EFFECT OF CONSERVATION AGRICULTURAL PRACTICES ON SOIL CARBON AND NITROGEN LOSSES THROUGH EROSION
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Date
2019-09
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Sher-e-Kashmir University of Agricultural Sciences and Technology, Jammu, Jammu
Abstract
A study was carried to assess the impact of tillage and surface cover on temporal changes in the soil organic carbon and nitrogen pools and their losses through erosion under maize crop. Three tillage variations i.e. conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) were employed, and were combined with management practices such as intercropping (i), mulching (m) and residue retention (30%) (r). As a general trend among all the treatments, organic carbon (OC) slightly increased from before crop sowing to 30 DAS, then decreased at 60 DAS and then more or less levels of OC towards the harvesting stage. However, potassium permanganate oxidizable C (KOC) was highest at the beginning of the crop cycle and the values decreased towards 30 DAS and 60 DAS and then an increase in its content was observed as it progressed towards the harvesting. Labile fraction breaks down relatively quickly, and is an active source of nutrition. KOC, SMBC and OC ranged between 916-1082 mg kg-1, 25.8-34.5 mg kg-1 and 0.32-0.41 %, respectively. However, there was no significant difference between the treatments. The highest POC was observed in ZTr (329.7 g m-2) which was statistically at par with CTi, MT, MTm, MTi, MTr, ZT and ZTm whereas the least was observed in CT (204.7 g m-2) which was statistically at par with all the treatments except ZTr. Greater variability was observed in POC content than in SOC content due to tillage, indicating that this form of C was more sensitive to alterations in the soil than SOC and could serve as an early indicator of sustainability of adopted practices. Maximum nitrate content was observed at 30 DAS due to the higher decomposition rate. NH4-N was highest in the samples analyzed before the sowing of crop, decrease towards 30 DAS and then as it progress further, an increase in amount of NH4-N was observed in general. It was observed that the application of residue or mulches or intercropping with pulses effectively reduced the dissolved C losses. Overall OC losses through sediments ranged from 10.25 kg ha-1 (ZTm) to 48.31 kg ha-1 (CT), with significant differences among conventional and zero tilled plots. Significantly higher concentration of NO3-N were observed in runoff from zero tillage plots. NO3-N losses in runoff occurring throughout the growing season was maximum in ZT. Total ammonical N loss in runoff was maximum in CT (0.547 kg ha-1) while the minimum NH4-N loss occurred in ZTr (0.362 kg ha-1). Maximum Kjeldahl N loss was observed in CT while the minimum amount of N loss in sediments occurred in ZT treatments. Unlike runoff water, which was not affected by tillage practices in general, there were significant differences in the amount of sediments eroded, which translated into higher amounts of Kjeldahl N being lost under conventional tillage systems. Zero tillage with soil cover, either though mulching, residue retention or intercropping could be more effective option in reducing carbon and nitrogen losses, than zero tillage alone.
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