Soil moisture and temperature effects on nitrogen release from organic nitrogen sources

Nitrogen release from organic N sources is controlled by the soil environment. Soil incubation was conducted to evaluate the effects of soil moisture (50, 70, and 90% of water holding capacity) and temperature (15/10, 20/15, and 25/20 degrees C [14/10 h]) on N release from four organic N sources. Differential N release kinetics of the N sources were determined by measuring ammonium- and nitrate-N contents periodically over 12 wk. Net N released, as a percentage of organic N, was greatest in the order: urea (91-96%) > blood meal (BM) (56-61%) > alfalfa pellets (AP) (41-52%) > partially composted chicken manure (CM) (37-45%). Increasing soil moisture increased net N released from AP and CM by 12 and 21%, respectively, but did not significantly affect net N released from urea and BM. Increasing temperature increased net N released from AP, BM, and CM by 25, 10, and 13%, respectively, but did not significantly affect net N released from urea. The results indicate that soil moisture and temperature influence N availability from organic N materials differently depending on source of N. In greenhouse production systems, where irrigation and temperature can be controlled, fertilizer management that considers both source of N and soil environment may improve the effectiveness of organic N materials.