Preparation for 2022 fertiliser application decisions

Fiona Leech, Senior Agricultural Officer, South East Local Land Services, Yass

Good soil fertility is required to sustain productive pastures for livestock production and annual soil testing is an extremely useful tool to help guide future fertiliser applications. With the current rise in fertiliser prices, it becomes even more important that fertiliser application decisions are based on sound knowledge of where soil nutrient levels currently sit in pasture paddocks.

In most years mid to late spring is an ideal time for soil testing as soil is usually moist allowing soil cores to be taken quickly and easily, with cores holding together well ensuring an accurate sample is taken. Soil sampling at this time of year usually coincides with maximum growth, allowing an assessment of whether nutrient levels can support maximum pasture growth. However, with the extended spring season that we are experiencing across the South East region soils have continued to remain moist allowing additional time to take soil samples to aid fertiliser application decision making for 2022.

It must be remembered that in any farming business enterprise where products are being sold off-farm, soil nutrients are also being removed in the process and must be replaced if the system is to remain in balance. It is well recognised in pasture research that nitrogen (N), phosphorus (P) and sulphur (S) are key elements that drive pasture growth and are depleted as product is sold off-farm. In pasture systems, legumes are used to supply N to the pasture while P, S and other elements that may be limiting (e.g. Molybdenum, Potassium) will need to be physically applied to the pasture.

There are a range of fertiliser types on the market for use on farm. They include mineral, manure, compost or microbial formulation type fertilisers. Whatever fertiliser you are considering it is vital to first understand your soil chemical status and recognise any obvious key soil nutrient limitations for plant growth. With this information you can then evaluate suitable fertilisers to address these limitations. Always seek out a nutrient analysis of the fertiliser that you are considering to ensure that you will be addressing your key soil nutrient limitations. If considering alternative type fertilisers always ask fertiliser companies to provide replicated trial data to demonstrate any claims being made regarding the product.

Fertiliser applications on pastures commonly occur in the summer-autumn period prior to the autumn breaking rains for the forthcoming season. Soil testing in the spring period prior will allow time for decision making to then occur around fertiliser use.

As the South East region came out drought in early 2020, we have been faced with two very productive years resulting in considerable pasture growth. Such years draw soil nutrient levels down, however, given lower stocking rates commonly held coming out of drought, soil nutrients have been currently transferred into plant material much of which will cycle back through the system although very slowly. Nutrients held in plant material grown over the last two years take time to break down and release nutrients back into the soil for plants to access. If fertiliser has not been applied for a number of years due to the drought and associated financial pressures, it may be clear that key elements like P and S will need addressing in part to ensure pastures are responsive for our next season. Remember the trace nutrient Molybdenum (Mo) is also critical to productivity in our pasture systems and as a rule of thumb should be applied approximately every 5-6 years to pastures in this region. Note that soil testing is not a useful method for monitoring soil Mo levels given it is only present in soil in trace amounts. Application history is a preferred guide to determining the need for an Mo application.

Our South East Local Land Service offices have NSW DPI soil testing kits available. If you are interested in soil testing while soil conditions continue to remain moist please contact your nearest office and ask to speak with the local agricultural officer to help guide you through the process. Our agricultural officers can help interpret your NSW DPI soil test results to identify any key limitations and discuss fertiliser choices as required.

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