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TECHNICAL REPORTS

Waste Management

Gaseous Nitrogen Emissions and Forage Nitrogen Uptake on Soils Fertilized with Raw and Treated Swine Manure

^a Agriculture and Agri-Food Canada, Soils and Crops Research and Development Centre, 2560 boul. Hochelaga, Québec, QC, Canada, G1V 2J3
^b Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, 2000, rue Collège, C.P. 90, Sherbrooke, QC, Canada, J1M 1Z3
^c Institut de Recherche et Développement en Agroenvironnement, 2700, rue Einstein, Québec, QC, Canada, G1P 3W8

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

Received for publication February 13, 2007.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 
Treatments to reduce solids content in liquid manure have been developed, but little information is available on gaseous N emissions and plant N uptake after application of treated liquid swine manure (LSM). We measured crop yield, N uptake, and NH₃ and N₂O losses after the application of mineral fertilizer (NH₄NO₃), raw LSM, and LSM that was decanted, filtered, anaerobically digested, or chemically flocculated. The experiment was conducted from 2001 to 2003 on a loam and a sandy loam cropped to timothy (Phleum pratense L.) with annual applications equivalent to 80 kg N ha^–1 in spring and 60 kg N ha^–1 after the first harvest. Raw LSM resulted in NH₃ emissions three to six times larger (P < 0.05) than mineral fertilizer. The LSM treatments reduced NH₃ emissions by an average of 25% compared with raw LSM (P < 0.05). The N₂O emissions tended to be higher with raw LSM than with mineral fertilizer. The LSM treatments had little effect on N₂O emissions, except for anaerobic digestion, which reduced emissions by >50% compared with raw LSM (P < 0.05). Forage yield with raw LSM was >90% of that with mineral fertilizer. The LSM treatments tended to increase forage yield and N uptake relative to raw LSM. We conclude that treated or untreated LSM offers an alternative to mineral fertilizers for forage grass production but care must be taken to minimize NH₃ volatilization. Removing solids from LSM by mechanical, chemical, and biological means reduced NH₃ losses from LSM applied to perennial grass.

Abbreviations: LSM, liquid swine manure • DM, dry matter

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 
SWINE production is concentrating on fewer and larger farms in several countries, resulting in increased manure loading rates and overfertilization of soils. Separation of liquid animal manure into dry matter (DM)-rich and clarified liquid fractions is proposed as an option to improve manure nutrient management and avoid overfertilization (Pain et al., 1978; Møller et al., 2000). The DM-rich fraction contains most of the initial P and can be exported at a reasonable cost to other areas, whereas the liquid fraction contains most of the initial N and is preferably applied on-farm because of its high water content. Mechanical, chemical, and biological treatments for the separation or digestion of solids in liquid animal manure affect the distribution of manure nutrients in the liquid fraction (e.g., Pain et al., 1978; Sommer and Husted, 1995; Møller et al., 2000) and can thus affect the cycling of manure N after land application (Kirchmann and Lundvall, 1993; Sørensen and Thomsen, 2005).

Ammonia volatilization is of particular concern after field application of liquid manure and can result in the loss of a substantial portion of applied N. Mechanical separation of liquid manure was found to decrease NH₃ emissions compared with raw manure (Vandré et al., 1997; Amon et al., 2006). This difference was attributed to lower solid content in the separated than in raw manure, which improved its infiltration below the soil surface. However, some studies reported similar NH₃ losses between separated and raw manure (Thompson et al., 1990; Mattila and Joki-Tokola, 2003). Stevens et al. (1992) found that significant reduction in NH₃ losses was achieved by mechanical separation provided that the removal of solids was extensive enough to increase slurry infiltration in soil.

Anaerobic digestion also decreases the solid content of liquid manure and may thus help to reduce NH₃ emissions after field application. Studies dealing with the effect of anaerobic digestion of manure on NH₃ emissions in the field yielded contrasting results, with some authors reporting lower emissions with digested than with raw manure (Rubaek et al., 1996), whereas others found similar (Pain et al., 1990; Wulf et al., 2002a; Chantigny et al., 2004) or higher emissions (Amon et al., 2006). This discrepancy among studies is likely explained by the increase in pH of liquid manure during anaerobic digestion, which increases the potential for NH₃ loss from digested products and can offset the benefit of improved infiltration (Pain et al., 1990; Wulf et al., 2002a).

Significant N₂O emissions usually follow field application of liquid animal manure. The effects of manure treatments on N₂O emissions can also be variable. Some authors reported similar N₂O emissions between treated and raw liquid manure for mechanical separation (Clemens et al., 1997) and anaerobic digestion (Wulf et al., 2002b), whereas others reported decreased emissions after separation (Amon et al., 2006) and anaerobic digestion (Rubaek et al., 1996; Petersen, 1999; Vallejo et al., 2006). Wulf et al. (2002b) reported similar N₂O emissions between anaerobically digested and raw manure when applied to arable soils but higher emissions with the digested manure when applied to grassland soils.

Liquid swine manure (LSM) is rich in mineral N and was found to be an efficient fertilizer for crop production (Burns et al., 1987, 1990; Morris and Lathwell, 2004; Adeli et al., 2005). By modifying N distribution and by affecting gaseous N losses, treatments to remove solids in LSM could influence N availability to plants after land spreading. Plant N uptake was reported to be similar or slightly increased with mechanically separated (Mattila et al., 2003; Sørensen and Thomsen, 2005) and anaerobically digested (Rubaek et al., 1996) than with raw liquid manure.

Because most studies investigated only one type of manure treatment at a time, it is not possible to state whether the discrepancies among studies on the effects of treatments on gaseous N emissions are due to differences in treatment type, manure source, or environmental conditions. Moreover, these studies were generally conducted on dairy cattle manure, and few studies examined the effects of manure treatments on gaseous N emissions and plant N recovery at the same time. The present field experiment aimed at comparing the effects of various treatments to remove solids in LSM on the short-term NH₃ and N₂O losses and crop yield and N uptake after land application of the liquid fraction to two soils cropped to perennial forage grasses.

	Materials and Methods

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 
Manure Collection and Analysis
Raw LSM was obtained during winters of 2001, 2002, and 2003 from a commercial finishing hog operation. The animals were fed a corn-soybean based diet and raised on slatted floor with minimal use of bedding. The LSM was collected by composite subsampling during the emptying of the transfer tank so that the composition of the collected LSM reflected the average composition of LSM in the transfer tank. The LSM had been accumulating for about 48 h in the transfer tank at time of collection. The total volume of collected LSM was thoroughly stirred, and part of it was transferred into a cool-temperature, batch anaerobic digester (Massé et al., 1996). The rest was stored for 6 wk in four 1-m³ plastic containers. Containers were hermetically closed during storage period. After this period, the upper half of raw LSM was pumped out of two plastic containers and transferred in an empty 1-m³ container. This manure was labeled "Decanted LSM" and was assumed to represent the clarified fraction of LSM after natural settling of solids at the bottom of a storage tank. Manure from a third plastic container was allowed to drain through a bed of wood shavings and saw dust (50:50, v/v). The filtrate (about 80% of the initial LSM volume) was collected in an empty plastic container and labeled "Filtered LSM." Manure in the fourth plastic container was used as is and labeled "Raw LSM." After standing for 1 mo in the batch digester, anaerobically digested LSM was transferred into a 1-m³ plastic container and labeled "Digested LSM." A fifth LSM type was obtained from the transfer tank of a second finishing hog operation equipped to remove solids with a Ca-based coagulant. Animal and manure management were similar to those practiced on the first hog operation. Briefly, LSM was pumped from the transfer tank to a treatment tank where coagulant and pressurized air were injected into the manure so that particulate matter aggregated and floated on the top of the tank. Floating material was removed with scrappers, and 1 m³ of the treated liquid fraction was collected in a plastic container and labeled "Flocculated LSM." Details about coagulant composition and dosage were not available.

The five plastic containers with the various LSM types were transported to the experimental sites and continuously stirred during field applications. On each application date, a 2-L composite sample was collected from each LSM type for analysis. The LSM samples were first homogenized with a Polytron (Model PT 3100; Kinematica AG, Littau-Lucerne, Switzerland), and pH was measured by direct reading with a glass electrode. Dry matter content was determined as the weight of materials remaining after drying 100 mL of LSM at 55°C for 96 h. Total C concentration was measured by injecting homogenized LSM into an automated combustion C analyzer (Model Formacs; Skalar Analytical, De Breda, The Netherlands).

Total N and P concentrations of the homogenized LSM samples were determined by acid digestion modified from Isaac and Johnson (1976). Briefly, 2 mL of LSM were mixed with 1.5 mL of a H₂SO₄–SeO₃ solution and 2 mL of H₂O₂ (30% v/v) in a 100-mL digester tube and allowed to react on the bench until foaming ceased. The tubes were then placed on a block digester set at 100°C for 30 min to evaporate water. After water evaporated, the block digester was set at 400°C, and the tubes were allowed to react for 40 min once the digester set point was reached. The tubes were cooled to room temperature, and the volume was completed to 100 mL with deionized water. The concentrations of NH₄⁺ and PO₄^3– in the acid digests were measured with an automated continuous-flow injection analyzer (Model QuickChem 8000 FIA+; Lachat Instruments, Loveland, CO).

The mineral N content in LSM was determined by shaking 10 mL of LSM with 50 mL of 1 M KCl solution for 60 min. The extract was filtered with pre-washed (1 M KCl) filter papers (Whatman #42). Blank samples were used to detect any N contaminations. The NH₄⁺, NO₃^–, and NO₂^– concentrations were measured in the extracts with the automated continuous-flow injection analyzer described previously. The sum of NO₃^––N and NO₂^––N contents accounted for <0.1% of total LSM mineral N.

Study Sites and Experimental Set-up
The experimental sites were located near Québec City (46°48' N; 71°23' W), Canada, on a loam (loamy, mixed, frigid, Typic Humaquept) and a sandy loam (sandy, mixed, frigid, Typic Dystrochrept), with mean annual temperature of 4°C and mean annual precipitation of 1100 mm. Before the experiment, the loam had been cropped to a pure stand of timothy, and the sandy loam had been cropped to a mix of timothy and red clover (Trifolium pratense L.). Both soils were plowed under in autumn 1999, and timothy (cv. Champ) was sown in spring 2000. At the beginning of the experiment in April 2001, the loam had a pH of 6.1, a total C content of 1.8 mg kg^–1, a total N content of 0.14 mg kg^–1, a clay content of 227 g kg^–1, and a sand content of 355 g kg^–1. The sandy loam had a pH of 6.5, a total C content of 2.1 mg kg^–1, a total N content of 0.14 mg kg^–1, a clay content of 171 g kg^–1, and a sand content of 726 g kg^–1.

Agronomy plots were established on both soils on April 2001 and arranged as a randomized complete block design with four replications. Each plot was 3 x 7 m. Seven treatments were applied on May 2001: unfertilized control; mineral fertilizer; and the raw, decanted, filtered, digested, and flocculated LSM. The various LSM were applied as evenly as possible on the surface of the plots with watering cans. There were 28 agronomy plots (seven treatments, four replications) at each experimental site. In addition to the 28 agronomy plots, six 0.5 x 2 m plots were established at each site to accommodate six wind tunnels to measure NH₃ emissions (Rochette et al., 2001). These small NH₃ plots were located about 2 m away from the agronomy plots and managed in the same way. Only one wind tunnel was used for each of the five LSM types and the mineral fertilizer at each site.

The experimental treatments were applied to the same plots for three consecutive years (2001, 2002, and 2003) and were applied to agronomy and NH₃ plots on the same day. The total amount of N applied for each growing season was set to 140 kg ha^–1 and split 80 kg ha^–1 in spring and 60 kg ha^–1 after the first harvest (recommended rates). The amounts of N applied in the various treatments are reported in Table 1 . Spring applications were performed between 8 and 23 May of each year, and the applications after the first harvest were performed between 18 and 25 June (i.e., 1 to 6 d after harvest). All LSM types were applied based on their total N content. Nitrogen was applied as ammonium nitrate in the mineral fertilizer treatment. Phosphorus (50 kg P₂O₅ ha^–1 as superphosphate) and potassium (80 kg K₂O ha^–1 as KCl) were supplied each year to the mineral fertilizer plots, whereas the LSM-treated plots received P and K only from the manure applied. The control plots did not receive fertilizers.

Soil N₂O fluxes were measured on the agronomy plots at approximately 1, 3, 7, 14, and 21 d after every N application using non-flowthrough, non–steady-state chambers (Rochette and Hutchinson, 2005). One Plexiglas frame (0.3025 m² and 0.14 m height) was inserted to a depth of 0.1 m in every agronomy plot and left undisturbed for the duration of the experiment. On every sampling date, the frame was tightly fitted to a vented and insulated Plexiglas chamber (0.3 m in height) covering the same area as the frame. Air samples (20 mL) were collected from the chamber headspace at 0, 10, 20, and 30 min after chamber deployment. Air samples were collected with a syringe through a rubber septum and immediately transferred in pre-evacuated 12-mL glass vials (Exetainers; Labco, High Wycombe, UK). Gas samples and quality controls were analyzed for N₂O concentration within 10 d using a gas chromatograph equipped with an electron capture detector (Rochette and Hutchinson, 2005). The soil-surface N₂O emission rates were calculated using the equation and nonlinear model proposed by Rochette and Hutchinson (2005). N₂O losses were estimated for 21 d after every N application by linearly interpolating emission rates between measurement dates. Cumulative N₂O losses for a given year were calculated as the sum of the two 21-d measurement periods of that year.

Soil Sampling and Analyses
Soils were sampled on the same days as N₂O flux measurements. In each agronomy plot, three soil cores (0–0.2 m) were manually collected with a Dutch auger (0.053-m diam.) and pooled to make one composite sample per plot. Soil samples were immediately brought to the laboratory in plastic bags, and large soil aggregates were manually broken to make homogeneous samples. Exchangeable NH₄⁺ and NO₃^– were measured on the day of soil sampling. Briefly, 20 g of field-moist soil were extracted with 100 mL of 1 M KCl solution for 60 min on a reciprocal shaker. The extracts were centrifuged (10 min, 3000 x g), filtered using pre-washed filter papers (Whatman #42), and frozen (–20°C) until analyzed by colorimetry with an automated continuous-flow injection analyzer as described for mineral N determination in LSM.

Forage Sampling and Analyses
The first harvest was taken between 13 and 20 June of each year, and a second harvest was taken between 26 July and 1 August. Dry matter yield was determined by harvesting forage at a 5-cm height above the soil from a 0.9 x 7-m area in each plot using a self-propelled flail forage harvester (Carter MGF Co., Brookston, IN). The harvested forage was weighed, and a fresh sample of approximately 500 g was taken from each plot, weighed, and dried at 55°C in a forced-draft oven for 3 d for determination of percentage DM. Dried samples were ground using a Wiley mill (Standars model 3; Arthur H. Thomas Co., Philadelphia, PA) fitted with a 1-mm screen. Forage N concentration was determined using a method adapted from Isaac and Johnson (1976) as described for total N determination in LSM. Crop N uptake was calculated as the product of forage N concentration and DM yield.

Statistical Analyses
Analyses of variance were performed using the GLM procedure of SAS (SAS Insitute, 1999) to test the treatment effects on cumulative NH₃ and N₂O losses, and forage DM yield and N uptake. When the treatment effect was significant (P < 0.05), a LSD test was performed to determine significant differences among treatments. The ANOVA were performed separately for each experimental site for each experimental year (2001, 2002, and 2003) and for the average values obtained over the 3 yr. Because wind tunnels were not replicated at each experimental site, we could not analyze the treatment effect on NH₃ loss at each site. We therefore considered sites as random effects, and the site x treatment interaction was used as the error term to test the treatment effect.

	Results and Discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 
Liquid Swine Manure Characteristics
The composition of each LSM type was consistent across years, with CVs lower than 20% for most characteristics measured in the manure collected from 2001 to 2003 (Table 2 ). Solids removal increased the pH of LSM, particularly with anaerobic digestion, which increased pH by almost one unit. This effect of anaerobic digestion was noted in previous studies (Pain et al., 1990; Kirchmann and Lundvall, 1993; Chantigny et al., 2004) and was mainly attributed to the decomposition of volatile fatty acids into methane during the digestion process (Sommer and Husted, 1995).

The flocculated LSM originated from a different LSM source for which we had no sample of the raw manure. Therefore, it cannot be directly compared with the other LSM types. However, both hog operations were managed in similar ways in terms of animal diet, and both LSM sources used for treatment were collected as relatively fresh material from the transfer tanks. In addition, LSM from finishing hog operations in the province of Quebec contains on average 35 kg DM m^–3, 3.5 kg N m^–3, and 0.9 kg P m^–3 (CRAAQ, 2003). Assuming that the original LSM used for flocculation was similar to the provincial average, we estimated that the flocculation process removed about 75 to 80% of initial P from LSM.

Overall, the various treatments used to remove solids reduced LSM DM content with a consequent reduction in P but a minimal effect on N. Such effects of solids removal were previously reported for various methods of mechanical separation (Pain et al., 1978; Møller et al., 2000; Sørensen and Thomsen, 2005). In the present study, we found that chemical separation (flocculation) and anaerobic digestion can also reduce DM and P content of LSM (Table 2). As a result, the N/P ratio of LSM increased after solids removal, especially for the flocculated LSM, which had a N/P ratio of 17.

Soil Mineral N Content
Because mineral fertilization was applied as NH₄NO₃ and 60 to 80% of LSM N was present as NH₄⁺ at time of application (Table 2), soil NH₄⁺ content was markedly increased in both soils after every N application (Fig. 1 , 2 ). This increase was generally similar among N treatments but was short-lived as the soil NH₄⁺ content generally returned to values similar to the unfertilized control 7 to 21 d after application. Soil NO₃^– content increased immediately after application of NH₄NO₃ but increased gradually for 1 to 2 wk in manured plots as a result of nitrification of NH₄⁺ applied with LSM. The increase in soil NO₃^– content did not compensate for the decrease in soil NH₄⁺ content, indicating that amounts of NO₃^– in soil samples were the net result between nitrification and other NO₃^––consuming processes. Some NO₃^– leaching below 20 cm depth might have occurred after precipitation, especially in the sandy loam (Chantigny et al., 2001), but this was not monitored in the present study. The rapid decrease in soil NH₄⁺ content was most likely due to plant N uptake and microbial immobilization, which are typically high under forage grass systems (Schimel, 1986; Recous et al., 1997). As a result, soil NO₃^– content generally remained below 15 mg N kg^–1, and soil mineral N content (NH₄⁺ + NO₃^–) was generally close to background levels 21 d after N application (Fig. 1, 2).

View larger version (24K): [in this window] [in a new window]   Fig. 1. Soil NH4+ and NO3– concentrations in the 0- to 0.2-m soil layer after application of mineral fertilizer and various types of liquid swine manure to a loam in 2001, 2002, and 2003. Each year, N sources were applied in spring and after the first harvest of hay. Arrows indicate the time of N applications. Vertical bars indicate SD of the means.

View larger version (22K): [in this window] [in a new window]   Fig. 2. Soil NH4+ and NO3– concentrations in the 0- to 0.2-m soil layer after application of mineral fertilizer and various types of liquid swine manure to a sandy loam in 2001, 2002, and 2003. Each year, N sources were applied in spring and after the first harvest of hay. Arrows indicate the time of N applications. Vertical bars indicate SD of the means.

View this table: [in this window] [in a new window]   Table 3. Cumulative NH3 losses measured after application of mineral fertilizer (MF) and raw and treated liquid swine manure (LSM) to timothy in 2001, 2002, and 2003 (values are means of the two soil types).

View this table: [in this window] [in a new window]   Table 4. Soil water content and air temperature at time of N application to a loam and a sandy loam cropped to timothy in 2001, 2002, and 2003.

Nitrous Oxide Emissions
In the present study, N₂O was assumed to derive mostly from denitrification because significant N₂O emissions were essentially and consistently measured after precipitation (data not shown). The estimates of N₂O losses were 2.6 to 5.1 times lower in the sandy loam than in the loam soil (Table 5 ). This is likely because of the coarser texture and better drainage/aeration conditions in the sandy loam, which were less conducive to denitrification than in the loam.

View this table: [in this window] [in a new window]   Table 5. Cumulative N2O–N losses measured after the application of mineral fertilizer (MF) and raw and treated liquid swine manure (LSM) to a loam and a sandy loam cropped to timothy in 2001, 2002, and 2003.

The digested LSM was generally associated with significantly lower N₂O losses than the other LSM types (Table 5). Losses were 54 to 69% lower with the digested than with raw LSM in the loam soil and 17 to 71% lower in the sandy loam. This apparent depressive effect on soil N₂O emissions was also reported by others for digested cattle manure (Rubaek et al., 1996; Petersen, 1999; Amon et al., 2006) and swine manure (Vallejo et al., 2006). Nyberg et al. (2004) concluded that some compounds present in anaerobically digested manure may have a depressive effect on soil ammonia oxidizers, thereby reducing the supply of substrate for N₂O production through nitrification and denitrification. Alternatively, Vallejo et al. (2006) argued that because most easily degradable C present in manure is decomposed during anaerobic digestion, the C remaining in the digested manure is more stable and, therefore, less likely to stimulate denitrification and N₂O production as compared with the undigested manure.

Crop Yield and N Uptake
Application of mineral fertilizer and LSM significantly increased forage DM yield and N uptake as compared with the unfertilized control (Tables 6 and 7 ), except for the loam soil in 2002. Presumably, environmental conditions were particularly favorable to indigenous soil N mineralization in the loam soil in 2002, which resulted in high crop N uptake and DM yield in all experimental treatments including the unfertilized control.

In the present study, crop N uptake was most of the time significantly lower with the various LSM types than with the mineral fertilizer (Table 7), indicating that manure-derived N was less available to plant. This difference might be due to the presence of organic N in LSM (Table 2), which is not readily available to the plant. However, the difference may also be explained by the significantly greater NH₃ volatilization with LSM than with mineral fertilizer (Table 3) because NH₃ volatilization directly decreased the amounts of readily available manure N.

Even though the differences were not always statistically significant, crop N uptake tended to be higher with treated than with raw LSM (Table 7). Increased plant N recovery after solids removal was reported by Rubaek et al. (1996), Mattila et al. (2003), and Morris and Lathwell (2004) for cattle manure and by Sørensen and Thomsen (2005) for swine manure. On average across sites and LSM types, LSM treatments reduced NH₃ losses by 5.5 kg N ha^–1 (Table 3), whereas crop uptake was increased by 4.5 kg N ha^–1 in the loam and 12.8 kg N ha^–1 in the sandy loam (Table 7). This is in agreement with Rubaek et al. (1996), who reported increased plant N uptake only where treated manure resulted in lower NH₃ losses than untreated manure. We therefore hypothesized that the greater crop N uptake with the treated than with the raw LSM was partly due to the reduction in NH₃ losses. However, the lower C content of the treated LSM may also have resulted in a greater N availability compared with raw LSM because the decomposition of LSM C may induce soil N immobilization (Kirchmann and Lundvall, 1993), thereby interfering with plant N uptake.

	Perspective and Conclusions

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 
The present study looked at gaseous N emissions and plant N uptake from only the liquid fraction of treated hog manure even though a DM-rich fraction is often produced at the same time. The main purpose for hog manure treatment in the area of study is to extract and export P from operations facing surplus P problems due to local regulations for field application of manure based on crop P requirements. In this situation, only the liquid fraction remains on-farm, whereas the DM-rich fraction is exported to composting or organic fertilizer plants. In other areas, however, manure treatment can be viewed as an option for optimized on-farm nutrient management (Møller et al., 2000). In this case, a thorough assessment of the liquid and DM-rich fractions is required because some benefits found with the liquid fraction may be partly offset by lower N efficiency and greater environmental losses with the DM-rich fraction (Sørensen and Thomsen, 2005; Amon et al., 2006).

Removing solids in LSM by mechanical, chemical, or biological means seemed to be a valid option to reduce gaseous N emissions after land application. All LSM treatments reduced NH₃ emissions (average reduction of 25%) relative to the untreated LSM, and anaerobic digestion also significantly reduced N₂O emissions.

Liquid swine manure, treated or untreated, offers an alternative to mineral fertilizers for the production of forage grasses under the cool and humid climate of eastern Canada. Forage DM yields with LSM were on average >90% of those obtained with mineral fertilizer. However, management practices that minimize NH₃ volatilization should be used where LSM is applied because it emits significantly more NH₃ than mineral fertilizers, such as ammonium nitrate. In perennial forage systems where incorporation of manure may disturb the rooting system, removing solids from LSM before land application is an option to significantly reduce NH₃ losses and thereby to improve the fertilizer efficiency of LSM.

	ACKNOWLEDGMENTS

 
This study was funded by the Québec Hog Producers Federation (FPPQ) and the Agriculture and Agri-Food Canada Matching Investment Initiative. We thank Johanne Tremblay, Normand Bertrand, Nicole Bissonnette, Patrice Jolicoeur, and Danielle Mongrain for their assistance in various aspects of this study.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 
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	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Perspective and Conclusions REFERENCES

 

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