Nature of Competition between Weeds and Rice for Nitrogen Under Dry Land Conditions

Abstract

The nitrogen content of weeds was significantly higher than that of Dular rice-straw, but with Taichung Native i rice in winter there was no significant difference between the nitrogen in weed samples and rice plants at the tillering stage. Rice straw contained a higher proportion of nitrogen where there were three hand weedings. The total dry matter of rice was much reduced by weed competition. Weed species contained much nitrogen at the vegetative, flowering and post-flowering stages, indicating severe competition for nitrogen by weeds throughout the growth of rice under dry land conditions. Competition between cereal crops and weeds is principally for nitrogen in years of normal rainfall, with the most intense competition in the early stages of crop growth (Blackman and Templeman, 1938), though Singh and Singh (1939) found that maximum uptake of nitrogen by weeds occurred at the pre-flowering stage. Legumes are generally rich in nitrogen, but Campbell (1924) observed that of all the weeds examined under average field conditions, Amaranthus retrojlexus. L. (pig-weed) contained the highest proportion (3-7 per cent) of nitrogen. Asana (1951) reported the uptake of 19-5 kg. nitrogen/ha, by wheat (Triticum aestivum L.). Mukhapadhyay and Verma (1967), conducting crop/weed competition trials for wheat, stated that the elimination of weed competition at the early stage of the crop (first 4 weeks) led to higher uptake of nitrogen and heavier yields of wheat compared with later weeding at 6 weeks from sowing. The present experiment was therefore undertaken to study the extent of weed/rice competition under different weed control methods in relation to nitrogen. MATERIALS AND METHODSThe field trials were conducted at the Sriniketan Farm, Visva-Bharati, in laterite sandy loam soil at pH 5-5-6-O. The soil had 0-038 per cent nitrogen and 0-3 per cent organic carbon, and was poor to very poor in phosphate. The trials were conducted with various combinations of chemical and mechanical methods of weed control in the rainy (kharif) season of 1967 and 1968 on autumn rice, variety Dular (a photo-insensitive, short-duration (90 days) upland rice variety of West Bengal) under dry upland conditions. There were twelve treatments (Tables 1 and 2) replicated three times in a randomized block design. In 1968 a similar experiment was repeated except that the MCPA, MCPA -f MCPA, MCPA + one hand weeding and 2,4-D treatments were omitted because of poor results in 1967,

Response of transplanted rice to nitrogen fertilization under different weed management practices

“…Weeds can grow faster than crop plants, and thus take a lead in absorption of available nutrients, resulting in poor nutrition of crop plants. Usually nitrogen is the first nutrient to become limiting as a result of crop-weed competition (Chakraborty, 1973). Accordingly nitrogen fertilization has been found to compensate for yield losses from poor weed control in some circumstances but at the same time it proportionately increases the growth of weeds (Singh et a/., 1975;Okafor and De Datta, 1976;Kakati and Mani, 1977), and in heavily weed-infested fields, fertilization of rice crops can depress yields due to competition for light (IRRI, 1973;De Datta ef a/.. 1969;Pande and Bhan, 1966).…”