Weed management in rice: Wheat rotation by allelopathy

Rice is major crop in India and its cultivation in northwest India started 25 to 30 years ago in assured irrigation areas during the summer rainy seas on. In this region, rice-wheat rotation became most popular owing to its hi gh yields; however, these crops are highly infested by the weeds, thus farm ers use herbicides for their control. Hence, this rotation consumes a maxim um quantity of herbicides in this region, which has resulted in several pro blems (environmental pollution, human health hazards, development of herbic ide resistance in weeds). Thus, serious ecological questions about the reli ance on herbicides for weed control in this rotation have been raised. One of the alternatives to overcome these problems is with the use of allelopat hic strategies, including the use of weed-smothering crops for weed managem ent and for the sustainability of agriculture. The field, pot culture, and laboratory studies have shown that inclusion of weed-smothering crops in rotation considerably reduced the weed population in the current and succeeding crops. Early summer (April-June) fodder crop s of sorghum, pearlmillet and maize drastically smothered the weed populati on and biomass. The residual suppression effect of peralmillet also persist ed in the next crop up to 45 days. Thus, it is conceptualized that the incl usion of such summer fodder crops before the rice crop in the rice-wheat ro tation may provide satisfactory weed control in the succeeding rice crop an d may minimize the use of herbicides. Likewise, the replacement of wheat by winter fodder crops of oat and berseem (Trifolium alexandrinum) may also h elp in the control of winter weeds. Hence, further studies in this directio n may provide satisfactory weed management in rice-wheat rotation and may m inimize the use of herbicides and thereby help indeveloping sustainable agr icultural practices.