Exploration of Agronomic Efficacy and Drought Amelioration Ability of Municipal Solid-Waste-Derived Co-Compost on Lettuce and Maize

Organic soil amendments, such as composts, mitigate the negative impacts on the environment that are caused by poor waste management practices. However, in the sub-Saharan African region, and Malawi in particular, studies investigating the agronomical efficacy and their ability to ameliorate drought stress when used as a soil amendment are minimal. This study aimed to evaluate the efficacy of sewage sludge and municipal solid waste (MSW) co-compost to ameliorate drought stress and improve crop productivity. Three experiments were conducted (i) to determine optimal application rate for co-compost, (ii) to evaluate yield response of maize and lettuce to co-compost application under contrasting soils, and (iii) to assess the effect of co-compost under water-limited conditions. Our results indicate that an application rate of 350 g co-compost per station was the most effective. This rate is 50% and 37% lower than the currently recommended rate for applying conventional compost to green vegetables and maize, respectively. In addition, under drought conditions, the co-compost application enhanced growth in lettuce, with less wilting, increased biomass and yield, approximately 130% greater leaf yield, and a 138% improvement in root growth. Furthermore, the relative root mass ratio (RRMR) was enhanced with the co-compost application by 103% under drought stress. This suggests that the co-compost amendment resulted in a greater allocation of biomass to the roots, which is a crucial morphological attribute for adapting to drought conditions. The concentration of K in the leaves and roots of plants treated with co-compost was significantly increased by 44% and 61%, respectively, under drought conditions, which may have contributed to osmotic adjustment, resulting in a significant increase in leaf relative water content (RWC) by a magnitude of 11 times. Therefore, in light of the rising inorganic fertilizer costs and the limited availability of water resources, these results demonstrate the potential of MSW and sludge co-composting in ameliorating the drastic effects of water- and nutrient-deficient conditions and optimizing growth and yield under these constraining environments.