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Published in J. Environ. Qual. 34:698-706 (2005).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS

Waste Management

Gaseous Nitrogen and Carbon Losses from Pig Manure Derived from Different Diets

Gerard L. Velthofa,*, Jaap A. Nelemansb, Oene Oenemaa and Peter J. Kuikmana

a Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, the Netherlands
b Department of Soil Quality, Wageningen University and Research Center, P.O. Box 8005, 6700 EC Wageningen, the Netherlands

* Corresponding author (gerard.velthof{at}wur.nl)

Received for publication July 23, 2004.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Manipulation of the diets of pigs may alter the composition of the manure and thereby the environmental and agricultural qualities of the manure. Laboratory studies were performed to quantify the effect of manipulation of pig diets on the chemical composition of the derived manure (slurry), the potential emission of methane (CH4) and ammonia (NH3) during anaerobic storage of the manure, and the potential nitrous oxide (N2O) and carbon dioxide (CO2) emission after application of the manure to soil. The diets differed in contents of crude protein and salt (CaSO4), and the type and contents of nonstarch polysaccharides (NSP). Emissions of NH3 and CH4 during storage were smaller at a low than at a high dietary protein content. The emission of NH3 was significantly related to the contents of ammonium (NH4), total N, and pH. The emission of CH4 was significantly related to contents of dry matter, total C, and volatile fatty acids in the manure. The effect of manure composition on N2O emission markedly differed between the two tested soils, which points at interactions with soil properties such as the organic matter content. These types of interactions require soil-specific recommendations for mitigation of N2O emission from soil-applied pig manure by manipulation of the diet. From the tested diets, decreasing the protein content has the largest potential to simultaneously decrease NH3 and CH4 emissions during manure storage and N2O emission from soil. An integral assessment of the environmental and agricultural impact of handling and application of pig manure as a result of diet manipulation provides opportunities for farmers to maximize the value of manures as fertilizer and soil conditioner and to minimize N and C emissions to the environment.

Abbreviations: DM, dry matter • DOC, dissolved organic carbon • NSP, nonstarch polysaccharides • VFA, volatile fatty acids


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE NUMBER OF PIGS in the world has doubled since the early 1960s and reflects the increase in pork consumption. The volume of produced pig manure has correspondingly increased. Manure produced in intensive livestock systems is generally recycled inefficiently and leads to leaching of nitrogen (N) and phosphorus (P) to ground and surface waters and emissions of greenhouse gases (CH4, N2O, and CO2) and other harmful gases (NH3 and NOx) to the atmosphere (Berges and Crutzen, 1996; Ferm et al., 1999; Husted, 1994; Sherlock et al., 2002; Smith et al., 1998). Environmental legislation and the public concerns about the ecological risk of pig farming have increased pressure on pig farmers to minimize unwanted emissions. Measures and tools for farmers are required to achieve agricultural systems in which high quality food is produced with a minimal negative environmental impact.

The impact of nutritional measures on the performance and profitability of animal production has traditionally been the prime focus in livestock nutrition research. However, animal nutrition also strongly affects the plant availability of nutrients in the manure and the nitrogen and carbon transformations and losses during its storage and after its application to soil (Canh et al., 1998a; Gerdemann et al., 1999; Jongbloed and Lenis, 1998; Kreuzer et al., 1998; Misselbrook et al., 1998; Paul et al., 1998; Sørensen and Fernandez, 2003). Knowledge about the integral effects of dietary composition on manure composition and N and C losses during manure storage and after application to soil is required to decrease the emissions of harmful compounds from intensive animal production systems to the environment.

The content of plant-available N (NH4 and easily mineralizable organic N) in manures strongly determines the value of animal manures as N fertilizer. Manures rarely contain NO3, because the anaerobic conditions during storage inhibit nitrification and any formed NO3 is rapidly denitrified. The percentage of NH4–N in total N of animal manures increases as the diet contains more protein (Canh et al., 1998a). Part of the organic N in manures is rapidly mineralized after soil application and considered readily available for plants. Chadwick et al. (2000) showed that the N mineralization rate is negatively related to the C to organic N ratio of manures. Sørensen and Fernandez (2003) found similar results and showed that the plant availability of pig manure N decreased when the contents of low-fermentable fibers in the diet increased.

Gaseous C and N emissions to the atmosphere occur at various stages in the chain of manure production, storage, and application to the fields. Changes in manure management may affect the emissions in different parts of this chain. Good insight in the C and N flows in the whole chain and interactions between these flows is required to derive mitigation options and to avoid unwanted trade-offs. Robertson et al. (2000) showed that whole system analysis of greenhouse emissions from agricultural soils reveals a number of mitigation options.

Emission of NH3 from animal manure during storage is largely controlled by the NH4 content and the pH of animal excreta. The NH4 content can be adjusted by changing the protein content in the diet and the pH by adding acidifying salts or changing carbohydrate composition in the diet. The NH3 emission from stored pig manures decreased with 10 to 12.5% for each percent decrease in the content of dietary crude protein (Canh et al., 1998a). The NH3 emission from soil-applied manure is not only affected by the NH4 content and pH of the manure, but also by the application technique, weather conditions, and soil properties (Huisman et al., 1997). The production of CH4 during anaerobic storage of animal manure is controlled by type and contents of organic compounds in the manure. Changes in type and content of proteins and polysaccharides in the diet alter the manure composition (Canh et al., 1998b) and may influence CH4 emission. Emission of N2O from soil-applied animal manures is controlled by the amount of applied N and C (e.g., Velthof et al., 2003). The larger the amount of applied mineral N and easily mineralizable N, the larger the risk on N2O emission. Moreover, application of easily degradable C with manures increases potential denitrification in the soil and thereby risk of N2O emission. Paul and Beauchamp (1989) showed that volatile fatty acids (VFA) in animal manures are effective C sources for denitrifying soil bacteria. Increasing contents of fermentable polysaccharides in the pig diet increase the contents of VFA in pig excreta (Canh et al., 1998b) and may thus enhance denitrification and N2O emission after application to soil.

This paper presents results of an integral study in which the effects of dietary composition on N and C transformations and losses during manure storage and after manure application to soil are quantified. A series of laboratory studies were performed to quantify the effect of changes in dietary composition of pigs on the chemical composition of the produced manure, the potential emission of CH4 and NH3 during anaerobic storage of the manure, and the potential N2O and CO2 emission after application of the manure to soil. The diets differed in protein content, salt content, and the content and type of NSP, by which a wide range of C and N contents and pH of the manures were obtained. The integral effects of changes in dietary composition on environmental and agricultural performance of the pig manure are discussed.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A series of experiments and chemical analyses were performed using 10 manures selected from a feeding trial with pigs with four dietary factors (Fig. 1) , as described by Bakker et al. (2004).



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  		Fig. 1. Schematic presentation of the different experiments and analyses.

 
Feeding Trial with Pigs
A feeding trial with pigs was performed in 2000 to test the effects of four dietary factors on animal performance and NH3 emission (Bakker et al., 2004), namely, (i) the crude protein content; (ii) the addition of urine acidifying salt (CaSO4); (iii) the content of NSP (the total content of organic compounds minus crude protein content minus crude fat content minus sugar content minus starch content); and (iv) the content of fermentable NSP (NSP degraded by bacteria within the animal). The pigs were kept individually in metabolism cages (1.2 x 0.6 m) in an environmentally controlled room (20°C and 55% relative humidity), that allowed separate collection of urine and feces. For each dietary treatment there was one cage. The experimental period consisted of an adaptation period of three weeks followed by two experimental periods of each five days in which the urine and feces of each cage were separately collected. Urine was collected in a bucket via a funnel below the cage. Feces were collected in plastic bags (15 x 30 cm). The urine buckets and feces bags were changed twice a day, and mixed according to their original excretion ratio. Samples of 2 kg of the mixtures of urine and feces, from now on referred to as manures, were frozen in closed plastic bottles until examination (about two months later). The samples were thawed at 5°C. To activate bacteria, 1 mL of an extract of fresh pig manure was added to 1 L of manure and the manure was incubated for three days at 20°C. Possible N and C losses during this activation period were not recorded. Thereafter, chemical analyses and the experiments were performed. Dietary composition may also affect the volume of excreted N (e.g., Canh et al., 1998a, 1998b), but these effects fall outside of the scope of the current study. The focus of the current study was to quantify the effects of dietary composition on manure composition and on gaseous N and C losses during storage and after soil application. Ten dietary treatments were selected to obtain a wide range in manure composition. The effect of protein content can be assessed by comparison of Manures A and B and Manures C and D, that of addition of acidifying salt (CaSO4) by comparing Manures A and C and Manures B and D, that of addition of NSP by comparing Manures E and F, Manures G and H, and Manures B and I, and that of addition of fermentable NSP by comparing Manures E and G and Manures F and H (Table 1).


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  		Table 1. Contents of crude protein, CaSO4, and nonstarch polysaccharides (NSP) of the tested diets.

 
Characterization of the Manures
Before analysis for contents of total N and C, all manures were acidified to pH 4.0 with 4 M HCl to avoid NH3 losses and were dried at 70°C. Total C was determined using Kurmies method, that is, wet oxidation by sulfochromic acid (Houba et al., 1997), and total N was determined using spectroscopy after digestion of manure with H2SO4–salicylic acid–H2O2 and selenium (Temminghoff et al., 2000). All other analyses were performed in manure samples that were not acidified. The contents of NH4 and NO3 in the manure were determined using spectroscopy, after extraction of 500 mg of manure with 25 mL of 0.01 M CaCl2 (Houba et al., 2000). The dissolved C content in the 0.01 M CaCl2 extract was determined using a TOC/DOC analyzer (Houba et al., 2000). The contents of VFA in the manures were measured after extraction of 15 g of manure in 60 mL of water. The extracts were centrifuged, filtrated, and diluted with water (1:1), after which the VFA contents were determined with a Hewlett-Packard (Palo Alto, CA) 5890 gas chromatograph equipped with a flame ionization detector and using N2 as carrier gas (injection volume was 1 µL, internal diameter of the column was 2 mm, column was packed with 10% Fluorad FC-341 on Supelcoport 100-200 mesh). Column temperature, detection temperature, and injection temperature were 130, 280, and 200°C, respectively. All chemical analyses of the manures were performed on single samples.

Potential Emissions of Methane and Ammonia during Storage
To assess potential CH4 and NH3 emission during storage, samples of 200 mL of manure were anaerobically incubated at 35°C during 90 d. The high temperature was chosen to enhance emissions during the relatively short period of storage of 90 d. In practice in the Netherlands, manures are stored at lower temperature (<20°C), but for a longer time. The manures were incubated in 500-mL serum bottles with a stopper with septum. The experiment consisted of 30 bottles (i.e., 10 manures times 3 replicates). The bottles were randomly placed in the incubator and emissions of CH4 were measured 21 times during 97 d. The measurement frequency decreased from three times per week during the first two weeks to once per week from Week 5 onward. At each measurement time, the bottles were flushed with N2 for 10 min and closed with the stopper. The CH4 concentration in the headspace of the bottles was measured 180 min after closing the bottles using a Bruël & Kjær (Nærum, Denmark) photo-acoustic gas monitor (Yamulki and Jarvis, 1999). The inlet and outlet of the gas monitor was attached to the bottles with two Teflon tubes with needles that were inserted through the septa. In each bottle with manure, a small container with 3 mL of 3.2 M H2SO4 was placed to trap the NH3 volatilized from the manures. The H2SO4 was refreshed after 1, 8, 15, 22, 40, 62, 76, and 90 d. At the end, the NH4 contents of the mixed H2SO4 samples were analyzed to quantify the total NH3 emission during the incubation period of 90 d. After the incubation, the manures were analyzed for contents of dry matter, total N, and total C.

Potential Denitrification after Application to Soil
The potential denitrification was assessed in an incubation study with the 0- to 30-cm layer of a sandy soil from arable land in Wageningen (Table 2), using the acetylene inhibition technique (Yoshinari et al., 1977). The potential denitrification is here defined as the maximum rate at which NO3 will be reduced under anaerobic conditions at 20°C without addition of reductant. Differences in potential denitrification are mainly caused by differences in degradable C in the soil. Soil mixed with manure and an excess of NO3 was anaerobically incubated in incubation bottles with a stopper at 20°C. Manures were added at a rate of 100 mg N kg–1 soil and NO3 was added as KNO3 at a rate of 200 mg N kg–1. After application of manure and KNO3 the bottles were closed and flushed for 15 min with N2, and acetylene (C2H2) was added in the headspace with a syringe to adjust the headspace concentration of C2H2 to 5% (v/v). The soil moisture content was at field capacity. To increase microbial activity, a diluted extract of fresh pig manure (130 mL kg–1 soil of an extract of 50 g of fresh manure in 1 L of water) was added and the soil was pre-incubated before manure application for 4 d at 20°C. Any change in N2O concentration was measured 24, 48, and 72 h after closing of the stopper using a Bruël & Kjær photo-acoustic gas analyzer. All treatments were performed in triplicate.


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  		Table 2. Properties of the tested soils.

 
Potential Emissions of Nitrous Oxide and Carbon Dioxide after Application to Soil
The N2O and CO2 emissions following soil application of the manure were determined in an incubation study with the 0- to 30-cm layer of a sandy soil and a clay soil (Table 2). Samples of 120 g moist soil were incubated in 500-mL incubation bottles at 20°C. To increase microbial activity, a diluted extract of fresh pig manure (200 mL kg–1 soil of an extract of 50 g of fresh manure in 1 L of water) was added to both soils. Soils were pre-incubated before manure application for 4 d at 20°C. Manures were mixed through the soil. Soil moisture content was kept at field capacity for 14 d. Fluxes of N2O and CO2 were assessed from the increase in N2O and CO2 concentrations in the headspace following the closure of the bottles for 1 h. Concentrations of N2O and CO2 were measured using a Bruël & Kjær photo-acoustic gas analyzer. Emission of N2O and CO2 were measured 16 times during a period of 44 d. The total N2O and CO2 emission were calculated by linear interpolation of the measured fluxes at different times. Between the measurement times, the bottles were left open. The manures were applied as N fertilizer at a rate of 100 mg total N kg–1 dry soil. The N2O and CO2 emissions from a control treatment (i.e., no fertilizer) and a treatment with NH4NO3 fertilizer (application rate 100 mg total N kg–1 dry soil) were also determined. After 14 d, the moisture contents in both soils were increased to the liquid limit by adding 60 mL water kg–1 soil for the sandy soil and 15 mL kg–1 for the clayey soil (McBride, 1993). This was performed to simulate a wet period with high potential for denitrification following a relative dry period with high potential for mineralization and nitrification. All treatments were performed in triplicate.

Statistical Analyses
Differences between treatments were statistically assessed using ANOVA and LSD. Linear regression analyses were carried to assess relations between the N and C losses and chemical composition of the manures. All statistical analyses were performed with Genstat 5 (Genstat 5 Committee, 1993).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Effects of Dietary Composition on Chemical Composition of the Manure
From a comparison between Manures A and B and between Manures C and D it follows that a higher dietary protein content resulted in a higher pH, a higher total N content, similar total C content, and a higher fraction of NH4 in total N in the manure (Table 3). The low manure N contents by low protein diets are due to low urinary N excretion. Canh et al. (1998a) showed that a lowered protein content in the pig diet decreased total N excretion up to 35%. This was caused by a decrease in urine N excretion. Excretion of fecal N was not significantly affected by a lowered dietary protein content.


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  		Table 3. Chemical composition of the manures. All contents are expressed on a fresh weight basis.

 
Differences between Manures A and C and between Manures B and D suggest that addition of acidifying salt resulted in a lower pH, a higher total N content, and a higher VFA content of the manure. The higher total N contents in acidified Manures B and D are probably due to differences in N losses in the period before the manure was collected and in the activation period of three days.

Increasing the content of NSP in the diet (comparison of Manures E and F, G and H, and B and I) decreased pH, increased total C and N, increased the C to N ratio of organic matter, and increased the VFA content. A high level of NSP enhances microbial activity in the gut of pigs, favors the formation of VFA in excreta, and lowers the pH. Canh et al. (1998b) found that increased levels of NSP in the pig diet increased the fecal contents of VFA and decreased the pH of the produced manure.

Potential Emission of Methane and Ammonia during Storage
A lower protein content in the diet resulted in less NH3 emission (comparison of Manures A vs. B and C vs. D; Table 4). Adding acidifying salts reduced the NH3 emission at high crude protein contents (comparison of Manures B and D), but had no effect at a low protein content (Manures A and B). The emission of NH3 was positively and significantly (P < 0.05) related to NH4 content, total N content, and pH (Table 5). A multiple linear regression model with NH4 content and pH as explanatory variables explained 80% of the variance in NH3 emission:


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  		Table 4. Potential emissions of NH3 and CH4 during storage (90 d at 35°C).

 

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  		Table 5. Dependence of CH4 and NH3 emission from manures during storage on selected manure properties (regression analysis).

 
The CH4 fluxes during anaerobic storage ranged from <0.01 to 0.25 L CH4 per kg manure per day (not shown). This is in the range of CH4 fluxes commonly found during anaerobic fermentation of pig manure (Zeeman, 1991). The emission of CH4 was positively related to contents of dry matter, total C, and VFA (Table 5). The total emission of CH4 was smaller at lower protein content of the diet, especially for the non-acidified manure (comparison of Manures A and B and Manures C and D; Table 4). This effect is likely related to the low VFA content in the manures produced from the low protein diet (Table 3) as during anaerobic manure storage VFA can be transformed into CH4 (Zeeman, 1991). The emission of CH4 increased at higher total contents of NSP, especially when the content of fermentable NSP was high (Manures E and F and G and H). Emission of CH4 was lowest for the manure derived from the diet with lowest contents of NSP (Manure G) and this low emission is attributed to the low contents of total C and VFA in this manure (Table 3).

Emissions of CH4 and NH3 from stored manure were not related (Table 4) and have independent controlling factors. The emission of CH4 is controlled by the type and total amount of C in the manure, and of NH3 by the type and amount N and by the pH of the manure (Table 5).

Potential Denitrification after Soil Application
Denitrification in agricultural soil is unwanted because N is lost and it may give yield depression. Moreover, denitrification is a major source of the greenhouse gas N2O. Application of manure strongly increased the potential denitrification of the soil (Table 6). From regression analyses with the 10 manures it is concluded that the potential denitrification after manure application to soil was positively related to the amounts of added VFA and total C, but not to the amount of added dissolved organic carbon (DOC) (Table 7). The latter result suggests that DOC in manure is not an indicator for degradable C. The potential denitrification rate was also significantly related to the CO2 emission during aerobic soil incubation (Table 7). Production of CO2 in soil is an indicator for respiration and for the amount of easily degradable organic material. Denitrifying bacteria use organic carbon as energy source and increasing degradable C in the soil increases potential denitrification rate. Paul and Beauchamp (1989) showed that VFA are effective energy sources for denitrifiers. Because the manures in our study were applied at equal N rates, the highest denitrification potential were found for the manures with the highest ratio of C to N (Tables 3 and 7). Changes in the diet that result in a high ratio of C to N, such as decreasing protein and/or increasing NSP, increase the risk on denitrification losses when manure is used as N fertilizer.


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  		Table 6. Potential emission of N2O and CO2 and potential denitrification following application of manures to soil.

 

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  		Table 7. Dependence of potential denitrification from the sandy soil after application of manures on CO2 emission during aerobic incubation and manure characteristics (regression analysis).

 
Potential Emission of Nitrous Oxide and Carbon Dioxide after Soil Application
Potential emissions of N2O and CO2 were considerably higher from the unfertilized sandy soil than from the unfertilized clay soil (Fig. 2 and Table 6). This is probably caused by the higher denitrification potential in the sandy soil (Table 2), suggesting a higher content of degradable C in the sandy soil than in the clay soil. Also, the effect of manure addition on N2O emission differed between the two soils. The N2O emission factors that were found are (much) higher than those generally found under field conditions, especially for the sandy soil (e.g., Van Groenigen et al., 2004). In an incubation study there is no N uptake by the crop and no N is leached, thereby increasing mineral N contents in the soil for a more prolonged period than in the field. Therefore, the emission factors in Table 6 cannot be used for estimation of manure N2O emission in the field.



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  		Fig. 2. Time course of N2O fluxes (left figures) and CO2 fluxes (right figures) from the sandy soil (upper figures) and clayey soil (lower figures). Fluxes of the control, NH4NO3 fertilizer, and the manures with the lowest (A for the sand and B for the clay) and highest (I for the sand and F for the clay) total N2O emission are presented. Fluxes of the other manures are within the range of the presented manures.

 
Regression analyses showed that N2O emission from the sandy soil was negatively correlated with the CO2 emission and the amounts of added VFA (Table 8). By contrast, the N2O emission from the clayey soil was positively related to the CO2 emission, and the amounts of total C and DOC applied. The N2O emission from the soils was not significantly related to the amount of mineral N applied with the manures. The total C and DOC contents and the potential denitrification were much higher in the sandy soil than in the clayey soil (Table 2) and this may be the reason for the observed differences in manure-derived N2O emissions. High respiration rates coincide with a high oxygen consumption. The oxygen content affects the N2 to N2O ratio of the denitrification products (i.e., this ratio shifts toward N2 when the soil becomes more anaerobic) (e.g., Weier et al., 1993). We suggest that the negative relationship between N2O and CO2 emissions in the sandy soil is caused by an increased respiration on application of manure and a subsequent shift in the N2 to N2O ratio toward N2. We postulate that for the clayey soil addition of degradable C with the manures more strongly affected the potential denitrification than in the sandy soil and that the effect of the enhanced potential denitrification on N2O emission was larger than a shift in N2 to N2O ratio. Chantigny et al. (2004) also pointed at effects of soil type on transformations of applied pig slurry N. Using 15N labeled pig slurry, they showed that soil type significantly influenced the distribution of slurry N over the various soil and plant pools. Nitrification was higher in a sandy soil and ammonium fixation was higher in the clayey soil. Though emissions of N2O were not measured in their study, the observed differences might result in different N2O emissions of applied slurry N.


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  		Table 8. Dependence of N2O and CO2 emission in 44 d after soil application of manures on the added amounts of dry matter (DM), mineral N, total C, dissolved organic carbon (DOC), and volatile fatty acid (VFA) (regression analysis). All manures were applied at a total N rate of 100 mg N kg–1.

 
The absence of straightforward effects of dietary composition on N2O emission from the produced manure is most likely due to interactions with soil properties, including degradable C contents and actual oxygen consumption. These interactions strongly hamper a uniform strategy to mitigate N2O emission from soil-applied pig manure by manipulation of the diet. Soil-specific recommendations are thus required, but these recommendations demand a thorough understanding of the effects of soil and manure composition and their interactions on N2O emission.

Manure as a Source of Organic Matter
Organic matter in soils controls chemical, physical, and biological soil fertility. Soil organic matter is microbially degraded and organic matter should be added to the soil via manure and crop residues to maintain or increase the organic matter content. Manures consist of organic matter that is a mixture of readily degradable and more stable organic matter. The "stable" organic matter in manure is a prime source of soil organic matter. Stable organic matter is defined in the current study as the organic matter that is not emitted as CO2 within 44 d of aerobic soil incubation at 20°C. Figure 3 shows large differences in the amounts of added stable organic matter between the 10 manures. At an equal N application rate, the amount of added stable organic matter was highest for manures produced with diets with high content of NSP (Manures F and H) or low content of crude protein contents (Manures A and C). Sørensen and Fernandez (2003) found a significant relationship between the C mineralization of pig slurry and the total content of fibers. However, the crude protein content was not significantly related to slurry C mineralization in their study. The dietary crude protein contents were generally lower and the total C contents and the C to N ratio of the manures higher in the current study than in the study of Sørensen and Fernandez (2003). This may have contributed to the different effect of crude protein content on C mineralization of soil-applied slurry. Recommendations for farmers to apply organic matter to their soil are often based on a default manure composition. The results of Fig. 3 indicate that insight in the diet or chemical composition of the manure would enhance the validity of prognoses on effectiveness of using pig manure to maintain or increase levels of soil organic matter.



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  		Fig. 3. Amounts of applied stable and easily mineralizable organic C added to soil by manure at a rate of 100 mg N per kg soil. Easily mineralizable C is defined as the C that mineralized during aerobic incubation for 44 d at 20°C, while stable C is defined as the C that remained after this incubation (see Table 6). The left bars are results for the sandy soil and the right bars for the clay soil.

 
Integral Effects of Dietary Composition
We have shown that diet affects both the amount and composition of N and C in pig manure and thereby the potential gaseous N and C emissions, the amount of directly plant-available N, and the value of the manure as soil conditioner (i.e., source of stable organic matter). Changing the diet to decrease one specific gaseous emission may result in an unwanted increase in another gaseous emission (Fig. 4) . A lower dietary protein content decreased potential emissions of NH3 and CH4 from storage and potential N2O emission from the sandy soil, but increased potential denitrification of the sandy soil and potential N2O emission from the clayey soil (Fig. 4). This illustrates the potential to achieve lower emissions of CH4, NH3, and N2O from pig manure by decreasing the protein content of the feed. At lower dietary protein content the value of the manure as soil conditioner increased. However, this was at the expense of the N fertilizer value of the manure, because the risk on N losses by denitrification increased and the amount of directly plant-available N decreased. If the amount of applied plant-available manure N is not sufficient to meet crop demand, farmers may choose to apply additional chemical N fertilizer. The pigs need protein in terms of amino acids rather than in terms of total crude protein. There is a clear scope for farmers to lower dietary crude protein content by optimizing the diet composition and by supplementing essential amino acids to the pig diet with no effect on animal performance (Jongbloed and Lenis, 1998).



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  		Fig. 4. Effects of lowered protein content (comparison of Manures B and A), adding acidifying salt (Manures B and D), increasing total nonstarch carbohydrate contents (Manures I and B), and fermentable nonstarch carbohydrate content (Manures E and G) on potential NH3 and CH4 emission during anaerobic storage, denitrification potential (DNP) after soil application, potential N2O emission after application to a sandy and clayey soil, the content of mineral N in the manure, and the content of stable organic matter (OM) in the manure (i.e., the residual organic matter after incubation of manure in soil at 20°C during 44 d).

 
The effect of the other tested diet manipulations were smaller and show partly opposite effects on the emissions (Fig. 4). Adding salts affected emissions and composition of the manure to a lower extent than decreasing protein content. Increasing the content of total NSP strongly increased the CH4 emission from the manure during storage (Fig. 4). The effects on NH3 and N2O emissions were relatively small in comparison with the effect on CH4. A higher content of fermentable NSP strongly decreased emission of CH4, but increased emissions of NH3 and N2O from the sandy soil. The amount of stable organic matter was also smaller at higher contents of fermentable NSP.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Manipulation of the diet of pigs strongly affected the composition of the manure, the potential NH3 and CH4 emissions during storage, potential N2O and CO2 emission after soil application, the content of plant-available N, and the value of the manure as source of stable organic matter. From the tested diets, decreasing the crude protein content of the diet had the largest potential to simultaneously decrease NH3 and CH4 emissions during manure storage and N2O emission from soil. The effect of manure composition on N2O emission markedly differed between the two tested soils, which points at interactions with soil properties such as the organic matter content. These types of interactions require soil-specific recommendations for mitigation of N2O emission from soil-applied pig manure by manipulation of the diet. Field trails in combination with modeling will provide insight in the overall agricultural and environmental performance of soil-applied manure. An integral assessment of the environmental and agricultural impact of handling and application of pig manure as a result of diet manipulation provide opportunities for farmers to maximize the value of manures as fertilizer and soil conditioner and to minimize N and C emissions to the environment.


   ACKNOWLEDGMENTS
 
We acknowledge Willeke van Tintelen for invaluable technical assistance during incubation studies and Gertruud Bakker for providing the pig manures. This study was financed by the Dutch programme ROB (Reduction programme on non-CO2 greenhouse gases) under Contract 374299/0021 of NOVEM and the Dutch Ministry of Agriculture, Nature and Food Quality (Programme 415).


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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B. J. Kerr, C. J. Ziemer, S. L. Trabue, J. D. Crouse, and T. B. Parkin
Manure composition of swine as affected by dietary protein and cellulose concentrations
J Anim Sci, June 1, 2006; 84(6): 1584 - 1592.
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