Progressing the use of mill by-products in sugarcane production in Australia

Mill by-products such as filter press (mill mud), boiler or fly ash (mill ash) and the mixture of mill mud and mill ash (mud/ash) are valuable soil ameliorants that increase cane yield. However, there is little information on how mill by-products should be applied in the fallow prior to planting to maximize sugar production, minimize environmental impacts and optimize growers’ profitability. In this study, 11 research trial sites, with a wide range of soil characteristics, were established: four sites in the Herbert region, five sites in the Burdekin region, one site each in the Proserpine and Plane Creek regions. The trials consisted of a control treatment, which was the standard grower practice at each site based on soil test results, and a suite of mill by- products treatments either applied in bands in the planting line or broadcast and incorporated in the fallow prior to the wet season or shortly before planting after a wet season fallow. Mill by- products were banded at rates between 35-175 wet tonnes per hectare and broadcast at 140- 350 wet tonnes per hectare. In general, all mill by-products increased cane yield in plant-cane and first-ratoon crops compared to the standard grower practice. However, it was also observed that all mill by-products treatments decreased CCS in plant cane and first ratoons compared to the grower practice. Mill ash or mud/ash mixtures tended to outperform pure mill mud treatments both in terms of sugarcane yield and CCS. Banding of mill by-products at lower rates generally resulted in similar sugarcane yields and higher CCS than broadcast high rates of these products. These trials will be run over an entire crop cycle to develop a recommendation on how to maximise the economic benefit of applying mill by-products and to minimise their environmental impacts. Key words Mill mud, ash, mud/ash, sugarcane yield, CCS