Effects of biochar and mulch on selected soil physical and chemical properties, nodulation, and yield of mung bean (Vigna radiata)

Abstract

The lack of high-yielding and drought-tolerant crops, declining soil fertility, and climate change limit agricultural production in semi-arid areas, which must feed a growing population. The use of biochar and mulch as soil amendments, combined with a high-yielding, drought-tolerant legume (mung bean), may have significant potential in enhancing crop productivity and food security. Despite the limited information available from the literature, the purpose of this study was to determine the effectiveness of integrating biochar and mulch in improving selected soil physical and chemical properties, nodulation, and yield of mung bean in a semi-arid area. The experiment was conducted over two seasons, early summer 2023/24 and 2024/25, at the University of Venda, experimental farm. The experiment was laid out in a Randomized Complete Block Design with three replications and 8 treatments in 4 m2 plots. The treatments consisted of biochar (0, 5, 10, and 20 t/ha) and avocado leaves (0 and 4 t/ha) in a 4 × 2 factorial combination. The soil samples collected before planting and at harvest were analysed for moisture content, bulk density, porosity, pH, exchangeable Ca2+ and Mg2+, total nitrogen, available P, and potassium. While the mung bean parameters on nodulation (number of nodules per plant, nodule fresh and dry weight) and yield attributes (number of pods per plant and number of seeds per pod) were analysed using the Minitab version 19 program. Tukey’s honest significant difference test was used for the treatment mean separations at 5% probability level. The application of biochar and mulch had no significant effect on soil physical properties (Bulk density, porosity, and soil moisture content), although soil moisture content was significantly impacted by mulch during the 2024/25 summer season. Despite the lack of significant outcomes being portrayed, all mentioned properties increased with an increase in biochar application rates, except for bulk density. Soil organic carbon, pH, and available P were significantly affected by the application rates of biochar and mulch. Biochar application at 10 t/ha was the optimal rate for soil pH and available P, which subsequently increased the number of nodules, roots, and shoot biomass at the flowering stage. Biochar and mulch had no effect on the number of pods/plants, the weight of pods/plants, the number of seeds/pods, biomass, grain yield, or the harvest index in both trials. But mulch had a significant effect on the weight of the pods/plant in the second trial, while biochar positively influenced 100-grain yield in both trials. Soil moisture content was improved by 4 t/ha of mulch application. 10 t/ha of biochar only and biochar (10 t/ha) combined with 4 t/ha of mulch resulted in improved soil conditions and crop productivity. Future studies should extend experimental periods to give biochar and mulch sufficient time to have substantial effects on soil properties, as short-term studies led to a lack of variation between the treatments on the mentioned properties in this study.