Cover crops and cropping systems’ effects on N and related aspects of
crop production and environmental quality have been reviewed by
many authors (Russelle and Hargrove, 1989; Meisinger et al., 1991;
Dabney et al., 2001; Grant et al., 2002, Thorup-Kristensen, 2003; Reeves,
1994; Snapp et al., 2005; Crews and Peoples, 2005; Reeder and
Westerman, 2006; and Clark, 2007). We address the subject from the
perspectives of four diverse regions of the US: the Humid South, the
Humid North and Corn Belt, the Northern Plains, and the Irrigated
West. After definition of terms used herein and a general discussion of
the impacts and interactions of management options involving cover
crop species selection, planting date, crop rotation, and tillage, we
proceed to the regional perspectives. Following Russelle and Hargrove
(1989), we stress that opportunities exist for exploiting complementary
spatial and temporal niches reflected by such parameters as rooting
depth, water use, and N assimilation potential. The most sustainable
cropping systems will maximize uptake and cycling of N and water
without loss of nutrients from the system or creation of deficits that
reduce economic yield. Tonitto et al. (2006) discussed the potential for
diversified rotations using N and non-N-fixing cover crops to maintain
crop yields, while reducing N losses. While much remains to be learned
concerning N management in different cropping systems, much
knowledge has already been developed. Computer models have been
constructed to reflect this knowledge for use both as educational aids
and management tools to improve site-specific management.