Optimizing resource distribution and crop productivity in hedgerow intercropping by manipulating tree arrangement

Abstract

The potential of tree arrangement in optimizing radiation and soil water distribution and crop yield of hedgerow intercropping systems was investigated using a Jatropha curcas–Pennisetum clandestinum (kikuyu) system (Ukulinga, South Africa). Treatments (1110 t ha-1) of Jatropha-only (JO), single-row Jatropha and kikuyu (SR), and double-row Jatropha and kikuyu (DR) were used. Treatments had asymmetrical radiation distribution across tree–crop (T–C) interfaces and different radiation interception by trees (JO: 27 %, SR: 11 %, DR: 8 %). Soil water varied among treatments and was asymmetrically distributed showing no consistent trend towards trees. Evapotranspiration was higher (p\0.05) in SR than DR (13–65 %) and JO (16–37 %) for most part of the season. Estimated fine tree roots distribution was symmetrical in DR but not JO and SR. Total roots in SR were concentrated in the top 0.2 m (91 %) and beneath tree row (30 %), and varied inconsistently with distance from trees. Grass yields increased farther from tree rows and were higher in SR (8.7 t ha-1 in 2006–2007; 4.3 t ha-1 in 2007–2008) than DR (by \9 %). Radiation use efficiency of kikuyu (0.14–0.44 g MJ-1) also increased with distance from trees but irradiance correlated with grass yields poorly (R2\0.32) despite high rainfall and no nutrient limitation. Considering total productivity and evapotranspiration, DR was better tree arrangement than SR. Water availability dictated T–C interactions and intercrop yield more than radiation. It was possible to optimize radiation and water distribution and intercrop growth by manipulating tree arrangement without changing density.