High water application rates beneath the outer spans of center pivot sprinkler systems can cause runoff, erosion, and nutrient losses, particularly from sloping fields. This field study determined runoff, sediment losses, and nutrient loads (dissolved organic carbon [C], nitrate-nitrogen [NO 3 -N], ammonium-nitrogen [NH 4 -N], total phosphorus [TP], ferric-oxide strip phosphorus [FeO P], dissolved reactive phosphorus [DRP], potassium [K], calcium [Ca], magnesium [Mg], and sodium [Na]) in sprinkler runoff for two years after a single application of either stockpiled or composted dairy manure. We studied five treatments, including a nonamended control, in each of six blocks, with each block situated under a different span of a low-pressure, moving-lateral sprinkler system. In October of 1999, we incorporated 29.1 Mg ha -1 (13 tn ac Additional nonmonitored irrigations were made as needed to produce corn (Zea mays L.) silage each year. At 15 to 30 minute intervals after runoff began, we measured runoff rates and collected runoff samples to determine sediment and constituent losses for each monitored irrigation. None of the amendment treatments significantly affected runoff, sediment losses, or loads of dissolved organic C, NO 3 -N, NH 4 -N, TP, FeO P, or Mg when averaged across irrigations. Without exception, runoff, sediment losses, and loads of every measured constituent varied among irrigations after accounting for differences in water applied. Treatments influenced DRP, K, and Ca runoff loads. Loads of Ca decreased, but Na increased with increasing manure application rates. Relative to the control, manure DRP loads were five to six times greater, whereas compost DRP loads were similar.
Key words: center pivot-erosion-infiltration-nutrient losses-runoff-sprinkler irrigationSprinkler irrigation predominantly with center pivots is a common and rapidly expanding practice in the irrigated West. In 2008, nearly three-fourths of the irrigated land in the Pacific Northwest was irrigated with sprinklers (NASS 2010). More than 97% of the potato (Solanum tuberosum L.) growers in Idaho use sprinklers to irrigate their crops (Pehrson et al. 2010). Irrigation with moving-lateral systems, including center pivots, is growing worldwide. Moving-lateral systems are commonly replacing surface irrigation systems in the irrigated western United States. In more humid areas of the United States and the world, moving-lateral systems are being installed and used to supplement rainfall at critical crop growth stages or during times of drought (Frank 2001).As sprinkler-irrigated land area increases, concern arises over the transport of nutrients in runoff-particularly from beneath pivot outer spans-to nearby water courses (Alva et al. 2005;Lentz and Lehrsch 2010;Wilcock et al. 2011). Nitrogen (N) and P are important constituents of sediment and organic matter transported offsite in irrigation runoff (Heathwaite and Johnes 1996). As such, the N and P cause or accentuate eutrophication of surface waters (Correll 1998). One must r...