Survey of Wet and Dry Stress in Soybean in Japanese Farmers' Fields using Dry and Wet Indices Based on FAO56 Model

Abstract

Major factors that decrease soybean yields in Japan include excessive soil moisture and drought stress. In the present study, a WI (Wet Index) was developed using soil moisture estimates based on the FAO56 model to evaluate both risks of soil dryness and wetness. In addition, to assess the risk of wet losses, the days when ratio of WI was equal to one (RWI), which implied that soil moisture content reached a maximum, was adopted for every growth stage. When the relationship between WI or RWI and yield was evaluated using a partial correlation coefficient, WI had a positive correlation with emergence period approximately 30 -40 days after emergence, seed filling phase, and maturity phase, and RWI had a negative correlation with emergence period approximately 20 -30 days after emergence and approximately one week before flowering period. We evaluated moisture and drought stress risks, which present challenges in farmers' fields, and revealed the growing stages at which moisture and drought pose the highest risks. The results could offer critical insights for the estimation of dryness and wetness losses in the field.

Breeding of Rj Gene-Accumulated Soybean Genotypes and Their Availability for Improving Soybean Productivity

“…While the yield of "Sachiyutaka" decreased significantly, that of B × F − E, B × F − M, B × F − L, "Enrei," and "Fukuyutaka" tended to decrease, albeit without significant differences. "Enrei," "Sachiyutaka," and "Fukuyutaka" are soybean cultivars that are suitable or possible to cultivate in the Chugoku region of Japan, including Shimane prefecture, where the cultivation test was conducted in the present study [51,52]. Additionally, pod and seed numbers are the most important soybean yield components, which are primarily determined during the period from before and after flowering to pod set, including the beginning of the seed filling period [53].…”