Effects of crop rotation and nitrogen fertilization on soil nitrate concentration and corn yield
Ricardo J. Salvador
Increasing concerns about production cost and environmental impacts of N fertilization require improving N management. The objectives of this study were to evaluate effects of cropping sequences and N fertilization on (1) corn yield and yield stability and (2) soil nitrate concentration in two Iowa long-term rotation experiments and (3) to assess the performance of the late spring nitrate test (LSNT) to assess N availability for corn in several cropping sequences. The experiments were near Kanawha (20 yrs) and Nashua (26 yrs) and N fertilization rates for corn were 0, 90, 180, 270 kg N ha -1. Rotations in Kanawha were continuous corn with spring N (Csp), continuous corn with fall N (Cfl), corn-corn-corn-oat, corn-soybean, corn-soybean-corn-oat, corn-corn-oat-alfalfa, and corn-oat-alfalfa-alfalfa. Rotations in Nashua were continuous corn, corn-soybean, corn-corn-soybean, corn-corn-corn-soybean, and corn-corn-oat-alfalfa. The results indicated that corn yield was higher and yield response to N was lower in the order corn after alfalfa > after soybean or oat undersown with alfalfa, and after alfalfa. There were no significant differences between response to N of continuous corn and second- or third-year corn after soybean. On average, N rates producing maximum observed net returns ranged from 270 kg N ha-1 for corn after corn to zero N for corn after alfalfa. On average, Csp yielded 8.7 more than Cfl and the highest N rate used did not produce yield as high as those observed for corn in rotation. Corn yield across time was higher and more stable with N fertilization and when legumes were included in rotation. Observed maximum net returns to N increased over the time but the relative response to N fertilization did not change consistently. The highest soil nitrate concentrations were observed for corn after alfalfa and corn with N fertilization. Soil nitrate concentrations were higher for Csp than Cfl. Fertilization increased soil nitrate linearly for all corn crops and rates of increase were similar, except for smaller increases for Cfl and Csp. A certain nitrate concentration resulted in higher relative corn yield for corn after alfalfa. The results support guidelines for use of the LSNT test in Iowa.