Comparability of anaerobic swine lagoon effluent to commercial fertilizer on soil nutrient dynamics

The effects of swine effluent relative to commercial fertilizer on nutrient dynamics in two soils were studied. Swine effluent and commercial fertilizer were applied to established bermudagrass [Cynodon dactylon (L.) Pers.] on a slightly acid Vaiden silty clay (very fine, montmorillonitic, thermic, Aquic Hapludalfs) and to johnsongrass [Sorghum halepense (L.) Pers.] on a slightly alkaline Okolona silty clay (fine, montmorillonitic, thermic, Typic Chromuderts) from 1994 to 1996. Treatments were multiple effluent irrigations resulting in 4 nitrogen (N) rates from 0 to 665 kg N ha(-1) yr(-1). Treatments were arranged as randomized complete blocks and replicated four times. Commercial fertilizer treatments were applied at equivalent nitrogen-phosphorus potassium (N-P-K) rates. The extractable soil P, K, calcium (Ca), magnesium (Mg), copper (Cu), and zinc (Zn) at the top 5 cm of soil profile increased with increasing swine effluent application rates. For both soils, the high effluent and medium fertilizer treatments resulted in similar NO3-N concentrations when compared to lower application rates. Excessive soil NO3-N was observed with the high fertilizer treatments with concentrations of 50 mg kg(-1) or more for some depths of both soils. No significant differences in extractable soil K and P were observed between swine effluent and commercial fertilizer at the low and medium rates. However, at the high rate, P and K contents were greater for swine effluent than for fertilizer. Swine effluent applied at a rate equivalent to approximately 448 kg N ha(-1) y(-1) minimized soil residual NO3--N and salt content, and, appears to be the optimal rate under the conditions of this study.