Cropping System Effects on Nitrogen Removal, Soil Nitrogen, Aggregate Stability, and Subsequent Corn Grain Yield

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Abstract
Cropping systems can affect soil quality and productivity of subsequent crops. We conducted this study to evaluate effects of several annual and perennial crop species on N removal, residual soil N, aggregate stability, and subsequent corn (Zea mays L.) production. Thirteen cropping systems were grown with various rates of N fertilizer for 6 yr on a Typic Calciaquoll soil in central Iowa. Perennial plant species were then killed, corn was planted, and half of each plot was fertilized with 224 kg N ha−1 and half was left unfertilized. Plant analyses showed that the perennial C4 species, switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman var. gerardii), consistently removed the least N. There was little difference for soil total N, NH4‐N, or NO3‐N concentrations to a depth of 1 m among reed canarygrass (Phalaris arundinacea L.), switchgrass, sweet sorghum [Sorghum bicolor (L.) Moench], and alfalfa (Medicago sativa L.). Residual NO3‐N concentrations were higher to a depth of 1 m for subplots fertilized with 280 kg N ha−1 for 6 yr than for plots fertilized with less N. Aggregate stability did not differ following reed canarygrass, switchgrass, sweet sorghum, or alfalfa. Without N during the 7th yr, corn following sweet sorghum produced the lowest yield (7.5 t ha−1), whereas the highest yield following a nonlegume crop was for corn after big bluestem (11.8 t ha−1). Corn without N following soybean [Glycine max (L.) Merr.] yielded 11.1 t ha−1, while that following alfalfa yielded 13.6 t ha−1. Fertilizer N reduced the rotation effect, but increased profile N with both perennial and annual crops. Corn following reed canarygrass, big bluestem, alfalfa, soybean, and sorghum intercropped into alfalfa had significantly higher yields (14.1, 14.2, 15.7, 14.2, and 15.3 t ha−1, respectively) than corn following corn (13.0 t ha−1). Non‐N rotation effects (those remaining despite applied N) could not be explained by residual soil N or aggregate stability measurements.

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