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Land Application of Sewage Sludge: III. Nitrate Accumulation and Wheat Growth Resulting from Addition of Sewage Sludge and Wood Wastes to Soils¹

ABSTRACT

Anaerobically digested sewage sludge, and wood and bark residues were added to a Nunn clay loam at several mixtures and rates up to 224 dry metric tons/ha in laboratory and greenhouse studies to determine the effect on wheat (Triticum aestivum L. em. Thell) growth and on nitrate accumulation in the soil.

With increasing proportions of sludge and decreasing wood-bark residues, there was an increase in wheat growth at all application rates except 224 metric tons/ha, wherein the yield dropped with the 100% sludge treatment. Results were similar with the wood-sludge and bark-sludge mixtures with only slight variations.

Nitrate accumulation was low whenever the wood residue-sludge mixtures had more than 50% wood residue. Relative NO₃^–-N accumulation indices were determined for each application rate and each wood-bark-sludge combination, showing the N immobilization tendency of the wood-bark-sludge mixtures.

The relationship between wheat growth in the greenhouse and nitrate accumulation in the laboratory soils has a correlation coefficient of 0.82 (significant at 0.99 probability level). Therefore, the wheat growth may have been limited by lack of nitrate resulting from immobilization of N when high proportions of wood residues were added in the organic waste. Maximum wheat growth occurred with the same treatments in the greenhouse that caused the soil in the laboratory to accumulate about 300 ppm of NO₃^–-N in a 2 month period. For this study, near maximum wheat growth resulted from several different mixtures and rates of wood (W), bark (B), and sludge (S), including 224 metric tons/ha of WB-25%S-75%, 224 metric tons/ha of B-25%S-75%, 224 metric tons/ha of W-50%S-50%, and 112 metric tons/ha of W-25%S-75%.

Key Words: bark • NO₃^– accumulation • land application • municipal waste disposal or recycling

¹ Supported by the Rocky Mountain Forest & Range Exp. Sta., Forest Service, USDA, and by the Colorado State University Exp. Sta. and published as Scientific Series Paper No. 2029.

² Professor, Post Doctoral Fellow, and Research Wood Technologist, CSU, Agronomy Dep. and Rocky Mountain Forest & Range Exp. Sta., Fort Collins, CO 80523. Dr. Agbim is now lecturer in Soil Microbiology, University of Nigeria. Nsukka.

Received for publication December 27, 1974.