Soil hydro-thermal regimes and water use efficiency of rain-fed soybean (Glycine max) as affected by organic mulches

Soybean (Glycine max) is a commercially important oilseed crop across the world; it is also popularly used as vegetables, cookery and fodder crops in Japan. In areas with limited rainfall and high temperature, mulching can provide greater yield of rain-fed soybean by improving soil hydro-thermal regimes. However, organic mulching like rice straw and shaded newspaper being inexpensive, rapidly degradable, easy to use, and environment friendly may provide more benefits than plastic mulching. Field experiments with rain-fed soybean cultivation were done in 2015 and 2016 at Gifu University farm in Japan. The purposes were to investigate the effects of rice straw and newspaper mulching on moisture and temperature regimes of soil, soil-water consumption (SWC), soil-moisture extraction pattern (SMEP), total readily available moisture (TRAM), water use efficiency (WUE) as well as growth and yield of soybean. Mulching increased seasonal soil-moisture content with lesser fluctuations in the root zone compared to bare soil, and lowered soil temperature by 2 degrees C at 5 cm and 0.5-1.0 degrees C at 15-25 cm soil depths. Straw mulch reduced SWC by 41.8 and 13.9% in 2015 and 2016, respectively compared to bare soil; the corresponding reduction in SWC under newspaper mulch was 16.6 and 20.6%. Consequently, mulching improved WUE by 25-47% compared to bare soil. Mulching significantly (p <= 0.05) improved plant height, leaf chlorophyll content, nodulations, grain (pod) and seed numbers, biomass, and grain and seed yields of soybean compared to bare soil. Grain yield increased by 12-13% under straw mulching and 6.6-37.2% under newspaper mulching compared to bare soil. Newspaper mulch provided higher yield and WUE by maintaining lower soil temperature and SWC, and greater soil moisture compared to straw mulch. Thus, newspaper can be an alternative option to rice straw mulch for improving soil hydro-thermal regimes for rain-fed soybean cultivation.