Seasonal Biosolids Application Affects N Availability
Crop and Soil Environmental News, August 1997
Gregory Evanylo, ,
Nutrient and Waste Management
The following article is from a presentation made on August 12, 1997 at a YORK RIVER TRIBUTARY STRATEGIES Biosolids Field Day at the farm of L.C. Davis, New Kent, Virginia entitled "Nitrogen Availability from Winter- and Spring-applied Biosolids for Corn Production."
Approximately 30,000 acres of farm land receive applications of biosolids (sewage sludge) in Virginia. Application rates of biosolids are based on the plant available nitrogen (N) content of the materials and environmental factors. Nitrogen losses to ground and surface waters can occur if biosolids are applied at rates that supply more N than crops can utilize or if biosolids are applied at times of low crop N uptake.
A single organic N availability coefficient is employed for biosolids applied for corn in Virginia, regardless of whether the biosolids are applied to the soil in November or March preceeding the target corn crop. Use of appropriate organic N availability coefficients to calculate biosolids application rates is critical to prevent contamination of state waters. In addition, farmers must be confident that biosolids will supply the projected quantity of N to discourage unnecessary insurance applications of N fertilizer. The objective of this study is to compare winter- and spring-applied biosolids on N leaching and availability to corn.
Two soil series, a Bojac loamy sand and a Pamunkey silt loam, received biosolids (anaerobically-digested sludge from Chesterfield) at three rates in the winter (January 7) and in the spring (March 13) that supplied and estimated 0.5x, 1x and 1.5x the agronomic rates for corn for each soil type. A control treatment with no N and three rates of commercial fertilizer N were applied in the spring to compare with N availability from biosolids. Each of the 10 treatments (3 winter biosolids rates, 3 spring biosolids rates, 3 fertilizer N rates, and a control) were replicated three times on each soil type. Individual plots were 40 ft wide by 80 ft long.
Biosolids N composition ranged from 5.2-5.66 % TKN, 0.53-0.89% NH4-N, and 4.67-4.77 % organic N. Plant available N (PAN) calculated as: 0.85 (volatilization factor) x [NH4-N] + 0.20 (mineralization factor) x [organic N].
Agronomic N rate:
Agronomic biosolids rate:
100 lbs N/acre
160 lbs N/acre
Inorganic N was monitored by sampling the soil and analyzing for NO3-N and NH4-N: 1) after winter biosolids application, but before spring biosolids application (March 11); 2) at the 4-6 inch corn height; and 3) at the 10-12 inch corn height (recommended presidedress soil nitrate test stage of growth). Corn will be sampled from 8 center rows of each plot to estimate grain yield, which will be used with the soil data to demonstrate the relative N use efficiency and potential risk of N leaching to groundwater from winter- and spring-applied biosolids for corn production.
Table 1. Soil NO3-N concentrations from control and winter biosolids rates.
|Soil depth (inches):||0-10||10-20||20-30||0-10||10-20||20-30|
|Treatment||Soil NO3-N (mg/kg)|
|0.5x Agron. rate||6.5||4.7||3.8||6.9||4.4||5.0|
|1.0x Agron. rate||13.2||7.6||6.2||11.1||6.3||5.6|
|1.5x Agron. rate||8.0||5.7||4.6||11.5||8.0||6.5|
Soil NO3-N concentration was greater in the biosolids treatments than in the control for both soils at each depth 2 months after winter application and increased with biosolids rate.
Table 2. Soil NO3-N concentrations under corn at various growth stages.
|Corn height (inches):||4-6||4-6||10-12||4-6||10-12||10-12|
|Soil depth (inches):||0-12||12-24||0-12||0-12||12-24||0-12|
|Treatment||Soil Nitrate-N (mg/kg)|
A higher fraction of N was transported through the coarse-textured Bojac than the fine-textured Pamunkey from both biosolids and fertilizer. N from winter-applied biosolids was more mobile than from spring-applied, but less than from spring fertilizer in Bojac. Insignificant differences among treatments on soil N occurred in the Pamunkey. Timing of biosolids application appears to influence N leaching and availability. Further evidence will be supplied by corn yield data.