Soil, Maize Crop, and Kernel Composition Responses to Rotation and N Fertilizer Treatments.

Maize can utilize nitrogen (N) from inorganic fertilizers as well as from mineralized organic sources. We were interested in how maize responds to rotations that contain legumes. The objective of this 2-yr field investigation conducted on a long-term field study (started in 1990) was to measure effects of crop rotation (CC, continuous corn; CS, corn-soybean; CSWA, corn-soybean-wheat/alfalfa-alfalfa) and N fertilizer applications (based on yield goals of 8.5 or 5.3 Mg/ha, or no N fertilizer) on soil and crop characteristics. Planting-time soil samples (0-30 cm) revealed greater CEC, P (Bray-P1), K, S, and Ca (DTPA extraction) concentrations with increasing N fertilizer application rates. Soil nitrate N and Mn concentration increased while pH and P decreased with increasing rotation complexity. When measured at the VT stage, rotation treatments had no effect on plant height or LAI under high N fertilizer while CC plants had decreased height and LAI compared to other rotations under no N fertilizer. Grain yields across all N fertilizer rates were similar in the CS and CSWA rotations (about 7 Mg/ha). Yield under the CC rotation dropped (from about 6 Mg/ha at the high N to about 4 Mg/ha under no N) with decreased with N fertilizer rates. There were no differences in kernel protein across N fertilizer treatments for the CSWA rotation (105 g/kg), but kernel protein dropped (from about 95 g/kg under high N to about 75 g/kg under no N) in the CC and CS rotations. Oil was greater (about 37 g/kg) under CSWA rotation than under CC and CS rotations (about 33 g/kg). In conclusion, maize growth, yield, and kernel composition were more consistent under CSWA rotation than CC and CS across the three N fertilizer rates used in this study. Additionally, the CSWA rotation essentially replaced the need for inorganic N fertilizer applications.