Quantifying the response of crops to shelter in the agricultural regions of South Australia

Integrating belts of woody perennials into Australian farms is proposed as a method of enhancing crop productivity through shelter benefits while addressing natural resource management issues including groundwater recharge. This paper presents yield data from cereal and pulse crops collected from windbreak sites through the eastern agricultural districts of South Australia, using a harvester equipped with a yield monitor. The crop response followed the expected pattern of a competition zone of reduced yield of 1–4 tree heights (H) adjacent to the windbreak followed by a shelter benefit zone of unchanged or improved yield extending out to a maximum of 20H. The yield response in the sheltered benefit zone is +3.7% for all cereals (2.2H–9.7H) and is +14.0% for all pulse crops (1.7H–10.4H). Wheat and barley have similar results, with gains in the shelter benefit zones of 4.1% and 2.1%, respectively, with windbreak competition effects resulting in net yields of 3.0% for wheat and –1.1% for barley in the sheltered zones. Faba bean (Vicia faba) shows a strong consistent response to wind shelter, with a yield increase of 19.6% in the shelter benefit zone (1.5H–19.6H) and net gain of 19.1% in the sheltered zone (crop edge at 1.0H and extending to 19.6H). The response of cereals to sheltered effects varied across the years of the survey, with net positive results in 1997 (7.4%) and 1999 (7.5%) and close to zero in 1998 and 2000. A theoretical prediction of potential crop yield based on climate for the years of the survey showed that 1997 and 1999 had lower yield potential than 2000 and 1998. This suggests that the climatic conditions occurring during the growing season also influence crop shelter responses. Where cereals are the predominant crop the net yield returns from windbreaks would be small, even if root pruning could be successfully undertaken.

M. R. Bennell and A. P. Verbyla