Performance of New Herbicides on Productivity and Profitability of Aerobic Rice

Field experiment was conducted at

About 50 per cent of the world rice production area is affected by drought stress.When soil water content drops below saturation, yield losses occur, as rice is susceptible to drought (Bouman and Tuong, 2001).Aerobic rice is a new way of cultivating rice that requires less water than lowland rice.It entails the growing of rice in aerobic soil, with the use of external inputs such as supplementary irrigation and fertilizers and aiming at high yields (Wang et al., 2002).Aerobic soil conditions and dry tillage practices, beside alternate wetting and drying conditions are conductive for germination and growth of highly competitive weeds, which cause grain yield loss of 50-91 per cent (Singh et al., 2006).The labour requirement for weeding is a major impediment to the adoption of water saving aerobic rice and for increasing the productivity of traditional upland rice based cropping systems (Zhao et al., 2006).Herbicides are considered to be an alternative / supplement to hand weeding (Singh et al., 2006).In this background, this study was planned with the following objectives.To find out efficacy of new herbicides on weed control and growth and yield of aerobic rice.

Weed flora
The weed flora observed in the experimental field during the course of study consisted of grasses, sedges and broad leaved weeds.The predominant category of weed was broad leaved weeds followed by grasses and sedges.Grass density was significantly reduced by post-emergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS (T6) significantly to 16.0 m2.This was followed by sequential application of pre-emergence oxyfluorfen and post-emergence 2, 4-D on 30 DAS (T10) and post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9) with grass density of 18.67 and 22.00 m-2, respectively.But, treatment T9 was comparable with post -emergence bispyribac sodium alone on 20 DAS (T8).Sedge weed density was zero in postemergence application of bispyribac sodium alone on 20 DAS (T8) as well as sequence application of pre-emergence oxyfluorfen and post-emergence 2, 4-D on 30 DAS (T10).This was followed by postemergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS (T6) and post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9) which recorded sedge weed density of 1.00 and 2.33 m-2, respectively.
Post-emergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS (T6) significantly lowered the total weed density to 18.00 m-2.This was followed by sequence application of pre-emergence oxyfluorfen and post-emergence 2, 4 -D on 30 DAS (T10) and post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9).But post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9) was comparable with post -emergence bispyribac sodium alone on 20 DAS (T8).Post-emergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS (T6) significantly increased the WCE.It might be due to the use of mixture of herbicides which showed broad spectrum control of weeds.This is evident from earlier result that lower grass weed density and dry weight were obtained by fenoxaprop-p-ethyl 6.9 % EC from 47.44 to 60.38 g ha-1 (Mallick et al., 2009).Another result with metsulfuron-methyl + chlorimuron-ethyl at 4 g ha-1 provided excellent control of broad-leaved weeds and sedges (Singh and Tewari, 2005).
Post-emergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS (T6) provided a broad spectrum of weed control by significantly reducing the dry weight of grass, sedge, BLW and total weeds at 60 DAS.This weed management practice (T6) was followed by sequential application of pre-emergence oxyfluorfen and post-emergence 2, 4-D on 30 DAS (T10) and post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9).These treatments were found to be superior compared to farmers' practice of hand weeding twice and test chemical of pre-emergence application of pretilachlor (Table 1).

Grain and straw yields
The economic yield in the single usage of herbicide treatments were found superior to farmers' practices of hand weeding twice and test chemical pre-emergence application of pretilachlor alone.Postemergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9) recorded significantly higher grain and as straw yield (Table 1).The treatment post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9) recorded additional grain yield of 1770, 1933 and 2535 kg ha-1 compared to farmers practice, postemergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS (T6) and pre-emergence application of pretilachlor alone.This showed the superiority of the treatment T9 over all other common weed management practices of direct seeded rice.It might be due to the broad spectrum weed control, reduced weed growth and higher weed control efficiency at early stage crop weed competition caused by the mixture of herbicides.Similar results were also noticed with fenoxoprop at 0.06 kg ha-1 mixed with ethoxysulfuron at 0.015 kg ha-1 as post emergence produced significantly higher grain yield (Tiwari et al., 2010).

Economics
The economic evaluation of results indicated that post emergence mixture of fenoxaprop + ethoxy sulfuron on 30 DAS (T9) registered higher gross return (Rs.50915 ha-1), net return (Rs.28281 ha-1) and B:C ratio (2.25) (Table 1).This promising weed management treatment (T9) recorded additional gross return of Rs. 14205 ha-1 and net return of Rs. 17830 ha-1 compared to farmers' practice of hand weeding twice.This was achieved by way of effective, long term and timely broad spectrum control of weeds by these mixtures of herbicides which prevented the crop weed competition.As a result more uptake of nutrients and more crop growth resulting in higher grain yield were obtained in the above promising weed management practices.This was followed by post-emergence bispyribac sodium alone on 20 DAS (T8) and post-emergence azimsulfuron alone on 20 DAS (T7).Similarly, this treatment (T9) recorded additional gross return of Rs. 20300 ha-1 and net return of Rs. 20087 ha-1 compared to recommend pretilachlor -S alone (T2).Because in the later treatment (T2 ) only one chemical i.e. pretilachlor -S was used as pre emergence on 0-5 DAS without any follow up chemical or weeding.The farmers' practice of hand weeding twice registered higher cost of cultivation (Rs.26258 ha-1) and lower net return (Rs.20758 ha-1) as well as B:C ratio (1.79) which was probably due to higher labour cost involved for hand weeding twice.This is in line with Saha et al. (2005) who stated hand weeding as cost prohibitive method.It is concluded that post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS (T9) in aerobic rice is the appropriate weed management practice to control broad spectrum of weeds and to achieve higher productivity and economic returns in rice.