Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 15, 2004
Publication Date: October 31, 2004
Citation: Chaney, R.L., Codling, E.E. 2004. Bio-based plant nutrient products: heavy metal considerations. Proceedings of Workshop Bio-Based Plant Nutrient Products. p. 22-36.
Interpretive Summary: With the development of regulations to limit phosphate in runoff of agricultural fields (non-point sources), livestock manure issues have gained attention. If manures are applied as N fertilizers, phosphate accumulates in soils and increases the potential for runoff. Alternative methods for utilization of livestock manures include the production of bio-based plant nutrient products with sufficient benefit to promote sale to non-farm users. Revegetation of roadside soils, of disturbed and institutional soils, and fertilization of lawns and gardens appear to be high value markets, and some composted and matured organics can be used in potting media. The present paper summarizes information about the presence and potential for risk from trace elements present in manures and byproducts. One issue is the high levels of Cu and Zn in swine and poultry manures which result from feeding high levels to stimulate growth, levels far higher than needed to satisfy animal requirement for Cu and Zn. On the other hand, much of the concern about future plant toxicity from Cu and Zn in such products is based on studies in which soluble metal salts were applied, and extremely low pH occurred which can increase metal solubility and toxicity. Such studies are not an appropriate basis for setting limits since Cu and Zn in manure or biosolids have only caused adverse effects on plants when amended soils were allowed to fall to very low pH and sensitive crops (peanut, lettuce) were grown. Interestingly, when biosolids are rich in Fe added during sewage treatment to remove more soluble phosphate during wastewater treatment, the biosolids formed have stronger metal adsorption which reduces the phytoavailability of applied metals to plants. High quality biosolids have not caused adverse effects even which extreme cumulative applications. Such principles can be applied to produce soil conditioners which can be applied to urban soils to improve turfgrass cover and reduce risks to children of Pb present in such soils. Bio-based plant nutrient products can be designed to fill many market demands by application of research findings available today.
Livestock manure, biosolids, composts, and agricultural, municipal and industrial byproducts may be used as soil amendments to supply plant nutrients or soil conditioning to soils. Such amendments can replace purchased fertilizer amendments, and unique products may be manufactured by mixing different manures and byproducts together to achieve improved effectiveness or reduced environmental impacts. Phosphate in manure is an increasing concern because runoff of soluble P from manured fields may cause eutrophication of streams. Combining Fe or Al rich byproducts with manures can limit P solubility and reduce runoff by improved infiltration in organic matter enriched soils. Heavy metals are present in all soils and all amendments; the first potential adverse effect of elements commonly present in manures, biosolids and composts are summarized. Much research has been conducted on metals applied in biosolids, but more Zn, Cu and Cd are present in all US livestock manure than in all US biosolids. Research has now shown clearly that biosolids rich in Fe and phosphate have increased ability to adsorb metals, and the stronger adsorption of metals in soils amended with Fe-rich biosolids reduces the uptake and potential for phytotoxicity of metals. This finding indicates that the deliberate addition of Byproducts rich in hydrous Fe oxides could reduce the potential for adverse effects of biosolids and manure metals while reducing P runoff potential. Additionally, such mixtures can be amended with limestone containing byproducts to make amendments which counteract the acidification normally found with ammonium and sulfide in manures and fertilizers. Such mixtures have been used in reducing Pb risk from contaminated soils near smelters and in inner-cities, and to reverse the severe Zn phytotoxicity near smelters. Making bio-based plant nutrient products by mixing manures, biosolids, composts and byproducts generates products with exceptional ability to improve soils and remediate problem soils.