Potential for denitrification in irrigated rice soils of Swat and Peshawar valleys [Pakistan]
2003
Shah, Z. | Muhammad, D. (NWFP Agricultural Univ., Peshawar (Pakistan). Dept. of Soil and Environmental Sciences)
A major portion of nitrogen is lost from soil plant system via leaching, ammonia volatilization, denitrification, surface runoff, and gaseous plant emission. Denitrification and its possible correlation with soil properties was studied in soils collected at 0-10, 10-30, 30-60, and 60-90 cm depths from five irrigated rice fields in Swat and 4 in Peshawar valleys. The nitrate disappearance method over a range of anaerobic incubation period of 0, 2, 4, 8, 16 and 32 days at 30 degree C determined denitrification. The NO3-N concentration decreased progressively in soils of all depths with increasing incubation in both Swat and Peshawar soils indicating the occurrence of denitrification in the said soils. The decline was more in the top than in the lower depth. On average (0-90 cm), the level of NO3-N decreased from 225 mg kg-1 soil at day 0 to 175 mg at day 32 in Swat soil and from 200 mg at day 0 to 100 mg at day 32 in Peshawar soil. It was observed that an amount of 78 mg kg-1 of NO3-N was lost from Swat soils and 124 mg from Peshawar soils during 32 days of incubation period. The corresponding loss was 34% from Swat and 60% from Peshawar soils of the initial NO3 level occurred at the rate of 2.44 and 3.88 mg kg-1 soil d-1, respectively. The denitrification was significantly correlated with soil organic C (r = 0.64), total N (r=0.63) and EC (r = 0.55). The correlation of denitrification with other soil properties was either weak (e.g. soil texture) or nil (pH and C/N ratio). These results suggested that large potential for denitrification exists in rice fields of Swat and Peshawar valleys and that it was highly dependent on soil organic C and total N.
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