Nitrogen fertilization and cover crop effects on soil structural stability and corn performance

The effects of annual ryegrass (Lolium multiflorum L.), red clover (Trifolium pratense L.), and oilseed radish (Raphanus sativus L.) established in separate barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) plots which had received 0.5, 1.0, and 2.0 times the recommended nitrogen (N) rates (in Ontario) on soil structural stability and subsequent corn (Zea mays L.) growth and yield were investigated in field studies at Ayr and Woodstock, Ontario. Soil aggregate stability and corn growth and development were affected more by cover crops than applied N. Generally, aggregate stability was higher following cover crops than where no cover crops were used. Aggregate stability before spring tillage tended to be higher after oilseed radish than ryegrass and clover, a phenomenon which might be due to shortterm enrichment of soil stabilizing materials resulting from the over-winter kill of oilseed radish and early decomposition. However, after spring chisel plow, soil stability was higher after ryegrass and clover than oilseed radish. No significant interaction between N and cover crops on aggregate stability was observed. Corn following ryegrass was shorter and had fewer leaves at 3 and 6 weeks after planting and accumulated less dry biomass at silking compared to corn after red clover, oilseed radish and no cover check. Similarly corn grain yield was significantly lower when corn followed ryegrass than the other cover crop treatments. Corn was tallest and yielded highest after red clover. A net immobilization and late release of available N with ryegrass and a net mineralization of available N with red clover explains the growth and yield patterns of corn.