Influence of windbreak orientation, shade and rainfall interception on wheat and lupin growth in the absence of below-ground competition

Abstract

In the temperate cropping regions of Australia, the benefits of shelter from windbreaks are often offset by tree-crop competition. The aim of this trial was to quantify microclimate and crop growth close to shade-cloth windbreaks with various orientations, to determine the effect of shelter and above-ground competition on the growth and productivity of wheat (Triticum aestivum) and lupins (Lupinus angustifolius) in the absence of below-ground competition. The trial was conducted in southwestern Australia in 2000 and 2001. The windbreaks modified windspeed, temperature, light and rainfall both spatially and temporally. Consequently, there were spatial differences in the phenology, morphology and productivity of the crops and the incidence of fungal disease adjacent to the windbreaks. Mean grain yield within three times the height of the windbreaks (H) was 97, 102, 82, and 98% of yield beyond 3 H on the northern, eastern, southern and western aspects respectively for wheat and 99, 87, 90, and 87% respectively for lupins. Changes in windspeed and rainfall were not significantly correlated with the relative yield of either crop. However, photosynthetically active radiation was significantly correlated with yield for wheat but not for lupins. Given these responses, and the practical difficulties of reducing below-ground tree-crop competition to the point where light is more limiting for crop growth than water, it is recommended that windbreaks continue to be oriented primarily to protect against damaging winds, rather than to minimise shading in the medium and low rainfall areas of Australia.