Weed management in semi-dry rice of semi-dry rice Onattukara sandy plains

Abstract

The study entitled “Weed management in semi-dry rice of Onattukara Sandy Plains” was conducted at College of Agriculture, Vellayani during 2021-2023. The objective of the study was evaluation of ready-mix pre-emergence and post-emergence herbicides for weed management and their effect on growth and yield of semi-dry rice in Onattukara region. The field experiment was carried out in farmer’s field at Onattukara Sandy Plains (AEU 3) during kharif season 2023. The experiment was laid out in RBD with eight treatments and three replications. The treatments comprised pre-emergence (PE) pendimethalin + pyrazosulfuron ethyl 787 g ha-1 followed by (fb) post-emergence (PoE) triafamone + ethoxysulfuron 60 g ha-1 (T1), PE pendimethalin + pyrazosulfuron ethyl 787 g ha-1 fb PoE penoxsulam + cyhalofop butyl 135 g ha-1 (T2), PE pendimethalin + pyrazosulfuron ethyl 787 g ha-1 fb PoE bispyribac sodium 25 g ha-1 (T3), PE pendimethalin + pyrazosulfuron ethyl 787 g ha-1 fb mechanical weeding at 25 DAS (T4), PE pendimethalin 770 g ha-1 fb mechanical weeding at 25 DAS (T5), mechanical weeding twice at 15 and 30 DAS (T6), hand weeding twice at 15 and 30 DAS (T7), and weedy check (T8). Ready-mix formulations of pendimethalin + pyrazosulfuron ethyl, triafamone + ethoxysulfuron and penoxsulam + cyhalofop butyl were used in the study. Pre-emergence herbicides were applied on the next day after sowing and post emergence herbicides were applied at 25 DAS. Mechanical weeding was done with wheel hoe weeder. The short duration rice variety ‘Bhagya’ was used in the study. Weed management practices significantly influenced the growth parametres such as plant height, number of tillers per square metre, and dry matter per hill. In comparison to other weed management treatments, treatments (T1, T2, T3, and T4) that recieved PE pendimethalin + pyrazosulfuron ethyl had taller plants and more tillers per square metre at 20 DAS. PE pendimethalin + pyrazosulfuron ethyl fb PoE penoxsulam + cyhalofop butyl (T2) recorded significantly higher plant height (64, 92, and 106 cm), more number of tillers per square metre (486, 552, and 515) and dry matter production per hill (8.08, 14.47, and 17.70 g) at 40 DAS, 60 DAS and harvest. 98 Leaf area index (LAI) was higher in T1, T2, T3, and T4 at 20 DAS. Treatment T2 resulted in higher LAI at 40 DAS (3.27) and 60 DAS (6.23). Crop growth rate (CGR) observed in T2 during 20-40 DAS (18.20 g m-2 d-1) was higher and showed an increase during 40-60 DAS (21.29 g m-2 d-1). Relative growth rate (RGR) was higher in T2 during 20-40 DAS (0.057 g g-1 d-1) than T1, T3, T4, T5, and T6. During 40-60 DAS, RGR in T2 was comparable. Weed management practices significantly influenced the yield attributes of rice. Treatment T2 resulted in higher number of productive tillers per square metre (462), greater number of spikelets (120) and filled grains per panicle (108), heavier grains per panicle (3.09 g), and the lowest sterility percentage (10.40 %). The combination of PE pendimethalin + pyrazosulfuron ethyl fb PoE penoxsulam + cyhalofop butyl (T2) resulted in significant increase in grain yield (4960 kg ha-1), straw yield (6175 kg ha-1), and harvest index (0.45). Compared to treatment T7 (hand weeded twice at 15 DAS and 30 DAS) treatment T2 exhibited about a 40 per cent increase in grain yield. Treatment T2 had the lowest weed index (0.00 %), followed by T1 (7.63 %). Highest weed index in weedy check indicated that presence of weed resulted in 56.32 % yield reduction. Treatment T2 had the lowest weed index (0.00 %), followed by T1 (7.63 %). Highest weed index in weedy check indicated that presence of weed resulted in 56.32 % yield reduction. The major weed species observed in the experimental field were categorised in to grasses, sedges and broad leaf weeds. Oryza sativa f. spontanea, Isachne miliacea Roth ex Roem et Schult, Eleusine indica (L.) Gaertn, Echinochloa colona L., Sacciolepis interrupta (Wild). Stapf, and Paspalum distichum L. were the major grasses. Cyperus iria L., Cyperus difformis L., and Fimbristylis miliacea (L.) Vahl were the major sedges. Ludwigia perennis L., Melochia corchorifolia L., Marsilea quadrifolia L. and Monochoria vaginalis (Burm. f.) C. Presl ex Kunth were the major broad leaf weeds observed in the experimental field. Weed management practices significantly reduced the absolute density of weeds. The treatments T1, T2, T3, and T4 exhibited lower absolute densities of grasses, sedges, and broad leaf weeds at 20 DAS. Whereas, T2 resulted in lower absolute density at 40 99 DAS and 60 DAS. At 40 DAS, the relative densities of grasses (34.95%), sedges (33.73%), and broad-leaf weeds (31.21%) in T2 indicating a larger proportion of grasses in total weed population. Compared to other treatments, T2 significantly lowered weed dry weight at 40 DAS (14.68 g m-2) and 60 DAS (26.14 g m-2) which resulted in higher weed control efficiency of 82.83 %, and 80.77 % at 40 DAS and 60 DAS. The treatment T2 resulted in higher nitrogen (140 kg ha-1) uptake by crop at harvest and it was on par with T1. The phosphorus uptake was highest in T2 (34 kg ha 1). The higher potassium (118 kg ha-1) uptake was recorded in treatment T2 and was comparable with T1, T3 and T4. The treatment T2 recorded lower weed removal of N, P, and K at 40 DAS and 60 DAS. The post-experimental soil available NPK were also observed to be higher in T2. The soil enzyme activity was significantly influenced by weed management treatments. Among the treatments, T2 recorded higher dehydrogenase activity at 40 DAS and 60 DAS. Urease activity at 40 DAS and 60 DAS were higher in T2 and was comparable with T1 and T3. Considering the treatments, PE pendimethalin + pyrazosulfuron ethyl fb PoE penoxsulam + cyhalofop butyl (T2) resulted in highest gross income (₹ 204488 ha-1), net income (₹ 58943 ha-1) and Benefit: Cost ratio (1.41). It could be concluded from the study that, the pre-emergence application of ready-mix pendimethalin + pyrazosulfuron ethyl 787 g ha-1 at 0-3 DAS followed by post emergence application of ready-mix penoxsulam + cyhalofop butyl 135 g ha-1 at 25 DAS can be recommended as a cost-effective weed management practice for better weed control, higher yield and net income in semi-dry rice at Onattukara Sandy Plains.