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This article in JEQ

  1. Vol. 6 No. 4, p. 345-352
    Received: May 17, 1976



A Field Study of the Agricultural Use of Sewage Sludge: II. Effect on Soil N and P1

  1. K. A. Kelling,
  2. L. M. Walsh,
  3. D. R. Keeney,
  4. J. A. Ryan and
  5. A. E. Peterson2



Liquid digested sewage sludge applied at rates from 3.75 to 60 metric ton/ha significantly increased the concentrations of inorganic N, organic N, and Bray P1 extractable P in a sandy loam and a silt loam soil in south-central Wisconsin. Most of the applied inorganic N was as NH4-N and was nitrified rapidly. At sludge rates of 30 metric ton/ha or more, substantial losses of sludge-applied N occurred by leaching. Soil solution NO3-N concentrations exceeded 100 mg/liter at the 120- to 150-cm depth 10 weeks after the first sludge application on the permeable sandy loam, and after about 1 year on the silt loam. The N balance indicated that considerable amounts of N may have been lost by denitrification, volatilization, or both, where > 30 metric ton/ha were applied. Mineralization of organic N was more rapid than previously reported. Up to 50% of the applied organic N was mineralized within 3 weeks after the last sludge application. During the remaining 25 months of the experiment, the mineralization rate was essentially constant at about 250 mg organic N/kg of soil/year at the 60 metric ton/ha sludge rate, and 180 mg organic N/kg of soil/year at the 30 metric ton/ha rate.

Sludge applications resulted in immediate marked increases in Bray P1 extractable P. However, the extractable P levels decreased with time after sludge application, probably as a result of P fixation. Significant amounts of P remained available for at least 2 years at the higher treatment rates.

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