Wheat Improves Productivity and N Use Efficiency in Corn and Soybean Based Crop Rotations.

Integrated nitrogen (N) management strategies for corn (Zea mays L.)would be useful to reduce the reliance of fertilizer N.  The demand for fertilizer N has been increasing with more corn acres planted within shorter rotations coupled with increasing optimum N application rates.  The decline of crop rotation diversity is the result of higher frequencies of corn and soybean in the rotation at the expense of reductions of grasslands, forages and small grain cereals.  It is well documented that legume forages can reduce the requirement of fertilizer N for corn grown in the following year.  However, little is known of the significance of non-legume crop species such as wheat (Triticum aestivum L.) on the fertilizer N requirement for corn and grain yields of corn and soybean [(Glycine max (L.) Merr.].  We hypothesized that wheat is instrumental in the cropping system for maintaining or improving corn and soybean yields and reducing the reliance of fertilizer N for corn.  Seven crop rotations with different frequencies of winter wheat with and without underseeded red clover (Trifolium pratense L.) rotation were grown using two tillage systems (conventional moldboard plow vs. zone-tillage) and four long-term N regimes in Ridgetown, ON, Canada.   Wheat in the rotation increased corn and soybean yields, negated corn yield lags in the zone-tillage system, and reduced the fertilizer N requirement for corn.  Corn yields were less dependent on fertilizer N for high crop yields with wheat in rotation with corn and soybean, especially in the zone-till system and where red clover was underseeded in the winter wheat crop.  These results quantify the value of wheat in the cropping system for increasing corn and soybean yields and reducing the reliance of fertilizer N, even in the absence of underseeded red clover.