Swine lagoon effluent as a source of nitrogen and phosphorus for summer forage grasses

Efficient crop utilization of N and P derived from anaerobic swine (Sus scrofa domesticus) lagoon effluent is critical to minimizing offsite nutrient movement. The objective of this study was to determine the effects of variable rates of swine lagoon effluent and fertilizer N and P on yield and nutrient utilization of forage grasses on an acid Vaiden silty clay (very fine, montmorillonitic, thermic, Vertic Hapludalf) and an alkaline Okolona silty clay (fine, montmorillonitic, thermic, Typic Chromudert). Treatments were multiple effluent irrigations resulting in four N and P rates from 0 to 665 and 0 to 94 kg ha(-1) yr(-1) N and P, respectively. Fertilizer treatments were also established at equivalent N and P rates. Similar growth responses were obtained for bermudagrass [Cynodon dactylon (L.) Pers.] or johnsongrass [Sorghum halepense (L.) Pers.] regardless of nutrient source. Application of either effluent or fertilizer at rates >448 kg N ha(-1) did not effectively increase dry matter yield. Total N accumulation reflected both increasing dry matter yield and tissue N concentration while P accumulation depended primarily on increasing yield. Forage grass accumulation of N and P ws similar between sources, but recovery efficiency for both elements declined with increasing rates. Similarity in N and P availability of effluent to fertilizer simplifies nutrient management although potential N loss by NH3 volatilization is likely greater for effluent while fertilizer may result in greater end-of-season soil NO3--N levels at equivalent rates of applied N.