Timing of irrigation termination for 3 soybean cultivars in silty clay loam soil
1996
wanchai Thanomsub | Somchai Boonpradub | Santi Promkum | Anat Watanasit | Somyot Pichitporn | Thewa Maolanont (Department of Agriculture, Bangkok (Thailand). Field Crops Research Inst. Chainat Field Crops Research Center)
Optimum time to stop irrigation in relation to crop maturity can directly affect the costs of soybean production, particularly in the dry season. Responses of 3 soybean cultivars differing in maturity to timing of irrigation termination were examined on a silty clay loam soil at Chai Nat Field Crops Research Center between Dec. 1995 and Mar. 1996. The number of irrigation throughout the growing season was between 3 and 6, and total amounts of water applications were between 98 and 252 mm, depending upon timing of last irrigation and cultivars used. The responses in yields and yield components of 3 soybean cultivars to timing of irrigation termination were similar. LAI, LAD and CGR after flowering of irrigation applied through R1 and R3 stages were smaller than that of irrigation continued into R6 and full irrigation (FI). FI gave an average yield of 322 kg/rai, which was not statistically significant different with irrigation terminated at R6 stage. Irrigation terminated at R1 and R3 reduced yields up to 35 and 28 percent, respectively, compared to FI. Reduction in the number of pods/plant and seed size was the main factors causing lower yields of final irrigation at R1 and R3. The number of seeds/pod, however, was not significantly affected by timing of irrigation termination. There were no significant differences in yields among cultivars. Although, NS1 and ST2 produced smaller number of pods/plant than SJ5, they compensated by increasing the number of seeds/pod. NS1 had the greatest seed size, whereas ST2 and SJ5 produced the highest number of seeds/pod and pods/plant, respectively.
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