A Long-Term Look at Crop Rotation on Corn Yield and Response to Nitrogen Fertilization
Increasing concerns about fertilizer nitrogen (N) cost, public awareness of effects of excess N use on water quality, and corn after corn production in Iowa require a better understanding of long-term effects of N fertilization and cropping sequences on corn yield. Therefore, continuous research and management adjustments are needed to improve economic benefits from fertilization and water quality. Growing corn in rotation with grain or forage legumes reduces the need of N fertilizer compared with continuous corn because soil after legume crops have higher potential N availability than after corn. Previous research has shown that optimum N fertilization rates for corn are highest for continuous corn and are followed by corn after soybean and corn after alfalfa. Yet, another benefit of including legumes in the rotation, mainly forage legumes, is that corn yield is higher than for continuous corn even at very high N rates because of often poorly understood beneficial effects of the legumes on soil quality, reduced incidence of corn pests, and other factors. This presentation summarizes corn yield results from the two longest Iowa rotation studies experiments that have been evaluating effects of various cropping sequences and N fertilization rates on yield of several crops. These experiments provide very useful information for long-term implementation of cropping systems (such as continuous corn, corn after alfalfa, corn after soybean) and long-term fertilization strategies that short-term experiments on farmers' fields cannot provide. We focus the presentation on corn yield responses to N and stability over time. A unique piece of information provided by one of the experiments is the evaluation of yield and response to N of corn grown one, twice, or three times after a soybean crop, issues seldom investigated in other studies in Iowa and neighboring states.