Effects of variable rates, times and methods of application of swine manure on nitrate-nitrogen in subsoil water, crop yields, N uptake and recovery and soil residual nitrate-nitrogen: a three year study

Land application of swine manure offers the alternative use of its nutrients for crop production but growing concerns exist when not properly managed because of potential water quality problems;The field experiment consisted of 48 plots (15.24 x 3.04 m), located in a Clarion-Nicollet-Webster soil association. Corn (Zea mays L.) was rotated with soybean (Glycine max L.). Treatments applied were a factorial combination of Nitrogen (N) rates (0, 84, 168 and 252 kg-N/ha) of liquid swine manure and Urea-Ammonium-Nitrate (UAN) with methods of application (manure in spring, fall and side-dress; manure with nitrapyrin in fall and UAN side-dress), replicated three times. Ceramic cup lysimeters (5.08 x 12O cm) were used to collect subsoil water;Between 1996 and 1998, subsoil water Nitrate-N (NO3-N) means were lower at 84 kg-N/ha (5.76, 4.60 and 14.41 mg/L) and higher at 252 kg-N/ha (6.33, 8.14 and 19.27 mg/L) but N rate effects were non-significant. Methods of application significantly affected subsoil water N03-N in 1998 but were non-significant in 1996 and 1997. Sidedress applications had lower subsoil water N03-N concentrations even at the higher N rate while spring and fall manure applications had higher subsoil water NO3-N. Corn yields and total N uptake increased with N rate in 1998 and up to 168 kg-N/ha in 1996 and 1997. Nitrogen recovery decreased with increasing N rate. Higher NO3-N, corn yields and precipitation but lower N uptake and recovery were recorded in 1998;Residual soil N03-N increased with increasing N rate but decreased with depth, and at 0--30 cm, N rate effects were significant in 1998 but non-significant in 1996 and 1997;The effects of temperature (5, 20 and 35°C) and swine manure (168 kg-N/ha) on nitrification and N03-N leaching was investigated in 18 undisturbed soil columns. At 5, 20 and 35°C, the apparent nitrification rate constants and NO3-N means were 0.0026, 0.0253 and 0. 0046/week and 16.6, 89.5 and 45.1 mg/L, respectively. The inhibition of nitrification at 35°C may help explain the lower N03-N observed with side-dress applications;Careful swine manure N management is recommended because of potential increases in subsoil water NO3-N, surface soil NO3-N accumulation, reduced N recovery and limited yield responses at the high N rate