Soil and soil organic carbon effects on simulated Southern High Plains dryland Cotton production Soil and Tillage Research

The effect of increasing soil organic content (SOC) on the soil water retention and cotton yield productivity of two benchmark U.S. Southern High Plains (SHP) soils was estimated using pedotransfer functions and the CROPGRO-Cotton crop simulation model. Increasing plow layer (0−30 cm) SOC leads to increased wilting point (WP), field capacity (FC), and plant available water capacity (PAW = FC-WP) in both soils. The increase in a clay loam’s available water capacity is modest, with a 1% increase in SOC producing an additional 0.16 cm of PAW in the soil profile’s uppermost 30 cm. The fine sandy loam’s plow layer effect is twice that, with a 1% SOC increase producing a 0.32 cm PAW increase. These effect’s magnitudes were consistent with a recent meta-analysis of SOC on soil water retention, but considerably below those cited by national and regional extension services. As surface SOC levels in both soils were increased above baseline levels the fine sandy loam’s median simulated cotton lint yields were essentially unchanged, while clay loam yields decreased. The clay loam yield effect is attributed to increased soil evaporation rates. Conservation agriculture (CA) practices such as increased residue retention may compensate for these weak soil water retention effects, but cotton’s limited residue production would require winter cover crops or alternate crop rotations. As the success of terminated winter wheat – dryland cotton rotations is unclear in past SHP field studies, a CA sorghum-cotton rotation with periodic tillage is proposed as a SHP dryland production system.