Crop Nutrition Phosphorus Management Fact Sheet

Published: 2 Nov 2012

Image of Phosphorus Management Southern Region Fact Sheet

Phosphorus (P) fertiliser represents a substantial input cost in cropping systems. Soil testing provides an understanding of your fertility profile and is a vital step in making informed fertiliser decisions. Addressing low subsoil phosphorus (P) levels by soil testing and deep placement of P can bring yield increases across multiple cropping seasons.

  • After decades of consistent phosphorus (P) application, many soils now have adequate P status.
  • Before deciding on a fertiliser strategy, use soil testing to gain a thorough understanding of the nutrient status across the farm.
  • If the soil P status is sufficient, there may be an opportunity for growers to save money on P fertiliser by cutting back to a maintenance rate.
  • Consider other factors; if pH (CaCl2) is less than 4.5, the soil is water repellent or root disease levels are high, then the availability of soil test P is reduced and a yield increase to fertiliser P can occur even when the soil test P results are adequate.
  • Work with an adviser to refine your fertiliser strategy.
  • Phosphorus (P) reserves have been run down over several decades of cropping.
  • Adding fertiliser to the topsoil in systems that rely on stored moisture does not always place nutrients where crop needs them.
  • Testing subsoil (10 to 30 centimetres) P levels using both Colwell-P and BSES-P soil tests is important in developing a fertiliser strategy.
  • Applying P at depth (15 to 20cm deep on 50cm bands) can improve yields over a number of cropping seasons (if other nutrients are not limiting).
  • Addressing low P levels will usually increase potential crop yields, so match the application of other essential nutrients, particularly nitrogen (N), to this adjusted yield potential.

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