Deep Phosphorus Fertiliser Trials in NSW

Deep phosphorus (P) placement to improve crop productivity is being investigated in the central west of NSW, at Gilgandra and Nyngan. Led by Dr. Mike Bell (QAAFI), the trial investigates how deep P placement affects the fertility of the subsoil, and the economic effectiveness of deep P placement. The work is supported by GRDC funding under the More Profit from Crop Nutrition II program.

Phosphorus is a limiting nutrient in most grain crops, and fertiliser P is commonly a significant input cost. Previous research has indicated that a crops take up only a small amount of their total P from the fertiliser applied in a seeding-furrow. Crops obtain the majority of their total P uptake from other areas within the soil.

Crops in the northern region rely on stored soil moisture. The crop roots search deeper in the subsoil and use more nutrients from the subsoil. Dr Bell’s previous work indicated that these deeper parts of the soil profile (10 – 30 cm depth) in the northern cropping region are suffering nutrient rundown. Large areas in NSW and Queensland are affected. Phosphorus fertiliser applied to the topsoil does not replenish subsoil reserves, so deep placement of P fertiliser is an important technique.

This trial will inform new regional recommendations for growers in the northern part of NSW on the management of P to maximise yields and profitability. Most of the earlier work on deep P has taken place in Queensland.

The trials at the Gilgandra and Nyngan sites will investigate the benefits of a deep application of P over the following three to five seasons. Comparisons of different P-rates and treatment combinations from in the trial will define recommendations for the location and quantity of P applications in low-disturbance seeding systems.

Further information

GRDC: Deep P applications trialled in Central West NSW
GRDC: Strategic P placement offers yield opportunities for northern growers
GRDC: Deep soil tests reveal northern deficiencies


Tony Cox, NSW DPI.



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