Studies on Crop-Weather Relationship of Soybean

Abstract

In order to obtain the method to predict the developmental stage of soybean crop, relationships among a developmental rate, daylength and daily mean air temperature were investigated during the period from seeding to flowering. Three plots with respective daylength of 13.3, 14.3 and 15.3 hours were set under field conditions. In each plot 6 cultivars of soybean were seeded on 6 different dates (from May 10 to July 19 with 2-week intervals in 1985). Results obtained were as follows.(1) The mean developmental rate from seeding to flowering was linearly related to air temperature for each cultivar of each controlled daylength level. Linear regression equations for the relationships between the developmental rate and air temperature were obtained for 6 cultivars and shown in Table 1.(2) The regression lines shifted with the decrease of daylength, and consequently revealed the increase of the developmental rate (Fig. 2). The differences in their slopes were very little among the cultivars and/or the daylengths examined. The differences in a seeding-to-flowering period among cultivars were analysed in terms of the changes in regression lines, and we confirmed that they were due to difference in sensitivity to daylength.(3) Our results show that the developmental rate method proposed here predict accurately the flowering stage of soybean crop (Fig. 3).(4) Within a limited region and season, where the close correlation between daylength and daily mean air temperature is observed, the developmental rate of soybean can be calculated as a unique function of temperature. However, this simplified method, hitherto used, should not be applied to the case out of the range of the observed data.