Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 1, 2004
Publication Date: January 23, 2005
Citation: Chaney, R.L., Sikora, L.J., Davis, A.P., Kim, H. 2005. Making composts with lower water-soluble p and higher nutrient density [abstract]. Program for the US Composting Council Annual Meeting. p. 33-34.
Limits on soluble soil phosphate and soluble P in manure, composts, and by-products to protect against eutrophication of surface waters, the composting industry needs to come to grips with the low N to P ratio of composts. Because the N:P ratio is lower for manure and composts than for chemical fertilizers, soil P accumulates more rapidly and would bring prohibition of fertilizer-P additions until available soil P has declined. On the other hand, high slowly soluble N and P are important benefits of compost products that make composts especially valuable in remediation of infertile or contaminated soils.
One approach to aid compliance with expected P limits would be to incorporate P adsorbents into composts so the water solubility of compost-P would be much lower. Composts made entirely from plant debris have low levels of P-adsorbents. Inclusion of feedstocks that add hydrous Fe and Mn oxides can yield compost products with both the normal benefits of composts, but lower soluble P, and fertilizer value of Fe and Mn. Composting can also achieve reduction in pathogens. Other approaches to limit water soluble P will be summarized, including new 'High Available Phosphate' grains that can be used to prepare feeds that do not require P supplements, thus lower P in manure or composts. Addition of phytase enzyme to feeds is also making organic P more bioavailable for the livestock, and reducing the levels of Cu and Zn supplementation required for non-ruminant feeds. All alternatives may influence manure and compost management to comply with soluble P limits in soils. High Fe composts may even support 'edge of field' filtration to remove phosphate from runoff water.
In existing papers, we have shown that adding certain agricultural and industrial byproducts to manures, we can keep P solubility low and reduce the bioavailability of Pb in soil ingested by children. Composts rich in Fe and P aid formation of insoluble Pb pyromorphite in soil, while incorporation and establishment of turfgrass makes it difficult to move soil into homes where young children may ingest soil.
Central to development and commercialization of this concept is better information on which byproducts are most cost-effective for addition during composting to make 'remediation grade composts'. We have been evaluating levels and forms of Fe and Mn in by-products and evaluating their ability to reduce P solubility and increase heavy metal adsorption of organic amendments. Al addition can also reduce P solubility, but Al is not a nutrient addition to soils in contrast with Fe and Mn. Re-rich low P-solubility compost products need to have some Mn along with Fe so that soil Fe and Mn fertility is improved. Sandy and Coastal Plain soils strongly need enrichment in Fe and Mn to improve soil fertility so that pH may be managed at 6.5 rather than 5.5 yet prevent lime-induced Mn deficiency. Adverse effects of Zn in swine manure have been observed only on some very acidic Coastal Plain soils, pH < 5.0, and increased soil Fe and Mn can correct the deficiency in soil formation which encouraged such acidic soils. Further, addition of Zn, Cu and other elements in composted manures helps to maintain plant available forms of required microelements. Other recent experimental results on plant availability of trace elements in manures and byproducts will be presented to show further reasons compost products contribute to sustainable agriculture. Information will be discussed on trace elements in potential byproducts to be included in mixed compost feedstocks that require monitoring or management decisions to maintain production of high quality 'Tailor Made Composts' which are especially useful in soil remediation.