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chemical weed control in direct seeded rice

Two field experiments were conducted at Ngala in the Lake Chad Basin during the 1981 and 1982 wet seasons to investigate chemical weed control in direct-seeded, irrigated rice (Oryza sativa L.). Pre-plant-incorporated, pre- and post-emergence herbicides and their mixtures were tested in replicated, completely randomized block trials. Rice variety IR 28 was drilled each season at 125 kg/ha and fertilized with N (150 kg/ha) and P2O5 (40 kg/ha). In both seasons, the post-emergence herbicides propanil + oxadiazon at 3·0 + 1·0 kg a.i./ha, propanil+fluorodifen at 1·4 + 1·8 kg a.i./ha, propanil + bentazone at 3·6 + 1·5 kg a.i./ha and propanil at 3·6 kg a.i./ha as well as thiobencarb applied pre-emergence at 5·0 kg a.i./ha controlled the weeds effectively and gave similar grain yields to that from hand-weeding twice, and significantly higher grain yield than the unweeded control treatments. Grain yields similar to those from the ‘two hand-weeding control’ were achieved also by use of the herbicide dymrone at 3·0 kg a.i./ha, either soil-incorporated pre-sowing or sprayed before weed emergence. The herbicides gave satisfactory control of the weeds, which were predominantly the broad-leaved weed Luffa echinata Roxb., together with the grasses Sorghum aethiopicum (Hack.) Rupr. ex Stapf., Echinochloa colona (L.) Link, Eleusine indica (L) Gaertn, Digitaria sanguinalis (L.) Scop., Oryza longistaminata (Chev. & Roehr.), and sedges Cyperus rotundus L. and Cyperus esculentus L. The studies indicate that effective weed control by these herbicides and herbicide mixtures are dependable alternatives to hand weeding for direct-seeded, irrigated rice cultivation in the Chad Basin area.

Present address: School of Agriculture, Tafawa-Balewa College, Ahmadu Bello University, PMB 0248, Bauchi, Nigeria.

Tolerance of two scented rice cultivars (‘CSR 30′ and ‘Pusa 1121′) to azimsulfuron was evaluated using three herbicide rates (15, 25, and 35 kg ai ha −1 ) applied at 25 DAS. The experiment was conducted at two sites (Nagla and Taraori; Haryana, India) over two years (2010 and 2011) and arranged in a split-plot design with three replications at each site. Cultivars and herbicides were randomized to the main plots and the sub-plots, respectively ( Table 2 ). Seeds were planted in the last week of June in both years. Light irrigation was provided immediately after seeding. Pendimethalin (1000 g ai ha −1 ; PRE) was applied on the 3rd day of irrigation (field capacity) as a standard PRE practice in all treatments and azimsulfuron was applied at 25 DAS. Crop was raised with recommended agronomic practices as explained above for experiment 1. Plots were kept weed-free throughout the season using hand weeding. Visual injury was recorded at 21 d after azimsulfuron application (45 DAS) with reference to non-treated weed free plot for each cultivar in the respective block. Crop was harvested manually in second week of November 2010 and 2011 from two random spots (1 × 1 m and 3 × 3 m) area per treatment for accuracy and averaged, and yield was recorded at 13% moisture.

At Taroari location, POST application of bispyribac-sodium or azimsulfuron after PRE application of oxadiargyl or butachlor or pendimethalin or tank mix of bispyribac-sodium + azimsulfuron POST provided significantly higher B:C compared to all other treatments.

2.2. Experiment 2. Evaluating rice cultivars’ tolerance to azimsulfuron

Net returns for each treatment were calculated over variable cost of production ( Table 3 ). All inputs (pesticides/fertilizers/seeds) for each site were purchased from same source. Some of the operations were same at each site and facilitated by the same contractual-operator with same price. Irrigation was provided with electric motor pump sets with fixed electricity charges. The cost of human labour used for tillage, seeding, irrigation, fertilizer and pesticide application, weeding, harvesting and threshing of crops was based on actual cost to farmers and were estimated considering total acreage and person-hours. Similarly, the time required by a tractor-drawn machine/implement to complete a field operation such as tillage, seeding, and harvesting was recorded. Cost of such field operation was calculated by using time required by such operation, diesel consumed per unit time and market price of diesel. All these costs were summed up to calculate total variable cost of production. Sale price of ‘CSR-30′ was averaged over 2 locations to avoid any bias as sale price depends upon open market demand, local timing, and competition. Prices were estimated with average Dollar (US) -Rupee (INR) exchange rate in 2010 ($1 = 45.68).

Maximum numbers of effective tillers (398-446 m −2 ) were observed in the weed free treatment and as expected, minimum numbers of effective tillers (112-162 m −2 ) were recorded in non-treated weedy plots across the locations. The number of effective tillers m −2 were 375, 372, 368, and 363 with the sequential application of pendimethalin PRE fb bispyribac + azimsulfuron POST, pendimethalin PRE fb bispyribac-sodium or azimsulfuron POST, and oxadiargyl PRE fb bispyribac-sodium POST compared to 326, 307, and 112 with single application of oxadiargyl PRE, bispyribac-sodium POST and nontreated control, respectively, at Madhuban ( Table 7 ). However, at Taraori, maximum number of tillers m −2 were observed with pendimethalin PRE fb either azimsulfuron or bispyribac-sodium or azimsulfuron + bispyribac-sodium POST ( Table 8 ).

The sequential applications of PRE fb POST herbicides provided better weed control and resulted in higher grain yield compared to single application of either PRE or POST. However, the single application of bispyribac-sodium POST resulted in higher grain yield compared to oxadiargyl PRE at both the locations.

Crop growth and yield were enhanced by butachlor 1.2 + 2,4-DEE 1.5 lit ha -1 with 100% inorganic nitrogen.

Stale bed preparation by pre-puddling minimum tillage with glyphosate combine with post-plant pre emergence butachlor 1.25 kg ha -1 resulted in increased rice grain yield, net income and B: C ratio in rice-rice cropping.

Integrated weed management

Butachlor (1-2 kg ai/ha)
Alachlor (1-2 kg ai/ha)
Thiobencarb + 2, 4D
Isopropyl (0.75) ester (0.5 kg ai/ha)
Metsulfuron methyl (20 WP) (0.008 kg ai/ha)
Benthiocarb (1.5 – 2.5 kg ai/ha)
Propanil (2-3 kg ai/ha) (only post emergence)

In wet seeded rice, sowing with drum seeder and cono weeding (manual / power weeder) is done at 10, 20 and 30 DAS