Browsing by Author "Rigby, A"

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Productivity performance of climatological sub-regions within the Tully Mill area : ASSCT peer-reviewed paper
(ASSCT, 2019) Stringer, JK; Skocaj, DM; Rigby, A; Olayemi, M; Everingha, YL; Sexton, J
Inter-annual climate variability has a significant impact on productivity in the Wet Tropics region. Climate also varies spatially, yet the impact on productivity is less well known. Two distinct climatological sub-regions (northern and southern) have been identified within the Tully mill area based on total annual rainfall and annual average daily radiation. The wetter northern sub-region is characterised by lower radiation, lower temperatures and higher rainfall than in the drier southern sub-region. Mean cane and sugar yields were analysed for the two climate sub-regions using block productivity data obtained from Tully Sugar Limited for 2000 to 2017. After excluding 2011 (Tropical Cyclone Yasi), only farms with 15 or more years of data were included. The impact of spring-summer (SONDJF) rainfall and El Niño Southern Oscillation (ENSO) phases on cane and sugar yields in the two climate sub-regions was also analysed. On average, the northern, wetter climate sub-region yielded less cane and sugar yield than the southern, drier sub-region. There were significant differences between SONDJF rainfall terciles (dry, normal and wet) and ENSO phases (El Niño, Neutral and La Niña) for cane and sugar yields in the two climate sub-regions. Cane and sugar yields were significantly lower in years experiencing high SONDJF rainfall or in the La Niña phase. This analysis validates the results of the analyses used to derive the two climatological sub-regions in Tully. Improved knowledge of how climatic conditions influence sub-regional productivity performance will assist industry extension programs and on-farm management decisions.
Spatial distribution of potential soil constraints affecting nitrogen management in the Wet Tropics : ASSCT peer-reviewed paper
(ASSCT, 2019) Skocaj, DM; Schroeder, BL; Hurney, AP; Rigby, A; Telford, D
Position in the landscape and climatic conditions experienced during the growing season, especially following the application of nitrogen (N) fertiliser, has important implications for crop growth, N uptake and N losses. Understanding the spatial distribution of soils where crop growth and responsiveness to applied N may be constrained in wet or dry years will allow growers and advisors to refine N-management strategies. To identify soils where crop growth and responsiveness to applied N may be restricted, a system of grouping soils that better reflected agronomic performance under different climatic conditions was required. The categorisation system considered position in the landscape, N-mineralisation potential, soil water-holding capacity in both wet and dry years, propensity to waterlog in wet years and presence of a water table in wet years. In dry years, waterlogging and the presence of a water table do not impact crop growth to the same extent as moisture availability, and, hence, in dry years, it is more important to categorise soils based on water-holding capacity. The major sugarcane-growing soils in the Tully and South Johnstone mill areas were categorised using this system. This resulted in five soil groups to describe the impact on crop growth and N responsiveness in wet and dry years. Given the application of N fertiliser to ratoon crops predominately occurs around spring, wet years were defined as receiving high spring-summer rainfall, whereas dry years were defined as receiving low spring-summer rainfall. Classifying wet and dry years according to spring-summer rainfall also allows growers and advisors to refer to seasonal climate forecasting indices for guidance on the likelihood of experiencing a wet or dry year. In wet years, the impact on crop growth, responsiveness to applied N and potential for lower N uptake is greatest for soil group five. These soils tend to occur in the lowest positions in the landscape, experience severe waterlogging and a persistent water table. They are also subject to frequent water inundation following extreme rainfall events. The spatial identification of soil constraints will complement the development of whole-of-farm nutrient-management plans in the Wet Tropics region. Knowledge of soil constraints influencing sugarcane growth and responsiveness to N will allow growers and advisors to better identify areas where nutrient-management strategies may require further fine-tuning. This information may also be of value in improving other management decisions including varietal selection and harvest scheduling