PJB-2007-245
ROOT-INDUCED CHANGES IN SOME BIOLOGICAL AND BIOCHEMICAL CHARACTERISTICS OF SOIL SOWN TO WHEAT (TRITICUM AESTIVUM L.) AND CHICKPEA (CICER ARIETINUM L.)
S. GILL, F. AZAM AND A. KHARRAL1
Abstract
In a greenhouse experiment, wheat and chickpea were compared for root-induced changes in bacterial/fungal population of rhizospheric soil, microbial biomass, immobilization/loss of N applied as NH4+ and NO3-, dehydrogenase and nitrate reductase (NRA) and potential nitrification activity (PNA). Unplanted soil was used as a control for changes due to plant growth. Four varieties each of wheat and chickpea were grown in a greenhouse. Dry weight and % dry matter content of root and shoot portions were significantly different for the two crop types. On an average, varieties of chickpea gathered ca 2 times greater biomass pot-1 as compared to wheat. Both wheat and chickpea varieties had a significantly positive effect on dehydrogenase activity (DA) of the soil, the effect being significantly greater for the latter. Microbial biomass N content of planted soil that accounted for 2.7% - 3.5% of total N was significantly (P = 0.05) higher as compared to that of unplanted soil, was higher in chickpea than wheat rhizosphere, and was significantly correlated (P = 0.05; r = 0.092) with DA. On an average, the wheat varieties had an inhibitory effect on potential nitrification activity (PNA), while the chickpea varieties caused a significant (P = 0.05) increase over unplanted soil. With reference to unplanted soil, a significant (P = 0.05) inhibition of nitrate reductase activity (NRA) in wheat rhizosphere (>63%) and significant enhancement (16 folds) in chickpea rhizosphere was observed. Microbial biomass N content of unplanted soil was13.9 μg g-1 soil compared to18.5 and 22.1 μg g-1 soil planted to wheat and chickpea, respectively. It accounted for 2.7 – 3.5% of the total N under different crop varieties and was significantly correlated with DA (r = 0.92; n = 9; P = 0.05). Immobilization of labeled NH4+ was significantly higher in the rhizosphere soil of wheat than chickpea. A higher percentage of NO3--N than NH4+-N was immobilized in the rhizosphere soil of wheat compared to chickpea (30.2 vs 22.7 % of the applied), while more NO3--N was unaccounted in the rhizosphere soil of chickpea than wheat (37.3 vs 16.8%).
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