Nitrogen Contribution from Different Manure Sources: Field Studies.

Nitrogen fertilizer equivalencies (NFE) from manure are influenced by manure type, application method, crop selection, and environmental conditions. Much of the research to determine NFE of manure was conducted in tilled systems but many producers use no-tillage (NT) to reduce soil erosion and labor requirements. The objective of this study was to determine NFE for composted swine manure, poultry litter, and a processed biosolid in corn (Zea mays L.) and wheat (Triticum aestivum L.) produced in NT cropping systems. These studies were conducted at multiple sites from 2011 to 2014 on similar silt loam soils with no history of manure application. Manure applications occurred at planting using three N rates that were based on total N content. Urea-N was applied at five rates to calculate NFE. Substantial NFE variation was observed between and within cropping season, ranged from 0 to 97%, and was typically higher for corn than wheat. Composted swine manure resulted in the lowest product NFE regardless of year or crop. The biosolids typically had the highest NFE across all rates and products. Predicting NFE of these manure sources is difficult due to annual environmental variation. Different crop growth patterns between wheat and corn suggest that NFE should be determined for individual crops. Nitrogen fertilizer equivalencies developed for tilled fields appear to be higher than those for NT fields. All these factors should be considered when determining N application rates.