Pulse crops in rotation with cereals can be a profitable alternative to nitrogen fertiliser in central Queensland

Empirical and simulation results from three crop rotations incorporating cereals, pulses and nitrogen (N) fertiliser application were examined over 4 years in a subtropical environment, central Queensland, Australia. The hypothesis was that pulse crops in rotation with cereals would be a viable alternative to applying N fertilisers and would improve farm business economic performance provided the yield potential of pulses were not compromised by planting into very low soil water situations. Empirical data and simulations with the Agricultural Production Systems Simulator model were used to give insights into the N contribution, yield benefit to cereals and overall economic performance of the inclusion of pulses into the rotation. The field trial rotations included: rotation 1: sorghum and wheat in an opportunity crop rotation (called cereals-only), rotation 2; cereals grown following a fallow with a pulse crop immediately after (called cereal double-cropped pulse) and rotation 3, pulses grown following a fallow with a cereal crop immediately after (called pulse double-cropped cereal). Empirical and simulated results indicated that the cereal double-cropped pulse rotation produced the highest average annual gross margins using prices at that time. In the simulations, when pulse crops were included in the rotation, no additional N fertiliser was required and the lowest chance of negative gross margins was obtained. The cereal double-cropped pulse rotation produced the largest trial and simulated gross margins. The pulse double-cropped cereal rotation produced greater gross margins than the N-deficient cereals-only rotation but significantly lower than the cereal double-cropped pulse rotation. Simulations indicated that the cereals-only rotation could be made profitable when the soil was 'topped-up' to 100 kg available N/ha before planting, or by 40 kg N/ha to each cereal crop. Chickpea and mungbean contributed an average of 35 and 29 kg N/ha, respectively, in the field trial. A minimum of 100 mm of the stored soil water at planting was needed to reduce the risk of negative returns. By planting only when the soil contained adequate water, the cereal double-cropped pulse rotation may provide a valuable supplement to farm income while simultaneously reducing the need for N fertilisers on the cereals. Alternatively, in a rotation with cereals only, modest amounts of fertiliser N will maintain profitability with minimal levels of financial risk