Infiltration, Runoff, and Export of Dissolved Organic Carbon from Furrow-Irrigated Forage Fields under Cover Crop and No-Till Management in the Arid Climate of California

Development of best management practices (BMPs) such as conservation tillage and winter cover crop to mitigate runoff and reduce dissolved chemicals in irrigation runoff is an important objective for controlling surface water pollution attributable to agricultural activities. In this study, the effect of standard tillage (ST), ST with winter cover cropping (STCC), and no-till (NT) management practices on infiltration, runoff, and dissolved organic carbon (DOC) export from furrow-irrigated fields of 244-m length was investigated for summer 2007 and 2008 irrigations. The practices were implemented for 2 years. The average surface residue cover was 11, 44, and 32% for ST, STCC, and NT, respectively, for 2007 and 11, 59, and 61%, respectively, in the following year of the study. Two irrigations in each year were considered for the analysis. The runoff samples were collected from each tillage treatment using ISCO autosamplers at regular time intervals. The infiltration and runoff were estimated using a volume balance model (VBM) by considering a 0.2-m irrigation requirement. Converting from ST to STCC increased the infiltration by 14 and 43% and reduced the runoff by 48 and 43% in 2007 and 2008 irrigations, respectively; whereas, converting ST to NT enhanced the infiltration by 4% in both years and decreased the runoff by 19 and 23% in 2007 and 2008 irrigations, respectively. The authors observed only slightly higher DOC concentrations in STCC, but there was a 24% increase for NT in 2007 irrigations, and both compared to with ST ranged from 3.98 to 5.46 mg/L . The DOC concentration was not significantly different among the treatments in 2008 irrigations (3.48 to 4.6 mg/L ). Combining the runoff and DOC concentration effects, the DOC export for STCC was decreased by 55% in both years; whereas, it was decreased by 4 and 27% for NT in 2007 and 2008 irrigations, respectively, compared with ST. Although STCC and NT have higher concentrations, the reduction in export in these treatments is attributable to lower runoff. These results suggest that DOC export can be controlled with STCC practice. No-till showed the same trend, although these results must be confirmed after extended implementation of this practice.