Responses of different maturing soybeans to irrigation frequency and mulching

Response of different maturing soybean cultivars to irrigation frequency and mulching was examined in two consecutive growing seasons (1993/94 and 1994/95) at Chai Nat Field Crop Research Centre (CN.FCRC) and in the 1993/94 growing season at Phitsanuloke Field Crop Experiment Station (PL.FCES). A split-split plot design with 3 replicates was used. Irrigation frequencies, 42 mm of irrigation applied after every 60 and 120 mm cumulative pan evaporation and once at 50 percent flowering (I60, I120 and IF respectively) were deployed as main plots. Sub-plots were mulching with 2 tons of rice straw and without mulching, whereas 3 different maturing soybean cultivars were used as sub-sub plots. There were no interactions between soybean cultivars, irrigation frequency and mulching in each experiment. At CN. FCRC, average seed yields were reduced by 27-30 and 43-45 percent with reducing irrigation frequencies from I60 to I120 and IF, respectively Similarly, at PL. FCES seed yield decreased by 12 and 37 percent with decreasing irrigation frequencies from I60 to I120 and IF, respectively. An average seed yield of mulching was 10-12 and 18 percent greater than that of no mulching for the experiments conducted at CN. FCRC and PL. FCES respectively. A greater yield of the higher irrigation frequencies resulted from increasing pods/plant and seed size, whereas pods/plant was the main yield component responsible for yield difference between mulching and without mulching. At CN. FCRC, the intermediate cultivar, Chiang Mai 60 gave 3-5 percent seed yield greater than the earliest cultivar, Nakhon Sawan 1 and the latest cultivar, SJ. 5 which produced no significant differences in seed yield. At PL. FCES, Nakhon Sawan 1 and Chiang Mai 60 showed no statistically significant differences in seed yield but the both cultivars attained 16-22 percent seed yield greater than SJ. 5. Nakhon Sawan 1 produced the greatest seed size but Chiang Mai 60 and SJ. 5 compensated by having higher number of pods per plant.