MANAGEMENT OF THE INTERFACE BETWEEN SUGARCANE CYCLES IN A PERMANENT BED, CONTROLLED TRAFFIC FARMING SYSTEM

AN EXPERIMENT was conducted at Tully to assess the effect of different methods and timing of cane trash management and methods of legume management at the end of a cane cycle on the following sugarcane crop in a permanent bed controlled traffic farming system. Six cane trash management treatments were interacted with two legume management treatments and two rates of nitrogen fertiliser. Cane trash was either burnt or incorporated two months prior to soybean planting, incorporated one month or one week prior to soybean planting or retained on the surface when the soybean was planted. An additional cane trash management treatment involved leaving the ratoon establish with no soybean being included and either spraying out the ratoon or incorporating it at the same time as the soybean was incorporated, a simulated plough-out/re-plant system. Legume management involved either incorporating soybean into the surface of the bed at physiological maturity or leaving the soybean as standing residue. The two nitrogen rates were either nil or 150 kg/ha N applied at 90 days after planting. The inclusion of soybean increased cane and sugar yields by 27%, at least in part due to better nitrogen nutrition. However, there was a response to nitrogen fertiliser following soybean, an effect not measured previously in SYDJV experiments. This was probably associated with no nitrogen fertiliser being applied to the final ratoon in the last cycle and a general running down of soil N status. There was no impact on subsequent cane yield of the different cane trash management treatments although, when trash was retained on the surface, the response to nitrogen in the subsequent cane crop was greater than where it had been incorporated. Direct planting of cane into standing soybean produced higher yields than where the soybean biomass was tilled into the soil surface. Further, direct planting of cane into surface retained cane trash produced higher yields than where the cane trash was tilled into the soil surface. It is concluded that there can be flexibility in how cane trash is managed prior to legume establishment but that the best results will be obtained if cane trash is incorporated into the bed surface between one week and one month prior to soybean planting as opposed to retaining cane trash on the surface. Conversely, there is good evidence to support direct planting of cane into legume residue. It is argued that, although it may be possible to sustain yields in a permanent bed controlled traffic system without a legume break by using high rates of nitrogen fertiliser, cost factors, long-term soil health and environmental concerns will favour inclusion of the legume break. Finally, the cane trash management treatments imposed here were all with dry sugarcane trash. More adverse effects on soybean establishment and growth may well be recorded with fresh cane trash.