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Dolomite [CaMg(CO3)2] is used widely for soybean, Glycine max (L.) Merr. production in Japan to amend soil pH, although magnesium (Mg) in the dolomite can inhibit soybean growth and yield. The aim of this study was to determine the effect of Mg on soybean production in a paddy – upland rotation field in 2019–2020 by comparing the application of dolomite and calcite (CaCO3). The field test included three replications with three lime applications: control (no lime), dolomite, and calcite. The amounts of calcite and dolomite applied in each year were 253 and 259 g m−2, respectively. The soil pH was almost similar following the applications of calcite and dolomite, whereas the soil exchangeable Mg content was higher following the dolomite application than following the other applications. The shoot weight from the flowering stage to the harvest stage (R8) was significantly higher following the calcite application than following the other applications. However, the shoot weight at only R8 was significantly higher following the dolomite application than following the control application. In 2019–2020, the highest soybean yield was resulted from the calcite application (355 g m−2) followed by the dolomite application (312 g m−2) and the control application (260 g m−2). The severity of soil-borne diseases was lower following the dolomite application than following the control application, and even lower following the calcite application. Thus, the application of dolomite increased soybean yield by improving soil pH; however, Mg in the dolomite inhibited a further increase in soybean yield in a paddy – upland rotation field. [ABSTRACT FROM AUTHOR]

There have been few studies in Japan on the effects of the application of lime materials, especially in regard to the soil calcium-to-magnesium ratio (Ca:Mg). The aim of this study was to explore the effects of changes in the soil Ca:Mg on soybean growth via pot and field tests over two growing seasons: 2018–2019. The field tests were conducted in two different fields, one in each year, and the soil for the pot tests in both years was collected from the respective fields used in the field tests. In the pot test from 2018 to 2019, we adjusted the soil Ca:Mg ratio and soil pH using Ca(OH)2 and CaSO4, with three conditions: control (pH = 5.2, Ca:Mg = 1.3), CaMg (pH = 5.0, Ca:Mg = 2.6), and CaMg + pH (pH = 5.7, Ca:Mg = 2.4). Moreover, we added two further conditions for the pot test in 2019: CaCO3 (pH = 5.9, Ca:Mg = 1.8) and dolomite groups (pH = 6.4, Ca:Mg = 1.3). In the field test, we adjusted only the soil Ca:Mg ratio using phosphogypsum and had two conditions: control (pH = 5.0, Ca:Mg = 1.1) and gypsum (pH = 4.7, Ca:Mg = 1.9). In both tests, the application of Ca except for dolomite contributed to the increase in the concentration and uptake of Ca both in the whole plants and some parts of the soybean plants. Likewise, application of Ca except for dolomite contributed to a significant increase in the total number of pods. The weight of seeds and the total dry weight in the CaMg + pH and CaCO3 groups and in the gypsum plot were significantly higher than were those in each control group. Thus, the study suggests that the Ca:Mg ratio in soils with a low Ca:Mg ratio may limit soybean growth to a greater extent than does the soil pH. However, the effect of the interaction between the soil Ca:Mg ratio and soil pH on dry-matter production of soybeans was different between the pot and field tests, and further studies were needed to clarify the discrepancy. [ABSTRACT FROM AUTHOR]