Effects of two types of mulch on evapotranspiration, dry matter, and water use efficiency of soybean under different soil water content

Application of mulch is one technique to save water consumption and increase crop production. This study aimed to clarify effects of mulches and soil moisture conditions on biomass production, actual evapotranspiration (ET), and water use efficiency (WUE) of soybean [Glycine max (L.) Merr.]. Soybean was planted in clay pots with living mulch of white clover (CL) and shredded paper mulch (SP). Soil water content (SWC) in the pot was individually controlled at five levels by manual irrigation. The measured plant height, LAI, and the dry matter of the soybean were largest in the higher SWC with CL, and in the moderate SWC with SP, while the plant height of the clover in CL was higher in the lower SWC. The plant height, LAI, and the dry matter of the soybean were larger with SP compared with CL mostly in all SWC levels especially after the vegetative stage. The measured ET was significantly larger with CL compared with SP mostly in all SWC levels, e.g., the average ET in the whole period was 2.59 and 3.64 (mm/d) under the second wettest SWC level (33.6% and 33.4% in average) in SP and CL, respectively. One reason was considered as transpiration by the clover in CL. Another reason was the effect of reducing soil surface evaporation by SP that was demonstrated by the smaller ET in SP compared with measured evaporation from the bare soil pot particularly in the lowest SWC. The highest WUE for seed with SP (0.115 mg/g) was in the lowest SWC, while it was in the highest SWC with CL (0.035 mg/g). This study suggested that shredded paper mulch was effective for water saving cropping system with larger WUE compared with clover living mulch by a synergistic effect of the better growth of the soybean and the smaller ET.