Tradeoffs among ecosystem services and microbiome impacts associated with two cover crops for cocoa in South Sulawesi, Indonesia

Abstract

Cover crops could provide numerous benefits on cocoa farms, including promoting nutrient cycling, carbon sequestration, and active soil microbial communities. Despite growing interest in cover crops for cocoa, many knowledge gaps remain, particularly detailed species and management recommendations to maximize ecosystem services and optimize the soil microbiome in different geographies and production contexts. A field experiment was conducted in South Sulawesi, Indonesia to investigate the suitability of two potential cover crops, tropical kudzu (Pueraria javanica) and fodder sweet potato (Ipomoea batatas L. Lam), for cocoa agroforestry systems. Cover crops were terminated after 6 months due to leaf chlorosis and declining yields in 2-year-old cocoa trees, leading to an analysis of tradeoffs among supporting, regulating, and provisioning services and impacts on diversity and community composition of soil prokaryotes and fungi. Kudzu had a slight positive impact on N cycling, but both cover crops appeared to compete with cocoa for K, with lower yields in sweet potato plots. Among regulating services, cover crops tended to increase C sequestration but did not affect pest and disease incidence. Cover crop treatment accounted for a small but significant percentage of soil microbiome variation, likely driven by effects on soil pH and C, and altered the relative abundance of 155 microbial taxa. Functional-trait-based species selection and optimized management could help maximize the ecosystem services delivered by cover crops, including those mediated by the microbiome, and minimize negative impacts on cocoa productivity.