Nitrogen Dynamics in Lowland Rice as Affected by Crop Establishment and Nitrogen Management

Information on the dynamics of nitrogen as influenced by crop establishment method and N management strategy is meager, but such information is necessary in optimizing nitrogen input for lowland rice (Oryza sativa L.). A field experiment was conducted at the experimental farm of the International Rice Research Institute (IRRI), Philippines, during the wet and dry seasons of 2003 and 2004 to evaluate the effects of crop establishment and nitrogen management strategies for lowland rice on the dynamics of mineral N. The experiment was laid out in a split-plot design with four crop establishment methods as main plots and two N management techniques as subplots with three replications. Zero-N fertilizer (N-omission) micro-plots were embedded in each plot. Crop establishment method did not significantly influence uptake of in- digenous mineral N during the wet (44-55 kg ha(-1)) and dry (43-50 kg ha(-1)) seasons. Apparently, NH4+-N and NO3- -N accumulated in the top 20-cm layer of the soil during the wet season, resulting in relatively high initial N during the dry season. Crop establishment and N management strategies did not influence crop removal of N during a one-year period. Actual N balance across crop establishment methods during the one-year period ranged from 10 to 16 kg ha(-1), whereas the apparent N balance ranged from 45 to 99 kg ha(-1). A fertilizer recommendation should be developed based on the actual N balance along with the assessment of crop N requirement for a given yield potential. (C) 2007 by The Haworth Press, Inc. All rights reserved.