Soil testing to determine fertiliser applications

Key points

• Pre-season soil testing is essential to determine a crop nutrition strategy for the upcoming season
• Growers should aim to soil test at least 20 per cent of their cropping paddocks per year. It is recommended to soil sample paddocks with the same crop (for example, all paddocks to be planted with wheat)
• Yield, biomass and other maps from previous seasons will indicate low, medium, and high production zones. Soil testing should be conducted within each production zone to determine what is driving variation in the paddock
• Topsoil samples, taken with a 0-10 centimetre pogo sampler, are used to measure immobile nutrients such as phosphorus and trace elements
• Deep core soil sampling, using a utemounted hydraulic corer, can measure more mobile nutrients such as available nitrogen and assess subsoil constraints to root growth
• Target a minimum of six deep soil cores for each zone and a minimum of six topsoil (0-10cm) cores taken around each deep core location. A ratio of one sample taken on the previous crop’s row to eight to 10 samples inter-row is recommended by Fertcare
• The amount of plant available nutrient measured in the laboratory indicates if the soil nutrient supply is likely to be adequate or whether it needs to be boosted with fertiliser applications
• If the soil nutrient result is less than the critical level, the site is highly likely to respond to an application of that nutrient at rates potentially
  higher than was applied in the past or what is the standard practice
• Growers should work with their agronomist to determine a soil testing strategy pre-season. An agronomist can also help interpret and analyse the test results to determine a crop nutrient strategy for the season.

These measurements influence the supply of nutrients to the crop and indicate how plant growth and quality will respond to fertiliser applications at the start of or throughout a growing season.

The more growers can understand the soil in their paddocks, the easier it will be for them to optimise production.

Pre-season is an ideal time to soil test and plan a crop nutrition strategy for the upcoming season.