Use of mill by-products in the fallow in sugarcane production in Australia

Mill by-products such as mud, ash and mud/ash mixtures are known to increase cane and sugar yields. Traditionally, Australian growers broadcast these by-products in the fallow at rates greater than 150 t/ha. However, growers are now banding by-products at less than 100 t/ha, with few guidelines on how to maximise their returns from this practice. 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 and 100 t/ha and broadcast between 140 and 200 t/ha on cane yield, CCS and grower net revenue compared to standard grower fallow practices. The trials were harvested each year over the crop cycle using a commercial harvester. Tonnes of cane harvested and mill CCS provided by the receiving sugar mill were used to calculate tonnes of cane per hectare and grower net revenue per hectare using the Australian cane payment method for each plot in a trial. The application of mud, mud/ash and ash increased cane yield with ash ≥ mud/ash >> mud. The greater the quantity of by-product applied, the greater the cane yield. Conversely, CCS decreased linearly with the quantity of mud, mud/ash, or ash applied. CCS was lowest in mud << mud/ash ≤ ash. Cumulative grower net revenue at the end of the crop cycle was greatest in ash > mud/ash >> mud and was greatest at application rates of 35–50 t/ha > 70–100 t/ha > 140–200 t/ha. Broadcasting mud at 200 t/ha resulted in the growers not recovering the cost of application. Banding by-products containing mud/ash and ash at 100 t/ha or less resulted in the grower recovering the cost of the product by the second or third ratoon. By-products applied at rates as low as 50 t/ha reduced CCS, and further research is needed to improve guidelines on nutrient and water management so that growers using these by-products can maximize their profitability.