Water Management with Hedgerow Agroforestry Systems

Abstract

An outline of the methods used to integrate annual crop production with woody perennials, based on the spatial pattern in which trees are grown, is presented by Lal (1989). These methods range from random scattering of trees across a field to alternate strips of trees and annual crops. This latter system has been referred to as alley cropping, avenue cropping, or hedgerow cropping (Lal, 1989). Many of the concepts used to analyze tropical hedgerow systems could be validly applied to parkland and tree-pasture agroforestry (silvopastoral) systems, as well as to hedgerow systems in temperate environments. Some researchers have proposed that agricultural systems that contain multiple plant species can exploit more resources through temporal or spatial niche differentiation than can monocultural systems. Thus multiple plant systems can potentially complement each other with respect to resource use and therefore be more productive (Berendse, 1979; Anderson and Sinclair, 1993). More recently, Cannell et aI. (1996) have argued that, from a biophysical perspective, the "benefits of growing trees with crops will occur only when the trees are able to acquire resources of water, light and nutrients that the crop would not otherwise acquire." To address the question of whether and the degree to which agroforestry systems alter water fluxes relative to other agricultural systems, including the amount of water transpired by plants per given area of land per year, the major pathways of water inputs and losses in the soil-plantatmosphere system must be considered. Water is lost from the soil system as evaporation from soil and plant surfaces, as transpiration, as deep percolation, and as surface runoff. Increases in the amount of water used by plants in the system is therefore accompanied by, and in some cases contingent upon, decreases in water lost as evaporation, deep percolation and/or surface runoff. The importance of these various pathways for water loss will vary with climate, soil type and the landscape, as well as with the type and management of the cropping system. In addition, water can enter some plant-soil systems not only as precipitation infiltrating the soil surface, but also through the lateral movement of water beneath the surface. Some cropping systems may be able to access more of this water than others, thus increasing the amount of water available to plants.