Location: Hydraulics laboratory at USDA-ARS Northwest Irrigation and Soils Research Laboratory, Kimberly, Idaho.

Soil: Portneuf silt loam (Durinodic Xeric Haplocalcids), manured and non-manured top and subsoil: Olsen-P from 20 to 141 mg kg^-1, lime from 108 to 243 g kg^-1, organic carbon from 5.6 to 9.2 g kg^-1, pH ~ 7.8, EC from 0.5 to 0.9 dS m^-1, SAR from 0.4 to 0.8.

Soil containers: Steel boxes 1.5 m long,1.2 m wide, 0.2 m deep. Slope = 2.4%. Soil bulk density ~ 1.0.

Water:
1) Reverse osmosis (RO) water: EC = 0.02 dS m^-1, pH = 5.3, total P < 0.02 mg L^-1, ortho P < 0.002 mg L^-1 (SAR = N/A);
2) mix of half RO water and half tap water (RO/Tap): EC = 0.4 dS m^-1, pH = 7.5, SAR = 1.3, total P < 0.02 mg L^-1, ortho P < 0.01 mg L^-1 (Simulated Snake River water).

Water was applied through an oscillating sprinkler at 80 mm h^-1 with Veejet nozzle (8070) 3 m above soil surface with 20 mm water depth per irrigation. Nozzle pressure = 76 kPa; median drop size = 1.2 mm. Each test soil was irrigated three times: (a) initially air-dry and crumbly, (b) wet (24 hrs. after a), (c) dry and crusty (7 to 10 days after a).

Runoff and Sediment: Weighed gross runoff and subtracted weight of filtered and dried sediment.

 Phosphorus analysis:
(a) Two 60 mL water samples per irrigation. One sample filtered through 0.45 µm filter, stabilized with boric acid, analyzed for dissolved reactive P (DRP); second sample not filtered, analyzed for total-P, and for biologically available P by iron oxide impregnated filter-paper strip (FeO-P_w).
(b) Soil samples (~ 2 cm deep) prior to first irrigation, analyzed for inorganic (P_i) and organic Olsen-P, FeO-P_s, and water soluble-P (P_ws).
All P concentrations determined using molybdenum-blue method.