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Published online 25 January 2007
Published in J Environ Qual 36:440-447 (2007)
DOI: 10.2134/jeq2006.0222
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Waste Management

Factors Influencing the Concentration of Volatile Fatty Acids, Ammonia, and Other Nutrients in Stored Liquid Pig Manure

Kenneth L. Conn*, Edward Topp and George Lazarovits

Southern Crop Protection and Food Research Centre, Agriculture and Agri-Food Canada, 1391 Sandford Street, London, Ontario, Canada N5V 4T3

* Corresponding author (connk{at}agr.gc.ca)

Received for publication June 9, 2006.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
In order to minimize odor and manage nutrients in liquid pig manure we need to be able to predict what operational practices most influence the concentrations of volatile fatty acids (VFAs), ammonium nitrogen (NH4+–N), and other nutrients present in the manure. To determine this, we collected manure from 15 pig operations in southwestern Ontario in the fall of 2001 and 2002 and spring of 2002 and 2003. The manure was stored in concrete tanks at all operations. Manure from finishing pigs had the highest concentration of VFAs, NH4+–N, and other nutrients, followed by manure from mixed operations, and then manure from sow operations. The average concentration of total VFAs and NH4+–N in finishing pig manure was 166 mM compared with 36 and 99 mM, respectively, in sow manure. Total N, P, and K were 2.3, 2.5, and 1.7 times greater, respectively, in finishing pig compared with sow manure. There was no seasonal or year to year variation in amount. The diet of the pigs, use of feed additives or antibiotics, location of tanks, and whether the tanks were covered or mixed were not significant factors contributing to the difference in manure chemistry. The main reason for the differences between the three types of manure was manure dilution. The average dry matter content of finishing pig manure was 4.5 times that of sow manure. This was due to larger density of pigs in finishing compared with sow operations, less manure storage capacity per pig for finishing compared with sow operations, and more wash water being used for sow operations.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE accumulations of large volumes of liquid manure from pig operations and the offensive odors they create are major issues for pig producers and their neighbors. Several hundred odoriferous volatile organic compounds (VOCs) have been identified from pig manure (O'Neill and Phillips, 1992; Schiffman et al., 2001; Le et al., 2005) and these can be grouped into sulfurous compounds, phenols and indoles, ammonia and volatile amines, and volatile fatty acids (VFAs) (Le et al., 2005). Although VFAs have been the group most often associated with the unpleasant odor of manure (Zhu et al., 1999), it is the sulfurous, phenol, and indole compounds that appear to contribute the most to malodor (Le et al., 2005). Volatile fatty acid concentration, however, is a good indicator of the total VOC content of a manure because VFAs are produced through processes that lead to the formation of malodorous products (Zhu et al., 1999). The VFAs found in pig manure include acetic, propionic, n-butyric, iso-butyric, n-valeric, iso-valeric, n-caproic, and iso-caproic acids (Le et al., 2005). Acetic acid typically comprises 60 to 70% of the total VFAs, followed by propionic acid at 10 to 20%, and the remainder represents 10 to 20% (Cooper and Cornforth, 1978; Spoelstra, 1980; Conn et al., 2005). The acids with the most disagreeable odor are butyric, valeric, and caproic which also have lower odor-detection thresholds than acetic and propionic acid (Zahn et al., 2001a; Le et al., 2005). Thus, odor from VFAs is not proportionally related with the total VFA concentration but rather with the concentration of butyric, valeric, and caproic acids (Zhu et al., 1996, 1997).

The amount of VFAs and ammonia (NH3) that are volatilized from manure mainly depends on the manure pH and concentrations of VFAs and ammonium nitrogen (NH4+–N) in the manure. The lower the pH, the larger the proportion of VFAs in the volatile nonionized form (e.g., acetic acid) as compared with the nonvolatile ionized form (e.g., acetate) (Conn et al., 2005). The pKa values for VFAs range from 4.8 to 5 at 24°C (Perrin and Dempsey, 1974). The higher the pH, the larger the proportion of NH4+–N in the volatile nonionized form (NH3) as compared with the nonvolatile ionized form (NH4+) (Arogo et al., 2003b). The pKa of NH3 is 9.25 at 24°C. Little volatilization of VFAs or NH3 should occur from manures with pH values above or below 7, respectively, because almost 100% of the VFAs and NH4+–N are in the nonvolatile ionized forms (Arogo et al., 2003b; Conn et al., 2005; Le et al., 2005). The pH of pig manure generally ranges from 6.5 to 8.6 (Cooper and Cornforth, 1978; Conn et al., 2005). Thus, volatilization of VFAs and NH3 would occur from some manures.

Volatile fatty acids and NH3 in liquid pig manure are toxic to soilborne plant pathogens. Addition of manure at a rate of 9194 L ha–1 (22 700 L ac–1) to acidic soils can reduce the incidence of soilborne diseases of potato such as verticillium wilt (caused by the fungus Verticillium dahliae), potato scab (caused by the bacterium Streptomyces scabies), as well as populations of plant parasitic nematodes for up to 3 yr after a single application (Conn and Lazarovits, 1999). Manure was shown to be toxic to V. dahliae in acidic or basic soils but not in neutral pH soils (Conn and Lazarovits, 2000; Conn et al., 2005). Toxicity at low pH is due to VFAs in the manure (Tenuta et al., 2002; Conn et al., 2005) and at high pH it is due to NH3 (Conn et al., 2005). The toxicity of individual VFAs generally increases with the molecular weight (Tenuta et al., 2002). The EC95 value for NH3, acetic acid, and n-caproic acid against V. dahliae are 4.5, 26, and 4.1 mM, respectively (Tenuta et al., 2002; Tenuta and Lazarovits, 2002). Only the nonionized forms of VFAs and NH4+–N are toxic to plant pathogens such as V. dahliae (Tenuta et al., 2002; Tenuta and Lazarovits, 2002). This information allows one to predict where pig manure may be useful as a disease control product. However, we also need to know which manure potentially contains enough VFAs and/or NH4+–N to be useful.

The concentrations of VFAs and NH4+–N in pig manure vary widely (Arogo et al., 2003a; Le et al., 2005). We found this to be the case with a previous study of 19 manures collected over several years from various locations in southwestern Ontario (Conn et al., 2005). The total VFA concentration ranged from 9 to 400 mM and the NH4+–N concentration ranged from 96 to 500 mM. We did not have detailed information about the pig operations that these manures came from and thus no information as to possible reasons for the differences.

The objective of this study was to determine what factors might be responsible for the variation in concentrations of VFAs, NH4+–N, and other nutrients in manure from pig operations in southwestern Ontario that stored their waste as a slurry. This information could provide management practices to reduce odor emission where desired or needed, allow for the prediction of the potential fertilizer value of the manure, and predict which manure might be useful as a disease control product. Some factors examined included type of operation; number and diet of pigs; what antibiotics and feed additives were used; type, location, and capacity of manure storage systems; manure age; whether the storage systems were covered or aerated; and spring to fall and year to year variation.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Pig Operations and Manure Collection
Fifteen pig operations were included in this study. Information was collected about the type of operation, husbandry practices, and manure storage systems. Manure storage tanks were typically emptied for spreading in the spring and fall and thus manure storage ranged from 6 to 8 mo. All manure storage tanks received fresh manure from the barn either continuously or periodically. Manure samples were collected from storage tanks in the fall of 2001 and 2002 and spring of 2002 and 2003 when the tank was stirred and in the process of being emptied. At some sampling times a farmer had emptied a tank before a sample could be obtained. There was a total of 13 samples missed making the number of samples taken 47. Ten 500-mL aliquots of manure from 0.3-, 0.9-, 1.5-, 2.1-, and 2.7-m depths were taken using a sampling device consisting of a bottle and cork that could be opened and closed at the desired depth with a string. The ten aliquots of manure from each tank were pooled and transported immediately to the laboratory in a tightly-closed container. Manure samples were also taken from gutters inside some of the barns in the fall of 2002 and spring 2003 to compare the chemistry of the stored manure from tanks to fresh manure from inside the barn. This information would help determine the impact of storage conditions on differences seen in chemistry between manures. In the barns where there were sows, weaner, and finishing pigs, samples were taken from each group of pig if the gutters were accessible. These manure samples were typically 1 to several days old. All manure samples were stored frozen until analyzed.

Chemical Analyses of Manures
The pH of manure samples was determined using a polymer body pH electrode (Cole Parmer Instrument Co., Vernon Hills, IL). Dry matter, total nitrogen (N), total phosphorus (P), total potassium (K), calcium (Ca), magnesium (Mg), and organic matter were determined using standard methods in a commercial laboratory (A & L Canada Laboratories East Inc., London, ON). The concentration of total NH4+–N (ammonium plus ammonia) was determined by ion exchange chromatography and the concentrations of ionized plus nonionized forms of individual VFAs (acetic, propionic, iso-butyric, n-valeric, iso-valeric, and n-caproic) were determined by ion exclusion chromatography. Both methods used chemical suppression and conductivity detection (Dionex Model 100, Dionex Corp., Sunnyvale, CA). The analytical columns used were an IonPac ICE-AS1 for VFAs and an IonPac CS-12A for NH4+–N along with an AMMS ICE II chemical suppressor (Dionex Corp.). Particulates in manure samples were removed by centrifugation (10 min at 10 600 g) and 10-, 100-, and 1000-times dilutions made in water. The diluted manure samples were placed in vials which were introduced (40 µL) to the ion chromatograph using an autosampler equipped with a refrigerated chamber housing the vials (Waters 717plus, Waters Associates, Milford, MA). The individual concentrations of VFAs and NH4+–N from the appropriate dilutions were calculated by comparison to standards. This total value did not include n-butyric acid because its peak using the IonPac ICE-AS1 column could not be measured due to interference by an unknown peak that had almost the same retention time as n-butyric acid.

Statistical Analyses
A Kruskal–Wallis ANOVA on Ranks test was performed using Statistical Analysis System (SAS) (SAS Institute, Cary, NC, USA) for Windows version 9.1. Principal components analysis (PCA) was performed using the procedure in Minitab for Windows, release 13 (State College, PA, USA) to determine which, if any, factors accounted for the variability of the manure chemistry. A correlation matrix was used since the units of measures were different for some of the variables used in the analysis.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Types of Operations and Pig Husbandry
When the 15 farms were chosen for this study, we knew nothing about the type of operations at each farm nor anything about pig husbandry or manure chemistry at these farms. We did not want to introduce any bias into this survey. There turned out to be seven farrow to nursery operations (referred to as sow operations here), five finishing operations, and three farrow to finish operations (referred to as mixed operations here). The number of pigs per barn ranged from 140 to 2000 (Table 1). The average number of sows per barn was about 400 and for finishing pigs it was about 1200, a difference of 2.5 times (Table 1). The average number of pigs in the mixed operations was about 600. This is common because sows need more room to have their litters so the density of sows in a barn is less than for finishing pigs. A study by Harper et al. (2006) also found that the density of finishing pigs was 2.4 times that of sows in the operations they examined. The diet of the pigs was generally similar in that corn was the main component with all pigs also receiving premix (Table 1). The pigs also received some soybeans, barley, or wheat. Six of the operations used feed additives to help with nutrient uptake or odor control (Table 1). A variety of antibiotics were used in 11 out of the 15 operations (Table 1).


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  		Table 1. Pig operations examined in this study: type and pig husbandry.

 
Manure Storage Conditions
All the manure from these operations was stored in open or closed concrete tanks (capacity 136 000 to 1 800 000 L, Table 2). Two of the storage tanks were located under the barns, thirteen of the tanks were outside, nine of which were open and four of which were capped with a concrete cover. Taking the number of pigs into consideration (Table 1), the manure storage capacity per pig ranged from 390 to 9700 L (Table 2). The manure in two of the tanks was agitated by wind-powered circulators (Little River Pond Mill Circulators, Table 2).


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  		Table 2. Manure storage conditions at the pig operations examined in this study.

 
Seasonal Variation in Manure Chemistry
The values for every parameter measured in the 47 manure samples collected varied widely between farms (Table 3). This variability in the chemistry of pig manure confirms results of an earlier study with manures from southwestern Ontario (Conn et al., 2005) as well as reports by others (Arogo et al., 2003a; Le et al., 2005). There was no seasonal or annual variation in the composition of manure obtained from each of the mixed or finishing pig farms ({alpha} = 0.01; data not shown). Only two parameters (iso-valeric acid and total N) were significantly different (P = 0.04 and 0.02, respectively) between sampling dates for manures from sow operations. Table 3 shows the minimum and maximum values of the parameters measured at different sampling times, averaged for the seven sow operations and five finishing pig operations. For most parameters, the maximum average value for sow manure was lower than the minimum average value for finishing pig manure (Table 3). Thus, in general the chemical composition of stored manure from each farm was consistent over time. This is in contrast to some other studies that have reported significant seasonal variability in concentrations of VOCs in pig manure storage systems (Merrill and Halverson, 2002). DeRouchey et al. (2002) also found seasonal variation in the nutrient content of manure from Kansas swine lagoons but these differences were less than the differences found between sow and finishing pig manure.


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  		Table 3. Variation in the values of chemical parameters measured for manures from 15 storage tanks at four sampling dates.{dagger}

 
Comparison of Manure Chemistry between Pig Operations
Figure 1 shows that there was a relationship between type of operation (Tables 1, 2) and the variability in the VFA and NH4+–N concentrations in manure (Table 4). The data fit into three groups that identified the specific operation that the manures were collected from namely; finishing, sow, and mixed operations. One of the mixed operation sites clustered with the sow operations and one of the finishing pig operations did not cluster with the other finishing pig operations (Fig. 1). Composition of manure from mixed operations would be dependent on the relative number of each group of pigs inside a barn. Thus, manure from mixed pig operations could be more like that of sows or finishing pig operations, or anywhere in between.


Figure 1
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  		Fig. 1. Principal components analysis (PCA) plot of various pig operation manure chemistry. Values in parentheses indicate the contribution of the first principal component (PC1) or the second principal component (PC2) to the total variation in the chemistry of manure collected from storage tanks. Thus, 86% of the variability in the data could be explained by the type of pig operation. Circles were drawn to facilitate elucidation of the patterns. Pig operations were sow ({circ}), finishing ({square}), or mixed (sow, weaner, and finishing) ({blacktriangleup}).

 

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  		Table 4. Relationship between type of pig operation and chemistry of the manure.{dagger}

 
Table 4 shows the data for VFAs, NH4+–N, etc., averaged for the type of operation and sampling date. The average concentration of total VFAs was 166 ± 16, 86 ± 17, and 36 ± 4.4 mM in finishing, mixed, and sow manure, respectively (Table 4). These values for total VFAs fall within the range (30 to 400 mM) reported for liquid pig manure (Cooper and Cornforth, 1978; Paul and Beauchamp, 1989; Zhu et al., 1999). The amount of total VFAs in finishing pig manure in this study was 4.6 times higher than that found in sow manure. Also, while the concentration of all the individual VFAs were higher in finishing than sow manures, the relative amounts were different (Tables 4, 5). Acetic acid, which is the major VFA present, was 3.8 times higher while the other VFAs which ranged from 6.2 to 12 times higher in finishing pig compared with sow manure (Table 5).


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  		Table 5. Comparison of the values of chemical parameters measured between sow and finishing pig manure and between manure from storage tanks and inside barns.

 
The average concentration of NH4+–N in finishing pig manure was 166 ± 18 mM compared with 99 ± 7.0 mM in sow manure (Table 4). This was 1.7 times higher than in sow manure. These results are similar to a study that looked at NH3 emissions from pig manure in Utah (Harper et al., 2006). In that study, the amount of NH4+–N in finishing pig manure was 1.9 times greater than that in sow manure.

The values for all the other parameters measured in finishing pig manures were also higher than in sow manures (Tables 4, 5). For example, the total N, P, and K was 2.3, 2.5, and 1.7 times greater, respectively, in finishing pig compared with sow manure. The values for mixed pig manures were between those of sow and finishing pig manure values for all parameters measured (Table 4). These results are consistent with results of a survey of manure lagoons in Kansas (DeRouchey et al., 2002). In that study, the amount of N/P/K in finishing pig manure was 1.9, 1.7, and 2.1 times greater, respectively, than that of sow manure. It was also found in that study that concentrations of P in manure from lagoons increased in the summer and decreased over the winter. This was not the case in this study where there was no seasonal effect on amount of P. This information on relative amounts of nutrients between manures is important for nutrient management plans. These results will allow pig producers to better predict the relative amounts of nutrients in their manures. Manure from these three groups have to be applied at different rates to fields to optimize the amount of nutrients and avoid over-application.

Manure from storage tanks ranged from pH 6.2 to 8.2 and fresh manure from inside the barns from pH 5.7 to 8.1. The average pH of sow, finishing, and mixed pig manures from the tanks were 7.5, 6.9, and 7.3, respectively. Manure pH is considered to be controlled by the VFA content and buffering systems such as NH4+/NH3 and HCO3–/CO3–2 (Georgacakis et al., 1982; Paul and Beauchamp, 1989; Sommer and Husted, 1995). The relationship between VFAs, NH4+–N, and pH for the manures collected in this study is shown in Fig. 2. In general, manure pH increased as the ratio of VFAs to NH4+–N decreased (r = –0.73). Thus, for manures collected in this study, the ratio of VFAs to NH4+–N explained most of the observed differences in pH values. Since most of the manure pH values were around neutral pH, there would have been very little volatilization of VFAs or NH3 from these manures. This is because a neutral pH is two units below and above the pKa of NH3 (9.3) and VFAs (4.8–5.0), respectively (Tenuta et al., 2002; Conn et al., 2005). Farmers should not have to worry about significant N loss from their manure unless the pH approaches 8 or above. This also means NH3 and VFAs should not be contributing significantly to malodour from these manures. The presence of high levels of VFAs will prevent the pH from rising high enough to get volatilization of NH3. However, manure pH does not impact volatilization of other VOCs such as sulfurous, phenol, and indole compounds. These compounds appear to contribute the most to malodour (Le et al., 2005).


Figure 2
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  		Fig. 2. Relationship between volatile fatty acid (VFA), ammonium (NH4+) plus ammonia (NH3), and pH of manure (n = 72). Pig operations were sow ({circ}), finishing ({square}), or mixed (sow, weaner, and finishing) ({blacktriangleup}).

 
Other Factors Affecting Manure Chemistry
A variety of information was collected about the pig operations examined in this study to try to include all factors that might contribute to variation in amounts of VFAs, NH4+–N, etc., in manure (Tables 1, 2). It turned out that the type of operation was the major factor involved with number of pigs and manure-holding capacity being related to the difference between manure from different operations. The diet of the pigs in this study did not appear to be responsible for this difference. The diet was generally similar for all the pigs in that corn was the main component (Table 1). Diet can affect manure chemistry and subsequent release of malodour compounds (Otto et al., 2003; Le et al., 2005). For example, reducing the amount of protein can reduce NH3, VFAs, and other malodour compounds (Otto et al., 2003). However, Otto et al. (2003) found that the most abundant VFA (acetic acid) was not affected by diet. Feed additives to help pigs utilize nutrients or control odor and feed antibiotics were used by some of the farms in this study (Table 1). There was no consistent relationship between the use of feed additives or feed antibiotics and manure composition (Table 1). Feed and manure additives can have an effect on manure chemistry (McCrory and Hobbs, 2001; Coates et al., 2005). Likewise, there was no relationship between holding tank location (below the barn or adjacent to the barn), whether or not it was covered, and whether or not it was agitated and manure composition. This is in spite of the fact that VFAs and ammonia in pig manure that is agitated or open to the elements might be subject to atmospheric loss or aerobic biodegradation (Burton, 1992; Zhang and Zhu, 2003). Likewise, the composition of pig manure in open tanks might be expected to be more seasonally variable due to evaporation or precipitation. Overall, none of the manure storage variables had a consistent effect on manure composition.

Chemistry of Manure from Storage Tanks Compared with Fresh Manure
The VFA and ammonium content of freshly excreted manure obtained from within the barn varied with the type of operation, and were consistent with differences in the stored manure (Tables 4, 5). The average concentration of total VFAs and NH4+–N in fresh finishing pig manure was 212 ± 60 and 332 ± 41 mM compared with 41 ± 14 and 143 ± 26 mM in fresh sow manure, respectively (Table 4). This was 5.2 and 2.3 times higher than in sow manure, respectively (Table 5), which was a similar difference as for the manures from tanks. Likewise, the values for all the other parameters measured in finishing pig manures were higher than in sow manures (Tables 4, 5). The values of the parameters measured for manures from inside mixed operations generally showed that finishing pig manure had higher values than sow manure which was consistent with other sow and finishing pig manure data (Table 4). Overall, these results suggest that manure composition was generally stable under the storage conditions used here.

While finishing pig manure had higher values than sow manure for almost all the parameters measured (average of 4.9 times), the amounts in all the manures were generally a little lower (average of 1.5 and 1.2 times for sow and finishing pig manure, respectively) in manure from tanks compared with fresh samples from inside barns (Table 5). This could be due to degradation of the compounds measured and/or further dilution of the manure. Two exceptions to this were the concentrations of n-valeric acid and n-caproic acid which were higher in manure from tanks for both sow and finishing pigs (Tables 4, 5). Other studies have also shown that the proportion of individual VFAs in manure can change over time (Møller et al., 2004). This can be due to different rates of degradation or formation between VFAs.

Significant concentrations (50 to 150 mM) of total VFAs have been reported for fresh pig manure in other studies as well (Brown et al., 1997; Otto et al., 2003). Some studies have examined the concentration of VFAs inside the gastrointestinal tract of pigs and found total VFA concentrations up to 200 mM (Franklin et al., 2002; Otsuka et al., 2004; Manzanilla et al., 2006). The formation of VFAs in pig manure occurs in the gastrointestinal tract of pigs and during anaerobic storage of manure (Le et al., 2005). A study by Miller and Varel (2003) showed that the majority of VFAs produced during storage of manure occurs during the first few weeks after excretion from pigs.

Thus, while the amount of the parameters measured in the manures was generally a little lower in manure from tanks compared with fresh manure, the relative difference between manure from different operations was not affected by storage of the manure. This means that none of the storage conditions nor handling of manure by the farmers after the manure entered the tanks was responsible for the difference in manure chemistry seen between the type of operation. This limits the options these farmers have for manipulating manure chemistry to factors inside barns.

Contribution of Manure Dilution to Differences between Sow and Finishing Pig Manure Chemistry
The average percentage dry matter in finishing pig manure from storage tanks was 4.5 times greater than that from sow manure (Tables 4, 5). The difference was almost identical for fresh manure from inside the barns (Tables 4, 5). This difference could be related to the number of pigs, tank capacity, and tank capacity per pig at the different pig operations. The average number of pigs in the sow barns was 400 compared to 980 in the finishing barns (Table 1). However, the average tank capacity and average tank capacity per pig were 1290000 and 4400 L for sow operations compared with 660000 and 1300 L for finishing pig operations, respectively (Table 2). Thus, on average finishing pig operations had 2.4 times more pigs than sow operations but 3.4 times less capacity to store manure. The farmers also indicated that they use more wash water in sow than finishing pig barns. Thus, these factors would explain why manure was more concentrated from finishing compared with sow operations. Manure from mixed operations was between that of the other two groups (Table 4). This has implications for differential odor problems between sow and finishing pig manure because emissions of VOCs, NH3, H2S, and CO2 have been shown to be directly proportional to percentage solids in manure (Zahn et al., 2001b; Lim et al., 2003). To determine the extent that differences in dry matter content could explain the differences in the concentration of VFAs, NH4+–N, etc., the values of the parameters measured for each manure were adjusted for dry matter. Table 6 shows the comparison of the manure parameters measured between the finishing and sow manures before and after taking into account dry matter. There was no significance difference in the total VFA content between finishing and sow manure after dry matter was taken into account. This was also true for acetic acid, the major VFA present, but not the other VFAs. The other parameters that were not significantly different between the two groups of manure after adjusting for dry matter were total P, Ca, Mg, and organic matter. Thus, the difference in amounts of total VFAs, acetic acid, P, Ca, Mg, and organic matter between sow and finishing pig manure could be completely explained by differences in manure dilution. Differences in other parameters, such as NH4+–N, could not be completely explained this way.


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  		Table 6. Contribution of manure dilution for explanation of the difference in chemistry between sow and finishing manure.

 
Based on the information provided in this study, we can now be much more selective as to what operation we go to for manures having the highest potential for plant disease control in low or high pH soils as only manures from finishing pigs had sufficient VFAs and NH3, respectively, for this purpose. In addition to finishing pig manure having more VFAs than sow manure, the greater proportion of larger molecular weight VFAs in finishing pig manure would make this manure more toxic than sow manure because larger VFAs are more toxic than acetic acid to plant pathogens such as V. dahliae (Tenuta et al., 2002). The results of this study demonstrate that one factor farmers could control to manipulate the amount of VFAs and NH3, for example, would be manure dilution. If finishing pig manure from a particular operation was to be used as a disease control product, the concentration of VFAs could be maximized by minimizing the amount of wash water and rain entering the manure storage tank.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Concentration of VFAs, NH4+–N, and other nutrients in pig manure varied greatly between pig operations in southwestern Ontario. The type of operation (sow, finishing, or mixed) was the major factor determining differences in the amount of these compounds in manure. Manure from finishing pigs had the highest concentration of VFAs, NH4+–N, total N, P, K, and other nutrients, followed by manure from mixed operations, and then manure from sow operations. There was no seasonal or year to year variation in amount. The diet of the pigs, use of feed additives or antibiotics, location of tanks, and whether the cement tanks were covered or mixed were not significant factors contributing to the difference in VFAs, NH4+–N, and other nutrients between type of operation. The main reason for the difference in manure between the three types of pig operations was a difference in manure dilution. The average dry matter content of finishing pig manure was 4.5 times that of sow manure. This was due to larger numbers of pigs in finishing compared with sow operations, less manure storage capacity per pig for finishing compared with sow operations, and more wash water being used for sow operations. While the concentration of VFAs, NH4+–N, and other nutrients in fresh manure was a little higher than that from storage tanks, the relative differences between type of operation were already present in fresh manure.

The information from this study can be used to predict where odor control may be necessary and predict nutrient content. Also, based on the knowledge of the type of pig operation examined in this study, a prediction can be made about the potential of a manure to be used as a plant disease control product.


   ACKNOWLEDGMENTS
 
We thank I. Lalin for excellent technical assistance and J. Hill for the statistical analyses. This work was supported by a grant from Ontario Pork and AAFC MII.


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





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The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Soil Science Society of America Journal Journal of Plant Registrations The Plant Genome