EFFECT OF SUGARCANE TRASH RETENTION SYSTEMS ON FURROW IRRIGATION PERFORMANCE By Marcus Hardie 1,3 , Geoff Newell 2,3 and Steven Raine 2 1 Department of Primary Industry Water and Environment, Tasmania. 2 National Centre for Engineering in Agriculture, University of Southern Queensland, Toowoomba. 3 Formerly Bureau of Sugar Experiment Stations, Proserpine. Abstract Green Cane Trash Blanketing (GCTB) systems have not been adopted in many parts of the Australian sugar industry. Growers indicate that the primary obstacle in the adoption of GCTB systems is a lack of knowledge and information on the effect of trash retention on furrow irrigation systems. Trials were established in the Proserpine district to determine the effect of trash retention on furrow irrigation. Results from the trials have been simulated using the furrow irrigation modelling packages SIRMOD II and SRFR 4.06. Modelling tools were also used to ask ‘what if’ questions and extend the field results to different soil types and furrow irrigation scenarios. Field results demonstrated that trash retention increased the depth of flow in furrows and the wetted perimeter, slowed the advance rate, but did not overly affect irrigation efficiency. For growers intending to convert to GCTB systems, the furrow irrigation modelling indicated that they are likely to experience longer advance times or require higher inflow rates and deeper flow depths with GCTB systems. Losses to deep drainage are likely to be higher under GCTB systems, the highest losses are expected on low infiltration soils at moderate furrow lengths. Introduction Green Cane Trash Blanketing (GCTB) was initially practiced in the Australian sugar industry until the 1930s, when the spread of disease to cane cutters from contact with rat urine and labour shortages during World War II forced the cane to be burnt prior to cutting (Stewart and Wood, 1987). GCTB was re-introduced to the Australian sugar industry in the late 1970s to combat problems associated with the deterioration of burnt cane in wet conditions and soil erosion from high intensity rainfall (Wood, 1991). Advantages of GCTB that influenced growers to use the practice include reduced irrigations in dry years, improved soil structure, better weed control, flexibility with harvesting, reduced erosion and reduced labour (Norrish, 1996; Small, 2000). However growers in the Burdekin Delta and some of the wetter regions of the central Queensland district (ie. Mackay and Proserpine) have not adopted GCTB systems. One of the most commonly cited reasons for the poor adoption of GCTB systems is a lack of information and support for growers on the effect of GCTB with furrow irrigation. Growers have expressed a number of concerns about the potential effect of trash blankets including; overtopping of furrows, increased advance times, higher losses to deep drainage and reduced application efficiency (Holden and McMahon, 1997). This trial was conducted to investigate the effect of trash blankets on the performance of surface irrigation. Trial Design and Measurement Field trials were established in the Proserpine district to determine the effect of trash retention on furrow irrigation. Due to a high incidence of rainfall over the trial period, the opportunities for irrigation were limited. The field site was irrigated on the 17 th of October and 19 th of December 1999. The field site consisted of three blocks of five GCTB furrows and three blocks of five burnt (raked furrows), 30 furrows in total. The trial was harvested ‘green’ without the use of a trash fire. The burnt treatments were established by raking and burning trash after the site had been harvested.