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A Field Study of the Agricultural Use of Sewage Sludge: I. Effect on Crop Yield and Uptake of N and P¹

ABSTRACT

Anaerobically digested liquid sewage sludge was applied to field plots at rates of 0, 3.75, 7.5, 15, 30, and 60 metric tons dry solids/ha on a Warsaw sandy loam and a Piano silt loam during the summer of 1971. Additional experiments were established at both locations in 1972 and 1973 using the same treatment rates. Following sludge application the 1971 and 1972 trials were planted to rye (Secale cereale L.). After rye forage harvest the following spring, the residual crop responses were tested with corn (Zea mays L.) on the 1971 and 1972 experimental areas for up to 3 years. The 1973 plots were initially cropped to sorghum-sudan (Sorghum bicolor L. Moench x S. sudanese P. Stapf.) followed by 1 year of corn.

Yields of the first crop following sludge application typically increased significantly up to the 7.5-metric ton/ha rate on the silt loam soil, and up to the 15-metric tons/ha rate on the sandy loam soil. This corresponded to an application of 190 and 380 kg/ha of available N, and 183 and 366 kg/ha of total P for the 7.5 and 15 metric tons/ha rates, respectively. In some cases, the 30- and 60-metric tons/ha rates depressed the first crop yields, possibly because of large amounts of soluble salts in the sludge. Residual benefits from sludge were evident for at least 3 years at the higher treatment rates.

Increasing rates of sludge generally resulted in marked increases in the concentration of N and P in plant tissue. Total recovery by up to four successive crops averaged about 50% for available N and 7% for P at the low treatment rate, and about 14% for N and 3% for P at the highest treatment rate.

Key Words: recycling • crop uptake • slow release fertilizer • waste disposal • Secale cereale L. • Sorghum bicolor L. Moench x S. sudanese P. Stapf. • Zea mays L. • salt toxicity

¹ Research supported by the College of Agric. and Life Sci. (Proj. nos. 1602 and 1921), Univ. of Wisconsin, Madison, and by a grant from the Janesville Water Pollution Control Utility, Janesville, Wis. Parts of this paper were presented before Div. A-5 of the American Society of Agronomy, 13 Nov. 1974, Chicago, Ill.

² Research Assistant, Professors, Postdoctoral Fellow, and Professor, respectively, Dep. of Soil Sci., Univ. of Wisconsin, Madison, WI 53706. The senior author is currently Assistant Professor, Dep. of Natural Resour., Ball State Univ., Muncie, IN 47306, and J. A. Ryan is currently Soil Scientist, NERC, EPA, Cincinnati, OH 45200.

Received for publication May 17, 1976.