Impact of long-term zero tillage induced changes in soil properties on persistence of pendimethalin in different cropping systems
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Date
2020-05
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CCSHAU,HiSAR
Abstract
A field study on the ‘Impact of long-term zero tillage induced changes in soil properties on persistence of pendimethalin in different cropping systems’ was carried out during kharif 2019 in an ongoing experiment on conservation agriculture (CA) laid out in 2006 at Soil Research Farm, CCS HAU, Hisar, on an alluvial sandy loam soil. The experiment was laid out in split-plot design having three tillage practices i.e. zero tillage in both kharif and rabi seasons (ZT-ZT), conventional in kharif and zero tillage in rabi (CT-ZT) and conventional tillage in both the seasons (CT-CT), and two cropping systems i.e. mungbean-wheat (M-W) and sorghum-wheat (S-W). Pendimethalin available as Penda (30 EC) was applied @ 1.0 kg a.i. ha-1 immediately after sowing. Soil samples collected from different depths and times were analysed for soil properties and herbicide residues. Residues were extracted using column chromatography and analyzed on GLC. The results revealed that the ZT-ZT improved soil properties over CT-ZT and CT-CT practices, subsequently led to increase in half-life by 1.17 days over CT-CT in surface 5 cm soil. The ZT-ZT led to leaching of the herbicide beyond 15 cm upon 78.3 mm of rainfall after 5-6 days of its application. The cropping systems did not significantly influence the persistence. No residues were observed in grain of mungbean and straw of sorghum. A reversible change in the equilibrium of the population of soil microorganisms took place under different treatments, largely within 15 days of herbicide application. These microorganisms were significantly higher under ZT-ZT compared to other practices. Bacteria were sensitive to pendimethalin while fungi and actinomycetes showed moderate toxicity to the herbicide but actinomycetes grew exceptionally faster than bacteria and fungi during the season. Azotobacter and PSB experienced a moderate initial stimulation but higher simulation of Azotobacter under CT-CT accentuated them for efficient in utilizing easily available pendimethalin while steady growth of PSB towards harvest demonstrated their capability to utilize molecules that are adsorbed strongly to soil colloids. Herbicide under the two cropping systems had no significant influence on bacteria, actinomycetes and fungi but the population largely remained numerically higher under S-W during the season. Azotobacter and PSB, however, increased significantly at harvest in surface 5 cm and throughout the season in 5-15 cm soil depth under M-W. The study illustrated that the induced changes in soil properties under CA, though enhanced persistence but increased leaching emphasizing on potential risk of the herbicide for groundwater contamination, particulary, under shallow water-table conditions when applied during rainy season in light textured soils of semi-arid regions. The information concerning the toxic effect of the herbicide on agriculturally important soil microorganisms under long-term CA as a whole generated in present investigation has a greater significance under field conditions as the literature available is largely based either on laboratory or short-term field experiments.