The agronomic relevance of arbuscular mycorrhizas in the fertility of Australian extensive cropping systems

All available data on arbuscular mycorrhizal fungi (AMF) in Australian extensive cropping systems are reviewed in an agronomic framework. In the southern temperate and northern subtropical zones, 80–85% and 60%, respectively, of cropped area is winter cereals. In the south, non-mycorrhizal winter break crops are common and crops are often rotated with low input pastures.

In the north, continuous cropping with winter crops, summer crops and long (12–18 month) plant-free fallow is common. Only here does reduced colonization by AMF cause intermittent yield reductions, perhaps reflecting low phosphorus (P) soils, high crop growth rates and dry surface soil limiting P availability.

Soil temperatures below 10°C may limit the contribution of AMF to southern crops. In both zones, wheat yields are generally enhanced following fallows and non-mycorrhizal break crops, even under P limitation. AMF are unlikely to aid control of root diseases or dryland salinity adaptation; their role in soil structure and carbon sequestration requires clarification.

Organic crops are highly colonized, but invariably P deficient. Thus, little evidence supports consideration of AMF in farm management and many agronomic practices that underpin sustainable productivity reduce colonization. We hope this paper stimulates dialog between mycorrhizal researchers and agronomists to target high priority research.