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Subject: Soil Science × Author: Nandy, Suravi × End date: 2019 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    CARBON AND NITROGEN MINERALIZATION IN AN INCEPTISOL WITH AND WITHOUT STUBBLE ADDITION
    (AAU, Jorhat, 2019-07) Nandy, Suravi; Borah, Nilay
    A laboratory experiment was carried out to evaluate carbon and nitrogen mineralization in soil as influenced by rice stubble addition. Bulk surface (0-15 cm) soils (sandy clay loam with pH 4.6 and organic carbon 6.2 g/kg), collected from winter rice (variety - Ranjit) field after harvest of the crop, were processed and used to fill the PVC (polyvinyl chloride) pipes (diameter 9.0 cm) to a depth of 15 cm and incubated for 105 days imposing different treatments. Rice stubbles were treated in the field by spraying glyphosate (2.05 g a.i/l) and commercial yogurt (5 g/l) mixtures solution. Both treated and untreated stubbles were collected from the field, chopped into small pieces (1.5 to 2.0 cm long) and added to the columns with and without incorporation. A column was incubated without addition of the rice stubbles. The soil columns (over a layer of 10 cm sand) were kept in a tray filled with sand under constant saturation in a completely randomized design with four replications. The soil moisture content of the columns varied from 27.6 to 31.4 % (w/w) and the maximum temperature varied from 21.3 to 29.3 0C during the experiment. The CO2 evolution from the soils increased up to 6th week of incubation and maximum value (30.6 mg/kg soil) was observed with incorporation of treated rice stubble. The lowest value during this period was observed in soil without rice stubble and differed significantly to the treatments for each sampling stage. The CO2 evolution from the soils every third day after 6th week of incubation increased gradually reaching the peak at around 9th week after incubation in treatments receiving rice stubble. Thereafter, the CO2 evolution from the soils decreased gradually with a little rise at 12th week after incubation. Significant differences in CO2 evolution from the soils were not observed between incorporated and unincorporated treatments for both treated and untreated rice stubble, except a few occasions. The organic carbon content of the soils was not affected by the stubble management up to 42 days after incubation, which significantly increased due to incorporation of treated rice stubble up to 84 days, and due to addition of stubble at 84 and 105 days of incubation compared to soil without stubble. The labile organic carbon content of the soils significantly increased 42 days after incubation in soils with rice stubble, except untreated and unincorporated treatment compared to without stubble. However, the microbial biomass carbon was relatively non-significant, except at 63 days of incubation where incorporation of untreated and retention of treated stubbles showed higher significant contents over retaining untreated stubble or without stubble. The NO3-N significantly increased up to 84 days of incubation with stubbles, irrespective of incorporation and glyphosate-yogurt treatment compared to without stubble. The soil pH was affected only at 105 days after incubation, where it significantly decreased due to retention of treated stubble or incorporation of stubble compared to without stubble and retention of untreated stubble. However, the exchange acidity and total acidity in soils significantly increased after 63 days after incubation due to incorporation of treated or untreated stubble and retention of treated stubble. The cation exchange capacity, exchangeable cations, viz. NH4+, Ca2+, Mg2+ significantly increased with incorporation of rice stubble, while the effect for K+ was observed only with treated stubble incorporation. The available phosphorous (P) and potassium (K) significantly increased due to stubble incorporation, but available nitrogen was unaffected by the treatments.