Nonsymbiotic Nitrogen Fixation Associated With the Rice Plant in Flooded Soils

15N Dilution technique of assessing the contribution of nitrogen fixation to rice plant

“…In flooded soH, the presence of rice was accompanied by positive nitrogen balance, but in flooded fallow pots, a statistically significant amount of nitrogen was lost. The stimulative effect of the presence of wetland rice to nitrogen gain has been previously demonstrated (1). In the pots where the contribution ,of photodependent nitrogenfixing agents was minimized by shading the surface of pots, nitrogen gain was not statistically significant.…”

“…In the pots where the contribution ,of photodependent nitrogenfixing agents was minimized by shading the surface of pots, nitrogen gain was not statistically significant. App et al (1) detected nitrogen gain in similarly shaded pots after four or six continuous rice crops. We think, therefore, that the two crops reported here were not sufficient to detect nitrogen gain by heterotrophic nitrogen fixation.…”

Nitrogen Transformations in Submerged Soils

“…The N balances in the absence of applied N, when N losses are small or negligible, presumably approximate N inputs by the indigenous BNF system (App et al, 1980). Estimated BNF based on an N balance during 27 seasons of growing two irrigated rice crops per year without fertilizer N in the Philippines was 46 kg N ha −1 crop −1 .…”

Difference in Natural Abundance of15N in Several Rice(Oryza sativaL.) Varieties: Application for Evaluating N2Fixation

“…Rice varieties may differ in their reliance on N derived from photo dependent NlI-fixa-tion. Total N balance in a flooded rice-soil system enables to determine that the N gain is affected by the varieties and growing conditions (1,2,21), however, for routine screening it is a time-consuming and laborious method. Recently, a large number of reports dealing with the estimation of biological N2 fixation by the 15N dilution method have been published (5,15).…”