Winter Cover Crops in a Corn-Forage Sorghum Rotation in the Great Plains.

In Kansas, winter cover crops may play a role in the development of summer crops as cellulosic biofuel feedstocks.  Harvesting the entire above ground biomass maximizes potential biofuel production but leaves the soil prone to erosion during the winter.  Winter cover crops may facilitate maximum biomass harvest by protecting the soil from wind and water erosion.  Therefore, the objective of this research was to determine the effect of two winter cover crops on the growth of two biofuel crops, corn (Zea mays) and forage sorghum [Sorghum bicolor] in a corn-forage sorghum rotation and in continuous forage sorghum.  The two cover crops were Austrian winter pea (Pisum sativum) and winter wheat (Triticum aestivum).  Control plots were fallowed.  The experiment was done for two years (2010 and 2011) at two locations:  under rain-fed conditions in Manhattan (Belvue silt loam, annual precipitation 907 mm), and under irrigated conditions in Tribune (Richfield silt loam, annual precipitation 480 mm).  Two levels of nitrogen were added to the soil:  0 and 102 kg/ha N.  Grain and stover yields of the corn and forage sorghum were determined at harvest of the crops in the fall, and dry matter of cover crops was determined at their termination in the spring.  Cover crops had no effect on grain or stover yields of corn or sorghum at either location.  At Manhattan, addition of nitrogen fertilizer increased grain yields, but nitrogen had no effect on grain yield at Tribune, probably because the soil at Tribune had more residual nitrogen.  Except for Manhattan in 2011, the forage sorghum yielded more stover than did the corn.  These results suggest that, under both rain-fed and irrigated conditions in Kansas, winter cover crops can be included successfully in dedicated biofuel cropping systems and that forage sorghum might be more productive for bio-energy production than corn.