Time of Sowing effects on Phosphorus Requirements of two different wheat varieties

Sean Mason1,2, Glenn McDonald2

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


Crop phosphorus (P) acquisition from both soil P reserves and freshly applied P is controlled by climatic conditions that drive soil moisture and temperature. Soil conditions can change significantly across a typical sowing window and therefore this potentially impacts crop P requirements. Phosphorus responses trials performed in broad acre cropping regions of South Australia across two seasons and three times of sowing showed that P requirements can alter across sowing dates and between the two seasons. At the mid-North site in 2017 where starting soil moisture was high, low P rates (0-5 kg P/ha) were required to maximise wheat yields when sown in late April. Comparatively when the P response was assessed at the mid-May sowing time P requirements increased up to 50 kg P/ha which fluctuated slightly with variety. When the trial was repeated in 2018 at a close location with very similar starting soil P levels on marginal soil moisture, P requirements were 38-40 kg P/ha when Mace and Trojan were sown in late April compared to 41-48 kg P/ha for the mid-late May sowing time. This highlights that high starting soil moisture conditions at moderate temperatures can promote P acquisition from soil P reserves which would potentially place less reliance on P inputs. However, if soil moisture levels are marginal there is still a reliance on P inputs. Cooler temperatures associated with later sowing times place a higher demand on P applied as fertiliser.



The Australian Society of Agronomy is the professional body for agronomists in Australia. It has approximately 500 active members drawn from government, universities, research organisations and the private sector.

Photo Credits

David Marland Photography david_marland@hotmail.com Graham Centre for Agricultural Innovation, Charles Sturt University

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