Nutrient loads and sediment losses in sprinkler irrigation runoff affected by compost and manure

Abstract

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 [NO₃-N], ammonium-nitrogen [NH₄-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⁻¹) or 71.7 Mg ha⁻¹ (32 tn ac⁻¹) of dry manure or 22.4 Mg ha⁻¹ (10 tn ac⁻¹) or 47 Mg ha⁻¹ (21 tn ac⁻¹) of dry compost into a calcareous silt loam soil on slopes from 0.8% to 4.4%. In the spring of 2000 and 2001, we collected surface soil (0 to 30 mm [0 to 1.2 in]) from furrows to determine soil test phosphorus (STP). We applied 21 to 46 mm (0.8 to 1.8 in) of water at an average application intensity of 28 mm h⁻¹ (1.1 in hr⁻¹; peak intensity of 40 mm h⁻¹ [1.6 in hr⁻¹]) to 6.4 × 36.6 m (21 × 120 ft) plots six times in 2000 and two times in 2001. 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, NO₃-N, NH₄-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.