Encapsulated herbicide in preceding rice on weed growth and blackgram productivity in rice-okra-blackgram cropping system under tropical conditions

Weeds in the double cropping of rice are different from the rice-vegetable-pulse cropping system as there will be a shift in weed flora due to changes in the cropping system. Field experiments were conducted during the summer season of 2017 and 2018 to study the residual effect of encapsulated/loaded herbicide applied in preceding rice on weed control and productivity of black gram under the rice-okra-blackgram cropping system. The experiment consists of eight weed control treatments, viz. encapsulation of herbicide with zeolite, biochar, starch, water-soluble polymer, commercial formulation of herbicides, weed-free and weedy check of preceding rice and okra. However, the residual crop of black gram was sown without disturbing the layout of the preceding experiment. The residual effect of encapsulated herbicides expressed significant exerted difference in weed density and dry weight at 40 DAS, in both the years. Irrespective of weed control treatments, the residual effects of oxadiargyl-loaded biochar resulted in a 55.0% and 61.3% reduction in grass weed density and a 50.4% and 65.0% reduction in grass weed dry weight in 2017 and 2018, respectively when compared to the weedy control, which was comparable to all other herbicidal residual effects in blackgram. However, the residual impact of encapsulated/loaded herbicides did not significantly influence blackgram seed germination. Whereas, significantly higher clusters/plant (4.8, 7.2%) with high seeds/plant (20.0, 26.2%) and seed yield (108,101 kg) was recorded under oxadiargyl-loaded biochar compared to oxadiargyl loaded zeolite during 2017 and 2018, respectively. It can be concluded that the oxadiargyl-loaded biochar and zeolite releases active ingredients for a longer time which reduces the growth of later emerging weeds and the build-up of soil weed seed banks in succeeding crops.