Economics of sugar mill by-products as a source of nutrients in the Australian sugar industry in Mackay

The sugar industry produces a number of by-products during the process of sugar production including bagasse, mill or filter mud, ash, mill effluent, and trash. The Australian sugar industry has a long history of utilising these by-products primarily as a source of energy but also as a source of nutrients and as soil ameliorants. The re-use of mill by-products has been mutually beneficial to the farming and milling sectors as well as supporting the industry’s endeavours to be viewed as clean, green. and responsible. However, current practice distributes mill mud back to farms within close proximity to the mills and at high application rates due to high freight and distribution charges for distances further from the mill. The continued application of these by-products at high rates, without appropriate recognition of the soil condition and crop requirements. has raised a number of concerns including over-fertilisation and heavy metal concentration as well as offsite effects such as impact on the riverine environment. Application rates of 150 and 100 tlha are less expensive than commercial fertiliser for distances up to 20 km from the mill, while application rates of 75 and 50 tlha are less expensive up to 40 km. An application rate of 25 t/ha is less expensive up to 60 km, but the application rate of 12.5 t/ha is less costly for all the distances compared to the application of traditional fertiliser.