Interaction of 15N-labelled ammonium nitrogen with native soil nitrogen during incubation and growth of maize ( Zea mays L.)

Abstract

A laboratory incubation experiment and a pot experiment on maize ( Zea mays L.) were madee to study the interaction with native soil N of 15N-labelled ammonium applied at 25. 50. 100 or 200 μ g N g −1 soil. Incubation of soil for 4 weeks showed a significant enhancement in mineralization of native N (added nitrogen interaction. ANI) due to applied N and the effect increased with increased rate of application. The ANI occurred only during the first week of incubation and its extent was not affected significantly during the subsequent 3 weeks of incubation. The ANI was not observed in the pot experiment at any concentration of applied NH 4-N and was assumed to be due to the absence of root-driven immobilization and pool substitution in maize. Root growth showed a negative response to increased amounts of N addition. However. N uptake efficiency of plants (as revealed by total plant N) increased significantly at increasing rates of applied N but without the occurrence of ANI. Heavy losses of applied N occurred both in the incubation study (20 30%) as well as plant experiment (47–83%); the losses being more as the rate of applied N increased.