Cover Crop Water Consumption in Southeastern Washington Palouse.

This poster summarizes short-term water use by a 2014 spring planted cover crop mix versus three fallow systems: 1) bare soil, 2) wheat straw residue cover, and 3) full shade.  Our objective is to measure cover crop water usage in the Pacific Northwest (PNW) dryland cropping system. Cover crop as a replacement for, or supplement to fallow systems is not well documented for the PNW and is considered to be luxurious use of a scare water resource.  Historically, most precipitation events in the PNW occur during the winter months when temperatures are low, with infrequent and minor events during the season when temperatures support rapid plant growth.  Under PNW dryland cropping systems, precipitation is stored as soil water and reserved for consumption by the crop during the subsequent growing season.  In addition, fallow cropping is commonly practiced in these lower rainfall areas to extend the period of water sequestration.  It is well known that cover crop systems can improve soil health as demonstrated across the corn belt of the continental USA. Cover crops have not been adopted in the PNW because of production risks associated with luxurious water use. We compare the water balance trade-off required to build soil quality with a cover crop system versus that required for water storage under the conventional fallow system.  Cover crop biomass accumulation and water consumption rates will be reported and contrasted with evaporative water loss under fallow systems relative to evapotranspiration (ET) for locations in Southeastern Washington State.