Weed management for upland rice

Abstract

Rice is one of the principal food crops in Asia and can be grown in wetland and upland conditions. Upland rice is grown in rainfed, naturally well drained soils with bunded or unbunded fields without surface water accumulation. Moisture stress, weed infestation, poor soil fertility and incidence of pests and diseases are major problems in upland rice cultivation. Among these, weeds are considered to be most serious. Hence an effective and timely control of weed is essential to achieve higher productivity in upland rice. Field experiment was conducted at Agronomy Farm, College of Horticulture, Vellanikkara from June 2019 to September 2019 to develop cost effective weed management strategy for upland rice. The experiment was laid out in RBD with eight treatments and three replications. Treatments were T₁: Brown manuring (Cowpea) by application of 2,4-D on 25 DAS, T₂: In situ green manuring (Cowpea), on 25 DAS, T₃: Oxyfluorfen on the day of sowing fb HW at 30 DAS, T₄: Oxyfluorfen on the day of sowing fb bispyribac sodium on 20 DAS, T₅: Pyrazosulfuron on 6 DAS fb HW at 30 DAS, T₆: Pyrazosulfuron ethyl on 6 DAS fb bispyribac sodium on 20 DAS, T₇: Hand weeded control and T₈: Unweeded control. Dominant grass weed species observed were Echinochloa colona, Digitaria sanguinalis, Eleusine indica, Panicum maximum, Setaria spp, and Brachiaria spp. Dominant broad-leaf weed species were Alternanthera bettzickiana, Mitracarpus hirtus, Euphorbia hirta, Euphorbia geniculata, Ludwigia perennis, Scoparia dulcis, Ageratum conyzoides, Phyllanthus amara, Cleome burmannii, Commelina benghalensis, Lindernia crustacea, Catharanthus pusillus, Trianthema portulacastrum, Mollugo disticha and Hemidesmus indicus. Cyperus iria was the only sedge observed in the experimental field. Lowest weed dry matter production was recorded in hand-weeded control at 20 and 45 DAS. Application of oxyfluorfen fb HW at 30 DAS was as effective as hand weeded control and resulted in lesser weed count, weed dry matter, weed index and high weed control efficiency. Application of oxyfluorfen fb HW at 30 DAS resulted in maximum WCE of 92.60 % at 20 DAS and 98.58 % at 45 DAS. Lowest weed index was resulted from oxyfluorfen fb HW at 30 DAS (5.02 %) and was on par with pyrazosulfuron-ethyl on 6 DAS fb HW at 30 DAS (10.35 %). In situ green manuring and brown manuring resulted in significant reduction in weed dry matter production and high WCE at early stages of crop growth as compared to unweeded control, but it was not as effective as herbicide application. Application of oxyfluorfen fb HW at 30 DAS resulted in highest number of tillers per hill, leaf area index and number of hills/m². Hand-weeded control resulted in significantly higher grain yield (2888 kg/ha) and was on par with application of oxyfluorfen fb HW at 30 DAS (2743 kg/ha) and pyrazosulfuron-ethyl fb HW at 30 DAS (2589 kg/ha). Weed competition resulted in 78.05 % yield reduction in upland rice. Oxyfluorfen fb HW at 30 DAS resulted in highest straw yield (5898 kg/ha), which was on par with pyrazosulfuron-ethyl fb HW at 30 DAS (5886 kg/ha) and hand-weeded control (5415 kg/ha). Unweeded control resulted in significantly lower grain yield (634 kg/ha) and straw yield (943 kg/ha). Application of oxyfluorfen fb HW at 30 DAS resulted in higher N uptake by rice at all stages of observation and higher P uptake at harvest. At 30 DAS, application of pyrazosulfuron-ethyl fb bispyribac sodium resulted in higher P and K uptake by rice. At 60 DAS, the treatment brown manuring resulted in higher P uptake and application of oxyfluorfen fb bispyribac sodium resulted in higher K uptake by rice. At harvest, application of pyrazosulfuron-ethyl fb HW at 30 DAS resulted in higher K uptake by rice. Less N, P and K removal by weeds was observed in treatments oxyfluorfen fb HW at 30 DAS and hand-weeded control. Brown manuring resulted in higher organic carbon and soil microbial biomass carbon. Higher soil N and P availability was recorded in plots sprayed with oxyfluorfen fb bispyribac sodium and higher soil K availability was in pyrazosulfuron-ethyl on 6 DAS fb HW at 30 DAS. Application of oxyfluorfen 23.5 EC @ 0.15 kg/ha on the day of sowing fb HW at 30 DAS resulted in higher gross return, net return and B: C ratio, which was on par with pyrazosulfuron-ethyl 10 WP @ 0.03 kg/ha on 6 DAS fb hand weeding at 30 DAS. Hence, either of these pre-emergence herbicides followed by one hand weeding at 30 DAS can be recommended for a cost effective weed management in upland rice