Water and Energy Responses of Corn to Tillage in the Lower Mississippi Delta.

Tillage potentially modifies the physical properties of the soil. No-tillage (NT) systems leave residue on the soil surface, while conventional tillage (CT) buries and incorporates them into the soil. Residue on the soil surface can suppress evapotranspiration and reduce runoff losses of water, thereby increasing the amount of water infiltrating into the soil, while conventional tillage potentially increases the porosity of the soil, thereby increasing the infiltration rate until the tilled soil reconsolidates. All the above can change depending on the soil texture, rainfall intensity-duration-amount, and other climate factors. Therefore, the impact of tillage on location-specific cropping systems remains uncertain, especially in light of the high variability in soil properties and climates seen in the humid climate of the MS Delta region. A long-term field trial for assessing the impacts of NT vs. CT on corn- was started in 2009 in a Dundee silt loam soil at Stoneville, MS Delta. Corn yields in the CT systems were higher than in NT systems in all but one year to date. To understand the mechanisms behind the observed yield performance, we recently established a research program to monitor radiant energy, evapotranspiration, soil water, and physiological responses of corn under CT and NT systems. The ET estimation was accomplished by solving an energy balance equation representing a crop canopy-land surface for latent heat flux from measurements and estimates of sensible heat, soil heat, and net radiation fluxes. The sensible heat was quantified by computing aerodynamic and boundary layer resistances corrected for atmospheric stability and wind-speed effects. Along with grain yield, soil water, photosynthetic rate, and LAI were higher and stomatal conductance lower in the CT system compared to the NT system. Lower energy balance for evapotranspiration and slight reduction in actual ET in the NT system compared to the CT system were observed.