Abstract:
Low soil phosphorus (P) availability commonly limits yield in Australian broadacre organic production systems where superphosphate fertiliser is not permitted, and alternative P nutrition strategies are sought. Glasshouse experiments were conducted to investigate the potential of faba beans (Vicia faba L.) (FB), or field peas (Pisum sativum L.) (FP), grown in acidic sandy loam or alkaline clay, to accumulate P, which could then be supplied to a subsequent crop as part of a green manure rotation or after harvest. Another experiment investigated differences in growth and P acquisition between corn (Zea mays L.) cultivars: Hycorn 424 (a modern hybrid), and four traditional cultivars used in organic production. The experiments were carried out under conditions of P stress and had rock phosphate (RP), poultry manure (PM), or single superphosphate (SP) applied at 50kgP/ha. For FP, maximum P input to the soil from incorporation would occur at or after pod initiation. However, P uptake by both legumes in both soils from sparingly soluble RP was low, with fertiliser P-use efficiencies of 0–1.3% compared with 1.8–12.7% for PM and 6.1–9.9% for SP. In the corn experiment, P fertiliser source had much larger effects than cultivar on plant biomass and P uptake, with responses generally ranked SP>PM>> RP>Control. Hycorn 424 generally produced higher dry matter and P uptake than the traditional cultivars under all P treatments. The implications of these preliminary investigations for Australian broadacre organic agriculture are discussed.