Nutrients in runoff from a furrow-irrigated field after incorporating inorganic fertilizer or manure.

Use of dairy manure to supply crop nutrients is gaining broader acceptance as the cost of fertilizer rises. However, there are concerns regarding manure's effect on water quality. In 2003 and 2004, we measured sediment, NO3-N, NH4-N, K, dissolved reactive P (DRP), and total P (TP) concentrations in runoff from furrow irrigated field plots (6-7 irrigations yr(-1)) cropped to corn (Zea mays L.) in the semiarid climate of southern Idaho. Annual treatments included 13 (Year 1) and 34 Mg ha(-1) (Year 2) stockpiled dairy manure (M); 78 (Year 1) and 195 kg N ha(-1) (Year 2) inorganic N fertilizer (F); or control-no amendment (C). Available N in manure applied each year was similar to amounts applied in fertilizer. Constituent concentrations (mg L(-1)) in runoff ranged widely among all treatments: sediment, 10 to 50,000; NO3-N, 0 to 4.07; NH4-N, 0 to 2.28; K, 3.6 to 46.4; DRP, 0.02 to 14.3; and TP, 0.03 to 41.5. Over both years, fertilizer and manure treatments increased irrigation mean values (averaged across irrigations) for NO3-N runoff concentrations (M = 0.30, F = 0.26, C = 0.21 mg L(-1)) and mass losses (M = 0.50, F = 0.42, C = 0.33 kg ha(-1)) relative to the control. Over both years, the manure treatment also increased mean irrigation runoff concentrations of DRP (M = 0.19, F = 0.09, C = 0.08 mg L(-1)) and K (M = 1.13, F = 0.79, C = 0.62 mg L(-1)) compared with fertilizer and control plots. Average DRP and K runoff mass losses were 2.0 to 2.4 times greater in manure treatments than in control plots. Neither F or M affected season-long cumulative infiltration. Runoff DRP and inorganic-N losses appeared to be influenced more by the timing of the amendment application and environmental conditions than by the quantity of nutrients applied. Nutrient additions to furrow irrigated soils, whether from fertilizer or manure, can potentially increase nutrient losses in irrigation runoff, with the degree of impact depending on the nutrient, amount, and timing of application and whether inorganic fertilizer or manure was applied.