Effects of mulching on water use efficiency and nutritional composition of three underutilized crops in Mpumalanga Province.

Abstract

African agricultural systems are particularly vulnerable to changing climatic conditions, with water scarcity posing a major constraint in Sourthen Africa. Within this context, water scarcity in Sourthen Africa is projected to intensify, resulting in more financial and physical limitations as early as 2025. Projected climatic shifts are expected to intensity drought conditions and resource scarcity, particularly in regions with existing limitations, such as South Africa. In addition, as Africa's population grows, food demand is increasing daily. Underutilized legume crops play an essential role in climate resilience, thriving in extreme conditions (low soil fertility, drought, high temperature), and they have the capability to enhance soil health and boost food production. It is therefore vital to cultivate underutilized legume crops that survive under harsh conditions. In addition, animal protein is getting expensive for livelihoods with low incomes. The adoption of underutilized legume crops provides a highly important contribution strengthening the resilience of global food systems under increasing environmental and nutritional pressures. Therefore, legumes such as those that incorporate cowpea, Bambara groundnut, and common bean are one of the food sources that can help fulfil the sustainable goal of offering enough essential nutrients. Despite their high nutrient density, they have also been reported to have the capacity to improve soil fertility via the fixation of atmospheric nitrogen. However, these crops are not widely cultivated, and information remains vacant regarding their cultivation implementation. Previous literature demonstrates significant gaps: the impacts of various mulching treatments on the growth performance of underutilized legume crops are not well documented; furthermore, it is unclear how mulching affects symbiotic nitrogen fixation. Therefore, this study assessed the effects of mulching on the growth, symbiotic fixation of nitrogen, and nutritional composition of the previously mentioned crops above. To conduct the experiment, three underutilized legume crops such as bambara groundnut, common bean and cowpea were assessed under three mulching regimes (no mulch, plastic mulch, and pine bark mulch) using a randomized complete block design with four replications. The study set up was performed at the University of Mpumalanga, and standard cultivation practices (such as irrigation and weeding) were followed. Data was subjected to ANOVA using STATISTICA version 12.0. Regardless of the mulching material employed, data on cowpeas had the maximum plant height and chlorophyll content, common bean and Bambara groundnut under plastic mulch and pine bark, respectively, followed next. Collectively as a whole, the results of this study showed a strong association between δ¹³C, WUE, and dry matter, which are closely linked, as they are all regulated by carbon assimilation and stomatal control, this regulates water loss as well as CO2. Pine bark mulch substantially influences plant growth. In addition, cowpea-pine bark mulch (623.3 mg/100g) and common bean-plastic mulch (604.6 mg/100g) had a strong positive effect on potassium levels. Pine bark mulch (PBM) significantly improved the nutritional composition, particularly in minerals and vitamins. Interestingly, no mulch treatment resulted in the highest B carotene content of Bambara groundnut (53.5 mg/100g) and cowpea (49.4 mg/100g), suggesting that some nutritional traits may benefit from un-mulched conditions. The overall results demonstrate that all three legumes actively fixed atmospheric nitrogen and accumulated significant amounts of nitrogen in their tissues, despite variations in total N content due to differences in biomass and specific unit variations. Mulching significantly improved plant growth, nutritional composition of the underutilised crops investigated, and nitrogen fixation. This implies that by enhancing soil conditions, mulching promotes growth and nutrient uptake. This leads to higher yields of more nutritious, protein-rich legumes that strengthen food security, particularly for communities facing challenging environmental conditions. The findings of this study demonstrate that mulching positively influenced plant growth and nutritional composition of the underutilized crops investigated. This implies that by enhancing soil conditions, mulching promotes growth and nutrient uptake. Overall, the results demonstrate that mulching treatments played a vital role in promoting plant growth by improving soil microclimatic conditions, which in turn promoted greater carbon assimilation and stimulated biological nitrogen fixation, thereby contributing to improved nitrogen accumulation and biomass production in the legume crops.