Soil Amendment to Reduce Dissolved Organic Matter Loss From Soil- Laboratory Simulation Studies.

Water quality throughout south Florida has been a major concern for many years. Transport of dissolved organic matter (DOM) from land to water delivers nutrients (N and P), heavy metals (Cu and Zn) and pesticides, and has significant negative impacts on water quality. Laboratory incubation and column leaching studies were conducted to identify the critical factors or mechanisms that control DOM release in soils. After amended with different levels of varying organic materials including coniferous tree litters (pine needles) and deciduous tree litter (maple leaves), water plant residuals (WTRs), phosphatic clay, and chemical fertilizers (P fertilizer), two soils were subjected to 5 weeks incubation at room temperature. A  portion of the incubated soils was used for the analysis of water extractable organic matter, another portion of the soil samples (about 1.5 kg of soil of oven dry weight basis) were subjected to column leaching at time interval of 1, 3,7,14,28, and 56 days, respectively. Leachate was collected and analyzed for concentrations of DOC.

It is observed that 5% WTRs treatment resulted in the lowest extractable DOC percentage in the soil total carbon, and amendments of 1% phosphatic clay, 0.5% pine needle, 0.5% maple leaf, 1% WTRs, and 50 and 100 ppm KH₂PO₄ fertilizer did not change extractable DOC percentages as compared to Control.  However, amendments of 2.5% phosphatic clay, 1% pine needle and 1% maple leaf in the two soils resulted in greater percentages of extractable DOC. These results suggest that amendment of WTRs at 5% can significantly reduce the release of DOC in soils whereas amendment of organic materials (such as pine needles and maple leaf) and inorganic substances (such as phosphatic clay and WTRs) at low rates has a minimal effect on DOC release.

A general decreasing tendency of DOC in leachate with leaching events was observed for the soils with varying amendments, with peak concentrations of DOC occurring in the first leaching event and in the 14 days’ leaching event; afterwards, a decrease tendency in DOC in leachate was evident (28 and 56 days).  Organic material amendments (pine needle and maple leaf) at different levels resulted in higher DOC concentrations in leachate, whereas, amendment of 1% phosphatic clay resulted in the lowest DOC in leachate as compared to other amendments. Furthermore, 5% WTR amendment resulted in lower DOC in leachate than organic material amendments, but higher DOC in leachate than inorganic material amendments.

Key words: Dissolved organic carbon (DOC); Soil amendment; Column leaching; Soil total organic carbon (TOC).