Nitrogen mineralization from organic amendments is variable but predictable
Patrícia Lazicki, Daniel Geisseler, Margaret Lloyd
Abstract
Abstract To manage nitrogen (N) efficiently, organic growers must be able to predict the amount and timing of plant‐available N from organic amendments. In this study, we measured N mineralization from a variety of organic amendments, including composted animal manures and plant material, pelleted and granular organic fertilizer formulations, slaughter waste products, and hydrolyzed liquid fertilizers. In a laboratory incubation, we measured net N mineralization from materials mixed with either organically or conventionally managed soil at 23°C and 60% water holding capacity after 0, 7, 21, 42, and 84 d. We found that net mineral N change in the amended soils after 84 d of incubation fell into four categories: immobilization to 5% of applied N for yard trimmings composts, 15–30% for poultry manure composts, 35–55% for granular fertilizers, and 60–90% for quick release products. However, across all amendments the amount of plant‐available N after 84 d of incubation was well correlated with the carbon (C)/N ratio ( R 2 = 0.92). Within amendment types, the C/N ratio predicted N mineralization for yard trimmings composts ( R 2 = 0.91), manure composts ( R 2 = 0.81), and specialty fertilizer and slaughter products ( R 2 = 0.88) but not liquid products ( R 2 = 0.11). Soil management history did not consistently affect net N mineralization but may have influenced timing.