A knowledge of the value of the phosphorus in a sewage sludge relative to a conventional phosphorus fertilizer such as superphosphate can provide a strong economic incentive for farmers to accept sewage sludge as an application to agricultural land. A study of the literature showed a range of values. These appeared to be modified by method of assessment, by type of sludge, and by its metal content. An incubation study of soil-sludge mixtures showed that changes occurred in the values for solubility of phosphorus in 0.5 M sodium bicarbonate. A study of six crops and three soils indicated that the most suitable crop to indicate availability of phosphorus in sludge was spinach (Spinacea oleracea cv.) with ryegrass (Lolium perenne cv.) as the next best. Soil of any texture was suitable provided the initial bicarbonate solubility of phosphorus in the soil was less than 10 mg P kg-1. Data from the three studies carried out indicated that phosphorus in fresh undigested sludge was as available as that in superphosphate. Phosphorus in the digested sludge used was 60% as available as that in superphosphate.
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Marks, M.J. (1978), Evaluation of the nitrogen and phosphorus content of dried pelleted sewage sludge. Soil Science Annual Report, Wye Sah Centre, Ministry of Agriculture, Fisheries and Food (quoted by Williams, J. and Coker, E. G., in EEC (1981), pp. 291-307.
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Mordvedt, J.J. & Terman, S.L. (1978), Nutrient effectiveness in relation to rates applied for pot experiments; II phosphorus sources, Soil Science Society of America Journal, 42, 302-306.
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Pommel, B. (1981). Phosphorus value of sludges as related to their metal content. In EEC (1981), pp. 137-147.
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Porch, D., Bayley, R.W. & Bruce, A.M. (1977), Economic aspects of sewage sludge disposal. Technical Report TR 42. Water Research Centre, Stevenage.
27.
Porter, K. S. (Ed.) (1975), Nitrogen and Phosphorus: Food Production, Waste and the Environment. Ann Arbor Science Publications, Inc., Michegan.
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Webber, M.D. (1981), Phosphorus and water quality; Great Lakes and the phosphorus removal programe. In EEC (1981), pp. 5-19.
