Using soil and plant testing data to better inform nutrient management and optimise fertiliser investments for grain growers in the southern region

Using soil and plant testing data to better inform nutrient management and optimise fertiliser investments for grain growers in the southern region.
Project led by Harm van Rees and Sean Mason, Agronomy Solutions. Other partners CSIRO (economic analysis), AgCommunicators (extension), APAL (soil and plant testing), Landmark, private agronomists and farming systems groups (Sarah Noack co-ordinator).
Engage 100 growers (6 paddocks per grower = 600 paddocks total/yr) in the project to conduct soil testing and fertiliser demonstration strips.

On Eyre Peninsula, AIR EP contracted SARDI (Fiona Tomney) to deliver 5 farms on upper EP for soil and plant tissue testing and fertiliser demonstration strips.

Outcomes

One of the more interesting outcomes of this project is the finding that most of the project’s collaborating growers were using fertiliser phosphorus (P) and nitrogen (N) inputs that were a close match for the laboratory generated recommendation.  However, there are opportunities for farmers in the Southern region to further utilise soil test information to increase crop gross margins.  We found examples of both under- and over-fertilisation, and together with a greater consideration and management of within paddock production zones productivity and profitability can be improved.

Main conclusions:

• Soil type differences and varying levels of soil nutrient status within paddocks imply that improved nutrient management through zoning by soil type is likely to be economically worthwhile.  For practical considerations managing two or three zones per paddock is likely to be optimum
• The project outlined improved soil testing procedures especially in relation to sampling intensity (number of cores to be sampled per paddock zone)
• The project found that monitoring change over time in soil P status within zones will highlight the status of the soil P bank and warn growers if it is starting to be run-down
• Soil available N is highly variable and its status depends on previous crop type (ie. legume) and seasonal conditions (summer rain).  Management of N supply is improved if soil N status is measured and N requirements by the crop calculated (such as through the N-bank approach or the use of Yield Prophet^®)
• Tissue testing is useful to confirm inputs of major nutrients (N and P) but also, importantly, for essential nutrients such as Zinc and Copper.  Soil test results are not accurate enough for Zinc and Copper status. Status of Potassium and Sulphur plant levels across the Southern region provide a guide to current balances of these two important nutrients.
• In the Low and Medium rainfall zones it appears that P and N requirements are, in general, well managed. In the High rainfall zone P and N status appeared to be low relative to crop yield potential and there is an opportunity in the High rainfall zone to improve P and N management (through increased soil and tissue testing).
• Replacement programs for Phosphorus are acceptable if the soil characteristics are known (e.g. low to moderate PBI). Across several cropping regions a small number of paddock areas (e.g., 20-30%) have been identified as P deficient and require higher P requirements to amend. These areas are driven by soil pH (7.5-7.8), presence of soil carbonate (Ca or Mg) and high PBI values (> 100). For these soil types replacement P rates have not been adequate in maintaining unlimited P yield potentials.
• Relatively cheap paddock data layers including NDVI, yield and pH maps can be used to identify soil x production zones to improve targeted soil sampling programs which will enable improved monitoring of nutrient trends with time.

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