~ Pergamon Wal. Sci. Tech. Vol. 39, No. 12, pp. 361-364, 1999101999

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A SUMMARY OF THE AGRICULTURALISSUES RAISED AT THE CONFERENCE

Alan Frost

SAC, Bush Estate, by Penicuik; Midlothian, EH26 OPH. UK

INTRODUCTION

The conference ranged widely over the whole field of diffuse pollution and agriculture with many papersbridging the artificial divide, unavoidably created by the programming, between agricultural, catchment andurban issues. However, for the purposes of this summary, the papers can be divided into groups on the basisof the pollutant problem addressed. Three main themes appear: nitrogen, phosphorus and pesticides. Thissummary will attempt to examine the issues raised in these themes, the current state of knowledge in each ofthem and to identify any similar threads which run through all of them. iCI 1999 Published by ElsevierSCience Ltd on behalf of the 1AWQ. All rights reserved

KEYWORDS

Agriculture; diffuse pollution; nitrogen; pesticides: phosphorus.

NITROGEN

It was apparent from the papers offered that the science of nitrogen and its transformations and movementwithin soils is largely understood. However, as Bernard Tychon's paper demonstrated, to progress from thisbasic understanding to useful predictions of nitrogen pollution in any given field situation, requires a hugeeffort in characterisation of the soil and the hydrology of the site. Perhaps what is needed more than furtherstudy of the basic science, is the development of shortcut practical methods of predicting hard to measureparameters (such as for example, hydraulic diffusivity) from easy to measure parameters (such as texture).

Where problems in the science do exist. they tend to be in the scaling up of field observations to thecatchment scale. Marcel de Wit explained how huge reductions in the input of nitrogen fertiliser to the Elbecatchment in Germany had resulted in very little change in river concentrations even after five years.

Further problems exist in predicting the transport of nitrogen once it has left the well studied root zone enroute to surface or ground water. Hans Anderson demonstrated large (up to 83%) losses of leached nitratesomewhere within the transmission zone from soil to water. Clearly this is an area which would repayfurther study.

Methods discussed to control excess nitrogen pollution ranged from cover crops and use of high carbon tonitrogen ratio soil additions to promote denitrification to manipulation of soil water regimes using drainageagain to promote denitrification (Ng et at.). Several speakers discussed buffer zones with the importance oftheir position within the landscape being stressed by Martin Blackwell.

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362 A.FROST

Accurate fertiliser rate recommendations are clearly important but even the best predictions are subject tothe uncertainty of weather conditions after application. There was much discussion of the role of fertiliserrecommendations based on yield trials, as is current practice, for environmental protection. While theapproach of restricting nitrogen inputs to what is agronomically needed may be adequate in the case ofcereals, it certainly is not in the case ofleafy field vegetables.

PHOSPHORUS

While research in nitrogen movements, at least within the soil, appears to be largely complete, the wholefield ofphosphorus movement within soil is still very much an active research area. The fact that it has beenso for decades perhaps is an indication ofthe complexity of some of the problems.

Phosphorus movement associated with soil erosion was one topic addressed by several speakers. There is avery extensive literature on soil erosion dating back sixty years and more, but almost all of it is concentratedon protection of the eroding soil rather than the receiving external environment. A shift in perspective isrequired. For example, a soil conservation worker might consider a reduction in soil loss from 10tonnes/ha/annum to 2 tonnes/ha/annum to be a success but from a water quality standpoint, losses of 1 tonneper hectare per annum or less may pose serious threats to sensitive water bodies. The concept of soil losstolerance must be replaced by one of environmental tolerance which will be a function of the receivingwater body rather than the soil.

Issues such as connectivity and delivery ratio become far more important with the concept of "extendeddrainage networks" comprising not only rivers and ditches but also roads and tracks being introduced byAndy Fraser. The position of the eroding land within the landscape becomes of paramount importance asLouise Heathwaite demonstrated with the concept of "Critical source areas". Unless the eroded soil and itsassociated phosphorus reaches a water course, the erosion may be ofno significance.

A great deal of discussion centred on phosphorus leaching or dissolution with the need for an adequatesimple soil test being highlighted (Turner). Existing agronomic soil tests are not designed to predict thepoint at which phosphorus begins to leach from soils in damaging quantities and they may not be reliablepredictors of risk.

Dissolution is only part of the problem. Once the phosphorus is on the move, it still must travel manymetres or even kilometres through porous materials which in general will not be phosphorus saturated beforeit can enter surface water and cause a problem. A very interesting paper was presented by Rachel Matthewson colloidal phosphorus which may provide the answer to how some of what has traditionally been regardedas dissolved phosphorus makes this journey without being re-adsorbed. Rachel Oils offered anotherinteresting paper on the presence ofdissolved and colloidal phosphorus within drainage water in field drains,another "short cut" route from topsoil to water and one which will pose problems for possible controlmeasures such as buffer strips.

A study using phosphorus export coefficients was described by Sarah McGuckin. While such methods maylack the intellectual attraction ofmechanistic models, they do have the distinct advantage that they work andgive usable results. In time, they may be replaced by mechanistic models such as that described by JuorgGroenroos (Rekolainen et aJ.)but, as yet, the state of knowledge is probably inadequate.

Potential control methods for phosphorus pollution formed another major area of discussion. The use of theenzyme phytase to increase the availability of the phosphorus in animal feed was regarded as one method ofreducing phosphorus inputs to the environment. Treatment of animal manures with phosphorus adsorbingchemicals such as alum was also discussed but was less favourably viewed, both from the point ofview that,although immobilised, the phosphorus was still accumulating in the environment and still posed a potentialrisk and also from the point of view that to do so was a waste ofwhat is a valuable non-renewable resource.

Possible best management practices (BMPs) to reduce the risk of phosphorus pollution were discussed.These included buffer strips and phosphorus balance methods of determining phosphorus application rates.At least one speaker was of the opinion that the phosphorus problem was intractable and should be ignored

Agricultural issues raised at the conference 363

and efforts concentrated on actions such as biological lake remediation. There appeared to be two types ofproblem area. Those such as the Loch Leven catchment, visited on the field trip, with relatively low soilphosphorus levels and the possibility of a balance between phosphorus inputs and offtakes withoutdrastically reducing agricultural productivity, appeared to be amenable to solution by agricultural BMPsintroduced by traditional extension methods. Those such as Delaware, described by Tom Sim, where longterm intensive livestock production has resulted in soils with excessively high phosphorus status andphosphorus inputs exceeding offtakes by as much as 80 kg/ha/annum, do not appear to be susceptible tosuch agriculturaIly based solutions and may need legislation in the form of planning control if the problemscaused are to be addressed.

PESTICIDES

It was generaIly felt that there was not any significant requirement for further research and that the solutionsto any problems which may exist already are available. With the increased adoption of better products,better sprayers, better use of adjuvants and better training of operators most such problems will disappear.

OTHER POLLUTANTS LESS WELL COVERED

With the notable exception of an excellent paper by Anne Sansom, the whole area of suspended solids as anenvironmental pollutant in their own right was largely ignored. This is certainly an area where further effortis needed.

Similarly, again with the exception of a paper delivered by David Kay (Wyer et al.), agriculturally derivedmicro-organisms as a pollutant were ignored. I am confident that when this group meets again in two yearstime, there will be far more on this important topic.

CONCLUSIONS

This paper summarizes contributions at the 3rd International IAWQ Conference on Diffuse Pollutiondevoted to agricultural/rural platform, workshop and poster presentations. There were over 120 presentationsat the conference. Some papers mentioned in this summary are not included in this issue ofWater Science &Technology which contains selected peer reviewed articles. A complete set of papers is included in theProceedings referenced below that can be obtained from the Scottish Environment Protection Agency.

It is hard to draw concise conclusions from such a wide ranging meeting but certain key issues appearedwith sufficient frequency to merit noting.

With regard to the science the following areas stood out:

• In all the topic areas, the hydrology of the problem was important and was too frequently neglected.

• The position of fertilised soils or of BMPs such as buffer strips in the overall landscape was importantand was frequently insufficiently considered.

• Pathways of transport from soil through the unsaturated and saturated zones (or field drains) below needfurther elucidation.

• Scaling issues (lab, plot, field, catchment, river basin) are difficult to deal with and are poorlyunderstood.

• With regard to control measures, the following are urgently needed.

• BMPs suited to controlling low rates of soil erosion without excessive cost to the farmer must bedeveloped.

364 . A. FROST

• BMPs are required which are able to deal with pollutants in drain flow without disrupting drainageelsewhere within the field.

• A simple measure of environmentally acceptable levels of soil phosphorus is needed. The requirement isso pressing that, provided it works reasonably well in practice, such a test need not be well foundedscientifically.

• More effort and expenditure should be addressed at getting research findings into practice on the'farm.

In general, at least in the cases ofnitrogen and pesticides, the science is so far ahead ofnormal farm practicethat the environmental benefits to be attained from money spent on extension work, far exceed any likelybenefit from further research.

REFERENCES

Anderson, H. E., Kronvang, B. and Larsen, S. E. (1999). Agricultural practices and diffuse nitrogen pollution in Denmark:empiricalleaclnng and catchment models. War. Sci. Tech., 39(12), 257-264 (this issue).

Blackwell, M. S. A. (1999). The use of conventionally and alternatively located buffer zones for the removal of nitrate fromdiffuse agricultural pollution. War. Sci. Tech., 39(12), 157-164 (this issue).

De Wit, M. and Behrendt, H. (1999). Nitrogen and phosphorus emissions from soil to surface water in the Rhine and Elbe basins.War. Sci. Tech., 39(12),109-116 (this Issue).

Dils R. M. and Heathwaite, A. L. (1999). The controversial role of tile drainage in phosphorus export from agricultural land.War. Sci. Tech., 39(12), 55-61 (this issue).

Fraser, A. 1.,Harrod, T. R. and Haygarth, P. M. (1999). The effects ofrainfall intensity on soil erosion and particulate phosphorustransfer from arable soils. War. Sci. Tech.; 39(12), 41-45 (this issue).

Heathwaite, A. L. and Sharpley, A. (1999). Evaluation measures to control the impact of agricultural phosphorus on waterquality. War. Sci Tech., 39(12),149·155 (this issue).

Matthews, R. A., Preedy, N., Heathwaite, A. L. and Haygarth, P. M. (1999). Transfer of colloidal forms of phosphorus fromgrassland soils. Presented at the IAWQ 3rd International Conference on Diffuse PoIlution.

McGuckin, S. 0., Jordan, C. and Smith, R. V. (1999). Deriving phosphorus export coefficients for CORINE land cover types.War. Sci Tech., 39(12), 47-53 (this issue).

Ng, H. Y. F., Tan, C. S., Drury, C. F. and Gaynor, J. Do. (1999). Effects of controlled drainage and subirrigation on tile nitrateloss and com yields. Presented at the IAWQ 3rd International Conference on Diffuse Pollution.

Rekolainen, 5., Groenroos, J., Baerlund, 1., Nikander, A. and Laine, Y. (1999). Modelling the impacts of management practiceson agricultural phosphorus losses to surface waters ofFmland. War. Sci. Tech., 39(12), 265-272 (this issue).

Sansom, A. L. (1999). Upland vegetation management: the Impacts ofoverstocking. War. Sci. Tech.; 39(12),85-92 (this issue).Sims, J. T., Goggin, N. and McDermott, J. (1999). Nutrient management for water quality protection: integrating research into

environmental policy. War. Sci. Tech., 39(12), 291-298 (this issue).Turner, B. L. and Haygarth, P. M. (1999). Phosphorus leaching under cut grassland. War. Sci. Tech., 39(12),63-67 (this issue).Tynchon, B., Vander Borght, P. and De Backer, L. W. (1999). Water and nitrogen study through soils of a small agricultural

water catchment. War. Sci. Tech.; 39(12), 69-76 (this issue).Wyer, M. D., Crowther, J. and Kay, D. (1999). Catchment modelling of non-point sources as a tool for remediation of non­

sewage inputs of faecal indicators to coastal waters producing compliance with Directive 76/1601EEC. Presented at thelAWQ 3rd International Conference on Diffuse Pollution.