Manure and Fertilizer Management Influence on Soil Nutrient Levels and Grain Yields in Eastern South Dakota from 2003 to 2014.

Concentrated animal feeding operations (CAFOs) are required to hold a manure management permit in South Dakota. The permit encompasses available nutrients from manure, crop nutrient use and removal, soil test nitrate-N, and phosphorus and land availability for approved nutrient application rates. The management plan determines if nitrogen or phosphorus based manure application rates are used. Most CAFO’s start out following the nitrogen based plan as soil test phosphorus (P) levels are low to allow extra P applications beyond the agronomic needs of the crop. Manure nitrogen and phosphorus ratios are usually fixed and somewhat equal, and therefore soil P concentrations increase when following the nitrogen based plan. For these reasons, two manure management studies were initiated in 2003 to evaluate the long-term effects of soil properties and crop productivity following either the nitrogen or phosphorus based nutrient management plans. This resulted in five approaches: 1) crop nutrient requirements from fertilizer, 2) crop P requirements from manure, based on soil test and supplemented with nitrogen fertilizer as needed, 3) crop nitrogen requirements from manure, based on soil test, 4) double the crop nitrogen requirements from manure, and 5) non-limiting nutrients from fertilizer. During the project, soil test P decreased on the control plots, remained relatively steady on the crop nutrient requirements from fertilizer treatment plots, and significantly increased from both manure management approaches and the non-limiting nutrient fertilizer treatment. Soil organic matter and pH both increased with manure application. Corn and soybean grain yields were generally higher when nutrients were supplied from both fertilizer and manure, however manure treatment yields were generally the highest.