Winter Cover Crop Impacts on Runoff

A recent study at UC Davis by Prof. William Horwath and graduate student Cynthia Kallenbach compared furrow irrigation (FI) and subsurface drip irrigation (SDI) in tomatoes. The experiment also compared the effects of winter cover crops and tillage (standard versus no till) under each irrigation treatment. The tomato crop yields averaged 79 t ha-1 (36 tons ac-1) and did not vary significantly between irrigation, cover crop or tilage treatments. Water inputs were significantly different between subsurface drip irrigation and furrow irrigation, where 38cm (15 in) of water was applied to subsurface drip irrigation during the growing season compared to 89 cm (35 in) under furrow irrigation. Based on the these observations, subsurface drip irrigation was estimated to have between 40 and 50% higher water use efficiency compared to that of furrow irrigation in irrigated California tomato systems. In addition, the water filled pore space (WFPS) was much lower in the SDI compared to the FI in all treatments. The significance of lower WFPSbeside the critical water savings is the reduction in nitrous oxide emission in the SDItreatment. These additive benefits of water savings and reduced GHG emissions in SDIshow promise of increasing the sustainability of irrigated cropping systems. Additional studies with overhead sprinkler technology are being done at the UC West Side Research and Extension Center, Five Points and have shown similar water savings.

The seasonal water filled pore space (WFPS) in soils under subsurface drip (SDI) and furrow irrigation (FI) treatments. In each irrigation treatment the subtreatments included, tillage (CT=conservation tillage and ST=standard tillage) and winter cover crops (WLCC=winter legume cover crop and NCC=no cover crop). The results show significantly less WFPS, defined as soil pores filled with water, seasonally in the SDI compared to the FI.