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Abstract

A pot experiment was conducted to study the root-induced changes in potential nitrification (PN) and nitrate reductase activity (NRA) in the rhizosphere of 4 varieties each of wheat and chickpea using unplanted soil as reference. The two crop types were significantly different in gathering biomass over 21 days of growth; chickpea being twice more active when the values were averaged for 4 varieties. Wheat varieties had in general inhibitory and chickpea varieties a stimulatory effect on PN and NRA of the rhizospheric soil. On an average, NRA of the rhizospheric soil of wheat varieties decreased by 50% compared to unplanted soil i.e., non-rhizospheric or bulk soil. In contrast to wheat, chickpea varieties caused 5-30 times increase in NRA as compared to unplanted soil. When data for different varieties within a crop type were averaged, PN and NRA were 2 and 45 times higher in chickpea as compared to wheat. The two parameters were significantly correlated (r = 0.97, n = 9) suggesting the dependence of NR on In situ formation of NO3-. However, ratio of NRA/PN suggested chickpea varieties to be more efficient in inducing NO3- reduction than nitrification. In wheat varieties, NRA was not induced although NO3- was being formed at rates comparable to that in unplanted soil and in soil planted to two of the chickpea varieties. Significance of differential root-induced changes in PN and NRA to nitrogen nutrition of the two plant types is discussed.

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