Soil Analyses after Growth of Winter Cover Crops in a Corn-Forage Sorghum Rotation.

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 during the cover crop phase.  The experiment was done for two years 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.  Last year we reported results for the summer crops, i.e., cover crops had no effect on grain or stover yields of corn or sorghum at either location.  This year we report soil analyses.  After termination of the cover crops, the soil was analyzed at Manhattan in 2010 and 2011 and at Tribune in 2011 and 2012 for pH, organic matter (OM), total nitrogen (N), and total carbon (C).  Values were averaged over all treatments. In 2010 at Manhattan, the average and standard deviation were 5.8+0.6 (pH); 0.6+0.2% OM; and 0.48+0.15% C.  In 2011 at Manhattan, the values were 6.1+0.1 (pH); 1.0+0.2% OM; and 0.72+0.10% C.  In 2010 and 2011 at Manhattan, all samples had nitrogen values below the detectable limit (<0.1% N).  In 2011 at Tribune, the values were 8.0+0.1 (pH); 1.8+0.1% OM; 0.13+0.01% N; and 1.22+0.06% C.  In 2012 at Tribune, the values were 8.1+0.1 (pH); 2.1+0.1% OM; 0.14+0.01% N; and 1.28+0.06% C.  The results suggested that two years of growth of the cover crops increased the organic matter in the soil at Tribune, but had minimal effects on other measured parameters.