Nitrogen- Vs Phosphorus-Based Manure and Compost Management of Corn.

Application of animal wastes (manure and compost) to farmland is generally based on nitrogen (N) requirement of crops. However, long-term N-based application of animal wastes leads to surplus application of phosphorus (P) and potassium (K) compared to crop removal which can cause P runoff and forage quality concerns (high K forages). The objective of this study was to evaluate the impact of a change from N-based applications without incorporation to a P-based (crop-removal) management system with immediate incorporation of manure on (i) corn yield and quality, and (ii) soil test nitrate, P, and K over five consecutive crop years. A 5-yr field study was conducted with annual spring applications of two rates of composted dairy manure (45 and 77 Mg ha^-1), two rates of liquid dairy manure (63.5 and 180 kL ha^-1), and two inorganic N fertilizer rates (0 and 112 kg ha^-1). Highest dry matter yields were obtained with N-based manure applications (7.22 Mg ha^-1, averaged over 2003, 2004, and 2005). Shifting from N-based to P-based management resulted in 15 and 21% yield decrease in manure and compost treatments, respectively. Nitrogen-based compost application resulted in a 6-fold increase in soil test P between 2001 and 2006, consistent with a 5-yr P balance of 240 to 280 kg P ha^-1. The highest soil test K accumulation was also observed in N-based treatments, increasing Morgan K levels from 47 to 132 and 137 mg K kg^-1 in compost and manure treatments, respectively. Our data indicate that N-based manure management ensures crop productivity and quality beyond what can be obtained with fertilizer N only but also results in rapid increase in soil test P and K. Further studies are needed to determine a more accurate P-based manure rate.