Analysis of soil water dynamics in an agroforestry system based on detailed soil water records from time-domain reflectometry

Time domain reflectometry [TDR] was used to investigate the spatial and temporal variation in surface soil water dynamics under a number of types of vegetation, including both trees and crops grown in isolation, and grown together as an agroforestry system. The installation and operation of this technique are presented, and discussed in terms of its suitability to monitor rapid fluctuations in soil-water content in a spatially heterogeneous system such as that described in this experiment. The relatively small sampling volume of each of the TDR waveguides permitted discrete measurements to be made of soil water content (theta(v)). In the tree-only and tree+crop treatments, this revealed considerable variation in theta(v) resulting from spatial redistribution of rainfall under the tree canopies, with a significant input to soil close to the base of the trees being made by stemflow, i.e. water intercepted by the tree canopy and channelled down the stem. Over the experimental period tone rainy season) the TDR data suggested that net recharge to the soil profile in the sole crop system was 53 mm, almost 75% more than occurred in either of the two treatments containing trees, reflecting greater rainfall interception by the tree canopies.