Mechanical straw mulching of irrigation furrows : Soil erosion and nutrient losses

There is widespread concern about loss of sediments, NO 3 - , and phosphate into surface water from irrigated farmlands. We studied the effects of 900 kg ha -1 wheat (Triticum spp.) straw, mechanically applied to irrigation furrows, on sediments and on N and P losses in the runoff. The field was on a Nyssa silt loam soil (coarse-silty, mixed, mesic Xerollic Haplodurid) with 3% slope planted to onion (Allium cepa L.), and received 0, 50, or 200 kg P ha -1 incorporated to 0.1 m deep. Furrows were side-dressed with 200 kg ha -1 N. Averaged across 17 irrigations, straw reduced runoff volume by 43%. Cumulative sediment lost after 17 irrigations was 17 Mg ha -1 for mulched and 333 Mg ha -1 for unmulched furrows. Straw also reduced NO 3 - and NH 4 + losses in runoff solution and sediments. Total N losses during the first 6 irrigations were 33 kg ha -1 from mulched and 230 kg ha -1 from unmulched furrows. Straw effect on N loss was only through changes in the runoff volume and sediment loss. In contrast, as fertilizer P increased, PO 4 concentrations in runoff solution and sediments also increased. Averaged across the first 6 irrigations, straw mulch reduced PO 4 losses in the runoff solution by 59, 61, and 72%, for the 0, 50, and 200 kg P ha -1 treatments, respectively. Straw reduced PO 4 losses in the sediment 15-, 11-, and 15-fold for the 0, 50, and 200 kg P ha -1 treatments, respectively. Averaged across P fertilizer rates, total P lost after 6 irrigations was 18 kg ha -1 from mulched and 215 kg ha -1 from unmulched furrows. Mechanically applied straw mulch in irrigation furrows can substantially reduce soil erosion and N and P losses to surface water runoff.