Sean Mason1,2, Elizabeth Farquharson3,2, Lynette Schubert3
1Agronomy Solutions Pty Ltd, 3/11 Ridley Street, Hindmarsh SA 5007,
2School of Agriculture, Food and Wine, University of Adelaide, Waite Road, Urrbrae SA 5064,
3South Australian Research and Development Institute, Gate 2B, Hartley Grove, Urrbrae, SA, 5064
High commodity prices for several pulse (grain legume) crops over the last five years have meant that crops such as lentil and chickpea have become highly profitable and sowing frequency within rotations has increased significantly in cropping regions of South Australia. Limited information on the nutritional requirements of these pulses has meant that nutrient requirements cannot be calculated based on soil test levels. Recent trials by Wilhelm et al. (pers comm.) have focused on Phosphorus (P) requirements of selected pulses and attempted to determine soil P test critical levels compared to those established for cereals but these trials were not N limited (i.e. N fertiliser applied) and N fixation was thus not considered.
Two P response trials in the Mid-North and central Yorke Peninsula of South Australia investigated the response of lentils and chickpeas to P applications and measured the amount of N fixed with increasing P application. In-season assessments showed higher P requirements for both pulse crops (particularly lentils) compared to wheat. The increase in pulse biomass with increasing P rates coincided with increases in both nodule number but also nodule weight per gram of root. The benefits from optimising pulse production occurred at P rates higher than what is considered district practice for these crops. Dry seasonal conditions meant that the early season increases in biomass didn’t translate to grain in 2018. However, nitrogen fixation estimates (by 15N natural abundance) were highly related to early season nodulation, particularly for lentils.