Managing Runoff Water Quality From Recently Manured, Furrow Irrigated Fields.

Nutrient losses in furrow irrigation runoff potentially increase when soils are amended with manure. We evaluated the effect of tillage, water soluble polyacrylamide (WSPAM) and irrigation management on runoff water quality during the first furrow irrigation on a calcareous silt loam soil, which had received 45 Mg ha^-1 (dry wt.) dairy manure applied in the fall. In Exp. 1 the amended soil was rototilled and irrigated that fall; furrow inflows were either treated with 10 mg L^-1 WSPAM injected into furrow inflows only during furrow advance (Fall-WSPAM), or were untreated (Fall-Control).  In Exp. 2 the first irrigation on the amended soil was delayed until the following spring and treatments included rototilled WSPAM (Spring-WSPAM), with WSPAM applied as in Exp. 1,  and untreated rototilled (Spring-Control), or moldboard-plowed soils (Spring-Plow).  Experiment 3 also delayed irrigation until spring and compared conventional vs. buried lateral furrow irrigation systems.  We measured sediment, dissolved organic carbon (DOC), NO₃-N, NH₄-N, dissolved reactive P (DRP), and total P (TP) concentrations in irrigation furrow runoff.  Runoff mass losses from Fall-Control furrows were relatively large:  sediment, 4505 kg ha^-1; DOC, 10.7 kg ha^-1; NO₃-N, 28.1 g ha^-1; NH₄-N, 68.1 g ha^-1; DRP, 132 g ha^-1; and TP, 3381 g ha^-1. Delaying the first irrigation until spring or treating the fall irrigation with WSPAM reduced runoff component losses by 80 to 100% relative to Fall-Controls.  The Spring-Plow reduced runoff DRP mass losses by ~60% compared to spring rototill (Spring-Control).  The buried lateral furrow system decreased runoff mass losses for sediment, DOC, and TP by >80% relative to conventional irrigation.  This research demonstrated that several management practices may be successfully employed to substantially reduce offsite nutrient transport during the first irrigation on furrow-irrigated, manure-amended fields.