Interaction Between Belowground and Aboveground Resources in Tree-Crop Systems

Agroforests are intricate systems whose management relies on copious interactions among their components. Complex interactions between trees, crops, soil, and climate have a significant impact on the productivity of agroforestry systems. The system’s overall sustainability and yield are determined by its management and the harmony between positive and negative interactions. Intercropping of agricultural crops together with trees results in a number of changes through time and geography, mostly in response to environmental factors, biophysical interactions, and management choices (e.g., spatial-temporal selection). The essence and scale of interactions in agroforestry systems operate at the tree–crop interface (TCI) and soil–root interface (SRI). Ecologically, there exists complementarity when the relationship between the two is positive or synergistic, supplementary when the effect is neutral, and competitive when the interaction is negative or antagonistic. The selection of tree species is a crucial management action that affects the resource use between tree and crop components. Trees show either interference (shade effect, root competition, allelopathy, host for pests) or facilitation (nutrient pumps/safety nets, bio irrigators, mulch/litter production, amelioration of microclimate, erosion control, and reduction of weeds/pests). Several process-based models (WaNuLCAS, SCUAF, HyCAS, HyPAR, and APSIM) have been developed to simulate the intricate dynamics of tree–crop interactions. These models are known to simulate physiological processes that regulate growth influenced by abiotic environmental factors such as soil, climate, and management. Investigations examining interactions among trees and crops provide insight into how different agroforestry components share and use resources, as well as how one component affects the growth and development of others. In agroforestry, interactions are measured under two main categories that are indirect in sequential systems as opposed to direct in simultaneous systems. All agroforestry systems must demonstrate interactions between trees and agricultural components in order to succeed. Therefore, to enhance both traditional and emerging systems, a thorough understanding of biophysical interactions, both above and belowground, is necessary.