Studies On Ecology And Biology Of Red Sprangletop [Leptochloa Chinensis (L.) Nees] And Its Management In Direct Seeded Rice

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Date
1997-03
Authors
Pane, Hamdan
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Abstract
Studies on the ecology and biology of red sprangletop [Leptcx;hloa chinensis (l.) Nees] and its management in direct seeded rice were conducted at the laboratory and the greenhouse of the School of Biological Sciences, Universiti Sains Malaysia' (USM), Penang. Field surveys in the Muda ricefields and field trials at Alar Serdang, the Training Farm of Muda Agriculture Development Authority (MADA), Kedah, were also carried out. Ecological studies from the survey conducted in 1994 showed that the whole Muda ricefieldwas infested by 12 dominant weeds. The most dominant weed species was L. chinensis which heavily covered 75% of the sampling sites. From soil seed bank study, ten common weed species and seven other weed species which had relatively low numbers of seed emergence were recorded. The total viability of seeds germinated from the soil was about 29,551 seeds' m2 and it comprised 26.9% of L. chinensis seeds. From life-table study, under treatment of. 135 kg N ha-1 the total seed production from all survival adult individuals was 1,6 x 106 seeds. This value was 2.4 times higher than the total production of seeds from all survival individuals without nitrogen (0.67 x 106 seeds). Under substitutive competition with replacement series experiment, based on Relative Yield Total (RYT) value, growth characters and dry weight of straws were greater than 1.0. Ecologically, the values showed that both species were trying to avoid competition, indicating that there was no significant aggressiveness of red sprangletop competition against rice crop. The populations of red sprangletop collected from Muda area and Balik Pulau did not show much morphological differences. L. chinensis has three groYw1h stages; first. slow growing stage [within the first 3 weeks after emergence (wae)]; second, active growing stage (3 to 9 wae) and finally, maximum growing stage (9 to 15 wae). M uda populations produced 0.95 x 105 to 1.09 x 105 seeds and Balik Pulau populations produced 0.21 x 105 to 0.73 x 105 seeds, respectively. An additive competition trial 'indicated that the rice yields declined significantly when the rice plants competed with the weed at a density of 16 plants per-m2 and yield decreased as the weed population increased. Evidently, the critical period for controlling red sprangletop in direct seeded rice was initiated from 2 to 4 wae. From a management aspect. the species could be suppressed with the flooding from 2.5 to 5.0 cm water depth at 0 and 7 days after emergence·(dae). Different rates of nitrogen were tested and the results showed that the competition of red sprangletop in rice caused 39-48% yield reductions, irrespective of nitrogen level. Nitrogen absorbtion by red sprangletop ranged from 0.03 to 0.13 g per-plant (4.0 to 21 kg N ha"1). Propanil and thiobencarb separately or mixed as an earty postemergent herbicide controlled red sprangletop effectively. Foliar application of fenoxaprop-P - ethyl proved to be the best among all tested herbicides.
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Red Sprangletop [Leptochloa Chinensis (L.) Nees] , Seeded Rice
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