Combining δ13C measurements and ERT imaging: improving our understanding of competition at the crop-soil-hedge interface

Abstract

Hedgerow cropping decreases erosion in hillside agriculture but also competes for water and nutrients with crops. This study combined two methods for an improved understanding of water and nutrient competition at the crop-soil-hedge interface. δ13C isotopic discrimination in plants and soil electrical resistivity tomography (ERT) imaging were used in a field trial with maize monocropping (MM) vs. leucaena hedgerow intercropping with and without fertilizer (MHF+ and MHF−) in Thailand. Hedges significantly reduced maize grain yield and aboveground biomass in rows close to hedgerows. ERT revealed water depletion was stronger in MM than in MHF+ and MHF- confirming time domain reflectometry and leaf area data. In MHF+, water depletion was higher in maize rows close to the hedge compared to rows distant to hedges and maize grain δ13C was significantly less negative in rows close to hedges (-10.33‰) compared to distant ones (-10.64‰). Lack of N increased grain δ13C in MHF- (-9.32‰, p ≤ 0.001). Both methods were correlated with each other (r = 0.66, p ≤ 0.001). Combining ERT with grain δ13C and %N allowed identifying that maize growth close to hedges was limited by N and not by water supply. Combining ERT imaging and 13C isotopic discrimination approaches improved the understanding of spatial-temporal patterns of competition at the hedge-soil-crop interface and allowed distinguishing between water and N competition in maize based hedgerow systems.