Abstract
In Hokuriku area, the field converted from heavy clay paddy is often wet, but most of soybean is cultivated in such fields. Soybean differentiates flower buds in the rainy season, which is from late June to mid July, and is susceptible to wet conditions in this period. Soybean (Glycine max Merr. cv. Enrei) was cultivated in the field at the initial stage of conversion from heavy clay paddy, and the effects of the wet condition and application of coated urea were investigated. Field experiments were conducted in control and wet field. The wet field (6m width field) was ditched peripherally, and the ditch stored water in the rainy season. Five types of coated urea were broadcasted at a late of 10gN/m2 before rotary tillage. The types of coated urea were 4 parabola types (40-day, 70-day, 100-day and 140-day types), and 1 sigmoid type (100-day-S). The 40-day, 70-day and 100-day types dissolved a lot of nitrogen in the rainy season. Yield and nitrogen content decreased in the wet field. Yield decreased due to the decrease of pod number, and nitrogen content decreased due to the decrease of the amount of ureide-N which is mainly derived from N2 fixation. In some cases, application of coated urea abated these wet injuries, and the effect of the 40-day, 70-day or 100-day types was remarkable. The 40-day and 100-day types increased the yield, and the 70-day type increased the amount of ureide-N. It is suggested that the nitrogen dissolved during the rainy season abated the wet injury of soybean.
