Erosion and Hydrology of Steeplands Under Commercial Pineapple

Abstract

The pineapple growing industry of south-east Queensland began as a “pioneer” industry because farmers could purchase and develop steep sloping land with a small amount of capital. Over a period of 50 years, considerable areas have been abandoned while other new areas have been developed. Such commercial farming is a source of agricultural pollutants that could endanger the quality of coastal habitats and the expanding tourism industry. This paper reports 3 years of soil erosion and hydrology results from one pineapple-growing farm. Field experiments were established to find out row lengths that would allow sustainable production from steep sloping land (33–38%). The farmer's up-and-down slope row lengths of 7 m were investigated, but also increased to 12 m and 22 m for comparison. It was found that the hydrology of the shaley regosol was influenced by exfiltration from small areas on the lower slopes. “Talc-like” lines of soil had high rates of transmissivity in parts of the midslope and water moved in these sub-surface lenses as hillslope throughflow before exfiltrating down slope. When events influenced by throughflow were deleted and runoff was separated into thunderstorms and rain depressions, it was found that row length affected peak runoff rates but not total depth of runoff. Soil erosion of 7 m and 12 m long rows was very similar but increased by 4 times due to rilling in the 22 m long rows. Multiple regression analysis showed that precipitation-related variables were important in un-rilled rows while runoff type variables were significant in rilling. Cumulative EI30 was found to be a useful surrogate for soil surface armouring and consolidation in the prediction of soil loss and sediment concentrations for events. Sediment concentrations were strongly influenced also by event type (thunderstorms versus rain depressions). Beta values (used as an index of soil erodibility) were also affected by event type, but showed a decline through time as the soil consolidated. The study established maximum permissible row lengths for the farming system studied and provided guidelines for improvement of the system.