Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2008
Publication Date: 6/18/2008
Citation: Paschold, J.S., Wienhold, B.J., Ferguson, R., Mccallister, D.L. 2008. Soil N and P availability for field applied slurry from swine fed traditional and low phytate corn diets. Soil Science Society of America Journal. 72:1096-1101. Interpretive Summary: Swine production generates large amounts of waste. While this waste contains nutrients that may serve as fertilizer when applied to agricultural fields proper application is difficult because the ratio of nutrients in the waste is different than what a crop requires. Application of waste to meet the nitrogen needs of a crop results in application of excess phosphorus which increases the potential for environmental contamination. Corn containing phosphorus in forms that can be more readily utilized by swine has been developed. Swine fed corn diets with more highly available phosphorus produce waste that has a nitrogen to phosphorus ratio closer to what a crop needs than swine fed traditional corn diets. Two field studies were conducted to compare nitrogen and phosphorus availability in soils receiving waste from swine fed highly available corn diets to that in waste from swine fed traditional corn diets. Nutrient availability was similar for both swine waste sources. When surface applied to a rainfed no-tillage field, nitrogen was 70% available and phosphorus was 100% available. When tilled into an irrigated soil, 40% of the applied nitrogen and 60% of the applied phosphorus was available during the year of application and 30% of the applied nitrogen and 40% of the applied phosphorus was available the following year. Highly available phosphorus corn diets reduce the phosphorus content of swine waste but not the availability of nitrogen and phosphorus in that swine waste.
Technical Abstract: Swine (Sus scrofa) slurry contains nutrients essential for crop production but usually contains more P relative to N than is required by most crops. Land application at rates to meet the crop N needs results in accumulation of excess P creating the potential for negative environmental impacts. Diet modifications such as low phytate corn (Zea mays L.) (LPC) have resulted in improved bioavailability of P and reduced manure P content. Field studies have not been conducted to determine the effect changes in manure nutrient content resulting from LPC diet modifications will have on crop N and P availability. A study was conducted to compare in situ availability of N and P at two sites. One site received three annual additions of manure from swine fed LPC and traditional corn (TC) diets and inorganic fertilizer surface applied to rainfed no-tillage sorghum (Sorghum bicolor (L.) Moench.). A second site received a one time application and incorporation of the same nutrient treatments to irrigated corn. Surface applied swine slurry exhibited year-to-year variation in N and P availability likely due to differences in weather among years. Potentially mineralizable N was 70% of applied N and available P was 100% of applied P for manure from both diets. Incorporation of swine slurry reduced potentially mineralizable N to 40% that applied the year of application and 30% that applied the year after application and reduced available P to 60% that applied the year of application and 40% that applied the year after application for both diets. Reduced availability with incorporation is due to possible placement of slurry below the sampling depth or immobilization when slurry is incorporated with the abundant crop residue. Modified diets reduce the P content of manure but not the availability of N and P in that manure.