Development of a Method for Scoring Early Growth in Soybean Based on the Leaf Area Development Model

Abstract

Delayed early growth, mainly due to excess water stress, can be a critical cause of low soybean yield in Japan. However, effective treatment for improving early growth, such as drainage improvement, would be difficult to conduct in all the fields, especially in those covering hundreds of hectares of land. Under such situations, the sowing date can differ among fields and the plant population may vary with the number of deaths. Therefore, we aimed to develop a method for scoring early growth in soybean available under different sowing dates and plant populations. First, the parameters of the leaf area model in a cultivar ‘Ryuho’ were acquired from the cultivation at 3 planting densities and 4 sowings, which enabled calculation of leaf area based on the accumulated temperature. The growth score was calculated as the ratio of the remotely-sensed leaf area to the values calculated from the leaf area development model. Second, the formula for calculating days from sowing to the start of the leaf area model was acquired from the experiment of 5 sowings. Finally, the relationship between the growth score and final grain yield was evaluated in the actual farmer’s field, where there was a significant correlation (r = 0.70, p < 0.01). Adjustment of our method to other cultivars, locations, and cultivating methods is a future task for realizing stable production of soybean in the farmer’s fields.