Remediation of Former Sugar Cane Land with Dairy Effluent along the Hamakua Coast, Hawaii.

Soils of land along the Hamakua Coast, Hawaii were returned in extremely nutrient deficient condition with the cessation of sugar cane. Much of this land reverted to pasture usage. Soil analysis of samples collected from Island Dairy, Ookala, Hawaii pastures indicate nutrient concentrations (%N<.5 and K<115, Ca<125 and Mg<60 mg kg^-1) well below recommended nutrient concentration levels for these soils. The installation of a commercial subsurface irrigation system was implemented to utilize dairy effluent and provide nutrients. Effluent nutrient concentration was N>150, P>30, K>150, and Na>40 mg kg^-1. Field irrigation tubing was placed at a 16 inch depth in 15000 square foot plots and supplied on a nutrient demand basis followed by fresh water irrigation based on 0.5 ET. Forage is cut at an approximate height of three feet and used as green chop or ensiled. The tropical grass Pennisetum purpureum produced forage yields as high as 50,000 kg/ha per year dry matter with lagoon effluent. The major challenge of this commercial effluent irrigation is applying the proper balance of nutrients and water. Initial estimates from Island Dairy indicate that 20% of the irrigation requirement can be from effluent while the remaining requirement will be fresh water. This subsurface application system produces very high yields of forage that are a quality addition to feed for dairy milk production. This reuse of dairy effluent (formerly a waste product) to the growth of tropical forages feed supplements, contributes to cattle feed requirements, and may be a significant factor in reducing feed costs (that have risen over 30% this year) thereby helping maintain dairy farming in Hawaii.