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On the low‐P soils in southeastern Australia, organic crops differ from conventional ones primarily in the use of relatively insoluble, as opposed to soluble, P fertilisers and in the non‐use of herbicides. As organic management, particularly elimination of soluble fertilisers, is often claimed to enhance grain mineral concentrations, we examined grain from wheat on paired organic and conventional farms in two sets of experiments: (1) four pairs of commercial crops (1991–1993); and (2) fertiliser experiments on one farm pair where nil fertiliser was compared with 40 kg ha⁻¹ of P as either relatively insoluble reactive phosphate rock or more soluble superphosphate (1991 and 1992). All wheat was grown following a 2–6 year legume‐based pasture phase. Both conventional management and the superphosphate treatment greatly increased yields but reduced colonisation by mycorrhizal fungi. While only minor variations …