EFFECT OF CRITICAL WEED COMPETITION PERIOD ON YIELD AND FIBER PROPERTIES OF COTTON (Gossypium barbadense, L.) IN NEW LANDS

Abstract

Two field experiments were conducted in a highly calcareous sandy clay loam soil at Nubaria Agric. Res. Station, Agric. Res. Center, Behera Governorate, Egypt during 2012 and 2013 seasons. The objectives were to study the effect of critical weed competition period on plant growth, seed cotton yield, its components and fiber properties of the Egyptian long-staple cotton cultivar Giza 86. The experimental design was a complete randomized block design with four replications. Each experiment included fourteen treatments in two groups, the first group included seven weed-free periods which were weed-free for the 3, 6, 9, 12, 15, 18 weeks from sowing and weed-free for the whole season, respectively, and the second included seven weed competition periods which were weed competition for the 3, 6, 9, 12, 15, 18 weeks from sowing and weed competition for the whole season, respectively. Results indicated that the fresh weight (g/m 2 ) of broad leaf weeds, grassy weeds and total annual weeds decreased by 93.1, 93.7 and 93.3%, respectively, with increasing weed removal periods to 18 weeks from sowing as compared with weed competition for the whole season treatment. Also, the effect of weed removal and weed competition periods were not statistically significant on position of 1 st sympodial node, no. of open bolls and no. of non open bolls/plant, where as the effect was statistically significant on the plant height, no. of sympodial branches/plant and no. of monopodial branches/plant. Weed competition for the whole season reduced seed cotton yield per feddan by 41.1% as compared with weed-free for the whole season. The results showed that the critical period of weed competition to cotton crop start 3 weeks after planting and continue until 18 weeks from planting and the critical competition point where yield losses from early or late competition after 15 weeks from planting were equal. From these results, weed control strategies in cotton should be done through 3-18 weeks from planting and cotton can be considered as week competition for weeds especially in the earlier periods of growth, which extend to the fifteen week from planting. All fiber properties were not affected significantly by weed removal and weed competition periods, except fiber strength.