Effect of Rotation and Nitrogen Application On Corn and Soybean On An Irrigated Sandy Soil.

A five year study was designed to determine the rotation effect of soybean on corn and the value of both a corn/soybean and corn/corn/soybean rotation on sandy loams soils. There were four objectives: 1. Estimate the ‘N credit' of soybean for the following corn crop. How this is determined depends on several factors, but the economic optimum N rate might be different by about 11 kg N/ha (10 lb N/ac) when the N rate is determined by the UNL procedures and a corn/nitrogen price ratio is 8 which is similar to the long term value ($3.20/bu corn, $0.40/lb N).  2. Determine if there is a difference in potential yield due to soybean in a corn/soybean and corn/corn/soybean sequence compared to corn/corn/corn. The 3 year rotation had very little agronomic effect on the second year of corn, except that there was about 250 kg/ha (4 bu/acre) more yield than in continuous corn. 3. Determine the effect of continuous soybean on soybean yields. Continuous soybean yielded 4.10 Mg/ha (60.9 bu/acre) , which was statistically the same, but less than soybean in the corn/soybean rotation which averaged  4.27 Mg/ha (63.4 bu/ac) over the length of the experiment.  Soybean every third year averaged 4.17 Mg/ha (61.9 bu/ac). Since continuous soybean is unlikely, the difference between soybeans every other year and every third year is minimal, and beyond the precision of this experiment to differentiate. However, we only measured the second cycle of the rotation. A longer experiment might find differences increased over time. 4. Determine the effect of nitrogen application during early reproductive stage(R1) to soybean. There was no yield response to nitrogen in any of the five years. Average yields were 4.31 Mg/ha (64 bu/ac) where no nitrogen was applied, which was the highest yielding treatment compared to the average of the other nitrogen applications.