Spatial variability of regolith leaching and salinity in relation to Whole Farm Planning

Abstract

An electromagnetic induction (EM31) survey was carried out on a 700-ha property in the western basalt plains of Victoria. The apparent electrical conductivity (EC_a) was interpreted in terms of the inferred salt content and, hence, the degree of leaching or recharge through the upper 5 m of the regolith. The focus of the survey was to determine the spatial variability of EC_a across a landscape of low relief which included salt lakes. The area mapped is subject to regional groundwater discharge. All parts of the property exhibited hydrological ‘sinks’ and ‘trenches’ of relatively low EC_a values, interpreted as areas of preferential recharge or leaching through the regolith. They ranged in size from 200 to 500 m in diameter and/or length and were not related to relief. This apparent hydrological ‘holeyness’ of the upper regolith suggests local recharge into the regional groundwater system. This finding has important implications for Whole Farm Planning and Environmental Management Strategies as local recharge can be reduced by manipulating ground cover and land-use practices. Both the mean and standard deviation of EC_a values across the property provide a rational basis for planning land management practices. The location of hydrological ‘holes’ can be built in as significant layers in Whole Farm Plans to minimise water entering the water table and/or salt lakes.