Monday, November 13, 2006 - 9:00 AM

Impact of N and Water on Crop Productivity and N and Water Use.

Ki-In Kim, The Ohio State Univ, 2021 Coffey Rd, 210 Kottman Hall, Columbus, OH 43210, David Clay, South Dakota State Univ, Plant Science Dept., Brookings, SD 57007, C.G. Carlson, South Dakota State Univ, Plant Science Dept, Brookings, SD 57007, and Sharon Clay, South Dakota State Univ, 1110 42nd St., Brookings, SD 57006-6201.

Recent research suggests that yield based N models have a poor relationship with economic optimum N rates. The objective of this study was to determine the impact of N and water on crop productivity and N and water use. Field experiments were conducted in Aurora, South Dakota, 2002, 2003, and 2004. Treatments were natural rainfall, natural rainfall + irrigation, and four N rates (0, 56, 112, 168 kg N/ha). Plant samples were analyzed for 15N, and total N using isotope ratio mass spectrometer. Grain yields were increased by N and water. Plant N uptake was higher at the 112 kg N/ha and 168 kg N/ha than 0 and 56 kg N/ha. Nitrogen use efficiency decreased with increasing N. The amount of N derived from the soil using δ15N approach were 80, 99, 96, and 70 kg N/ha for the 0, 56, 112, 168 kg N/ha, respectively. Soil N mineralization was higher in irrigated (86 kg N/ha) than non-irrigated treatments (72 kg N/ha) on unfertilized plots (p-value = 0.06). These results suggested that N mineralization was a function of soil moisture. Applying these findings to the fields with variable water contents can result in differential N requirements.