Use of compost to mitigate the salt effect of sediment from Taylor Creek in south Florida

Disposal of a large quantity of sediment dredged from Indian River Lagoon and tributaries remains a great challenge in south Florida. The sediment from Taylor Creek contains relatively low organic matter (total C <5%) and nutrients (0.3% total N), but a large amount of salts (>2%). Therefore, the sediment cannot be used directly as a soil amendment because of the adverse effects of salt on seed germination and subsequent plant growth. Addition of compost (of biosolids and yard waste) substantially increased organic matter, nutrient contents, and moisture-holding capacity, reduced soil pH, and diluted the salt. Plant tests indicated that even 20% of sediment in the sediment-compost mixture resulted in <20% germination of Japanese millet (Echinochloa esculenta). However, seed germination was improved significantly by placing a thin layer of compost (1-2 cm) on top of the mixtures, with a germination rate of >70% in mixtures with 80% or less sediment. At 100% sediment, no plant survived, but plant growth as measured by plant height and biomass yield increased with increasing proportion of compost. Plant analysis did not indicate deficiency of nutrients at the high proportions of sediment, but revealed a very high sodium concentration in the plant shoot. A significant negative correlation occurred between shoot dry matter yield and plant sodium concentration. A column leaching study indicated that it may take 6 months of rainfall in the Indian River area (approximately 700 mm) to reduce the salt concentration in the sediment to below critical levels for plant growth. Therefore, for the beneficial re-use of this sediment for plant/crop growth, it is essential to overcome the high-salt constraint by amending the sediment with compost and/or leaching of the excess salts.