Nutrient budgeting in extensive grazing systems

Chief investigator: Dr Rowan Smith

Funding body: NRM North

Video of Rowan talking about this project.

Nutrient Management Leaflet (PDF 459KB)

Rowan SmithThis study sought to evaluate the nutrient soil condition of a range of pasture types on extensive grazing properties in the Northern Midlands. The project aims to reduce fertiliser applications where they are not needed to reduce the risk of nutrient runoff into waterways and save money. It aims to provide a tool for farmers to better target their fertiliser applications to the requirements of individual paddocks or groups of paddocks, rather than a blanket approach. On each property we have endeavoured to only take soil tests from pastures, but in some instances we have included lucerne and lupins as part of the sampling as they were used for grazing and there were not enough grass based pastures. We sampled ten pastures on each of the properties across a range of pasture types from newly renovated pastures, degraded pastures, to native run country. Soil pH and electrical conductivity as well as macronutrients including phosphorus, potassium and sulphur were all measured as part of the study. These results have allowed a comparison to be made with the optimum levels for pasture production. Nutrient maps have been drawn up to display variability in nutrients across the property. Recent soil tests from other companies have also been included to provide more coverage in the soil maps given only ten samples could be taken as part of the project on each farm.

Using the farm data provided by the farmer/landowner we have been able to construct a nutrient budget for the property. The complexity of farms in this region has required us to include cropping as part of the budget given that many fodder crops and crop residuals are included in the grazing rotations. Important information collected for the nutrient budget is; the sales of livestock and livestock products such as wool; the import and export of crops and fodder; and the import and application of fertilisers.

Conclusions

The mean soil pH and levels of major nutrient phosphorus, potassium and sulphur are generally in the optimum range for pasture production in the Northern Midlands. Some pastures require the soil pH to be lifted or phosphorus levels to be increased into the optimum range. Consideration of the effects this may have on native species is important in bush run type pastures. Potassium and sulphur levels are generally in the optimum range. However, there were a few instances of very high levels. Very high levels of potassium can cause animal health issues and thus it is important to monitor grazing of these paddocks. Most farms could benefit from reallocation of nutrients; that is more targeted applications that suit the individual paddock or group of paddocks specific needs. The inaccurate farmer predictions of nutrient levels indicate that soil testing is a worthwhile. Soil sampling can save money and can allow more targeted applications. The introduction of more cropping and irrigation onto these properties will have impacts on soil nutrients and these needs to be considered. The use of nutrient maps and nutrient budgeting can have great benefits for farmers planning fertiliser applications. Further work is required to assess the applicability of the NutriMatch calculator to extensive grazing systems of the North Midlands of Tasmania.