Changes in Soil Attributes Following Low Phosphorus Swine Slurry Application to No-Tillage Sorghum

Swine (Sus scrofa) slurry can serve as an excellent fertilizer source. Application at rates to meet crop N requirements can result in excess soil P due to low manure N/P ratios. Low phytate corn (LPC) (Zea mays L.) stores a greater proportion of P as phosphate than does traditional corn (TC) increasing bioavailability of P in pig feed grain. Improved utilization of feed P reduces P concentration in manure and soil P accumulation. However, the potential effects of LPC manure on other soil properties are not known. Changes in soil attributes over 3 yr were compared for soils receiving LPC manure, TC manure, inorganic fertilizer, and no nutrients in no-tillage sorghum [Sorghum bicolor (L.) Moench] on a Sharpsburg clay loam (fine, smectitic, mesic Typic Argiudolls). Soil physical properties exhibited values that should not inhibit crop growth. Several soil chemical properties differed by year and treatment. Particulate organic matter (POM), NO₃–N, pH, and extractable P increased with manure additions. Extractable P content was greater with addition of TC than LPC manure. Soil chemical properties exhibited values acceptable for crop production, but increasing extractable P increases the potential for environmental contamination. Biological soil properties varied in their response to treatments. Microbial biomass C decreased in the control and increased in manure treatments. The Soil Management Assessment Framework (SMAF) was used to conduct a dynamic soil quality assessment. The SMAF index values were similar across years in the control and inorganic fertilizer treatments and increased in both manure treatments. Manure additions improved soil properties affecting crop production, with P accumulation and the potential for environmental contamination being lower with LPC manure. LPC manure applied at rates to meet crop N requirements will have slower soil P accumulation rates and a lower potential for P contamination of the environment.