Integrated weed management for rice based cropping system of Onattukara tract

Abstract

Field experiments were conducted at Rice Research Station, Kayamkulam from April 1996 to May 1998 to study the effect of integrated weed management practices for rice-rice-sesamum cropping system of Onattukara tract. The experiment was laid out in randomised block design with twelve treatments during the first crop season and in split plot randomised block design with twelve treatments and twelve residual effects during second crop season and with twenty four residual effects during the third crop season. Rice varieties Bhagya and Dhanya and sesamum variety Thilak were used for the study during the first, second and third crop seasons respectively. Results of the study revealed that grasses, broad leaved weeds and sedges competed with the crop plants in the rice-rice-sesamum cropping system. The herbicide treatments significantly reduced the monocot, dicot and total weed population in the cropping system. Pendimethalin pre-emergence application alone or integrated with hand weeding/2,4-D post emergence significantly reduced the weed growth during the first crop season whereas thiobencarb pre-emergence + hand weeding reduced the weed growth in the second crop of rice. The weed count and dry matter accumulation by weeds in the sesamum crop during the third crop season was significantly reduced by the carry over effect of herbicide

2 treatments applied both to first and second crop rice compared to the carry over effect of herbicide treatments applied to first crop rice alone. The herbicide treatments significantly influenced the growth and yield attributing characters .of the first and second crop of rice. The residual effects of previous weed control treatments on the growth and yield of sesamum was not significant. Pendimethalin pre-emergence + hand weeding or its integration with 2,4-D post emergence influenced the growth characters of first crop of rice, thiobencarb pre-emergence + hand weeding found to exert considerable influence on the growth and yield of second crop of rice. Weedy check recorded the lowest yield and under weed free situation the crop plants had registered maximum growth and yield. The yield loss due to weed indicated by the weed indices was maximum under weedy check and minimum for pendimethalin pre- emergence + hand weeding and thiobencarb pre-emergence + hand weeding applied to first and second crop of rice in rice-rice-sesamum cropping system. The weed management practices and their carry over effects had significant influence on the uptake of nutrients by the crop and weeds during the first, second and third crop seasons. Unweeded check exploited the available nutrients and water resulting in better weed growth and dry matter accumulation through out the cropping system. The soil nutrient status was also affected by the weed management practices studied. The N, P, K status of soil was high for weedy check

3 compared to herbicide treatments and weed free treatments owing to poor crop utilization of the nutrients. The herbicide treatments applied both to the first and second crop of rice and their carry over• effects on third crop of sesamum had no significant effect on the population of soil organisms. Economic analysis revealed that herbicide treatments were remunerative compared to weedy check and farmers practice in the first and second crop seasons. The residual effects of weed management practices had not influenced the economics of sesamum crop during third crop season. Bioassay studies revealed no phytotoxic concentration of herbicide residues in the soil after the rice-rice-sesamurn cropping sequence.