Comparisons between paired old and new land sites for sugarcane growth and yield and soil chemical, physical, and biological properties

Results are summarised of initial studies by the Yield Decline Joint Venture into differences in crop growth and yield, and soil chemical, physical, and biological properties between paired old and new ·land sites in north Queensland. The paired sites were located in the Tully, Herbert, and Burdekin areas in 1993/94, and yield decline has been recorded in all three areas. The studies were part of a program aimed at identifying the major factor/factors responsible for yield decline. The results indicate that all old land is degraded relative to new land but that the degraded soil properties are not consistent across sites. Thus a wide range of soil factors may be implicated in yield decline with the relative importance of each varying between locations and being dependent on soil type, environment, and crop management. In general, the results indicate that old land is likely to be more acid, have lower cation exchange capacity, have more exchangeable aluminium and manganese, have less copper and zinc, have less microbial biomass, have greater soil strength, have lower infiltration and water holding capacity, and have more root pathogens, but all of these factors were not important at all sites. Crop yields are also likely to be lower on old land. It is suggested that there are many complex interacting factors involved and that the long term solution to yield decline will be based on improved farming systems.