Water Use of Double Crops in No-till Cropping Systems in Oklahoma.

According to many researchers, water shortage will be one of the most important ecological and economic issues in the 21^st century. In rain-fed agricultural systems, water use efficiency is an essential consideration.  No-till cropping system intensification is a promising alternative to increase rainfall use efficiency. The objective of this experiment was to determine the water use of four summer double crops after no-till wheat at two sites in the Southern Great Plains. Sorghum (Sorghum bicolor ssp bicolor), Soybean (Glycine max) and Sunflower (Helianthus annus) were used in this experiment.  Soil water content to 2-m depth was measured weekly with a neutron probe. In addition, bulk density, soil texture, and soil water retention at -0.03 MPa and -1.5 MPa were determined. Crop growth stages were recorded using appropriate phenology scales. Digital images were taken to follow crop canopy evolution. Grain yield and total dry biomass were determined to calculate water use efficiency.   In 2009, growing season evapotranspiration was ~5 cm greater for sorghum and soybean than sunflower. Therefore, plant available water at the end of the summer was greater under sunflower.