Viability of Semi-Arid Dryland Cover Crop Systems in the U.S. Central Great Plains.

Producers are interested in growing cover crops and reducing fallow. Growing a crop during the fallow period would increase profitability if crop benefits exceeded expenses. Limited information is available on growing crops in place of fallow in the semiarid central Great Plains. A study at Garden City, KS from 2007–2012 evaluated cover crops, annual forages, and grain peas grown in place of fallow in a no-till wheat-fallow system. Another study started in 2010 at Akron, Co, Sidney, NE and Garden City, KS evaluated cover crops grown in place of fallow in a wheat-summer crop-fallow rotation. Growing a cover, hay, or grain crop in place of fallow reduced the amount of stored soil moisture at wheat planting. On average, cover crops stored slightly more moisture than hay crops, but this soil moisture difference did not affect wheat yields. Wheat yield following the previous crop was dependent on precipitation during fallow and the growing season. In the dry years, growing a crop during the fallow period reduced wheat yields, yet in wet years growing a crop during the fallow period had little impact on wheat yield. The length of the fallow period also affected yields of the following wheat crop. Soil moisture following grain crops was less than cover or hay crops, and this difference resulted in reduced wheat yields following grain crops. Cover crops did not improve wheat yield. Stored soil moisture was lowest among winter crops that produced a lot of biomass or the cover crop cocktail (6-species mixture). Spring crops and low biomass crops had the least negative effect on stored soil moisture. Winter and spring lentil had the least negative impact on wheat yield, and yielded similar to fallow when averaged across years. Winter crop treatments tended to reduce yield more than spring crop treatments, which was due to more moisture available in the spring crop treatments at wheat planting. These results do not support the claims that cover crops increase soil moisture relative to fallow. To be successful, the benefits of growing a crop during the fallow period must be greater than the expense of growing it plus compensate for any negative yield impacts on the subsequent crop. Cover crops always resulted in less profit in fallow, while forages and grain peas often increased profit compared to fallow. The negative effects on wheat yields might be minimized with flex-fallow, which is the process of only growing a crop in place of fallow in years when there is ample soil moisture at the time of making the decision to plant.