Nutrient content after the application of mill by-products and implications for nutrient management

Mill by-products such as Mud, Ash and Mud/Ash mixtures are known to increase cane yield and sugar yield. Australian growers broadcast and band these by-products in the fallow at rates greater than 150 t/ha and less than 100 t/ha, respectively. Eight commercial-size replicated, randomised strip trials were established in bare fallows between Ingham and Proserpine to investigate the impact of by-products banded between 35-100 t/ha and broadcast between 140-200 t/ha on crop nutrient uptake and accumulation compared to standard grower fallow practices. The trials were harvested each year over the crop cycle using a commercial harvester. Plant material was collected from the harvested cane supply and analysed for nutrient content. The application of Mud, Mud/Ash and Ash resulted in the luxurious accumulation of nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) in the cane supply. The application of Mud, Mud/Ash and Ash increased N, Ca and Mg in the crop with Mud > Mud/Ash >> Ash. Similarly, P increased in the crop with Mud >= Mud/Ash >> Ash. Crop K and S also increased after the application of mill by-products, however Ash > Mud/Ash >> Mud. The results from this study should be used to revise the SIX EASY STEPS? nutrient management program guidelines for reducing macronutrient fertiliser rates after the application of mill by-products, to ensure excess nutrients are not applied to sugarcane crops that might have both agronomic and economic consequences for growers.