REDUCING THE ENVIRONMENTAL IMPACT AND OPTIMISING NUTRIENT REQUIREMENTS FOR MILL MUD APPLICATIONS IN CANE FARMING OPERATIONS

A SIGNIFICANT source of nutrients for growing sugar cane in all sugar milling regions is derived from filter mud (also known as mill mud). Mill mud is a by-product of the sugar milling process and is considered a rich source of nutrients, in particular nitrogen, phosphorus and calcium. Mackay Sugar (MSL) produces approximately 400 000 tonnes of mill mud per year which is subsequently returned to cane fields in trucks. By elevating the tipper body and using a paddle in the tailgate, these trucks have traditionally distributed the mud in a largely ad hoc manner. The trucks are driven over the field applying mud at a nominal rate of 150 tonnes of wet mud per hectare (t/ha), but in-field measurements show wide variability in application rates. Mackay Sugar had deemed this method of application as unacceptable to their growers and has set about finding alternative solutions to application rates and methods. Mackay Sugar, in association with Reef Catchments Mackay Whitsunday, funded a project that sought to address the issues of mill mud application. Consolidated Plastics and Epoxy Qld Pty Ltd were engaged to design and fabricate the applicators to be fitted onto the back of the existing mud truck fleet. The brief details of the design included: the ability to spread across three rows; the ability to control the rate at differing row spacing; control of the rate to a minimum of 50 tonnes of wet mud per hectare; must not add excessive weight to the back of the truck; and applicators must be able to be fitted onto existing truck bodies and use the existing truck hydraulic components with minimum truck modifications. The resultant applicators have been established and fitted to several trucks applying mud throughout the Mackay Sugar region in 2010. This method of application has delivered the following benefits: mud has been placed in the centre of the plant growth row; no mud is distributed onto the wheel tracks where the ground is more likely to have been compacted and is therefore more prone to water runoff; mud is incorporated into the soil soon after application when planting or tillage occurs; and mud has been distributed over an increased area. This paper describes the design and development of the applicators and details the improvements made from prototype to the current applicator. In association with the improved application method and lower application rates, Mackay Sugar introduced a quota system for the distribution of mill mud from its factories.