Intensified No-till Cropping Systems for More Efficient Use of Precipitation In Oklahoma.

Water is often the limiting factor for rainfed cropping systems in the Southern Great Plains. Currently, a large amount of Oklahoma’s cropland is in conventional tillage wheat monoculture in which much of the annual rainfall is lost as evaporation during the 3-mo summer fallow period. The objective of this research was to discover how cropping intensification, crop diversity, and tillage elimination affect soil water storage, soil water dynamics, and productivity. Five crop rotations of varied intensity and diversity were studied: continuous conventional till wheat (CT W), continuous no-till wheat (NT W), no-till wheat/double crop grain sorghum-full season soybean (NT W/DC GS-SB), no-till wheat/double crop soybean-full season corn (NT W/DC SB-CN) and no-till wheat/double crop sunflower-full season grain sorghum (NT W/DC SF-GS). Soil water content to 2-m depth was measured weekly with a neutron probe. Soil water storage efficiencies during fallow periods were analyzed using a system precipitation storage index (SPSI), which compares fallow evaporation with precipitation during the same period. For wheat monoculture average SPSI was 11%, whereas intensified-diversified cropping systems had a SPSI of 22%. Although systemic fallow efficiencies were significantly different between wheat monoculture and intensified-diversified cropping systems, still about 80% of rainfall was lost even in the most efficient fallows. On the other hand, for intensified-diversified cropping systems ~85% of total rainfall occurred during the growing season, in contrast to only 48% for the continuous wheat systems.  In conclusion, fallow periods were inefficient regardless of cropping intensification, and shifting fallow periods from summer to winter months led to increased capture of rainfall in the intensified-diversified cropping systems.