Effect of composting on nutrient loss and nitrogen availability of cattle deep litter

European Journal of Agronomy 14 (2001) 123 – 133 www.elsevier.com/locate/eja

Effect of composting on nutrient loss and nitrogen availability of cattle deep litter S.G. Sommer * Research Centre Bygholm, Danish Institute of Agricultural Sciences, Department of Agricultural Engineering, PO Box 536, DK-8700 Horsens, Denmark Received 3 March 2000; received in revised form 11 July 2000; accepted 2 August 2000

Abstract Nitrogen and carbon emissions and plant nutrient leaching during storage of solid deep litter from dairy cow houses was examined in this study. Included was an assessment of the potential for reducing emission and leaching losses by compaction, mixing and by covering the deep litter. During a composting period of 132 days from October 1998 to March 1999, emissions of NH3, N2O and CH4 and leaching of nutrients during composting were measured. Denitrification was estimated as N unaccounted for in N mass balance calculations. During mixing of the deep litter, N was lost and the emission and leaching losses during composting were consequently low compared with the other treatments. Covering the compost with a porous tarpaulin or compacting the compost reduced emission losses to 12–18% of total-N compared with a loss of 28% during composting of untreated deep litter. Most of the nitrogen loss was due to NH3 volatilization; leaching accounted for about one fifth of the N losses and only a little N was lost due to denitrification. Leaching loss of potassium (K) was 8 – 16% of the amount present at the start of the experiment; compaction and a cover reduced the volume of liquid leaching from the heaps and K loss. Less than 0.3% of the total-N was emitted as N2O, and CH4 emission was between 0.01 and 0.03% of the C in the stored deep litter. The yield level of barley was poor in this study and the fertilizer effect of compost was low. The yield response of barley showed that compost had a significantly lower fertilizer efficiency than deep litter applied to the field directly after emptying the animal house. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Solid manure; Storage; Composting; Ammonia; Greenhouse gas; Nnitrogen availability

1. Introduction Solid manure amounts to about 20% of all the manure produced in Denmark (Poulsen and Kristensen, 1998); at present farmyard manure consti* Tel.: +45-7629-6063; fax: + 45-7629-6100. E-mail address: [email protected] (S.G. Sommer).

tutes the majority of this solid manure. However, for animal welfare reasons there is an increasing interest in loose housing systems built with solid floors strewn with straw, and these systems are expected to increase the amount of deep litter produced (Andersen et al., 1999). It is the policy of the Danish government that 10–20% of Danish agriculture should be organically farmed (Danish

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Agricultural Advisory Centre, 1998), and this change may further increase the production of solid manure, as organic farmers tend to keep their animals on deep litter. Danish farmers have a tendency to empty their dairy cow houses and store the deep litter in the field until they spread the deep litter in spring, and organic farmers have a tradition of composting deep litter. During storage 20 – 40% of the N in deep litter stored in heaps may be lost during the composting process that starts in most deep litter heaps and most of this N is lost through gaseous emission (Karlsson and Jeppson, 1995; Eghball et al., 1997). The Danish government intends to reduce the amount of N imported to farms as feed and fertilizers, and thus, a reduction in the amount of N loss from agriculture is needed in order to maintain crop production on traditional farms. In organic farming systems, N is mainly provided by N-fixing leguminous plants, and as much as possible of this N has to be transferred in manure from grazed pastures to arable fields in rotation. The efficient use of manure-N for plant production is therefore essential if plant production is to be maintained in both conventional and organic farming systems. Emission from livestock manure contributes significantly to atmospheric nitrous oxide (N2O) and methane (CH4). In Denmark anthropogenic emission of CH4 is 430 000 t per year, of which 172 000 t is emitted during collection and storage of manure and from manure applied to the soil. The emission of N2O is 36 000 t per year, of which 7000 t is emitted from animal manure (Petersen and Sommer, 1999). Emissions of CH4 and N2O from livestock manure contributes 5 – 6% to the global emission of CH4 (Hogan et al., 1991; Rotmans et al., 1992) and 7% to the global emission of N2O (Khalil and Rasmussen, 1992). Composting processes have been examined and gaseous emissions of oxidized and reduced N have been measured during composting of municipal litter or livestock manure that is turned frequently, often several times each week (Martin and Dewes, 1992; Hellmann et al., 1997). However, there have been few studies of nutrient losses during the storage and composting of deep litter that has not been mixed before storage or during

the storage and composting period. We believe that it is necessary to study the losses of nutrients during storage and composting of deep litter, focusing on ammonia (NH3) volatilization and denitrification losses. Furthermore, techniques for the reduction of losses need to be developed; one mode of action may be a reduction in NH3 volatilization by reducing air exchange through the heap either by covering or by compacting the heap (Karlsson, 1996; Lammers et al., 1997). Increasing immobilization through mixing and crushing the deep litter immediately before storage may also reduce gaseous losses, as indicated in the study of Sommer and Dahl (1999). Gaseous emission of N and C and leaching losses of N and P during composting of deep litter were quantified in this study. Emissions of NH3, CH4 and N2O were measured using chamber techniques. Liquid from the compost was collected in order to estimate leaching losses of nutrients. Furthermore, the loss of N caused by denitrification was estimated using a mass balance equation. The four compost heaps were either mixed with a manure spreader, compressed with a front loader, covered with a tarpaulin or left untreated. The yield response of spring barley was used to estimate the 1st year fertilizer value of the compost and of fresh deep litter; for comparison, pig slurry was injected in a parallel experiment.

2. Materials and methods

2.1. Treatments Gas emission and leaching losses of nutrients were measured during composting of four pilotscale heaps of deep litter derived from the same mat in a dairy cow house. The litter was stored in heaps 3.7 m long, 1.9 m wide and 1.3 m high on a sealed surface (4× 2 m), with the collection of run-off in closed containers buried in the soil. The amounts and composition of the deep litter used for composting are given in Table 1. In the experiment (from 23 October 1998 to 4 March 1999; 132 days), the deep litter was treated as follows: (1) compacted with a front loader; (2) cut and mixed by treating the material three times with a

Sampling occasion

Treatment

Density (t m−3)

Amount (t)

Composition (g kg−1) DMa Ash

Total-N

TAN

NO3−N

P

K

C

Before composting

Compacted Cut Covered Untreated

0.49 0.30 0.38 0.42

1.680 1.100 1.260 1.480

377.0 358.0 358.3 360.4

(52.7) (10.1) (36.8) (13.1)

50.7 55.5 50.1 52.9

(2.5) (2.7) (4.1) (3.1)

8.8 6.9 7.8 8.7

(0.3) (0.2) (0.9) (0.2)

3.2 1.6 2.3 2.5

(0.5) (0.2) (0.1) (0.1)

0.03 0.05 0.02 0.02

(0.03) (0.02) (0.01) (0.02)

1.14 1.27 1.19 1.15

(0.0) (0.1) (0.3) (0.1)

9.8 9.7 10.0 10.9

(0.6) (0.4) (1.1) (1.0)

160.3 149.5 153.5 153.8

(24.2) (3.8) (17.5) (5.9)

After composting

Compacted Cut Covered Untreated

N.m.b N.m. N.m. N.m.

1.520 1.000 1.120 1.420

259.9 234.1 264.6 204.2

(17.1) (25.6) (18.6) (19.1)

56.6 59.6 64.7 44.8

(6.4) (9.3) (7.4) (3.7)

8.0 6.8 7.4 6.4

(1.4) (0.5) (0.5) (0.2)

0.2 0.2 0.2 0.1

(0.0) (0.0) (0.0) (0.0)

0.40 0.17 0.64 0.43

(0.35) (0.03) (0.08) (0.19)

1.53 1.40 1.56 1.22

(0.1) (0.2) (0.1) (0.1)

9.6 7.5 13.2 7.4

(2.4) (1.2) (1.7) (1.8)

106.6 92.5 103.9 82.4

(5.0) (10.0) (7.8) (7.9)

a b

DM: dry matter. N.m.: not measured.

S.G. Sommer / Europ. J. Agronomy 14 (2001) 123–133

Table 1 Quantity and composition of stored deep litter from housing of dairy cows before and after composting [SE in parentheses (n= 3)]

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manure spreader immediately before initiation of the experiment; (3) covering the heap with a porous tarpaulin; and (4) no treatment. Ammonia volatilization was determined using a dynamic chamber technique (Sommer and Dahl, 1999) each day for the first 7 days and every 2nd day in the period 8 – 28 days. The measurements of NH3 emission from the untreated deep litter failed due to malfunction of the technique. Methane and N2O emissions from each heap were determined using four static chambers (Mosier, 1989). During the measurement periods of 20 min, two chambers were mounted on top of the heap and two chambers on the upper half of the side of the heap. The emissions were measured every 3rd day during the first 21 days, twice a week during the period 21–60 days and once a week during the period 60–124 days. Air temperature and the temperature 0.4 m above the bottom of the deep litter heaps were measured with PT100 and thermocouple sensors (Kontram A/S, Copenhagen, Denmark). The sensors were connected to a datalogger (Datataker DT200; Data Electronics Ltd., Australia). Gas composition in the heap was measured by collecting gas samples from inside the heaps at a point 0.4 m above the bottom of the heap (Petersen et al., 1998).

2.2. Nutrient composition At the beginning and end of each 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 − 18°C. Before analysis, the organic material was thawed to 0°C and a 2-l sample was finely chopped with a cutting 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 (total-N), total ammoniacal N (TAN), NO− 3 , P and K.

2.3. Fertilizer efficiency of manure A field farmed according to the regulations for organic farming situated at Askov experimental station was selected for the manure treatments. The field was on a sandy loam soil (Soil Taxonomy System) with 10.6% clay, pH 6.6, CEC 120 mmol kg − 1 dry soil and 27 g C kg − 1 (Hansen, 1976). In total, 36 experimental plots (14×5 m2) were allocated to the study. On 31 March 1999, the composted deep litter was applied to the plots at a rate of 59 t ha − 1 and incorporated by mould ploughing into the soil immediately after application. For comparison, fresh deep litter was applied and incorporated at 59 t ha − 1, and pig slurry was injected to 5–8 cm depth at application rates of 7.4, 14.8, 22.2, 29.6 and 37.0 t ha − 1. The composition of the composts is given in Table 1. Pig slurry composition was 35.3 g DM l − 1, 3.7 g total-N l − 1 and 2.6 g TAN l − 1, fresh deep litter composition was 188.6 g DM l − 1, 6.5 g total-N l − 1 and 1.6 g TAN l − 1. The manure was applied to 14 ×4 m2 of the plot, leaving an untreated area of 14 × 1 m2 between the manure-amended parts of the plots. There were three replicates of each treatment and six untreated plots were included in the study. The spring barley was drilled in rows 12 cm apart on 20 April 1999 at a sowing rate of 167 kg grains ha − 1. The barley was harvested on 13 August 1999 from 10× 1.43 m2 of the plot. Grain and straw yields were recorded and samples of grain and straw were analysed for DM and total-N contents.

2.4. Calculations Previous studies have shown that little or no trace gases are emitted from the bottom half of the heap, because the high temperature in the compost generates an efflux of air through the top and upper parts of the heap and air intake from the lower parts of the sides (Fernandes et al., 1994; Hellmann et al., 1997). Therefore, the emissions of greenhouse gases in Figs. 3 and 4 are given as the mean of emissions measured with the four chambers mounted on the upper half of the heaps.

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Total recovery (R kg t − 1) of N, P, K, DM and C was calculated with the mass balance equation: R = (Cstart ×Qstart-Cend ×Qend) where Cstart and Cend are the component concentration (kg t − 1); and Qstart and Qend the mass (t) of the heap at the beginning and end of a composting period. The results from the study of yield of barley fertilized with compost or deep litter in spring were tested with a one-way analysis of variance (Proc. GLM; SAS Institute, 1989). A linear regression analysis was used to test the response of DM yield in relation to the application of pig slurry to spring barley (Proc. Reg; SAS Institute, 1989). For the purpose of keeping the illustration simple the figures are only depicting temperature, gas emission and gas composition of the cut and mixed and the compacted litter.

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3. Results and discussion

3.1. Temperature and O2 concentration in the compost The composting of the deep litter in the four heaps was characterized by an initial increase in temperature to between 60 and 70°C (Fig. 1). The temperature declined slowly from this level and after 20–30 days the temperatures were between 10 and 35°C. After c. 30 days the temperature increased by 5–10°C; this increase was related to the growth of fungi, which is inactivated at the initial high temperatures of the compost (Hellmann et al., 1997). The high temperature generates an upward airflow and consequently air mostly enters through the lower section of the heap. The temperature increase is generated by aerobic metabolism of microorganisms in the heap, and is therefore affected by the availability of O2. Oxygen in the heap is replenished by air flowing into the heap, and therefore affected by the air exchange that is strongly related to air-filled space within the heap (Jeris and Regan, 1973). Thus, in the compacted compost the O2 concentration was low for 50 days, indicating a reduced air exchange compared to the other treatments with low O2 concentration only in the first 30 days (Fig. 1).

3.2. Greenhouse gases

Fig. 1. Air temperature and temperature readings during storage of deep litter from dairy housing (top). Variation in O2 concentration of the heaps (bottom). The figure depicts trials with deep litter compacted at storage and litter cut and mixed.

During the first 20 days of composting, the CO2 concentrations were highest in the cut and mixed deep litter, and during the next 40 days the CO2 concentration was highest in the compacted heap (Fig. 2). Cutting and mixing the deep litter may have increased the degradability of the litter and thus microbial transformation of C to CO2. The enhanced concentration of CO2 during the 20–60 day period may have been caused by the low air exchange in the compacted deep litter. The CO2 concentration in the untreated heap and in the heap covered with tarpaulin followed the pattern of the cut and mixed litter, but at a lower level. In spring 1999 after 90 days of composting the CO2 concentration increased in the untreated heap, reflecting the increase in compost temperature;

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Dahl, 1999). Methane emission from the cut and mixed and the compacted heap was between 44 and 48 g C t − 1, which is 0.03% of the total-C in the compost (Table 2). Apart from in the cut and mixed heap, the N2O concentration in the heaps was close to the ambient concentration during 0–20 days (Fig. 4), because nitrifying and denitrifying (i.e. N2O-producing) microorganisms are generally not thermophilic (Hellmann et al., 1997). After the temperature had declined, N2O concentrations increased in all heaps. In the compacted heap, a high N2O concentration was measured for the entire low-temperature period. It has been shown Fig. 2. CO2 concentration in heaps of deep litter over 124 days. The figure depicts trials with deep litter compacted at storage and litter cut and mixed.

that is, indicating metabolism by cellulose- and hemicellulose-decomposing microorganisms (Herrmann and Shann, 1997). Emission of CO2 was not measured with the static chamber technique due to high CO2 concentrations (\ 10 000 ppm). At high concentrations of the acid gas CO2, the emission of the gas will be reduced by placing a chamber on the humid heap with a high pH. Methane concentrations were high in the cut and mixed heap from day 0 to 25 and in the compacted heap from 0 to 50 days of composting (Fig. 3). The high CH4 concentration is enhanced by an increase in the number of methanogenic microorganisms in the thermophilic phase (Hellmann et al., 1997), and the increase in production rate of CH4 with increasing temperature (Husted, 1994). In both heaps O2 concentrations were low initially (Fig. 1), and the combination of low O2 concentrations and high concentrations of CH4 in the heap indicates that the interior of each heap was partly anaerobic during this period. Methane emission was high from 0 to 40 days from the compacted and from the cut and mixed deep litter (Fig. 3). An increase in the emission from all heaps was measured after 100 days. Peak emission rates varied between 2 and 7 mg CH4-C t − 1 min − 1 and were within the range determined in previous studies (Husted, 1994; Sommer and

Fig. 3. CH4 concentration in heaps of deep litter (top) and emission from two deep litter heaps over 124 days (bottom). The figure depicts trials with deep litter compacted at storage and litter cut and mixed.

S.G. Sommer / Europ. J. Agronomy 14 (2001) 123–133 Table 2 Cumulative emission of nitrous oxide (N2O) and methane (CH4) during 124 days of compostinga Treatment

Nitrous oxide N2O-N (g N t−1)

Compacted 27.01 Cut 7.40 Covered 16.73 Untreated 10.67 a

Methane CH4-C

(% total-N) (g C t−1)

(% C)

0.3 0.1 0.2 0.1

0.03 0.03 0.01 0.01

48.06 44.05 9.36 7.56

The emission is given as% of initial contents of C and N.

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heaps, and N2O in compost with high concentrations of TAN is probably produced both during nitrification and also as an intermediate product of denitrification (Lipschultz et al., 1981; Petersen et al., 1998). In the heap with cut and mixed deep litter, N2O emissions were significant after 2 days of composting, and after 17–20 days an increase in N2O emission from the other three heaps was measured. High N2O emission was measured between 20 and 60 days of composting; the highest N2O emissions of up to 1.2 mg N2O-N t − 1 min − 1 were from the compacted heap and from the heap with cut and mixed deep litter. A similar trend in the time course of N2O emission rate has been shown both in studies of compost that was turned weekly or several times a week (Czepiel et al., 1996) and untreated compost (Petersen et al., 1998). The emission rates found in this study were in agreement with the emission rates from turned livestock waste in wind rows and from composted sow manure (Czepiel et al., 1996; Petersen et al., 1998). Nitrous oxide emission was in the range 7.4–27.0 g N t − 1 or about 0.1–0.3% of the total-N in the compost (Table 2). The highest emission was from the compacted compost and the lowest from the cut and mixed compost.

3.3. Ammonia (NH3) emission

Fig. 4. N2O concentration in heaps of deep litter (top) and emission from two deep litter heaps over 124 days (bottom). The figure depicts trials with deep litter compacted at storage and litter cut and mixed.

that there are both aerobic zones with nitrification and anoxic zones with denitrification in compost

Ammonia was emitted from the heaps during the first 20 days after establishment (Fig. 5), a loss pattern similar to the findings of Lammers et al. (1997) and Karlsson (1996). The accumulated NH3 volatilization from the compacted and tarpaulin-covered heaps was similar and higher than that from the cut and mixed heap (Table 3). In contrast, a Swedish study showed that a tarpaulin cover reduced NH3 emission to about 10% of the emission from uncovered compost (Karlsson, 1996), indicating that the porosity of the tarpaulin should be low or that there should be no air exchange through the cover if NH3 emission is to be reduced by covering the heap. The emission was 40% lower from the heap with cut and mixed litter than from the compacted deep litter and from the covered heap (Table 3). The low emission from the cut and mixed litter may be related to the low initial TAN content of

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the litter (Table 1), showing that N must have been emitted during the pretreatment of the compost. Ammonia emission during composting was low compared with losses measured by Lammers et al. (1997), probably because immobilization in the animal house had reduced the TAN concentration of the litter stored in the heaps. Furthermore, the litter had a high C:N ratio of c. 20.

3.4. Mass balance and leaching losses of nutrients

Fig. 5. Emission rate (top) and accumulated loss of NH3 (bottom) over 32 days from three heaps of composted deep litter from the housing of dairy cows. The deep litter was either compacted at storage; cut and mixed or covered with a porous tarpaulin.

The reduction in C content was between 40 and 49% of the initial C content (Table 3) and at a level similar to previous measurements (Sommer and Dahl, 1999). The measured emission of CH4 was low and CO2 may have accounted for most of the C reduction. Leaching losses of P were less than 2.4% (Table 3) of the initial content, because P precipitates as solids that are not easily dissolvable. The loss of P was similar to the findings of Petersen et al. (1998) and Eghball et al. (1997). The concentration of P increased during composting as a consequence of the low losses of P and a reduction in the amount of deep litter. Potassium leaching was 8–16% of the initial K content, as shown previously (Petersen et al., 1998). The leaching loss is due to a high mobility of K salts that are easily dissolved in water. Compaction and covering with tarpaulin reduced leaching to 8–11% as compared to losses of 14–16% of K from the untreated and mixed composts. The lower leaching losses from these

Table 3 Differences in nutrient, dry matter (DM) and C content estimated as the changes in mass balance during composting of deep litter from 23 October 1998 to 4 March 1999 (132 days). Pool sizes in % of the nutrient or C at start. Phosphorus and potassium were only lost due to leaching, and there were no measurements of change in different DM and C pools Treatment

Compacted Cut Covered Untreated a b

Nitrogen

Phosphorus

Potassium

Dry matter

Carbon

Differencea (%)

Leaching (%)

NH3 loss (%)

Unaccounted (%)

Leaching (%)

Leaching (%)

Differencea (%)

Differencea (%)

18 11.6 15.4 27.7

2.3 2.9 2.6 3.4

14.9 7.2 16.7 N.m.b

1.0 1.4 0 N.m.

1.8 2.4 1.7 1.7

11.2 15.5 8.2 13.8

38 41 34 45

39.9 43.9 39.9 48.5

Difference in the amount of components in the deep litter before and after composting. N.m. not measured.

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Table 4 Dry matter and nitrogen yield of spring barley unfertilized or after spring application of 59 t ha−1 of deep litter and composta Application rate

No manure Fresh deep litter Compacted compost Cut compost Covered compost Untreated compost

Grain yield

Grain+straw yield

85% DM (t ha−1)

Fertilizer efficiencyb

Amount (t ha−1)

NH4-N (kg N ha−1)

Total-N (kg N ha−1)

85% DM N (t ha−1) (kg N ha−1)

N (kg N ha−1)

0 59

0 94

0 383

1.15B 2.07A

13.3BC 24.6A

2.48B 4.22A

23.7B£ 37.5A

0.200

59

16

389

1.42B

16.7BC

2.69B

25.5B

0.067

59 59

9 21

348 436

1.23B 1.60B

14.2BC 19.4AB

2.85B 31.0B

26.6AB 29.6AB

0.030 0.091

59

14

377

1.16B

12.8C

2.47B

22.0B

0.014

a Within a column means followed by the same letter are not significantly different according to Fisher’s LSD at a 0.05 probability level. b The efficiency of manure defined as fertilizer equivalent (fe) is the amount of total-N applied in slurry (Nslurry) required to achieve the same yield as 1 kg total-N applied in deep litter or compost nitrogen (Nsolids ). fe= Nslurry/Nsolids.

heaps were probably a consequence of a lower infiltration of water into the heap. Less than 4% of the initial N leached from the compost. The leaching losses of N were higher than those determined by Eghball et al. (1997) and Petersen et al. (1998). The concentration of TAN in the effluent was 0.02 – 0.43 g l − 1 and the NO− concentration was 0.1 – 0.3 mg l − 1: the 3 highest concentration was measured when emptying the containers the first time after the initiation of the experiment. The low concentration of NO− 3 in leachate from compost heaps is in accordance with previous observations of nutrient composition during composting of animal manure (Eghball et al., 1997; Petersen et al., 1998). According to the mass balance equation, N losses due to leaching, NH3 emission and denitrification were between 12 and 28% of the initial N. The N loss was lowest from the cut and mixed manure and highest from the untreated manure. The mass balance calculation confirms the findings from the emission measurements, showing low losses from cut and mixed deep litter due to N emission during pretreatment. The total losses were smaller than losses determined from pig solid manure and cattle manure (Petersen et al., 1998), probably because the C:N ratio of the deep

litter used in the study of Petersen et al. (1998) was between eight and ten, which is much lower than the C:N ratio of 20 found in this study. The high C:N ratio may have enhanced immobilization and thereby reduced nitrification and denitrification. It has been shown by Kirchmann (1985) that an increase in the C:N ratio significantly reduces N losses during storage and composting of livestock solid manure. The amount of N not accounted for in the mass balance was low, showing that little N had been lost through denitrification. Petersen et al. (1998) have previously measured denitrification losses of 13–33% N during composting. Apart from causing a high N loss before storage, cutting and mixing the deep litter may have contributed to an even distribution of N and C, which enhances N immobilization, and the destruction of the straw surface may furthermore improve the availability of the C to microorganisms. The immobilization may have contributed to a low loss of N during composting.

3.5. Fertilizer efficiency of compost and deep litter In the field study, pig slurry was applied by injection for the purpose of relating the fertilizer

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value of the compost to the effects of a well-known manure. The amount of N applied in pig slurry ranged from 25 to 140 kg N ha − 1. The grain yield (85% DM) varied from 1.15 to 2.98 t ha − 1 at the slurry application rates chosen. The yield was 20–30% lower than seen in previous experiments applying pig slurry to spring barley (Petersen, 1996). A linear equation gave the best fit of the relation between grain yield and the application of total-N in pig slurry (F(grain) = 0.127× (total-N)+10.96, r 2 =0.80). Grain yield was significantly affected by the pretreament of the deep litter (P B 0.05). The yield of barley on plots amended with fresh deep litter was significant different from untreated plots (PB 0.05). In total, 94 kg TAN ha − 1 was applied in fresh deep litter compared with application rates of less than 21 kg TAN ha − 1 in the composts. Thus, yield corresponded both to total-N application and to the relation of TAN to total-N in applied manure. The findings in this study confirm the results of Paul and Beauchamp (1993) showing that grain yields from plots fertilized with composted and solid beef cattle manure were 10% of the yield in plots fertilized with urea. Fertilizer equivalent (fe) was calculated as the amount of total-N applied in slurry needed to give the grain yield (85% DM) of 1 kg N of compost or fresh deep litter (Table 4). The fe of the untreated deep litter corresponds to the ratio of TAN:total-N in the litter, indicating that the yield response was related to the NH4-N application rate. In plots amended with compost, the fe values were between 0.014 and 0.091, confirming that fertilizer efficiency of compost and deep litter is poor. The lowest fe was measured in plots amended with cut and mixed compost and untreated compost, indicating that the N lost during composting was the labile fraction of the deep litter.

4. Conclusions Ammonia volatilization reduced the content of inorganic N during composting of deep litter. As

a consequence of a high C:N ratio in deep litter, leaching losses of N were low. Compacting the compost initially with a front loader and covering the manure with a porous tarpaulin reduced the gaseous emission of N in this study. Cutting and mixing the deep litter prior to composting caused a high emission of N prior to composting and the emission was therefore low during the composting period. Dry matter loss during 132 days of storage was between 39 and 43%. During composting, the emission of N2O was 0.1–0.3% of total-N and CH4 emission was 0.01–0.03% of total-C. Leaching losses of K were 11–16%, and about 2% of N and P was leached from the compost. Composting reduces the 1st year fertilizer value of the deep litter, because losses of N during storage reduced the TAN available to plants after application in the field.

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