Recycling Agricultural By-Products To Grow Sugarcane On Sandy Soils In South Florida.

The use of agricultural by-products as organic fertilizer could improve sugarcane (Saccharum spp) yields grown on sandy soils with low organic matter (OM) content. This study was designed to investigate three types of agricultural by-products in the Everglades Agricultural Area for their potential use as organic soil amendments and substitute inorganic phosphorus (P) fertilizer to grow sugarcane on sandy soils in south Florida. The mesocosm experiment lasted twelve months during which sugarcane was grown in lysimeters using mill mud, mill ash, a 50/50 mix of mill mud and mill ash, and water lettuce (WL) at a high, medium, and low application rate. We hypothesized that these amendments would add OM and increase microbial activity, therefore adding nutrients to sandy soils to increase sugarcane yield.  The composition of each amendment and their effects on soil properties, plant growth, and the microbial community was compared to a control containing diammonium phosphate, the conventional fertilizer used to grow sugarcane on sandy soil. Soil tests included pH, OM content, cation exchange capacity, total P, mehlich-3 P, NO₃-N, NH₄-N, and TKN. Microbial analyses included microbial biomass P, carbon, nitrogen, and phosphatase activity. Plant growth was determined by measuring plant height, number of stalks, leaf nutrient composition, and sucrose content. The treatments amended with mill mud and a 50/50 mix of mill mud and mill ash served as valuable organic amendments since they significantly increased sugarcane biomass, sucrose content, and available nutrients in leaf tissue and soil. The mill ash and WL treatments failed to significantly increase sugarcane biomass and sucrose yield after one year; however, the mill ash treatment may be beneficial in the long term due to its high carbon:nitrogen ratio.