R.C. DALAL1, W.M. STRONG1, E.J. WESTON2 and J. GAFFNEY3
1Queensland Wheat Research Institute;
2Pasture Management Branch;
3Economic Services Branch; QDPI, Toowoomba, Queensland, Australia.
Fertile soil is the basis of sustainable agriculture. Continuous cultivation and cereal cropping lead to the depletion of soil fertility, low crop yield and poor grain quality. It is estimated that 1.2 M ha of the total cropping area of 1.5 M ha in southern sub-tropical Queensland are affected by soil fertility decline, with a consequent reduction in crop yield and grain quality valued at an output loss of $324 M/yr. There is an urgent need to adopt fertility restorative practices to maintain economically viable farming enterprises.
Legume based leys, grain legumes, fertiliser N and zero-tillage were compared for their effectiveness in restoring or maintaining soil fertility and for sustaining wheat yield and quality on a fertility- depleted brigalow soil at Warra on the western Darling Downs. Both annual N fertilizer application and zero tillage accompanied by N application maintained wheat yields although they are uncertain options for long-term fertility restoration. The grain legume, chickpea, provided a moderate level of N supply to the following wheat crop but it is also an uncertain option for fertility restoration. Pasture leys based on annual and perennial legumes, with or without grasses, provide a useful option for fertility restoration. One year medic and lucerne leys contributed to soil N to a moderate level although lucerne leys may have an adverse effect on the moisture available for following crops. Grass–legume mixed pastures increased soil fertility as measured by an increase in soil total N.
Of these options, pastures based on annual and perennial temperate legumes and tropical grasses have the potential to increase or maintain soil fertility. Legume leys and especially grass–legume pasture leys will play a key role in future ecologically and economically sustainable farming systems.