Bioavailability of Nitrogen Released From Organic Amendments and Cover Crops in Broccoli, Corn and Potato.

Nitrogen (N) in agricultural soils is greatly influenced by biologically dynamic processes, such as N mineralization or immobilization from organic amendments and cover crops.  The net outcomes of these processes are often difficult to predict and, consequently, it is difficult to synchronize amendment addition with plant demands.  Plant Root Simulator (PRS)™-probes are a proven tool for accurately measuring net N mineralization and/or immobilization in dynamic soil systems. In Western Oregon, Sullivan (2008) showed that incorporation of a vetch cover crop and feather meal provided the greatest N supply rates to the PRS™-probes and also to the indicator crop of broccoli. Whereas the oat cover crop and feather meal reflected lower N supply rates and consequently inferior yield of broccoli. A similar study done by Bary and Cogger (2008) in Northwestern Washington demonstrated that feather meal increased N supply rates to sweet corn as measured by the PRS™-probes. When intercropped with cover crops (vetch, rye/vetch, fallow), the feather meal application showed higher N supply rates as compared to no feather meal addition. Sharifi et al (2009) used PRS™-probes to evaluate N supply from hog manure-sawdust compost and pelletized poultry manure to potato crop in Atlantic Canada. The cumulative PRS™-probe N supply rates were significantly related to total plant N uptake (r = 0.77). These studies demonstrate that organic soil amendments have a very dynamic influence on soil N supply.  Accounting for the impact of soil temperature and moisture affords the PRS™-probes more sensitivity and responsiveness in assessing the soil N supply rate, thereby facilitating more powerful inferences regarding organic N turnover.