Crop Nitrogen and Phosphorus Utilization following Application of Slurry from Swine Fed Traditional or Low Phytate Corn Diets

Field application of swine (Sus scrofa) slurry provides essential nutrients for crop production. The N to P ratio for slurry is lower than needed by most crops resulting in P accumulation when applied at N rates required for crop growth. Low phytate corn (Zea mays L.) (LPC) contains similar amounts of total P but less phytate P than traditional corn (TC) resulting in improved P bioavailability and reduced P excretion by monogastric animals. While manure from swine-fed LPC diets has a higher N to P ratio than that from TC diets, field studies comparing crop utilization of nutrients from LPC manure have not been conducted. A field study was conducted to compare N and P utilization by no-tillage rainfed sorghum [Sorghum bicolor (L.) Moench.] receiving three annual surface applications of nutrients (inorganic fertilizer, LPC slurry, and TC slurry) and by irrigated corn receiving one incorporated application of nutrients. Sorghum grain and total dry matter N utilization exhibited a year by treatment interaction but total dry matter N utilization was similar for both manure types in all years (61.2 ± 2.6% for TC and 53.8 ± 2.6% for LPC). Grain P utilization was similar for inorganic fertilizer and manure but differed among years (44.4 ± 7.0% in 1999, 25.1 ± 1.4% in 2000, and 57.0 ± 2.2% in 2001). Corn grain N and P utilization did not diff er among nutrient sources in the year of application (50.7 ± 2.4% for N and 40.4 ± 3.0 for P) and increased little in the year following application (62.2 ± 3.0% for N and 50.2 ± 4.5% for P). Crop N and P utilization from LPC manure and TC manure was similar and nutrient guidelines developed for TC swine slurry should also apply for LPC slurry