Responses of different Maturing Soybeans to Timing of Irrigation Termination

Abstract

The optimum time to stop irrigation in relation to crop maturity can directly affect the costs of soybean production, Responses of 3 maturing soybean cultivars to timing of irrigation termination were examined on a silty clay loam soil at chai Nat Field Crop Research Centre in two condsecutive years (December 1995-March 1996 and January-April 1997, The number of irrigation throughout the growing season was between 3-6 for the 1995/96 experiment (Expt I) and 2-7 for the 1997 experiment (Expt II). Total amounts of water applications were between 98-252 mm and 87-294 mm. , depending up on timing of last irrigation and cultivars used, for Expt I and Ii respectively. The responses in growth, yields and yield compo-nents of 3 soybean cultivars to timing or irrigation termination were similar in both seasons. Leaf area index, leaf area duration and crop growth rate after flowering of irrigation applied through R1 and R3 stages were smaller than that of irrigation contimued into R6 and full irrigation (FI). FI gave and average yield of 322 and 211 kg/rai for Expt I and II, which was not statisticlly significant difference with irrigation terminated at R6 stage. Irrigation terminated at R1 and R3 reduced yields up to 35 and 28%, respectively, respectively, compared to FI. Reduction in the number of pods/plant and seed size was the main factors causing lower yields of last irrigation at R1 and R3. The number of seeds/pod, however, was not significantly affected by timing or irrigation termination. SJ. 5 generally gave a higher yield than Nakhon Sawan 1 (NSD. 1) and Sukhothai 2 (ST. 2) particularly in the Expt II. NS. 1 had the greatest seed size, whereas ST. 2 and SJ. 5 produced the highest number of seeds/pod and pods/plant, respectively.