CONTROLLING SPRINKLER IRRIGATION RUNOFF, EROSION, AND PHOSPHORUS LOSS WITH STRAW AND POLYACRYLAMIDE

ABSTRACT. Controlling runoff and soil erosion are important for maintaining soil productivity and reducing off-site impairment due to sediment and nutrient enrichment. Previous research has shown that crop residue and polyacrylamide (PAM) can reduce runoff and soil erosion. We compared the combined effects of surface residue and PAM on runoff soil loss, and phosphorus loss from sprinkler irrigated soil in the laboratory. We hypothesized that surface residue would enhance the effectiveness of sprinkler-applied PAM by allowing PAM to stabilize the soil surface with less disturbance by water drops. Steel boxes (1.5 m long, 1.2 m wide, and 0.2 m deep) were filled with Roza loam (fine, smectitic, mesic xerertic Haplocambids) and irrigated at 80 mm h- 1 for 15 min. Wheat straw was applied for two separate tests (70 % and 30 % straw cover). The PAM was applied at 0, 2 or 4 kg ha- 1 during the first irrigation, followed by two water-only irrigations. Applying PAM to straw-covered soil controlled runoff, erosion, and phosphorus losses equally or better than using either PAM or straw alone. The 70 % straw cover reduced cumulative runoff for the three irrigations 75 to 80% compared to 30 to 50 % reduction with PAM alone. Polyacrylamide alone or 30 % surface cover alone produced similar results, both reducing cumulative runoff 10 to 20 % compared to untreated bare soil. Since runoff, erosion and phosphorus loss were reduced when PAM and surface residue were used individually and to a greater extent when used together, management choices should depend on overall costs and control needed to meet water quality and production goals