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Journal of Environmental Quality 32:681-686 (2003)
© 2003 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORTS
Waste Management

Swine Effluent Irrigation Rate and Timing Effects on Bermudagrass Growth, Nitrogen and Phosphorus Utilization, and Residual Soil Nitrogen

A. Adeli*,a, J. J. Varcob and D. E. Rowea

a USDA-ARS, Waste Management and Forage Research Unit, Mississippi State, MS 39762
b Plant and Soil Sciences Dep., Mississippi State Univ., Mississippi State, MS 39762

* Corresponding author (aadeli{at}ra.msstate.edu)

Received for publication December 31, 2001.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Maximizing utilization of effluent nutrients by forage grasses requires a better understanding of irrigation rate and timing effects. This study was conducted in 1998 and 1999 on a Vaiden silty clay (very-fine, smectitic, thermic Aquic Dystrudert) soil to determine the effects of swine lagoon effluent irrigation rate and timing on bermudagrass [Cynodon dactylon (L.) Pers.] growth, nitrogen (N) and phosphorus (P) recovery, and postseason soil profile NO-3–N. Treatments consisted of swine effluent irrigation at the rates of 0, 5, 10, 15, and 20 ha-cm. Two additional treatments included 2.5 ha-cm applied on 1 September and 1 October in addition to a base summer rate of 10 ha-cm. In both years for early to mid-season irrigation, bermudagrass dry matter yield quadratically increased with increasing swine effluent irrigation rates. Averaged across years, effluent irrigation in October resulted in 30% less dry matter than in September. For late-season irrigation, apparent N recovery averaged 59% less and P recovery averaged 46% less with a delay in irrigation from 1 September to 1 October. The greatest quantity of soil NO-3–N was associated with both the greatest effluent rate and October irrigation treatments. Minimal yield benefit was obtained when effluent was applied at rates greater than 10 ha-cm during the summer months. Late-season irrigation, especially after 1 October for areas with similar climatic conditions, should be avoided to maximize synchronization of nutrient availability with maximum growth rates to minimize potential offsite movement of residual soil N and P.


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
RATES AND TIMING of swine effluent irrigation applied to crops and pastures are important for minimizing adverse effects on soil and water quality. Confined swine feeding operations in the southern USA produce large quantities of waste that typically are flushed into anaerobic lagoons to facilitate decomposition. To prevent lagoon overflow, permits require surrounding crop and pasture land to be irrigated with effluent. Lagoon effluent is a solution containing multiple nutrients, including N, P, K, Ca, and Mg, and micronutrients (Sutton et al., 1982). Proper management of swine lagoon effluent on cropland is important for improving the economics of crop production and for minimizing adverse effects on soil and water quality. Nitrogen, P, and K are the most agronomically important nutrient elements, while N and P also pose an environmental hazard.

Improving the utilization efficiency of nutrients derived from effluent by forage grasses requires a better understanding of irrigation rate and timing effects relative to the growth potential of the forage grass in question. Burns et al. (1990) reported that ‘Coastal’ bermudagrass yield responding to a swine lagoon effluent N rate of up to 670 kg ha-1. Also, evidence was presented for declining recovery rates of N and P with increasing effluent irrigation rates. Eichhorn (1989) found maximum bermudagrass yields at 448 kg N ha-1 from fertilizer, and while N removal continued to increase up to 672 kg ha-1, apparent N recovery decreased. Morris and Celecia (1962) found greater N uptake by bermudagrass when fertilizer N was applied in spring as compared with the fall. Osborne et al. (1999) reported decreased N recovery by bermudagrass with increasing fertilizer N application rates and when N fertilization was delayed until late summer as compared with application in early spring.

Rates and timing of application of manure-derived N can affect both the availability of N for crop growth and the amount of NO-3–N remaining in the soil profile. King et al. (1990) reported NO-3–N accumulation at a depth greater than 60 cm with excessive effluent N rates applied to bermudagrass. Reduced N recovery by bermudagrass with late summer fertilization (Osborne et al., 1999) suggests increased soil NO-3–N levels before the onset of dormancy. Sloan et al. (1999) found evidence for swine effluent irrigation applied to pasture grasses elevating NO-3–N levels in shallow ground water and subsequent transport into surface waters.

To reduce the potential for environmental degradation due to excessive residual soil levels of nutrients derived from effluent, application rates must not exceed the plant and soil buffering capacities. At the initiation of this research, swine producers in Mississippi were allowed to begin effluent irrigation 1 March and continue until 31 October according to their permits. This interval extends outside of the most active period of growth of summer grasses such as bermudagrass. Although fertilizer N sources and rates have been extensively evaluated for bermudagrass (Burns et al., 1987, 1990), relatively little is known about temporal bermudagrass response in terms of yield and nutrient utilization to late-season swine effluent application. Given this background, the objective of this study was to determine swine effluent irrigation rate and timing effects on bermudagrass growth, N and P recovery, and postdormancy soil profile NO-3–N.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Research was conducted in 1998 and 1999 on the premises of a commercial swine facility located near Brooksville, MS on previously established research plots. Swine effluent used for irrigation was taken from an anaerobic lagoon at a farrow to finish swine operation. Historical site management including treatments, soil characterization, and cultural practices can be found in Adeli and Varco (2001). Physical and chemical characteristics of the Vaiden soil are shown in Table 1. Particle size analysis was determined by the hydrometer method (Day, 1965), organic matter was determined by the acid dichromate digestion method (Peech et al., 1947), and pH was determined in a 1:1 soil and water suspension. Swine effluent irrigation was initiated each May and continued through August. Swine effluent was applied to ‘Alicia’ bermudagrass at rates of 0, 5, 10, 15, and 20 ha-cm, equivalent to approximately 0–0, 213–43, 381–75, 528–108, and 660–145 kg N–P ha-1 in 1998 and 0–0, 215–31, 365–74, 516–118, and 670–163 kg N–P ha-1 in 1999 (Table 2). On 1 September and 1 October each year, 2.5 ha-cm was applied to a base rate of 10 ha-cm applied from May through June (Table 2). This was done to determine the effects of late-season swine effluent application on N and P uptake and recovery by bermudagrass and residual soil N. The experiment was arranged as a randomized complete block and treatments replicated four times. Individual plot dimensions were 3.66 by 3.66 m with 3.05-m alleys.


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  		Table 1. Initial soil chemical and physical properties of the study site.

 

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  		Table 2. Nitrogen and P applied from swine lagoon effluent irrigation in 1998 and 1999.

 
Swine effluent was applied in 0.64 ha-cm increments up to 1.25 ha-cm in a given day, depending on antecedent soil moisture content. Irrigation was repeated until each incremental rate was achieved (i.e., 5, 10, 15, and 20 ha-cm), at which time irrigation ceased to allow the forage adequate time to grow and facilitate a hay harvest (Table 3). For each effluent irrigation event, 1.25 ha-cm of clean water was applied to check plots. This was done to minimize growth differences between treatments as a result of water availability. A 1500-L water-wagon was used for delivery of irrigation water and swine lagoon effluent to the plots. Effluent subsamples were obtained for every tank-full and stored on ice for transport to the laboratory. Electrical conductivity and pH of effluent samples were determined immediately. Samples were preserved by acidifying to attain a pH < 2 with H2SO4 and then frozen until analysis (Greenberg et al., 1992). Effluent samples were digested for total N determination with a modified micro-Kjeldahl procedure described by Nelson and Sommers (1973). The digest was analyzed with a phenol–hypochlorite colorimetric assay described by Cataldo et al. (1974). Total inorganic N of the effluent was analyzed with steam distillation (Bremner and Keeney, 1965). Total P content of effluent was analyzed by using a H2SO4 and HNO3 acid digestion procedure (Greenberg et al., 1992). Digested samples were analyzed for P with a colorimetric assay developed by Murphy and Riley (1962).


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  		Table 3. Irrigation and harvest schedule for 1998 and 1999. Each irrigation event supplied 5 ha-cm of effluent.

 
The bermudagrass sward was harvested after allowing at least 21 d of growth after completing each incremental treatment application rate. A total of six harvests was made each year and yields were added together as final yield. Two swaths (total of 2.77 m2) were harvested from each plot with a rotary mower set at a cutting height of 7 cm. Fresh weights of harvested forage were taken and subsamples were dried at 65°C for 48 h in a forced-air oven. Dried plant material was ground in a Wiley mill to pass a 2-mm sieve. To determine total P content, 1-g samples were dry-ashed according to procedures outlined by Isaac and Kerber (1971). Total P of the digests was measured with a colorimetric assay on an automated segmented flow-analyzer (Flow Solution III Analyzer; Perstorp Analytical, Perstorp, Sweden). Nitrogen content of forage was determined with an automated dry combustion analyzer (Model NA 1500 NC; Carlo Erba, Milan, Italy). The quantity of N and P removed in the harvested forage was calculated as a product of N and P concentrations and dry matter yield for each harvest. Apparent N and P recovery values were calculated by dividing the total quantity of nutrient harvested less the amount harvested for the control plots by the amount of the nutrient applied in the effluent and multiplied by 100.

With the onset of dormancy signaled by a killing frost, soil samples were taken at depths of 0 to 5, 5 to 15, 15 to 30, 30 to 60, and 60 to 90 cm. Composited soil samples consisted of nine random cores per plot. Samples were frozen at -4°C to prevent N transformations prior to analysis. Soil NO-3–N was determined by extracting soil samples with 1 M KCl. Extracts were analyzed for NH+4–N and NO-3–N by colorimetric analysis (Greenberg et al., 1992) with an automated segmented flow analyzer. Soil NH+4–N accumulations were weighted for each depth and summed across depths for each treatment to obtain total NH+4–N accumulation in the soil profile.

All statistical analyses were performed with the Statistical Analysis System (SAS Institute, 1985). The general linear model was used to perform analyses. Analysis of variance were conducted by year. Statistical tests were performed at a 0.05 level of significance.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Effluent Analysis
Yearly average analyses of swine effluent samples obtained from each irrigation event are shown in Table 4. Average N concentration of swine effluent ranged from 420 and 423 mg L-1 in May to 308 and 312 mg L-1 in October in 1998 and 1999, respectively (data not shown). Effluent N existed primarily as NH+4–N (82% of the total N) with minimal NO-3–N (2.6% of the total N). The predominance of NH+4–N shows the lagoon was anaerobic. Similar to N, lagoon effluent P is primarily in the chemical form available for plant utilization indicating the swine lagoon effluent is chemically similar to commercial fertilizers. These results are similar to the work of Sutton et al. (1978) and previous research at this site (Adeli and Varco, 2001).


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  		Table 4. Average analysis for swine effluent used for irrigation in 1998 and 1999.

 
Dry Matter Yield
Bermudagrass dry matter yield increased significantly with increasing swine effluent application rates during the most active period of growth. Dry matter yield responded quadratically to increasing swine effluent application rates and ranged from 3112 and 1900 kg ha-1 with no effluent to 13 000 and 11 670 kg ha-1 with application of 20 ha-cm effluent in 1998 and 1999, respectively (Table 5). Although residual soil P and K increased from swine effluent applications in 1998 (data not shown), overall dry matter production was lower in 1999 compared with 1998. This is probably related to lower rainfall received in 1999 (Table 6). Little advantage in yield of bermudagrass was obtained from effluent application at rates greater than 10 ha-cm, which was equivalent to 373 kg N ha-1.


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  		Table 5. Effects of swine lagoon effluent in-season and late-season irrigation on bermudagrass yield in 1998 and 1999.

 

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  		Table 6. Monthly precipitation received at the experimental site.

 
For late-season irrigation in both years, bermudagrass yields increased significantly in response to both September and October irrigations when compared with the 10 ha-cm base rate (Table 5). However, dry matter yield was much less in October than in September. The results of this study agree with other researchers (Osborne et al., 1999; Morris and Celecia, 1962) who found that delaying fertilizer N application resulted in lower yield potentials.

Nitrogen and Phosphorus Removal
Maximizing efficiency in recovery of applied N decreases the potential for NO-3–N leaching. In 1998, regression analysis indicated a strong quadratic response in N removal (P < 0.01, r2 = 0.95) to increasing swine effluent application rates during the most active period of growth (Table 7). In 1999, N utilization by bermudagrass showed a similar trend (P < 0.05, r2 = 0.92), but the absolute quantity removed each year was dependent on yield, because plant N concentrations were not different (data not shown). Total N removal ranged from 40 and 27 kg N ha-1 with no effluent application to 302 and 265 kg N ha-1 with application of 20 ha-cm effluent in 1998 and 1999, respectively (Table 7).


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  		Table 7. Effects of swine lagoon effluent in-season and late-season irrigation on N and P removal by bermudagrass in 1998 and 1999.

 
Irrigation on 1 Sept. 1998 resulted in considerable N removal, but the same rate applied on 1 October was about 50% as efficient (Table 7). In 1999, both late-season irrigations resulted in limited N removal by bermudagrass. Averaged across years, bermudagrass utilized 50% less N from swine effluent applied in October than in September. Lower N removal in October is probably related to cooler temperatures and shorter days, which could have slowed the growth of bermudagrass. Recently, Adeli and Varco (2001) showed a strong dependency of N uptake with effluent irrigation on bermudagrass dry matter production potential.

For both years, P removal by bermudagrass increased quadratically with increasing swine effluent loading rates (r2 = 0.93 and 0.92, respectively) (Table 7). For 1998 and 1999, total P removal by bermudagrass ranged from 7 and 4 kg P ha-1 with no effluent applied to 34 and 22 kg P ha-1 with 20 ha-cm effluent, respectively. Since plant P concentrations were not different (data not shown), lower P removal by bermudagrass in 1999 is probably related to lower yields than in 1998.

Nitrogen and Phosphorus Recovery
Apparent N recovery was calculated by subtracting N removal for the control treatment from removal for effluent treatments and dividing by the N rate applied (Table 8). Apparent recovery of applied N in the harvested portion is an important indicator of N use efficiency and potentially reflects relative quantities of N remaining in the soil. In 1998 and 1999, apparent N recovery tended to decrease with increasing swine effluent application (Table 8). In 1998, during the most active growth period, apparent N recovery decreased from 64% with irrigation of 5 ha-cm (213 kg N ha-1) effluent to 40% with 20 ha-cm (660 kg N ha-1). This is in agreement with the results of studies conducted by Eichhorn (1989) and Osborne et al. (1999), who found that apparent N recovery by bermudagrass decreased as fertilizer N rates increased from 224 to 672 kg N ha-1. In 1999, apparent N recovery ranged from 49% with 5 ha-cm effluent (215 kg N ha-1) to 36% with 20 ha-cm effluent (670 kg N ha-1). Apparent N recovery in 1998 from September-applied effluent N was favorable and comparable with early season applications, while N recovery for October irrigation was drastically reduced. Both September and October effluent irrigations events resulted in lower N recovery in 1999 than in 1998 and are probably the result of reduced growth potential and greater NH3 volatilization potential due to warmer and drier conditions (Burns et al., 1987; Fenn and Kissel, 1974; Osborne et al., 1999; Sharpe and Harper, 1997).


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  		Table 8. Effects of swine lagoon effluent in-season and late-season irrigation on N and P recovery by bermudagrass in 1998 and 1999.

 
Although total P removed in harvested forage increased with increasing effluent rates, apparent recovery of applied P decreased (Table 8). In 1998, apparent P recovery decreased from 40% with irrigation of 5 ha-cm (43 kg P ha-1) to 18% with 20 ha-cm effluent (145 kg P ha-1). In 1999, apparent P recovery ranged from 28 to 11% with application of 31 and 163 kg P ha-1, respectively. Recovery of P dramatically decreased both years when swine lagoon effluent was applied late in the season (Table 8). It is apparent that increasing application rates of swine effluent–derived P will probably increase residual soil P, while late-season application would have the most dramatic effects. Lowered P uptake efficiency and concomitant soil P increases, mainly at the surface, would probably increase the potential for P transport in runoff.

Residual Soil Nitrate
Total soil profile (0–90 cm) residual NO-3–N is shown in Table 9. Nitrate accumulation in the soil profile varied slightly from 1998 to 1999. In 1998, residual NO-3–Nranged from 5 kg ha-1 with no effluent applied to 41 kg ha-1 with 20 ha-cm effluent cm (660 kg N ha-1). In 1999, residual NO-3–N ranged from 2 kg ha-1 with no effluent applied to 32 kg ha-1 with application of 20 ha-cm (670 kg N ha-1). This amount of residual N may not represent a great environmental risk, but it illustrates that N applied in excess of N accumulated in the plant is a potential risk to the environment. Since applied effluent N was primarily NH+4–N (Adeli et al., 1995; Schmidt, 1998), lower accumulation of soil profile NO-3–N and plant recovery in 1999 was probably related to greater NH3 volatilization due to warmer and drier conditions (Burns et al., 1987; Fenn and Kissel, 1974; Osborne et al., 1999; Sharpe and Harper, 1997). In both years, the greatest accumulation of soil profile NO-3–N was obtained when swine effluent was applied at the greatest rate (20 ha-cm), which was equivalent to 665 kg N ha-1. This response to N is similar to NO-3–N accumulation patterns reported by King et al. (1990) and previously reported N fertilization and effluent irrigation results at this site (Adeli and Varco, 2001). For both years, the pattern of NO-3–N distribution in the soil profile showed that the greatest amount of residual NO-3–N accumulated in the top 30 cm of the soil profile (Fig. 1 and 2) . This could be related to the fact that limited precipitation, especially from July to October, prevented the leaching of NO-3–N into the lower depth. Only in 1998, with the greatest effluent N rate, was there an increase in residual soil NO-3–N in the 30- to 60-cm depth. These end of season profiles suggest limited NO-3–N leaching below the 90-cm depth during the active period of growth. Effluent N application rates at 516 kg N ha-1 or greater resulted in the greatest residual N levels in 1999, the drier of the two years. September irrigation tended to increase residual soil NO-3–N levels with results comparing most closely with the 660 kg N ha-1 rate in 1998 and the 365 kg N ha-1 rate in 1999. October irrigation averaged a twofold increase in residual N compared with irrigation in September.


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  		Table 9. Effects of swine lagoon effluent in-season and late-season irrigation on residual soil NO-3–N in the top 90 cm of soil profile in 1998 and 1999.*

 


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  		Fig. 1. Effects of swine effluent in-season and late-season irrigation on residual soil NO-3–N in 1998.

 


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  		Fig. 2. Effects of swine effluent in-season and late-season irrigation on residual soil NO-3–N in 1999.

 

   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Results from this study indicate little advantage in bermudagrass dry matter production and uptake of N and P from swine effluent application rates greater than 10 ha-cm (373 kg N ha-1 and 75 kg P ha-1) during the summer months. For areas of similar climatic conditions and growth potential of bermudagrass, late-season irrigation, especially after 1 October, should be avoided to minimize potential offsite movement of residual soil N and P. These results support the NRCS's Waste Treatment Lagoon Code 359, which was modified January 2000 to read, "unless cool season forages are present, application should be postponed between October 1 and March 31 ..." (Mississippi Natural Resources Conservation Service, 2000).


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Contribution of the Mississippi Agric. and Forestry Exp. Stn., Journal Paper no. J10263.


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


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