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TRACE ELEMENTS AND BENEFICIAL USE OF ORGANIC RESOURCES
Citation:
Chaney, R. L., S. L. Brown, A. P. Davis, J A. Ryan*, AND U. Kukier. TRACE ELEMENTS AND BENEFICIAL USE OF ORGANIC RESOURCES. Presented at Conference on Composting in the Southeast, Palm Harbor, FL, 10/6-9/2002.
Description:
This paper summarizes information on risk assessment for metals (Cd, Pb, As, Zn, Cu, Hg) in compost products used in agriculture or horticulture, and progress in research to develop and demonstrate the use of Tailor-Made Composts to remediate metal phytotoxic soils. Research has increasingly illustrated the role of inorganic adsorption surfaces in composts and biosolids in adsorption of metals in the amendment and in amended soil. In general, hydrous oxides of Fe and Mn with high surface area can persist in amended soils, and limit solubility, phytoavailability, and bioavailability of soil metals including Zn, Cd, Ni, Cu, and Pb. We conclude that the ratio of metals to metal adsorption and chelation ability of a compost controls the availability of metals to serve as fertilizers or to cause adverse effects. This relationship supports limiting metals in composts and/or increasing the adsorbents in composts. And such products can be used as effective Zn, Cu, Fe and Mn fertilizers if Fe and Mn are balanced for plant nutrition during addition of adsorbents to composts. Further, high Fe additions to organic products can help limit P leaching and runoff, of increasing importance in soil management.
The ability of a Fe and Mn rich compost, biosolids, or manure to adsorb or precipitate soil metals and correct the severe infertility of metal contaminated mine wastes or smelter contaminated land can provide comprehensive remediation of a metal phytotoxic site if sufficient limestone or alkaline byproduct is added to make and keep the site calcareous. The combination of alkalinity, sorption, and plant nutrients reduce solubility of Zn, Cd, Pb, Ni, and Cu, preventing phytotoxicity and reducing bioavailability of soil metals to animals which ingest soil. Highly effective revegetation of long dead smelter or mine waste killed ecosystems was achieved at numerous locations using the "Tailor-Made" approach.
Our ongoing research is learning how to find and use low grade Fe and Mn industrial byproducts to improve and add value to composts. But Fe and Mn industrial byproducts are usually oxides with low surface area and little value in metal sorption or fertilization. We hoped that composting could convert these low value industrial byproducts into compost amendments which limit phosphate solubility, provide persistent metal and P adsorption capacity (Codling et al., 2000), and supply effective fertilizer value; but anaerobic digestion will be required to dissolve byproduct Fe and Mn oxides. Anaerobic digestion and/orcomposting can be low cost methods to combine different organics and mineral byproducts into soil valuable conditioner/fertilizer products to solve difficult environmental remediation problems.
Further, demonstration of the effective use of composts to remediate metal toxic soils illustrates the low potential for metal toxicity from such materials; only extremely low soil pH management can allow Zn and Cu added with composts to comprise risk to sensitive plants, pH levels which are well below those recommended for crop production. Thus improved understanding of the role of constituents in composts and biosolids in adsorption or precipitation of metals has supported development of a highly effective soil remediation technology and a new market for compost products enriched in Fe and Mn.