CN Balance Deep CompostingNutrient and Carbon Balance During the Composting of Deep LitterNutrient and Carbon Balance During the Composting of Deep Litter

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J. agric. Engng Res. (1999) 74, 145}153

Nutrient and Carbon Balance during the Composting of Deep Litter

S. G. Sommer; P. Dahl

Research Centre Bygholm; Danish Institute of Agricultural Sciences, Department of Agricultural Engineering; P.O. Box 536, 8700 Horsens,Denmark; e-mail: Sven G. [email protected]

(Received 11 September 1998; accepted in revised form 29 May 1999)

During the storage of solid animal manure, biological transformation of nitrogen (N) and carbon (C) may

increase the temperature from 60 to 703C,i.e. composting. Composting may cause emission losses of ammonia

(NH

) and carbon dioxide (CO

). Furthermore, plant nutrients may leach from the compost heaps. During

a composting period of 197 day from September 1997 to April 1998, emission of NH

, nitrous oxide (N

O),

methane (CH

) and CO

was measured using dynamic chambers covering three heaps of deep litter from

a house with dairy cows. Leaching of nutrients during composting was determined. Denitri"cation was

estimated as N unaccounted for in an N mass balance. The heaps were either mixed once after 30 days,

compressed initially or left untreated. Compacting the heap caused a temperature increase from 10 to 50}603C.

The temperature increased from 30 to 403C in the heap being mixed. From both the compacted and mixed heap,

the cumulative ammonia volatilization was 0)2 kg N/t corresponding to between 2

)6 and 3% of the total N. Half

of this amount was lost from the untreated heap in which the temperature only increased marginally in the "rst

days after the start of the experiment. Cumulative CO

losses were 33 (19%), 20 (12%) and 17 kg C/t (10%) from

the litter mixed after 30 days, compressed deep litter and untreated deep litter, respectively. Emissions of N

O

and CH

were low. Nitrogen losses due to leaching were (0)8% of the initial N. Total nitrogen losses due to

denitri"cation, NH

emission and leaching was from 5 to 19% of the initial N, the lowest from mixed and the

highest from untreated litter.

1999 Silsoe Research Institute

1. Introduction

Solid manure amounts to about 20% of the Danish

manure(Poulsen & Kristensen, 1998). Farmyard manure

constitutes the majority of solid manure; however, an

increasing interest in loose housing systems built with

solid #oors strewn with straw for welfare reasons will in

future increase the amount of deep litter(Andersenet al.,

1999). It is the policy of the Danish government that

10}20% of Danish agriculture should be farmed in agree-

ment with the rules for organic farming. This will contri-

bute to an increased production of solid manure, asorganic farmers tend to have animals on deep litter.

During storage, 20}40% of N in deep litter may be

lost, mainly though gaseous emission (Karlsson & Jep-

pson, 1995;Eghballet al., 1997). The Danish government

intends to reduce the amount of N imported to farms in

feed and fertilizers, thus, a reduction in the loss of N fromagriculture is needed to maintain the plant production on

traditional farms. In organic farming, N is mainly pro-

vided by N-"xing leguminous plants, and as large a part

as possible of this N has to be transferred in manure from

the grazed "elds to "elds in rotation. E$cient use of

manure-N for plant production is, therefore, very impor-

tant if plant production is to be maintained in both

traditional and organic farming systems.

Composting processes and gaseous emission of oxi-

dized and reduced nitrogen has been measured during

composting of municipal litter or livestock manure beingturned frequently, often several times each week (Hell-

manet al., 1997;Martin & Dewes, 1992). However, there

are few studies of nutrient losses from deep litter during

composting. During storage, the deep litter will start to

compost and organic farmers will enhance the composting

Article No. jaer.1999.0446, available online at http://www.idealibrary.com on

0021-8634/99/100145#09 $30.00/0 145 1999 Silsoe Research Institute


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Table 1Quantity and composition of stored deep litter from housing of dairy cows. The deep litter was compressed, mixed after 30 days anduntreated. Volume of the deep litter heaps being 3, 3'2 and 3'6 m

3, respectively. (Standard deviation in bracket for two samples)

Sampling Treatment Amount, Composition, g /kgoccasion t

DM Ash Ntotal TAN NO3 P K C

Initial Untreated 0)720 422 (1) 61 (1) 8)4 (0)3) 0)54 (0)03) 0)20 (0)00) 1)43 (0)03) 13)5 (0)1) 177)9 (0)9)Compressed 0)980 379 (50) 52 (6) 7)5 (1)1) 0)63 (0)04) 0)13 (0)04) 1)21 (0)20) 12)0 (1)3) 160)3 (24)2)

Mixed 0)660 409 (11) 59 (2) 8

)3 (0

)1) 0

)60 (0

)04) 0

)25 (0

)04) 1

)40 (0

)02) 13

)7 (0

)5) 172

)4 (4

)8)

End Untreated 0)810 214 (9) 46 (2) 6)0 (0)2 0)21 (0)02) 0)00 (0)00) 1)16 (0)04) N.D. 85)98 (6)1)Compressed 0)990 229 (5) 55 (4) 6)5 (0)3) 0)26 (0)02) 0)00 (0)00) 1)31 (0)07) N.D. 91)65 (4)3)Mixed 0)810 202 (3) 46 (3) 6)4 (0)4) 0)23 (0)02) 0)00 (0)00) 1)17 (0)05) N.D. 79)20 (3)0)

DM, dry matter; TAN, total ammoniacal nitrogen.

process by mixing the heap once after one month, be-

cause they believe that composting improves the fertilizer

value of organic manure.

Gaseous emission of N of C and leaching losses ofN and P during composting of deep litter has been

quanti"ed in this study. A movable dynamic chamber

was used to determine gaseous losses, and liquid from the

compost was collected for the purpose of estimating

leaching losses of nutrients. Furthermore, the loss of

N caused by denitri"cation was estimated as a di!erence

by means of a mass balance. Techniques for reducing the

losses were developed and tested.

2. Material and methods

2.1. reatments

Gas emission and leaching losses of nutrients were

measured during 197 days, composting in three pilot-

scale heaps of deep litter from the housing of dairy cows.

The litter was stored in heaps with a length of 3)7 m,

width of 1)9 m and height of 1)3 m on a sealed surface

(length of 4m, width of 2 m), with collection of runo!to

closed containers buried in the soil. The amount and

composition of the deep litter used for composting isgiven inTable 1.In the experiment from 29th September

1997 to 14th April 1998, the deep litter was mixed by

treating the material three times with a manure spreader

on the "rst day of the experiment. Immediately after this

treatment, three portions of the litter were stored under

the following conditions: (1) compressed once during

storage, (2) mixed once by turning the heap manually

after 30 d, and (3) untreated.

2.2. Dynamic chamber

The dynamic chamber consists of a mobile chamber

covering the storage during measurements, a ventilatorfor suction of air through the chamber, and equipment

for measurement of gas, temperature and wind velocity.

A "eld laboratory placed close to the experimental area

provided the supply of electricity (340 V AC) to the venti-

lators and instruments for measurement of gas emission.

The three mobile chambers on wheels had the dimen-

sions: height, 1)6 m; width, 2 m; and length 4 m. The

chambers were made of marine plywood and mounted

on a metal frame, with only one gable closed by plywood,

the opposite end being open for facilitating the chambers

to be moved over the heaps, and connected to a station-

ary gable placed at the end of the sealed surface. The

gable on the chambers had an opening for incoming air.

A steel tube (length of 2 m, inner diameter of 0 )40 m) with

a ventilator was connected to the stationary gable. A rec-

tangular metal frame was mounted on the sealed surface

perpendicular to the stationary gable. The dimensions

(length of 4 m, width of 2 m) of the frame allowed it to "t

closely with the chambers when mounted. Air was drawn

through the chamber by the ventilator, enabling mea-

surements of the #ux of gases to and from the chamber.

Air#ow through the dynamic chamber was measured

with cup anemometers in the steel pipe, the air#ow ratescould be adjusted from the "eld laboratory. Air temper-

ature and the temperature 0)40 m above the bottom of

the deep litter heap was measured with PT100 and ther-

mocouple sensors (Kontram A/S, DK-Copenhagen). The

sensors were connected to a datalogger (Datataker

DT200, Data Electronics Ltd, Australia).

One-quarter of an hour before a measurement, the

chambers were moved over the deep litter heap and "xed

S . G . S O M M E R ; P . D A H L146


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to the stationary gable. When measuring emissions of

NH

, the wind speed was adjusted to 3 m/s; and when

measuring emission of N

O, CH

and CO

, the wind

speed was adjusted to 1)2 m/s. Atmospheric NH of air

#owing into the chambers and from each chamber was

determined with two active denuders (Ferm, 1979) at

each sampling occasion. For the analysis of CH

, N

O

and CO

, four gas samples of 55 ml were taken with

syringes both at the inlet of the chamber, and from the

steel tube 30 cm from the gable on each measuring occa-

sion. The samples were stored as described below for gas

samples taken from the deep litter heap. The emission

was calculated as the di!erence in the #ux between the

incoming and outgoing gases. Determination of emission

was stopped in January 1997 after 87 days, because no

gas emission could be detected in January. Concentra-

tions of gas in and emissions from the heaps were deter-

mined twice on the "rst day, once each day from day 2

to 6, twice per week from week 2 to 5, once each week

from week 6 to 8 and once every fortnight from week

9 to 12.

2.3. Gas-phase composition

For the determination of CH

, N

O, CO

and oxygen

(O

) gas samples were collected from the centre of thedeep litter heaps by modifying the technique ofPetersen

et al. (1998). The two ends of a #exible, but rigid plastic

tube with an internal diameter (i.d.) of 10 mm and con-

taining four holes, 2 mm in diameter, per cm length were

connected to two 2 m lengths of gas-tight Te#on tubes

(i.d. 2 mm). The Te#on tubes were connected to a dia-

phragm pump (Model 5002, ASF GmbH, Germany).

A silicone tube was inserted into the rigid tube, but after

2}3 weeks no air samples could be collected, and on day

30 the silicone tube was removed from the rigid plastic

tube in the heap that was mixed after 30 days. A septumfor gas sampling was located immediately after the dia-

phragm pump, continuously circulating air through the

tubes during an experiment. Four samples of 60 ml were

taken at each sample collection with syringes. The gas

samples were transferred to 5 ml glass bottles "tted with

butyl rubber septa. When transferring a sample to the glass

bottle, an extra needle was inserted through the rubber seal

and the bottle was #ushed with 45 ml of the gas in the

syringe; then the needle penetrating the septum was re-

moved and the 15 ml remaining in the syringe was injected.

2.4. Nutrient composition

At the initiation and the conclusion of the experiment,

two samples each of 2 l of organic material were taken

from each heap. Samples of liquid (0)5 l) leaching from

the dung heap were taken when the containers were

nearly full and emptied. The samples of organic material

and liquid were stored at !183C.Before analysis, the organic material was thawed to

03C and the sample of 2 l was "nely chopped with a cut-

ting machine. Representative subsamples of about 500 g

of the chopped material were then cut into small pieces

and from this material 100 g was taken for analysis. All

manure samples were analysed for dry matter (DM), ash

content, total C, Kjeldahl N (N

), total ammoniacal

nitrogen (TAN), NO

, P and K.

2.5. Analysis

2.5.1. Ammonia

The concentration of ammonia in the air from the

background and from the dynamic chamber was deter-

mined by active denuders (Ferm, 1979). An active de-

nuder consists of a glass tube (length 500 mm, inner

diameter 7 mm) coated on the inside with oxalic acid,

through which air is drawn at a "xed air#ow. A dia-

phragm pump provides suction and a critical ori"ce

adjusts the air#ow to exactly 0)9 l/min through the de-

nuder. All NH#owing into the tube is absorbed by the

oxalic acid. After exposure, the amount of NH

absorbedin the tubes was determined, by dissolving the coating in

5 ml water and analysing NH

concentration using

a QuickChem 4200 (Lachat Instruments WI, USA).

2.5.2. Methane,nitrous oxide,carbon dioxide and oxygen

Nitrous oxide and CH

were measured on a Hewlett-

Packard (5890, series II) gas chromatograph with an

electron capture detector and a #ame ionization detector.

It was equipped with a 1)8 m3 mm column with

porapak Q 80/100 for N

O; with Ar/CH

(95/5) used as

carrier gas at 30 ml/min; and temperatures of injectionport, oven and detection were 110, 40 and 3203C, respec-

tively. Methane was isolated with a 1)8 m3 mm column

with poropak N 80/100; He was used as a carrier gas at

30 ml/min; and temperatures of injection port, oven and

detection were 110, 40 and 2703C, respectively. Oxygen

and CO

were measured on a Varian 3350 gas chromato-

graph equipped with a thermal conductivity detector. It

was equipped with a 1 m3 mm column with Molecular

Sieve 5A 60/80 for isolating O

and a 2 m3 mm Haysep

R 80/100 for CO

. The carrier gas was He at a #ow rate

of 30 ml/min, and the temperatures of oven and detectorwere 30 and 1903C, respectively.

2.5.3. Nutrient composition

Total ammoniacal nitrogen and NO

in the solid

manure were extracted in 1 M KCl for 30 min, "ltered

147COMPOSTING OF DEEP LETTER


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before analysis with a QuickChem 4200 #ow injection

analyser (Lachat Instr. WI, USA). Dry matter was deter-

mined after drying at 1053C for 24 h, and ash content at

5503C for 4 h. Total C was determined by dry combus-tion (Leco model 521-275), K by #ame photometry

(FLM3, Radiometer) after incineration and dissolving in

acid, and P was measured colorimetrically (Spectronic

1001, Braush & Lomb) after incineration and dissolving

in acid, and a colouring reaction with ammonium molyb-

date vanadate. Total nitrogen was analysed using

the Kjeldahl method and a Kjellfoss 16200

(Copenhagen, DK). Total-nitrogen, P, K, TAN and NO

in the leachate from the dung heap were determined

without extraction.

2.6. Calculations

The average NH

concentrationC

in g NH

-N/m

in the air passing through two Ferm tubes used at each

sampling occasion was calculated by the following equa-

tion:

C"

(C#C

!2C

)

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CN Balance Deep CompostingNutrient and Carbon Balance During the Composting of Deep LitterNutrient and Carbon Balance During the Composting of Deep Litter