattle houses is generally allowed to accumulate in the house throughout the winter. Therefore, there is not the same limit on storage capacity that may force farmers to spread slurry at unsuitable times during the winter. Other benefits of solid manure include a more rapid decline in numbers of faecal indictor organisms (FIOs) than in slurry stores, if composting processes are allowed to generate heat and increase temperatures within the heap. Because of their low moisture content, solid manure can be spread on fields with much less risk of soluble or suspended material (N, P or FIOs) entering field drains or entering watercourses in surface run-off. Losses following spreading will only occur where there is heavy rain in the days following application. Compared with slurries, less of the N is present in a readily-available mineral form. Typically, 50-70% of the N in slurries may be present as ammonium-N, compared with < 25% in fresh cattle FYM and < 10% in stored FYM. Solid manures contain both aerobic and anaerobic micro-sites where ammonium-N can be nitrified to NO3, providing a source of N2O emission by denitrification, hence the greater N2O emissions compared to the baseline. This can occur as the bedding material builds up in the animal house, and particularly once the bedding has been removed from the building and stored in heaps. Slurry, on the other hand, is anaerobic (until the time it is spread onto land) and there is little or no N2O emission from slurry based buildings or slurry stores. Straw use will encourage bacterial immobilisation of readily available nitrogen, resulting in a lower potential for NH3 emission. Increasing the straw use in a beef cattle solid manure system can reduce NH3 emissions further (Gilhespy et al., 2009), In addition, the presence of a straw layer will reduce air movement, and hence volatilisation, from urine which has infiltrated below the surface layer of the bedding. The reduced nitrate leaching from the straw based system reflects the lower available N content of the FYM.

15

This management practice is potentially applicable to all cattle farms which currently handle all or part of their manure as liquid slurry. Studies have shown that for pigs, emissions from straw-bedded housing can be greater than from slurry-based, slatted floor systems, because of pig behaviour in moving the straw bedding to preferential lying areas (Chambers et al., 2003). Dairy cow cubicle housing would not be suitable as straw-bedded loose housing, so substantial changes to buildings would have to be made. There may be reluctance to move to a solid manure management system for dairy cows due to animal hygiene and milk quality issues. Solid manure requires a source of suitable bedding material and is less-suited to regions where little straw is produced. There may be additional labour costs associated with spreading straw in the animal house. Solid manure is less easily handled than liquid slurries. It cannot be pumped and is unsuited to umbilical spreading systems. Grassland farms provide only limited opportunities for incorporating solid manures into the soil after application. C sequestration is not as great as one might have expected due to the straw returns to land, but this is not factored into the current model structure of SIMSDAIRY. Nitrate losses are reduced due to the l less available N applied in FYM. Use lower stocking density systems; reduce stocking rate by 20% Livestock excreta deposited in the field and applied in manures are important sources of N, P and FIOs. Reducing stocking rates will reduce the quantities of nutrients and potential pathogens added to the soil and available for loss. Much of the NO3 leached from pastures originates from the high concentrations of NO3 present in urine patches. With lower stocking rates, there will be fewer urine patches and less N available for leaching and N2O emissions. Fewer livestock will produce less manure and there will, therefore, be less risk of loss when this is spread on fields. There will be greater flexibility in when to apply manure so as to avoid high-risk times. As the farm will need to produce less forage, fertiliser rates can also be reduced. Reducing stocking rates will also reduce the physical damage to soils that can exacerbate the transport of pollutants to watercourses. Trampling by livestock causes poaching and compaction of the soil, which reduce plant uptake of nutrients and increase the risk of pollutant losses in surface run-off. Similarly, overstocking can destroy fragile vegetation and expose bare soil, which increases the risk of soil erosion and loss of P on soil particles (particularly in localised areas in the uplands). Reducing the stocking density should improve animal welfare and is also likely to improve biodiversity indices and soil quality. The method would be relatively simple to implement but would have a serious impact on profitability. The main factor limiting its adoption would be the major reduction in farm income resulting from reduced stock numbers Extended grazing; increase number of grazing days by 20% Increasing the number of grazing days results in a fewer days that stock are housed. This results in greater quantities of urine and faeces being deposited in the fields and on tracks (and possibly outdoor yards). Farm level ammonia emissions should therefore be reduced compared to if urine had been deposited onto solid concrete floors where there is no infiltration and emissions continue from the soiled surface until the urine is scraped or washed into the slurry stores. The 3% reduction of NH3 emissions on the medium intensity dairy farm is consistent with the 1-2% reduction estimated by Webb et al. (2005). At pasture, urine rapidly infiltrates the soil, reducing emissions. Reduced slurry production in-house means a reduced source of CH4 from the slurry store. Ammonia emissions from the slurry storage are not likely to change, as ammonia emissions are related to the surface area of

16

slurry in contact with the air, and not slurry volume per se. A greater proportion of N is deposited to land via the grazing animals, and this return of nutrient is likely to less uniform and hence utilised less efficiently than nutrients in slurry, and may increase the risk of losses to water courses (NO3) and to air (N2O). Increased time in the fields grazing is likely to result in improved animal welfare compared to being housed indoors for longer, with reduced risk of respiratory problems, mastitis and lameness, as long as weather and soil conditions are monitored and stock are withdrawn from the fields when conditions are unsuitable.

Table 12. Effect of IFM practices on environmental losses from dairy farm systems (% change from baseline) (losses expressed per litre milk)


L milk N2O-N NH3-N CH4 CO2 NOx GHG C seq

Use of higher quality feeds for better efficiency, e.g. use of maize silage in the diet

Wilts. (int) Lancs. (med) Leic. (ext)

0 1 1

1 5 4

-1 -1 -1

0 0 0

-1 -1 -1

-10 -12 -11

0 1 1

-7 -7 -7



6 3

-5 -3

-2 -2

2 0

35 12

-7 -1

3 1

5 25

Reduce fertiliser N use, reduce by 20%

All -7

-17 -5 0 -5 -5 -6 9


All 0 2 -13 0 0 0 1 0


All 0 2 -10 0 0 0 1 0

Cover slurry stores All 0 0 -9 0 0 0 0 0 Use of nitrification inhibitors


2 2

-46 -63

7 -1

0 0

0 0

-5 -2

-13 -15

-7 2


All 1 -10 -10 -1 173 -2 -76 -1



0 0 0

57 52 45

0 -2 -4

11 11 11

0 0 0

1 1 1

24 22 20

2 2 2

Use of lower stocking density systems, e.g. reduce stocking density by 20%


-4 -14

-28 -20

-4 -1

0 4

-3 -8

-4 5

-7 -4

7 44

Extended grazing; Increase number of grazing days by 20%


0 -5

2 16

-4 7

-1 0

-3 2

-1 79

-1 1

5 -6

Some improvement on milk quality might be expected, although the exact level of nutrition can be finely tuned whilst stock are indoors, compared to grazing. One might expect greater potential for soil damage if stock are kept at pasture for longer, especially during wet conditions, and hence soil could be more prone to erosion and loss of nutrients and carbon, if the number of grazing days are increased, but much depends on soil type and weather conditions. There will be a reduced labour cost and less feed and conserved forage requirement for stock which stay at pasture for longer, assuming there is adequate forage for grazing.

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Table 13. Effect of IFM practices on score matrices of other on-farm benefits (% change from baseline)


Milk composition

Biodiversity Animal welfare

Landscape Soil quality

Net margin (£ per farm)

Use of higher quality feeds for better efficiency, e.g. use of maize silage in the diet

Wilts. (int) Lancs. (med) Leic. (ext)

-2 -2 -2

15 16 15

0 0 -1

0 0 0

0 1 -4

-6 -5 -5



1 1

-6 -1

0 0

0 0

0 1

-10 -1

Reduce fertiliser N use, reduce by 20%

All

0

28

-1

0

-1

1


All 0 0 0 0 0 -17


All

0

0

0

0

0

0

Cover slurry stores All 0 0 0 0 0 -10 Use of nitrification inhibitors


0 0

-8 -1

-1 0

0 0

-3 0

1 1


All

0

-6

0

0

2

-2



0 0 0

8 2 -4

16 32 48

0 0 0

1 1 1

-4 -7

-18 Use of lower stocking density systems, e.g. reduce stocking density by 20%


0 0

40 94

7 8

0 0

26 15

-3 -12

Extended grazing; Increase number of grazing days by 20%


2 3

20 -20

1 -4

0 0

5 -37

7 -7

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BEEF AND SHEEP Baseline losses Table 14 summarises the baseline losses for each of the four beef and sheep farming typologies; lowland beef, lowland sheep, upland beef and upland sheep. The more intensive lowland systems result in greater losses of most pollutants. Table 14. Baseline losses from the beef and sheep farming systems.

kg/ha Lowland beef Lowland sheep Upland beef Upland sheep N2O-N 2.96 2.67 0.88 0.88 NO-N 0.05 0.05 0.07 0.07 NH3-N 20 18 13 13 NO3-N 21 23 7 8 CH4-C 86 52 45 50 C storage 500 500 650 650 GHG CO2eq 2723 1921 1221 1324 IFM Practices The introduction of IFM practices result in some increases and some decreases in pollutant losses for the different farming systems (Tables 15, 16, 17 and 18). Table 15. Effect of IMF practices on losses from the Lowland Beef system (percentage difference from baseline). kg/ha Reduce

fertiliser N use by 20%

Switch from FYM to slurry (broadcast)

Switch from FYM to slurry and inject slurry

Extended grazing, increase grazing days by 20%

N2O-N -7 -58 -55 -6 NO-N -3 -41 -41 -40 NH3-N -4 113 35 -3 NO3-N -3 -27 -21 1 CH4-C 0 -1 0 -1 C storage 0 0 0 0 GHG CO2eq -2 -20 -19 -2 Production -3 0 0 1 Reducing the fertiliser N use by 20% results in reduced losses of N containing pollutants, but a small decrease in productivity. Switching from a solid manure system to a slurry based system results in decrease in N2O emissions and a large increase in NH3 emissions. There is no marked difference in CH4 emissions. A switch from solid manure to slurry where the slurry is injected and not surface broadcast also results in a decrease in N2O emissions, but the increase in NH3 emissions is much smaller Increasing the number of grazing days marginally increased nitrate leaching, whilst direct N2O emissions appear to have been reduced. Losses of these forms of N depend on when the additional grazing begins. For example Webb et al (2005) estimate changes in direct N2O emissions to be negligible at the farm level, if additional grazing begins in early spring and even a reduction was simulated if grazing continued for longer in the autumn. Within farm, the current NGAUGE simulation showed an increase in direct N2O emissions from the grazed fields. However, this was countered by the reduced FYM production and subsequent reduction in N2O emissions from the application of those manures.

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Table 16. Effect of IMF practices on losses from the Lowland Sheep system (percentage difference from baseline).

kg/ha Reduce fertiliser N use by 20%




N2O-N -7 -59 -56 -13 NO-N -3 -40 -40 -13 NH3-N -4 127 39 -14 NO3-N -3 -16 -10 2 CH4-C 0 -1 -1 -1 C storage 0 0 0 0 GHG CO2eq -3 -26 -25 -6 Production -3 1 1 1 Reducing the fertiliser N use by 20% results in lower losses of N containing pollutants, but also a reduction in productivity. Whilst switching from a solid manure to a slurry based system might be unlikely for a sheep system, the modelling illustrates that it would reduce N2O emissions and nitrate leaching, but increase NH3 emissions markedly. Injection of the slurry produced would reduced the NH3 emissions considerably. Ammonia emissions are markedly reduced by increasing the number of grazing days, as more urine is deposited onto soil where it rapidly infiltrates (compared to the impermeable surfaces of the farm steading). This agrees with the results of modelling the effects of extended grazing on N losses by Webb et al. (2005). Extending the grazing season results in a small increase in nitrate leaching, but counter-intuitively, N2O emissions decrease as a result of extended grazing. This is based on the model simulation where the increase in direct N2O from grazed land is more than offset by the lower N2O losses from the smaller quantity of FYM applied to land. Webb et al. (2005) concluded that direct N2O emissions can be little affected by extended grazing. Table 17. Effect of IMF practices on losses from the Upland Beef system (percentage difference from baseline). kg/ha Reduce





N2O-N -4 -28 -27 -12 NO-N -7 -34 -34 -14 NH3-N -3 59 12 -3 NO3-N -29 16 32 -3 CH4-C 0 0 0 -1 C storage 0 0 0 0 GHG CO2eq -1 -6 -6 -3 Production 1 1 1 1 Reducing N fertiliser use results in a reduction in all N containing pollutants, particularly nitrate losses. Whilst switching from a solid manure to a slurry based system reduces N2O emissions considerably and increases NH3 emissions and nitrate losses. Injection of the slurry reduces the NH3 emissions but increases nitrate leaching. Increasing the number of grazing days results in lower NH3 losses as one might expect with more urine deposited on impermeable surfaces, but counter-intuitively increases the N2O emissions, which is discussed above.

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Table 18. Effect of IMF practices on losses from the Upland Sheep system (percentage difference from baseline). kg/ha Reduce





N2O-N -3 -28 -27 -3 NO-N -5 -34 -34 -6 NH3-N -3 59 12 -9 NO3-N -24 13 26 -6 CH4-C 0 0 0 0 C storage 0 0 0 0 GHG CO2eq -1 -6 -5 -1 Production 1 1 1 1 Reducing N fertiliser use results in a reduction in all N containing pollutants, particularly nitrate losses. Whilst switching from a solid manure to a slurry based system reduces N2O emissions considerably and increases NH3 emissions and nitrate losses. Injection of the slurry reduces the NH3 emissions but increases nitrate leaching. Increasing the number of grazing days results in lower NH3 losses, as one might expect with more urine deposited on impermeable surfaces, but counter-intuitively increases the N2O emissions, which is explained above.

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INDOOR PIGS Baseline Losses Livestock housing is the main source of NH3 emissions from the indoor pig (and combinable crop) farming system (almost 60% of the total). Manure spreading (slurry and solid manure) is also a significant source, almost 30% of the farm total (Table 19). Table 19. Sources of ammonia losses from the combined pig and combinable crops model farms. Source of ammonia Ammonia loss

(kg NH3-N/farm) % total NH3-N loss from farm

Livestock Housing 5,912 57 Slurry storage 137 1 Solid manure heaps 1,165 11 Slurry application 1,729 17 FYM application 1,471 14 Total farm loss 10,415 100 IFM Practice At the farm level, reducing stocking rate and installing air scrubbers are the most effective individual IFM methods at reducing NH3 emissions (Table 20). Farm level reduction could be increased if multiple methods were introduced.

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Table 20. Percentage change in ammonia emissions from each source on the combined indoor pig and combinable crop farms following introduction of IFM practices. Management practice Housing Slurry

storage Solid manure heap

Slurry application

Solid manure application

Total

Use of phase feeding -5 -5 -5 -5 -5 -5 Frequent removal of slurry from below the animal house

-11 8 0 8 0 -5

Use of mechanical separation of slurry

0 -9 12 -32 12 -2

Solid manure storage; composting

0 0 100 0 -50 4

Solid manure storage; covering heaps

0 0 -65 0 33 -3

Method of manure application; band spreading

0 0 0 -23 0 -4

Method of manure application; rapid incorporation

0 0 0 -23 -30 -8

Bedding type; change from solid manure to slurry system

16 139 0 139 0 8

Bedding type; change from slurry to solid manure system

-6 -90 62 -90 62 -4

Use of lower stocking density systems, e.g. reduce stocking rate by 20%

-20 -20 -20 -20 -20 -20

Use of powered ventilation systems; install air scrubbers to buildings

-34 27 0 26 0 -15

Establish areas of vegetation on site for conservation purposes; establish tree shelter belts around buildings and manure stores

-5 -3 -2 2 6 -2

Use of phase feeding Phase feeding through more precise matching of the ration to the individual animal’s nutritional requirements should reduce N excretion. Nutrients are utilised more efficiently and less of the dietary N (and P) is excreted, thereby reducing the N content of manures. This reduces the amount of N available for loss, NH3 emission from the point of excretion onward, and when these manures are applied to fields. Livestock at different growth stages or stages of the reproductive or lactation cycle have different optimum feed requirements. However, because of limited labour and housing facilities, livestock with different feed requirements are often grouped together and receive the same ration. As a result, some stock will receive higher levels of N than they can utilise efficiently and will excrete the surplus. Greater division and grouping of livestock on the basis of their feed requirements allows more precise formulation of individual rations. This will reduce N and P surpluses in the diet and reduce the amounts excreted. There will be

23

less N applied to land in manures and therefore smaller losses in surface run-off and by leaching. The method is applicable to all livestock systems except those based primarily on grazing. It would be effective at reducing losses N in run-off from heavier soils and in reducing NO3 leaching from free-draining soils. In the ruminant sector, this method reflects current practice where cows are grouped according to yield. However, practical application may be difficult on dairy units where cows are fed a single diet across a range of yields. There is limited scope for improvements in the poultry sector, where phase feeding is already widely used. There is great potential for phase feeding in the pig sector to reduce N (and P) excretion. Frequent removal of slurry from beneath pig housing This involves replacing slurry storage beneath slats for typically a 1-6 month period, with frequent removal of slurry to an outside, covered store, using vacuum removal systems operated at least twice per week. The NH3 emission from a slatted-floor pig house derives both from manure deposited to the slat surfaces and also from the slurry in the below-slatted floor storage area. Frequent removal of the beneath-slat source will reduce the overall NH3 emission from the pig house. Removal to a covered store (see earlier) will prevent further emissions during slurry storage. This method could be applied to all slatted-floor pig housing, subject to sufficient outside covered storage capacity being available. The method is most suited to purpose-built new installations. There may be considerable reluctance to the retro-fitting of pig housing and there is a requirement for additional covered storage capacity. Use of mechanical separation of slurry Mechanical separators are used on farm to remove solid material from slurries, resulting in two slurry fractions; a solid fraction which can be stacked and managed separately from the liquid fraction. The liquid fraction can be pumped further, as it has a lower dry matter content and infiltrates the soil quicker, thus potentially reducing NH3 emissions at land spreading. The addition of a ‘solid manure’ heap means that some NH3 emissions will occur from this source and after applying to land. Overall, the whole farm loss of NH3 is marginally reduced through slurry separation. An added advantage of slurry separation is that it effectively increases the slurry storage capacity, allowing more timely applications of slurry. Solid manure storage; composting Turning the solid manure heap encourages naturally occurring microflora to degrade cellulose and other carbon compounds in the manure (or other added material) to produce a more friable, stable, and spreadable product with reduced volume. In the process, the manure is sanitised as microbial activity increases heap temperature sufficiently to kill pathogens and weed seeds, and the readily available N content is reduced, thereby lowering NO3 losses when the compost is spread. The whole process should be carefully managed to ensure that the heap temperature increases to above 55oC for three days after each turn. Typically, the heap should be turned twice in the first 7 days to provide aeration and the development of high temperatures. The readily available N content of farmyard manure is typically reduced from 25% to 10% of the total N (Anon, 2010), so N losses following land spreading are likely to be lower. Some N is bound into organic forms and some is lost to the atmosphere as NH3 and N2O. Turning of the pile allows mixing and the further degradation of material and ensures that all parts of the pile are treated. Composting has no effect on the proportion of readily available N in poultry manure.

24

Solid manure storage; covering heaps The solid manure heap is covered (i.e. with heavy duty polythene sheeting), in a similar manner to a silage clamp, and the sheeting provides a physical barrier preventing the release of NH3 from the manure heap to the air. The NH3-N that is retained in the heap using this method will be lost at land spreading, if the manure is not incorporated rapidly (see earlier). Some studies have shown that a combination of manure compaction and covering can reduce losses (Chadwick, 2005). In some cases this method may be impractical, e.g. where heaps are added to frequently. Method of manure application; band spreading Use trailing hoses to apply slurry in narrow bands (typically 5-10 cm width at a spacing of 20-30 cm). Slurry is delivered onto the soil by hoses or ‘shoes’, where the slurry is placed below the growing canopy. In a similar way to slurry injection, these slurry spreading methods reduce the surface aresto airflow. Placing the slurry below a plant canopy provides further protection from airflow. The method requires that slurry is applied at rates that result in the slurry remaining in discrete bands and that slurry infiltrates into the soil, otherwise the bands of slurry spread out across the soil surface negating the benefit. The trailing shoe may be better suited to grassland, whilst trailing hoses can be used on both grassland and arable crops. These slurry application methods, if managed well will also reduce odours and distribute slurry more uniformly across the field, as well as keeping the canopy clean of slurry. This provides farmers with greater flexibility about when they can apply slurry, compared to conventional surface broadcasting. Method of manure spreading; rapid incorporation See earlier dairy section. Bedding type; change from slurry to a solid manure system See earlier dairy section. Bedding type; change from a solid manure to a slurry system This method is where the manure from housed animals is collected as a solid rather than where animals are kept on a slurry based system. It’s main benefit would be in reducing N2O emissions, and it will increase NH3 emissions. Solid manures contain both aerobic and anaerobic micro-sites where NH4-N can be nitrified to NO3, providing a source of N2O emission by denitrification. This occurs in the bedding in the animal house and in the solid manure heap. In contrast, slurry remains anaerobic (until the time it is spread onto land) and there is little or no N2O emission from slurry based buildings or slurry stores. A farmer would need to invest in slurry storage and pumps and spreading equipment. Buildings may need modification for collection and removal of the slurry. This change is unlikely, especially if located within an NVZ where manure management regulations are much stricter for slurries than solid manure. Use of lower stocking density systems, e.g. reduce stocking rate by 20% This is covered in the earlier dairy section.

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Use of powered ventilation systems; install air scrubbers to buildings Exhaust air from mechanically-ventilated pig housing is treated using acid scrubbers (or perhaps biotrickling filters) to remove NH3.While this method does not reduce the NH3 emission from floor and slurry surfaces within the house, it removes NH3 from the exhaust air-stream, thereby reducing the emission from the house to the wider environment. Ammonia is very readily absorbed by low pH solutions. Acid scrubbers mainly apply sulphuric acid in their recirculation water to bind NH3 as ammonium sulphate. Nitrogen is removed from the system by controlled discharge of the recirculation water. (In biotrickling filters, NH3 is converted to NO3 through bacterial action of the biomass held on the synthetic supporting material and in the recirculation water). As with acid scrubbers, nitrogen is removed from the system by controlled discharge of the recirculation water. This method is applicable to all mechanically-ventilated pig housing, although the very high conversion costs restrict application to new build only. High dust loading in poultry housing can complicate the reliable long-term functioning of current scrubbers and filters. The requirement for specific ventilation designs adapted to air treatment technologies restricts the practical application of this method to newly purpose-built facilities. Establish areas of vegetation on site for conservation purposes; establish tree shelter belts around buildings and manure stores Although this is not defined as an IFM practice in the list produced by this project, it is similar to the IFM practice to establish areas of vegetation for conservation purposes. The tree shelter belt disrupts air flow around the building or slurry storage facility, reducing the emission rate to some extent, and will also directly recapture a proportion of the NH3 emitted from the source. Trees need to be of a sufficient height to be effective and will take a number of years to establish. The effectiveness of this method in reducing NH3 emissions from manure source will depend on the height and canopy density of the shelter belt and the prevailing environmental conditions. With careful design of tree belts, it is thought that 5-10% of NH3 emitted from housing and storage can be reduced (Dragosits et al., 2006). If the additional retained N in the slurry is applied to land without any method to reduce emissions at this stage, e.g. incorporation in arable fields or use of shallow injection or trailing hose on arable or grassland, then some of the benefits achieved by the shelter belt will be negated. If land is taken out of agricultural production this will have a negative impact on farm margins.

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OUTDOOR PIGS Baseline Losses The only source of NH3 emissions on the outdoor pig farm is from the excreta deposited by the outdoor livestock. The loss from this source is 1,608 kg NH3-N for the farm. IFM practices The most effective methods to reduce NH3 emissions are to reduce stocking rates and to take land out of pig production to grow biomass crops (Table 21). Both methods would impact on the economics of the farming system. Table 21. Percentage change in ammonia emissions from the outdoor pig farm following the introduction of IFM practices. Management practice Outdoor losses only, from

excreta Use of lower stocking density systems, e.g. reduce stocking rate by 20%

-20

Use of renewable energy sources; grow biomass crops

-25

Establish areas of vegetation on site for conservation purposes; establish permanent woodland

-2

Establish areas of vegetation on site for conservation purposes; establish new hedges

-1

Establish buffer strips -3 Use of lower stocking density systems, e.g. reduce stocking rate by 20% See earlier dairy section. Use of renewable energy sources; grow biomass crops This IFM practice is not in the list of IFM practices, but is similar to, Establish vegetation for conservation purposes. This IFM practice could also take considerable land out of production, and hence reduce the area for the outdoor stock considerably. This would mean reducing the stock numbers appropriately. Hence there is a marked reduction in NH3 emission. Establish areas of vegetation on site for conservation purposes; establish permanent woodland This IFM practice is not in the list of IFM practices, but is similar to, Establish vegetation for conservation purposes. It would take land out of production and hence reduce the area for the outdoor stock. This would mean reducing the stock numbers appropriately. Hence there is a small reduction in NH3 emission. If the woodland was strategically placed around the farm, there may be additional NH3 mitigation through the reduction of airflow across source areas and interception / capture of N by the canopy. Establish areas of vegetation on site for conservation purposes; establish new hedges This IFM practice is not in the list of IFM practices, but is similar to, Establish vegetation for conservation purposes. It would take land out of production and hence reduce the area for

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the outdoor stock. This would mean reducing the stock numbers appropriately. Hence there is a small reduction in NH3 emission. Establish buffer strips Buffer strips can be used on sloping fields where grass buffer strips can be created along the land contour, in the valley bottoms or on upper slopes to reduce and slow down surface flow. They can also be established as riparian strips between agricultural land and a vulnerable watercourse. They are designed to reduce P and sediment losses and, where manures are applied to tillage land, ammonium, BOD and FIO losses by slowing run-off and intercepting the delivery of sediment. Ammonia emissions are reduced slightly as the stocking rate has been reduced in proportion to the land area taken out of production. Both the Entry Level and Higher Level Environmental Stewardship scheme offers options to establish in-field grass areas to prevent erosion and run-off. In-field buffer strips are applicable to all arable farming systems on sloping land. They are particularly suited to fields with long slopes, where high volumes of surface run-off can be generated. Riparian buffer strips are particularly suited to low-lying and gently undulating landscapes where the topography does not concentrate the flow into channels. They are potentially applicable to all farming systems. If land is taken out of agricultural production then this may require a reduction in stocking rate and hence a potential reduction in margin.

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POULTRY Baseline Losses Housing and manure spreading are the major sources of NH3 loss from the combined poultry and root cropping farming system (Table 22), representing 41% and 47% of the total, respectively. So, any IFM practice that can reduce either of these two sources will result in a marked reduction of emissions at the farm level. Table 22. Percentage change in ammonia emissions from each source on the combined poultry and root cropping farms following introduction of IFM practices. Source Ammonia loss

(kg NH3-N / farm) % of total NH3-N loss from

the farm Housing 5,098 41 Outdoor area 186 1 Manure storage 1,280 10 Manure spreading 5,847 47 Total 12,411 100 IFM practices Reducing the stocking rate reduces NH3 emissions proportionally, but would result in a lower farm margin, if diversification activities did not counter this. Incineration of a greater proportion of the poultry litter removed a significant source of N (and hence potential for NH3 emissions from manure storage and land spreading) from the farm. Manure incorporation also result in a marked reduction in NH3 loss from the poultry farming system (Table 23). Table 23. Percentage change in ammonia emissions from each source from the combined poultry and root crop farms following the introduction of IFM practices. Management practice Housing Outdoor

area Manure storage

Manure spreading

Total

Frequent removal of poultry manure from house

-13 0 3 2 -3

Frequent removal of manure form house via converting deep pit laying hen system to belt manure removal

-9 0 2 2 -3

Solid manure storage; composting

0 0 100 -9 6

Solid manure storage’ cover heaps

0 0 -65 6 -4

Method of manure application; rapid incorporation

0 0 0 -27 -13

Use of lower stocking density systems; reduce stocking rates by 20%

-20 -20 -20 -20 -20

Establish areas of vegetation for conservation purposes; establish tree shelter belts around buildings and manure stores

-5 -5 -4 1 -2

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Frequent removal of poultry manure from house Laying hen houses with manure belts typically remove manure on a weekly basis. This IFM method increases the frequency of manure removal to twice weekly, so that manure is removed before the peak rate of NH3 emission from the manure. The method can be applied to all laying hen houses with belt systems for manure removal. The method can be applied to all laying hen houses with belt systems for manure removal. Farmers would have to ensure that during manure storage and at land spreading, management practices were put into place to conserve N and prevent NH3 emissions, otherwise the benefit gained through this IFM practice may be lost. Frequent removal of manure form house via converting deep pit laying hen system to belt manure removal In a deep storage system, manure from laying hens drops to a pit below the cages where it is stored for a period of months before removal for land spreading. Conveyer belts below the cages remove the manure from the house (usually on a weekly basis). In this way, much of the NH3 emission from a given quantity of manure will occur after the manure has been removed from the house. Again, farmers would have to ensure that during manure storage and at land spreading, management practices were put into place to conserve N and prevent NH3 emissions, otherwise the benefit gained through this IFM practice may be lost. The method would be applicable to all deep-pit laying hen systems, but the practicalities of conversion will depend on individual building design and age. Solid manure storage; composting See earlier indoor pig section. Solid manure storage; covering heaps See earlier indoor pig section. Method of manure application; rapid incorporation See earlier dairy section. Use of lower stocking density systems; reduce stocking rates by 20% See earlier dairy section. Establish areas of vegetation for conservation purposes; establish tree shelter belts around buildings and manure stores See indoor pig section earlier.

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DISCUSSION Whilst it is tempting to take the exact values output by the models at face value, it should be noted that the modelling of baseline losses and as a result of IFM practices from the farm typologies relies on adoption of several assumptions and generic algorithms describing key processes. As such, deterministic model outputs are indicative, and not too much importance should be taken of the exact value. However, the modelling should be able to provide relative magnitudes of N loss pathways and the direction of change that results from a given IFM practice. Some IFM practices are relevant to all livestock outdoor farm typologies, e.g. reducing N fertiliser use, changing the number of grazing days and changing from a solid manure to a slurry based manure system. Reducing the fertiliser N use by 20% consistently reduced all forms of modelled N losses, but did result in decreased productivity. Increasing the number of grazing days should result in more N being deposited on soil (compared to impermeable surfaces) and if this in the wetter months, this can result in increased nitrate leaching and N2O emissions, although the modelling did not always show this. However, the modelling did illustrate that this IFM practice would usually reduce NH3 emissions. Changing from a solid manure system to a slurry based manure system consistently resulted in decreased N2O emissions and increased NH3 emissions. Whilst slurry injection could reduce those NH3 emissions, the NGAUGE modelling showed the potential for this slurry application method to increase N2O emissions. SIMSDAIRY simulations do not currently assume a reduction in CH4 emissions from the stored slurry as a result of biogas production. This could be changed for future simulations, but it is worth noting that since 85-90% of all CH4 emissions from the farm are from the rumen of the dairy stock, even if AD can reduce CH4 emissions by 50% from this stored manure, then the overall percentage loss (per ha) would be relatively small. For the Indoor pigs, reducing the stocking rate and installation of air scrubbers were the most effective IFM practices to reduce NH3 emissions, since almost 60% of all NH3 emissions from indoor pigs arise from the livestock housing. Manure application is also a significant source of NH3 emissions, so rapid manure incorporation can reduce those emissions markedly. For outdoor pigs, it is only IFM practices that result in a loss in income that seem to a have a large effect on NH3 emissions, e.g. reducing stocking rates or growing biomass crops. Whilst for poultry, housing and manure spreading are the main sources of NH3 emissions (41% and 47% of the total baseline loss, respectively). Thus, reducing the stocking rate and manure incorporation are the most effective management practices to reduce NH3 emissions. Frequent removal of poultry manure from the livestock building and converting to a belt removal system are effective in the house, but at the farm level have only a modest benefit (3% reduction). Whilst some aspects of the modelling have been validated, e.g. on the single pollutant level – there are few datasets that contain information about the effect of management practices on multiple pollutants. The body of evidence to provide data on multi pollutant losses is increasing (e.g. Defra project WQ0118) and will be valuable in validating models such as NGAUGE and SIMSDAIRY.

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REFERENCES Anon, 2010. Fertiliser Manual (RB209). 8th Edition. The Stationary Office.pp. 252. ISBN 978 0 11 243286 9. Brown L., Scholefield D., Jewkes E.C., Lockyer D.R. and del Prado A. 2005. NGAUGE: a decision support system to optimise N fertilisation of British grassland for economic and/or environmental goals. Agriculture, Ecosystems and Environment 109, 20-39. Chadwick D.R. and Pain B.F. 1997. Methane fluxes following slurry applications to grassland soils: laboratory experiments. Agriculture, Ecosystems and Environment 63, 51-60. Chambers B.J., Lord E.I., Nicholson F.A. and Smith K.A. 1999. Predicting nitrogen availability and losses following application of organic manures to arable land: MANNER. Soil Use and Management 15, 137-143. Chambers, B.J., Smith, K.A. and Pain, B.F. 2000. Strategies to encourage better use of nitrogen in animal manures. Soil Use and Management, Tackling Nitrate from Agriculture, 16, 157-161. Chambers B.J., Williams J.R., Cooke S.D., Kay R.M., Chadwick D.R. and Balsdon S.L. 2003. Ammonia losses from contrasting cattle and pig manure management systems. In: Agriculture, Waste and the Environment (Eds. I. McTaggart and L. Gairns), The Scottish Agricultural College, pp19-25.

Davison P.S., Withers P.J.A., Lord E.I., Betson M.J. and Strömqvist J. (in press). PSYCHIC – A process-based model of phosphorus and sediment mobilisation and delivery within agricultural catchments in England and Wales. Part 1 – Model description and parameterisation. Journal of Hydrology. Del Prado A., Scholefield D., Chadwick D.R., Misselbrook T.H., Haygarth P.M., Hopkins A., Dewhurst R.J., Jones R., Moorby J.M. , Davison P. , Lord E.I. , Turner M., Aikman P., Schroder J. 2006. A modelling framework to identify new integrated dairy production systems. EGF: 21st General Meeting on 'Sustainable grassland productivity", Badajoz, Spain, 3-6 April 2006. Del Prado A. and Scholefield D. 2006. Use of SIMSDAIRY modeling framework system to specify sustainable UK dairy farms. Aspects of Applied Biology 80,73-80. Di, H.J., Cameron, K.C. and Sherlock, R.R. 2007. Comparison of the effectiveness of a nitrification inhibitor, dicyandiamide, in reducing nitrous oxide emissions in four different soils under different climatic and management conditions. Soil Use and Management 23, 1: 1-9. Dittert K., Bol R., King R., Chadwick D. and Hatch D. 2001. Use of a novel nitrification inhibitor to reduce nitrous oxide emissions from 15N-labelled slurry injected into soil. Rapid Communications in Mass Spectrometry 15, 1291-1296. Dragosits, U., Theobald, M. R., Place, C. J., ApSimon, H. M., and Sutton, M. A. 2006. The potential for spatial planning at the landscape level to mitigate the effects of atmospheric ammonia deposition. Environmental Science & Policy 9, 626-638. Giger-Reverdin S., Morand-Fehr P. and Tran G. 2003. Literature survey of the influence of dietary fat composition on methane production in dairy cattle. Livestock Production Science 82, 73-79.

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Gilhespy, S. L., Webb, J., Chadwick, D. R., Misselbrook, T. H., Kay, R., Camp, V., Retter, A. L., and Bason, A. 2009. Will additional straw bedding in buildings housing cattle and pigs reduce ammonia emissions? Biosystems Engineering 102, 180-189. Hatch D., Trinidade H., Cardenas L., Carneiro J., Hawkins J., Scholefield D. and Chadwick D. 2005. Laboratory study of the effects of two nitrification inhibitors on greenhouse gas emissions from a slurry-treated arable soil: impact of diurnal temperature cycle. Biology and Fertility of Soils 41,225-232. Misselbrook, T. H., Smith, K. A., Johnson, R. A., and Pain, B. F. 2002. Slurry application techniques to reduce ammonia emissions: Results of some UK field-scale experiments. Biosystems Engineering 81, 313-321. Moir, J.L., Cameron, K.C. and Di, H.J. 2007. Effects of the nitrification inhibitor dicyandiamide on soil mineral N, pasture yield, nutrient uptake and pasture quality in a grazed pasture system. Soil Use and Management 23, 111-120. Portejoie, S., Martinez, J., Guiziou, F., and Coste, C. M. 2003. Effect of covering pig slurry stores on the ammonia emission processes. Bioresource Technology 87, 199-207. Ross C.A., Scholefield D. and Jarvis S.C. 2002. A model of ammonia volatilisation from a dairy farm: an examination of abatement strategies Nutrient Cycling in Agroecosystems 64, 273-281 Schils R.L.M, de Haan M.H.A., Hemmer J.G.A, van den Pol-van Dasselaar A., de Boer J.A., Evers A.G., Holshof G., van Middelkoop J.C.and R.L.G. Zom. 2007. DairyWise, a whole farm dairy model. Journal of Dairy Science 90, 5334-5346. Scotford, I. M., and Williams, A. G. 2001. Practicalities, costs and effectiveness of a floating plastic cover to reduce ammonia emissions from a pig slurry lagoon. Journal of Agricultural Engineering Research 80, 273-281. Smith, K. A., Jackson, D. R., Misselbrook, T. H., Pain, B. F., and Johnson, R. A. 2000. Reduction of ammonia emission by slurry application techniques. Journal of Agricultural Engineering Research 77, 277-287. Thomas C. 2004. Feed into Milk (FiM): A new applied feeding system for diary cows. Nottingham University Press, UK. Webb J. and Misselbrook T.H. 2004. A mass-flow model of ammonia emissions from UK livestock production. Atmospheric Environment 38, 2163-2176. Webb J., Chadwick D. and Ellis S. 2004. Emissions of ammonia and nitrous oxide following incorporation into the soil of farmyard manures stored at different densities. Nutrient Cycling in Agroecosystems 70, 67-76. Webb J., Anthony S.G., Brown L., Lysons-Visser H., Ross C., Cottrill B., Johnson P. and Scholefield D. 2005. The impact of increasing the length of the cattle grazing season on emissions of ammonia and nitrous oxide and nitrate leaching in England and Wales. Agriculture, Ecosystems and Environment 105, 307-321. Webb J., Ryan M., Anthony S.G., Brewer A., Laws J., Aller M.F. and Misselbrook T.H. 2006. Cost-effective means of reducing ammonia emissions from UK agriculture using the NARSES model. Atmospheric Environment. 40, 7222-7233. Defra projects AC0209. Ruminant regimes to reduce methane and nitrogen emissions. WQ0106. Cost curves for multiple diffuse pollutants - DP-ALL.

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APPENDIX 1. Model Farm Typologies Model pig farm typologies

Indoor pigs

The ‘Indoor pigs’ typology was defined as having 204 dry sows (120kg lwt.), 159 farrowing sows (200kg lwt.), 1,272 weaners (10 kg lwt.), 983 first stage grower (35 kg lwt.) places, 621 second stage grower (65 kg lwt.) places, 247 finisher (95 kg lwt.) places and 32 pigs over 110 kg live weight. The total undiluted excreta production was 4,390 tonnes annually (Smith et al., 2000). The proportions of manure managed as FYM and slurry were consistent with the default assumptions in the NARSES model (Webb and Misselbrook, 2004). FYM was stored in an open field site. Slurry was stored in a pit below slatted floors in the livestock building, providing 3 months storage capacity. During storage the excreta was diluted with rain from the loading area, resulting in a slurry volume of 1,500 m3 and a dry matter content of 4%. The total N content of FYM and slurry was 25,100 kg N annually. Currently 90% of pig diets manufactured in UK contain phytase and this was reflected in the total amount of P produced (6,310 kg P). The slurry and FYM was exported to the ‘Combinable cropping with manure’ farm typology.

Combinable cropping with pig manure The combinable cropping farm with manure was 172 ha in size with the same cropping and cultivation as for the combinable cropping farm without manure. It received all the solid manure (FYM) and slurry produced on the ‘indoor pig’ farm. This amounted to 25,100 kg total N, resulting in a total NVZ livestock manure N farm loading of 146 kg N/ha. In total, 30% of the pig FYM was spread direct and 70% was stacked in field heaps for >3 months prior to spreading. The FYM was spread at 35 t/ha to 62 ha of winter barley, spring barley and oilseed rape land. Pig slurry was applied at 50 m3/ha to 54% (55 ha) of the winter wheat land (70% was spread from store and 30% was spread direct). Manure application timings were based on Smith et al. (2000) and the British Survey of Fertiliser Practice (2007) with approximately 50% of the pig slurry applied in autumn (August-October), 20% in winter (November-January), 30% in spring (February-April) and none in summer (May-July); of the pig FYM, 80% was applied in autumn (August-October), 10% in winter (November-January), 10% in spring (February-April) and none in summer (May-July). The crops received an average N fertiliser application rate of 180 kg N/ha and an average phosphate fertiliser application rate of 38 kg P2O5/ha (British Survey of Fertiliser Practice, 2004). Where manure was applied, adjustments were made to fertiliser application rates according to Goodlass and Welch (2005). On tilled land, 30% of N fertiliser was applied as urea (British Survey of Fertiliser Practice, 2004). On the ‘impermeable’ soil type, 70% of the land area was assumed to have functioning field drains.

Outdoor pigs

The ‘Outdoor pigs’ farm typology was defined as a breeding unit with piglets moved to a growing unit at 7 kg (a month old). It had 140 dry sows, 294 farrowing sows, and 6 boars. The total area of the farm was 57 ha; 18 ha for the pigs, 36 ha of cereals (winter wheat, winter barley and spring barley) and 3 ha of rough/uncropped land. Outdoor paddocks were moved on to new ground every two years. The sows were assumed to deposit excreta across the whole of the free range dunging area (25 sows per ha over 18 ha). Farrowing huts were moved after every litter, but there was no collection or storage of manure. The annual excreta production was 1,500 m3 with a total N content of 9,200 kg N (Cotterill and Smith, 2009; Smith et al., 2000), resulting in a total NVZ livestock manure N

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farm loading of 161 kg N/ha. The total available N, allowing for volatilisation (25% of total ammoniacal-N), was 4,825 kg N annually. Cereal ground had pigs for two years out of every six. Sows were turned out onto stubbles, which became bare ground within a few weeks. Fertiliser applied to cereal crops in the first year after pigs included a reduction for the nutrients in deposited excreta, according to BSFP (2004) (i.e. half the cereal area received the "with manure" BSFP fertiliser rate and the remainder received the "without manure" BSFP fertiliser rate). The crops received an average N fertiliser application rate of 153 kg N/ha and an average phosphate fertiliser application rate of 29 kg P2O5/ha (British Survey of Fertiliser Practice, 2004).

Model poultry farm typology

The ‘specialist poultry’ farm typology was defined as having no land for crop production. It had 81,351 bird places, including layers (70% caged and the remainder ‘free range’), pullets, broilers, turkeys, breeding birds and ducks. In total, 90% of layer feeds and 40% of broiler rations contained phytase. Layers were kept on manure and ducks on FYM with the remaining birds on a litter based system. Total manure production was 2,157 m3 (Cotterill and Smith, 2009; Smith et al., 2000) with 34% of broiler and turkey litter sent for incineration (Webb and Misselbrook, 2004), leaving 1,718 m3 of poultry manure, litter and FYM for land spreading. The total N content of all the manure, post housing and storage, was 32,565 kg N annually. All the manure (apart from the 20% sent for incineration) was spread on the equivalent of two ‘Roots and combinable cropping with manure’ farms. The ‘specialist poultry’ farm had 625 m2 of general hardstanding with half of the runoff directed to drains and half collected as dirty water and spread on the ‘Roots and combinable cropping with manure’ farm. Roots and combinable cropping with manure The roots combinable cropping farm with manure was 180 ha in size with the same cropping and cultivation as for the roots combinable cropping farm. Each farm received half of the poultry manure produced and sent for land spreading on the ‘specialist poultry’ farm (20% of the poultry manure was sent for incineration). This amounts to 16,280 kg total N, resulting in a total NVZ livestock manure N farm loading of 90 kg N/ha. Half of the poultry manure was spread direct and half was stacked in field heaps for >3 months prior to spreading. The poultry manure was spread at 10 t/ha to 56% of the winter wheat, winter barley, potatoes and sugar beet land. In total 66 ha of tillage land received manure. Manure application timings were based on Smith et al. (2001a) and the British Survey of Fertiliser Practice (2007) with approximately 65% of the poultry manure applied in autumn (August-October), 15% in winter (November-January), 20% in spring (February-April) and none in summer (May-July). The crops received an average N fertiliser application of 149 kg N/ha and an average phosphate fertiliser application rate of 47 kg P2O5/ha (British Survey of Fertiliser Practice, 2004). Where manure was applied, adjustments are made to fertiliser application rates according to Goodlass and Welch (2005). On tilled land, 30% of N fertiliser was applied as urea (British Survey of Fertiliser Practice, 2004). On the ‘impermeable’ soil type, 70% of the land area was assumed to have functioning field drains.

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