Jeff Mitchell Paper for Symposium On “Improving Crop Water Productivity.

Increasing the amount of water that is transpired by a crop relative to the amount that is evaporated by the soil by reducing tillage or by maintaining surface residues may be a means for improving the water use efficiency of California crop production systems that frequently confront water shortages. Our past work with standard tillage operations following wheat silage harvest prior to corn seeding versus no-tillage, showed that 2.3 and 2.5 cm more water retained in the surface foot of soil under no-till than in tilled soil. In addition, in three field studies comparing residue effects on soil water evaporation, we also demonstrated that bare soil had about 1.4, 1.5 and 1.1 cm less water retained than under residues following 6-7 days of overhead sprinkler irrigation. Assuming a seasonal crop evapotranspiration demand of 30 inches, coupling no-tillage with high residue preserving practices could reduce summer season soil evaporative losses by about 10.2 cm or 13%. Current work is evaluating differences in soil water storage under winter cover crops compared with fallow. The effects of eliminating tillage and preserving surface residues on reducing soil water evaporation that we have shown add to the list of benefits of conservation tillage systems for California producers.