Cover Crops in Limited Irrigated Cropping Systems: Opportunities and Challenges for Sustaining the Ogallala Aquifer.

The decline in irrigation water availability, soil organic matter (SOM) content, and crop yields challenges the sustainability of dryland and limited-irrigation agriculture in the southern Ogallala Aquifer region. Cropping systems that integrate cover crops into crop rotations, reduce tillage intensity and frequency, and maintain residue covers have the potential to improve agricultural sustainability and profitability. Studies are conducted at the NMSU Agricultural Science Center at Clovis to evaluate the effects of cover crops (CC) on SOM dynamics, nutrient cycling, crop production, and profitability of a winter wheat-sorghum-fallow rotation. Soil samples were collected seasonally and analyzed for SOM pools and nutrients. Initial two-year results of ongoing research revealed that soil water content was 27% lower at CC termination than at CC planting, but it was approximately 115% at wheat planting in all CC treatments. Fallow plots had significantly greater available N at CC termination. Available N was not significantly different between CCs and fallow at wheat planting and harvesting while it was considerably lower in pea, pea-canola mixture, and pea-oat-canola mixture than fallow at jointing stage of wheat. Canola plots had greater potentially mineralizable carbon while a six-species mixture had significantly greater permanganate oxidizable carbon than other treatments. Economic analysis using Monte Carlo simulations show that the six species mixture yielded highest net return while canola provides a least risky option to include as cover crop. Crop diversification through cover cropping shows potential to increase SOM, improve nutrient cycling, and thereby support sustainable crop production in the southern Ogallala Aquifer region.