CAN LODGING BE CONTROLLED THROUGH IRRIGATION

LODGING is widespread in the Australian sugar industry particularly in the irrigated and high rainfall regions. Previous research has shown that lodging can reduce yields by as much as 25%. As far as is known, the effect of lodging on yield response to irrigation has not been considered. Growers need to assess yield and profit benefits before purchasing or storing more water and current estimates of yield responses to increased allocation could be misleading. The APSIM-Sugarcane model has been used to estimate such responses but these estimates do not take lodging into account because crop and climatic triggers for lodging have not yet been established. There is little published experimental data on marginal yield response to increased allocation. In recognition of this, two experiments (1 and 2) were conducted in the Burdekin where responses to allocations of 2, 4, 6, 8, and 10 ML/ha were measured. Each allocation was scheduled in the best possible way. An unlimited treatment was also included. In a third experiment at Bambaroo, three levels of irrigation (0.2, 1.1 and 1.7 ML/ha) were applied. Yield response to irrigation was measured at various stages of development and at harvest in all three experiments. The APSIM-Sugarcane model was set up to simulate these experiments and long-term simulations were done for the Burdekin to assess climatic and crop conditions for lodging. Simulation of the Burdekin experiments with APSIMSugarcane indicated that yield responses to irrigation in December and February were ‘normal’ in terms of the physiology of sugarcane as captured in the model. However, when the crop was harvested (July 2002 and August 2003), the high allocation treatments yielded far less than expected. The lack of response above 4 ML/ha was explained by invoking lodging rules based on crop biomass, rainfall and antecedent soil moisture. Lodging can be controlled to some extent by irrigation. The results have important implications for decisions about investment in irrigation infrastructure including on-farm dams. Lodging and consequent yield loss due to irrigation increases the risk of investments in supplementary irrigation in a way that may not have been considered before. Lodging may mean that high volumes of water may not always be required in some situations in full irrigation schemes even when the rainfall is low.