Effect of Different Herbicides and Allelochemicals on Weed Density and Soil Microbial Population under Direct Seeded Rice (Oryza sativa L.)

Abstract

The use of herbicides for weed control often catches the eye of environmentalists as it harms the soil microflora leading to deteriorated soil health. So, efforts are being made in order to use herbicides that can cause no or very less harm to the soil microflora. In this context, an experiment is planned to know the potential effect of different herbicides and allelochemicals on weed density and soil microbial population under direct seeded rice where herbicide weed management is widely adopted. The experiment is conducted during Rabi, 2020 and summer, 2021 in the red sandy loams of Gandhi Krishi Vignana Kendra (GKVK), University of Agricultural Sciences, Bengaluru by using randomized complete block design with three replications. Out of different treatments tried out, T4 i.e., bispyribac sodium 10 SC 40 g a.i. ha-1 as post emergence has reported superior weed control which is evident by the lower weed density (43.3 no. m-2) and weed dry weight (49.2 g m-2) followed by T1 i.e., bensulfuron methyl + pretilachlor 6.6 GR 660 g a.i. ha-1 as pre emergence (46.0 no. m-2 and 51.4 g m-2, respectively). When soil microbial population is considered all the allelochemical treatments has recorded higher microbial population but the weed control in these allelochemical treatments was not satisfactory. Among the herbicides, T1 i.e., bensulfuron methyl + pretilachlor 6.6 GR 660 g a.i. ha-1 as pre emergence has recorded higher microbial population of bacteria, actinomycetes and fungi (23.52 x 105, 15.30 x 104 and 12.45 x 103 CFU g-1 soil, respectively) over T4 i.e., bispyribac sodium 10 SC 40 g a.i. ha-1 as post emergence (21.83 x 105, 13.33 x 104 and 10.91 x 103 CFU g-1 soil, respectively). Hence, by taking both weed control and soil microbial population into consideration treatment T1 i.e., bensulfuron methyl + pretilachlor 6.6 GR 660 g a.i. ha-1 as pre emergence is concluded to be the better herbicide.