Agronomy Journal 93:1174-1181 (2001)
© 2001 American Society of Agronomy
WASTE MANAGEMENT
Swine Lagoon Effluent as a Source of Nitrogen and Phosphorus for Summer Forage Grasses
Ardeshir Adeli and
Jac J. Varco*
Dep. of Plant and Soil Sci., Mississippi State Univ., Mississippi State, MS 39762
* Corresponding author (jvarco{at}pss.msstate.edu)
Received for publication July 11, 2000.
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ABSTRACT
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Efficient crop utilization of N and P derived from anaerobic swine (Sus scrofa domesticus) lagoon effluent is critical to minimizing offsite nutrient movement. The objective of this study was to determine the effects of variable rates of swine lagoon effluent and fertilizer N and P on yield and nutrient utilization of forage grasses on an acid Vaiden silty clay (very fine, montmorillonitic, thermic, Vertic Hapludalf) and an alkaline Okolona silty clay (fine, montmorillonitic, thermic, Typic Chromudert). Treatments were multiple effluent irrigations resulting in four N and P rates from 0 to 665 and 0 to 94 kg ha-1 yr-1 N and P, respectively. Fertilizer treatments were also established at equivalent N and P rates. Similar growth responses were obtained for bermudagrass [Cynodon dactylon (L.) Pers.] or johnsongrass [Sorghum halepense (L.) Pers.] regardless of nutrient source. Application of either effluent or fertilizer at rates >448 kg N ha-1 did not effectively increase dry matter yield. Total N accumulation reflected both increasing dry matter yield and tissue N concentration while P accumulation depended primarily on increasing yield. Forage grass accumulation of N and P was similar between sources, but recovery efficiency for both elements declined with increasing rates. Similarity in N and P availability of effluent to fertilizer simplifies nutrient management although potential N loss by NH3 volatilization is likely greater for effluent while fertilizer may result in greater end-of-season soil NO-3–N levels at equivalent rates of applied N.
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INTRODUCTION
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LAND APPLICATION of manure-derived nutrients generated by large, confined swine-feeding operations has come under closer scrutiny by state and federal agencies due to heightened environmental concerns. Large quantities of waste are produced on individual farms and in warmer climates, it is typically flushed into anaerobic lagoons to facilitate digestion. The resulting effluent is a solution containing multiple nutrients, including N, P, K, Ca, Mg, and micronutrients (Burns et al., 1985). Of these nutrients, N and P comprise the most agronomically and economically important proportions of liquid swine manure (Sutton et al., 1982). Burns et al. (1985) reported an average nutrient content of anaerobic swine lagoon effluent for multiple years of 234 and 59 mg L-1 N and P, respectively. Adeli et al. (1995) reported an average nutrient content of anaerobic swine lagoon effluent from a commercial facility in Mississippi of 420 and 61 mg L-1 N and P, respectively.
Swine wastes in the form of solid, slurry, and effluent have been applied to crops with varying yield response (Booram et al., 1974; Burns et al., 1990; Westerman et al., 1983; Sutton et al., 1982; Evans et al., 1977). Also, the effects of swine effluent on forage dry matter production have generally been evaluated at rates exceeding the most efficient crop nutrient utilization potential (Burns et al., 1987; King et al., 1990; Westerman et al., 1983). King et al. (1990) reported soil profile NO-3–N accumulation >35 mg kg-1 below a depth of 60 cm after 11 yr of applying 1340 kg ha-1 effluent N and noted appreciable profile NO-3–N periodically with 670 kg ha-1 effluent N. They concluded that a rate of 335 kg N ha-1 would not pose a pollution hazard to ground water.
Crop recovery of effluent-derived nutrients is variable and depends on the rate applied. In a study by Burns et al. (1985) on loamy sands, N recovery by ‘Coastal’ bermudagrass across a 7-yr period averaged 73, 57, and 34% for swine effluent N rates of 335, 670, and 1340 kg ha-1, respectively. Phosphorus recovery was 41, 28, and 17% with effluent application rates equivalent to 78, 153, and 301 kg P ha-1, respectively.
In practice, animal waste application rates are routinely based on crop N requirements (Sharpley et al., 1994). Availability of manure N is generally lower than commercial fertilizer sources due to a dependence on microbial activity for mineralization of organic N compounds and a greater potential for NH3 volatilization (Beauchamp, 1983; Klausner and Guest, 1981). Generally, N availability indices are used for manures in developing nutrient management plans, but in practice, may not be accurate (Lory et al., 1995). Additionally, manure storage and treatment can alter nutrient availability through both losses in nutrient quantity and mineralization. Evans et al. (1977) concluded that N derived from anaerobically digested swine lagoon effluent was more available to corn (Zea mays L.) than N derived directly from swine manure. Burns et al. (1987) noted greater recovery by Coastal bermudagrass of N and P derived from anaerobic swine effluent compared with a slurry.
The effects of commercial fertilizer on forage grass growth and nutrient assimilation is well documented (Robinson, 1996), but the relative efficiency of anaerobic swine lagoon effluent to equivalent N and P rates from fertilizer sources is not. Most studies have compared the effects of animal waste rates on crop growth using only a single rate of inorganic fertilizer N (Liu et al., 1997; Eghball and Power, 1999) or in combination with fertilizer (Jokela, 1992; Beauchamp, 1983; Schmidt et al., 1994). Thus, the objective of this study was to determine the effects of comparable rates of N and P derived from anaerobic swine effluent and commercial fertilizer on yield and N and P accumulation and recovery by forage grasses grown on an acid and alkaline soil.
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MATERIALS AND METHODS
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Research plots were established in 1994 on the premises of a new commercial swine facility located near Brooksville, MS. Two soil types were chosen for this study: an alkaline Okolona and an acid Vaiden, both with a silty clay texture. Both soils are representative of the Blackland Prairie major land resource area and initially tested very low (Vaiden) to low (Okolona) in P (Table 1). In 1994, summer annuals, including crabgrass (Digitaria sp.) and foxtail (Setaria sp.), dominated the Vaiden site while a dense stand of johnsongrass resulted after disking the Okolona site. In 1995, ‘Alicia’ bermudagrass was established on the Vaiden site by sprigging.
Irrigation of sites began in 1994 using anaerobic swine lagoon effluent applied at rates of 0, 2.5, 5, and 7.5 ha cm, and in 1995, the rates were doubled on the Okolona site. Rates were equal to 1994 rates during the establishment of bermudagrass in 1995 on the Vaiden soil but were doubled in 1996. Swine effluent was applied in increments of 0.64 up to 1.27 ha cm on a given day, depending on antecedent soil moisture content. For each effluent irrigation event, 0.64 ha cm of fresh water was applied to check and fertilized plots to dissolve and incorporate fertilizer. A 1500-L water wagon was used for delivery of irrigation water and swine lagoon effluent to plots. Effluent samples were obtained from every full tank and stored on ice in a cooler for transport to the laboratory. Effluent pH was determined after allowing samples to warm to room temperature. Effluent samples were preserved by acidifying to a pH <2 [2 mL L-1 sulfuric acid (H2SO4)] and freezing until analysis (Greenburg et al., 1992). Irrigation with swine effluent was initiated each May and continued through August. Yearly swine effluent and corresponding N and P application rates defined as low, medium, and high are shown in Table 2. For comparison, fertilizer N and P was applied at rates equivalent to effluent N and P rates. Fertilizer sources were ammonium nitrate [NH4NO3] (34–0–0) and concentrated superphosphate (0–46–0). To ensure an accurate comparison in N and P rate response, K was applied as muriate of potash [KCL] (0–0–60) to fertilizer treatments at an equivalent effluent K rate (Table 3). Treatments were replicated four times, and the experiment was arranged as a randomized complete block. Individual plot dimensions were 3.66 by 3.66 m with 3.05 m alleys.
Effluent samples were digested for total N using a modified micro-kjeldahl procedure described by Nelson and Sommers (1973). The digest was analyzed using a phenol-hypochlorite colorimetric assay (Cataldo et al., 1974). Total inorganic N 
of the effluent was analyzed using steam distillation (Bremner and Keeney, 1965). Total P of the effluent was analyzed using a H2SO4–HNO3 acid digestion procedure (Greenburg et al., 1992), and the digest was analyzed for ortho-P using a colorimetric assay (Murphy and Riley, 1962).
Forage grasses were harvested after completing each incremental treatment application (either 2.5 or 5 ha cm), allowing at least 21 d of growth for bermudagrass or appearance of the boot stage for johnsongrass. Two swaths (total of 2.77 m2) were harvested from each plot using a commercial rotary mower set at a height of 5 cm. Harvested forage was weighed, and subsamples were dried at 65°C for 48 h in a forced-air oven to convert fresh weights to a dry weight basis. Dried plant material was ground in a Wiley mill to pass a 1-mm sieve. Nitrogen content of forage was determined using an automated dry-combustion analyzer (Model NA 1500 NC, Carlo Erba, Milan, Italy). Total P content was determined by dry-ashing 1-g samples according to procedures outlined by Isaac and Kerber (1971). Total P was measured using a colorimetric assay on an automated segmented flow analyzer (Flow Solution III, Perstorp Analytical Environmental, Wilsonville, OR). Yield and tissue nutrient concentration were used to calculate total N and P content for each harvest and total N and P removal. Apparent N and P recoveries were calculated by subtracting N and P content of the nontreated check from each effluent and fertilizer treatment, dividing by the amount of nutrient applied in effluent or fertilizer, and multiplying by 100.
To determine residual soil profile NO-3–N, soil samples were taken in October 1996 after a killing frost. Nine soil cores, 5-cm diam., were randomly sampled and divided into depths of 0 to 5, 5 to 15, 15 to 30, 30 to 45, 45 to 60, and 60 to 90 cm. Samples were composited by depth, placed in plastic bags, and preserved in a freezer at -4°C. Soil NO-3–N was determined by extracting samples with 1 M KCL, filtering, converting NO-3 to NO-2 by reduction in a Cd coil, and colorimetrically determining NO-2 (Greenberg et al., 1992) on an automated segmented flow analyzer.
The General Linear Models (GLM) procedure in SAS (SAS Inst., 1985) was used to perform an analysis of variance. Data were analyzed using simple regression models, which included linear and quadratic trends. Analysis of variance was conducted by year and soil or site. Analysis of variance using single degree-of-freedom comparisons was performed to estimate fertilizer N equivalence of swine lagoon effluent. Statistical tests were performed at a 0.05 level of significance.
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RESULTS AND DISCUSSION
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Effluent Analyses
Yearly average analysis of swine effluent samples obtained from each irrigation event is shown in Table 3. Effluent N existed primarily as NH4/NH3–N (84%) with minimal NO-3–N content (2.2%). The predominance of ammoniacal N reflects the nature of anaerobic decomposition processes in the lagoon. The slightly alkaline pH is a reflection of the anaerobic nature as well. Similar to N, most of the P existed as water soluble ortho-P (80%), suggesting N and P availability should be similar to commercial fertilizers. However, due to the presence of organic compounds, it has been speculated that N availability could be decreased due to greater immobilization as well as losses via denitrification and NH3 volatilization (Cabrera and Gordillo, 1995). Similarly, more inorganic P may be immobilized due the presence of organic compounds (Chauhan et al., 1979). The N/P ratio ranged from 6.5 to 7.2 and averaged 6.7 for the 3-yr period. Relative to N, excess application of P is predictable using effluent because fertilized bermudagrass accumulates N and P in a ratio range of 9:1 to 12:1 (Robinson, 1996).
Dry Matter Yield
Dry matter yields of forage grasses were significantly increased with increasing rates of effluent and fertilizer N each year (Fig. 1). Regression analyses showed quadratic trends in total yield for all years and grasses, except in 1994 with summer annual grasses on the Vaiden soil where the trend was linear. Bermudagrass yield was not as great in 1995, the year of establishment, compared with 1996. A decline in johnsongrass yield from 1995 to 1996 may be related to a noticeably thinner stand caused by intensive hay cutting (Sturkie, 1930; Watson et al., 1970). For both bermudagrass and johnsongrass, it appears that N rates should not exceed approximately 450 kg N ha-1. This is in agreement with the work by Eichhorn (1989), who found a maximum dry matter yield for bermudagrass of 9.5 Mg ha-1 at a rate of 448 kg ha-1 fertilizer N.
For both grasses, no significant difference in cumulative dry matter yield was obtained between swine lagoon effluent and fertilizer application in 1995 and 1996, suggesting both nutrient sources were similar in nutrient availability at the rates used in this study. For both grasses, swine effluent increased dry matter yield slightly more than fertilizer did in 1994. This could be related to the greater supply of water provided by effluent irrigation.
Nitrogen and Phosphorus Dynamics
Tissue Nitrogen and Phosphorus Concentration
Application of swine effluent and fertilizer N significantly increased N concentration in both forage grasses for all years (Table 4). Overall, fertilizer resulted in the greatest values for all of the forage grasses each year. Effects of tissue N concentration for both sources were best described using quadratic response equations suggesting optimization of growth when sufficiency levels were reached or possibly a decline in assimilation efficiency with excessive rates. In contrast, effluent or fertilizer application in most instances did not significantly increase tissue P concentration (Table 4). In some cases, P concentrations declined, suggesting total P accumulation by forage grasses is most likely related to rates of dry matter production rather than tissue P content.
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Table 4. Effects of swine effluent and fertilizer rates on N and P concentration of summer annual grasses, bermudagrass, and johnsongrass.
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To determine the nature of N accumulation response to effluent and fertilizer N, dry matter yields of forage grasses were regressed against N concentration (Table 5). In 1994, a linear correlation resulted for both soils while in 1995 and 1996, dry matter yields were quadratically related to tissue N concentrations. This implies that N was either not diluted or only slightly diluted by increasing dry matter yields, which is in agreement with the work of Wiedenfeld (1988). Nitrogen accumulation, therefore, was a function of both tissue N concentration and dry matter yield. Regardless of N source, maximum dry matter yield of 9.3 Mg ha-1 was predicted with an N concentration of 30.0 g kg-1 for bermudagrass and 8.7 Mg ha-1 was predicted with an N concentration of 26.7 g kg-1 for johnsongrass in 1996 (data not shown).
Forage grass yields were also regressed against tissue P concentration (Table 5). In contrast to tissue N, summer annual grasses and bermudagrass dry matter yields were not highly correlated with tissue P concentration. For johnsongrass, the relationships were significant, but P concentration generally decreased with increasing effluent and fertilizer rates due to dilution by increased dry matter production (Jarrell and Beverly, 1981). Thus, the quantity of P removed by harvested forage grasses depends principally on dry matter yield. To attain P removal rates assigned in nutrient management plans, adequate N must be applied for optimal growth.
Nitrogen Accumulation and Recovery
Maximizing efficiency in recovering applied N decreases the potential for N loss by leaching and denitrification. Total N accumulation on both soils was increased substantially with increasing effluent and fertilizer application rates each year (Fig. 2). Regression analysis indicated quadratic trends in total N accumulation by summer annual grasses, bermudagrass, and johnsongrass in response to effluent and fertilizer N application rates. Soil N availability, estimated from N accumulation by the untreated checks and averaged across years, was 29 and 41 kg N ha-1 yr-1 for the Vaiden and Okolona soils, respectively. Regardless of N source, N accumulation was near 320 kg N ha-1 for bermudagrass in 1996 with 661 and 672 kg ha-1 effluent N and fertilizer N, respectively. An average accumulation of 235 kg N ha-1 by johnsongrass for 1995 and 1996 was found with 665 and 672 kg ha-1 effluent N and fertilizer N, respectively. For both grasses, no significant difference in N accumulation was found between swine effluent and fertilizer, indicating both sources provided a similar quantity of available N.
Recovery of N in the harvested portion is an important indicator of N use efficiency and potentially reflects relative quantities of N remaining in or lost from the soil. In 1995 and 1996, apparent N recovery tended to decrease with increasing effluent and fertilizer application rates (Table 6). No significant difference in N recovered by both forage grasses was observed between swine effluent and fertilizer-derived N. Apparent N recovery was less for johnsongrass compared with either summer annual grasses or bermudagrass. Lower N recovery by johnsongrass appears to be primarily related to lower yields.
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Table 6. Effects of swine effluent and fertilizer rates on N and P recovery by summer annual grasses, bermudagrass, and johnsongrass.
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Residual Soil Nitrate-Nitrogen Concentration
Residual soil NO-3–N concentrations following the 1996 growing season are shown in Fig. 3. Excessive soil NO-3–N was observed with the high fertilizer treatment, with concentrations of 
50 mg kg-1 for some depths of both soils. The high effluent and medium fertilizer treatments resulted in very similar NO-3–N concentrations but at 
20 mg kg-1 for the Vaiden soil and 30 mg kg-1 for the Okolona soil, they were somewhat elevated compared with lower application rates. Apparently, NH3 volatilization was greater with effluent as evidenced by similar plant recoveries between the sources but lower residual soil NO-3–N concentrations with effluent for corresponding N rates. Additionally, volatilization may have been greater from the Okolona soil due to an alkaline pH (Hoff et al., 1981) as evidenced by a greater discrepancy in soil NO-3–N concentrations between corresponding effluent and fertilizer treatments than for the acid Vaiden soil.
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Fig. 3. Effects of anaerobic swine lagoon effluent and inorganic fertilizer N application rates on residual soil NO-3–N, fall 1996.
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Phosphorus Accumulation and Recovery
Effluent irrigation rates resulted in cumulative P application of 59, 118, and 175 kg P ha-1 on the Vaiden soil and 72, 148, and 223 kg P ha-1 on the Okolona soil for low, medium, and high loading rates, respectively (Table 2). Phosphorus accumulation by bermudagrass and johnsongrass significantly increased with increasing swine lagoon effluent and fertilizer application rates in 1995 and 1996 (Fig. 4). Soil P availability, estimated from P accumulation by untreated checks and averaged across years, was 5 and 7 kg P ha-1 for the Vaiden and Okolona soils, respectively. For bermudagrass, P removal in 1995 was the lowest due to low dry matter production during the establishment year of Alicia bermudagrass. Phosphorus accumulation by bermudagrass exhibited a quadratic trend with swine lagoon effluent and fertilizer P application in all years except 1994 when no response to fertilizer P was evident. For johnsongrass, there was a quadratic trend in P accumulation with increasing rates of swine effluent and fertilizer P in 1995 and 1996. The trend was similar each year, but the absolute quantity removed depended on yield. At the greatest rate of P (90 and 84 kg P ha-1 for effluent and fertilizer, respectively), P accumulation by bermudagrass was 29 kg ha-1 for both sources in 1996 while P accumulation in 1995 and 1996 by johnsongrass averaged 24 kg ha-1 with 90 to 94 kg ha-1 effluent P and 22 kg ha-1 with 84 kg ha-1 fertilizer P. No difference in P accumulation was found between sources at near equivalent rates, suggesting effluent and fertilizer provided similar availability.
Although P removed in harvested forage increased with increasing effluent and fertilizer P rates, apparent P recovery decreased (Table 6). Linear decreases in recovery efficiency were observed, which suggests at greater rates, proportionally more P would remain in the soil. Overall, apparent recoveries of either effluent or fertilizer P were lower than for N from these sources. However, additional P can potentially be recovered if effluent application is discontinued, and only an N source is applied.
Nitrogen/Phosphorus Accumulation Ratios
The narrowest N/P ratios occurred with the untreated checks (6.8 for bermudagrass 1996 and 5.9 average for johnsongrass 1995 and 1996). The ratios increased to near 11 at the greatest effluent and fertilizer application rates for bermudagrass in 1996. For johnsongrass, an average ratio for 1995 and 1996 at the greatest application rate was near 10. An increase in the ratio from effluent or fertilizer application compared with the untreated check suggests N was the more limiting of the two nutrients on both of these soils. Compared with the average effluent N/P ratio of 6.7 (Table 3), soil accumulation of P would be expected given forage grass accumulation ratios 10.
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CONCLUSIONS
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For both grasses, no significant difference in dry matter yield was obtained between swine lagoon effluent and fertilizer in 1995 and 1996, suggesting that both nutrient sources were similar in availability of N and P at the rates used in this study. Application of effluent or fertilizer at rates >448 kg N ha-1 did not enhance dry matter yield and exceeded the crop utilization potential as evidenced by excessive soil profile NO-3–N concentrations after cessation of growth in the fall. Tissue N concentration in both grasses was highly correlated with dry matter yields, but P concentration was not. This indicated that N accumulation was a function of both tissue N concentration and dry matter yield, whereas P accumulation was most dependent on yield potential. Thus, forage grass removal rates of P as suggested in nutrient management plans are only attained at high rates of N. Application of N and P at rates that exceed efficient plant utilization, as evidenced by declining apparent recovery values, increases the potential for adverse effects on water quality. Similarity in N and P availability between anaerobic effluent and fertilizer simplifies nutrient management decisions due to the abundance of information available on fertilizer effects on forage grasses. However, potential N loss by NH3 volatilization is likely greater for effluent while fertilizer may result in greater residual NO-3–N levels at equivalent rates of N.
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NOTES
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Contribution of the Mississippi Agric. and Forestry Exp. Stn., Journal Paper no. J9713.
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M. R. McLaughlin, K. R. Sistani, T. E. Fairbrother, and D. E. Rowe
Effects of Overseeding Cool-Season Annuals on Hay Yield and Nitrogen and Phosphorus Uptake by Tifton 44 Bermudagrass Fertilized with Swine Effluent
Agron. J.,
March 1, 2005;
97(2):
479 - 486.
[Abstract]
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M. R. McLaughlin, K. R. Sistani, T. E. Fairbrother, and D. E. Rowe
Overseeding Common Bermudagrass with Cool-Season Annuals to Increase Yield and Nitrogen and Phosphorus Uptake in a Hay Field Fertilized with Swine Effluent
Agron. J.,
March 1, 2005;
97(2):
487 - 493.
[Abstract]
[Full Text]
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M. R. McLaughlin, T. E. Fairbrother, and D. E. Rowe
Forage Yield and Nutrient Uptake of Warm-Season Annual Grasses in a Swine Effluent Spray Field
Agron. J.,
November 1, 2004;
96(6):
1516 - 1522.
[Abstract]
[Full Text]
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H. K. Pant, M. B. Adjei, J. M. S. Scholberg, C. G. Chambliss, and J. E. Rechcigl
Forage Production and Phosphorus Phytoremediation in Manure-Impacted Soils
Agron. J.,
November 1, 2004;
96(6):
1780 - 1786.
[Abstract]
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M. R. McLaughlin, T. E. Fairbrother, and D. E. Rowe
Nutrient Uptake by Warm-Season Perennial Grasses in a Swine Effluent Spray Field
Agron. J.,
March 1, 2004;
96(2):
484 - 493.
[Abstract]
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D. E. Rowe and T. E. Fairbrother
Harvesting Winter Forages to Extract Manure Soil Nutrients
Agron. J.,
September 1, 2003;
95(5):
1209 - 1212.
[Abstract]
[Full Text]
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A. Adeli, J. J. Varco, and D. E. Rowe
Swine Effluent Irrigation Rate and Timing Effects on Bermudagrass Growth, Nitrogen and Phosphorus Utilization, and Residual Soil Nitrogen
J. Environ. Qual.,
March 1, 2003;
32(2):
681 - 686.
[Abstract]
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TOP
ABSTRACT
INTRODUCTION
