Soil Biodiversity and Litter Decomposition in Agroforestry Systems of the Tropical Regions of Asia and Africa

Abstract

This chapter gives an overview of the agroforestry practices and their role in improving soil biodiversity, soil ecosystem functions and services, and litter decomposition processes in the agroforestry systems of sub-Saharan Africa and Asia. Agroforestry covers a complex set of practices, and for brevity, we follow the broad categories of agrisilvicultural, agrosilvopastoral, and silvopastoral systems. We discuss the diversity of soil fauna and microorganisms, which are found in the surface layer of soil, and underpin a wide range of soil ecosystem services that are essential to the sustainability of agroforestry systems. The increase in the diversity of soil macrofauna, soil microbial biomass, and microbial diversity in agroforestry systems is due to the ameliorative effects of trees, and greater organic matter inputs with variable litter quality. The improved micro-climate and a higher supply of organic residues generate higher earthworm diversity in tree-based systems. Moreover, a mix of plant species in agroforestry systems allows a larger diversity and abundance of mycorrhizal fungi than monocultures. Through synthesisSynthesis of several studies, we show that the diverse plant communities and structures can modify the important soil functions and with possible feedback to the above- and below-ground components of both trees and crops. Studies evaluated provisioning, regulation and maintenance, and cultural servicesCultural services provided by soils; several reviews and meta-analysis indicate the beneficial impact of agroforestryAgroforestry on soil ecosystem servicesSoil ecosystem services including soil conservationSoil conservation, storage and cycling of nutrients, increasing infiltration rateInfiltration rates and soil moistureSoil moistures content, improving soil biological quality, controlling diseases and pests, and sequestering atmospheric carbon dioxide. The decomposition of litter in agroforestryAgroforestry system differs from that of natural forests and agricultural systems because of differences in the types and quality of organic residueOrganic residues inputs. We synthesized the literature on litter decomposition ratesLitter decomposition rates, mathematical models describing the pattern of litter decay, resource quality of litter, and the nutrient release patternsNutrient release patterns from decomposing litter in different types of agroforestryAgroforestry systems. In most studies, the single exponential mathematical model described the pattern of litter decomposition and nutrient release. The decomposition rate constantsDecomposition rate constants (k = 0.37–8.92 year−1) for various litter species are found to be highly variable and often related to litter qualityLitter quality and climatic conditions. The tree species in both traditional and modern agroforestry systemsModern agroforestry systems having a combination of low- and high-quality litter show a highly variable nutrient release patternNutrient release patterns from the decomposing litter. AgroforestryAgroforestry systems are highly efficient in improving soil biodiversitySoil biodiversity and litter decomposition processes leading to increase in the crop yield and sequestration of atmospheric carbon dioxide. However, there is a need for long-term studies on diversity of soil faunaSoil fauna, microorganisms, and litter decomposition for a better understanding of seasonal, short-term, and long-term effects of agroforestryAgroforestry practices.