Enhancing soil quality in intensive rice cultivation through short-term growth of green manure and its incorporation combined with rice husk or its ash: a laboratory incubation study

A novel approach, i.e. mung bean was grown in paddy soil for 1 month as a pre-rice crop, which is a short but a feasible period applicable to the current intensive rice monoculture cropping system in the Vietnamese Mekong Delta. This study aimed to assess how short-term growth of green manure and its incorporation combined with rice husk or its ash impact the soil quality of sandy loam soil and silty clay soil. Four treatments, viz. soil without mung bean (control), soil plus mung bean incorporation, soil plus mung bean and rice husk of 10 Mg ha-1, and soil plus mung bean and rice husk ash of 5 Mg ha-1, were established. Different soil parameters were determined to evaluate their initial effects after incubating for 60 days. In both soils, the incorporation of mung bean significantly increased beta-glucosidase, acid phosphatase, and urease activities, as well as C mineralization compared with control. Soil labile C was increased by 15-50% by incorporation of mung bean, irrespective of the application of rice husk or its ash, compared to that in control. The highest total C and available N were found in mung bean combined with rice husk followed by mung bean with rice husk ash, only mung bean, and control. Sandy loam soil with a lower exchangeable K level showed significant improvements in the exchangeable K content with rice husk and its ash amendments. Therefore, these practices, short-term green manure planting, could offer benefits to farmers for enhancing soil quality such as enzyme activities in the intensive paddy cultivation.