Comparing wheat grown in South Australian organic and conventional farming systems. 1. Growth and grain yield

Organic farming standards do not allow addition of water-soluble fertilisers and therefore it is likely that growth of organically grown crops will be limited by nutrient availability. However, in marginal rainfall conditions, when growth in conventional systems is limited by water availability, yields of organically grown crops could be comparable with those conventionally grown. Similarly, micronutrient-efficient plant varieties could be expected to perform comparatively better under organic farming conditions than they do in conventional systems, when compared with micronutrient-inefficient varieties. In this study, biomass and grain production of wheat from certified organic farming systems were compared with neighbouring conventional farming systems in 'across the fence' field trials in 1 moderate and 2 marginal rainfall areas of South Australia. Wheat varieties compared included 2 old wheat varieties developed under relatively low-input conditions (Baroota Wonder and Dirk-48) and varieties shown to be micronutrient-efficient (Janz and Trident) and inefficient (Yallaroi). The organic farming systems produced significantly less biomass than the conventional farming systems at late tillering in both the moderate and marginal rainfall areas. Grain yield was variable, but significantly lower in the organic farming system for 11 of the 14 comparisons. None of the varieties showed an adaptive advantage for 1 farming system over the other. The relative yield of the organic system, compared with the conventional system, was not associated with rainfall