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Mineralization of Nitrogen in Soils Amended with Organic Wastes¹

ABSTRACT

This study was conducted to compare the mineralization of N in soils amended with various sewage sludges, animal manures, and plant materials. In this work, field-moist soils mended with organic waste materials at a rate of 50 Mg ha^–1 were mixed with glass beads, packed in leaching columns, leached with 5 mM CaCl₂ to remove the mineral N, and incubated at 30°C. The leaching procedure was repeated every 2 weeks for a total of 26 weeks. The leachates were analyzed for NO^–₃-N. With the exception of alfalfa (Medicago sativa L.), in general, mineralization of N exhibited a slow initial rate, which was indicative of a lag period, followed by a rapid increase in rate, and subsequent slow rate of N release. The total N mineralized from the organic waste materials varied considerably, depending on the type of soil and organic waste material. The total N mineralized in five unamended soils ranged from 91 mg N kg^–1 with Lester soil to 337 mg N kg^–1 with Webster soil. The amounts of N mineralized in soils amended with sewage sludges and animal manures ranged from 156 to 668 mg N kg^–1 soil and from 176 to 617 mg N kg^–1 soil, respectively. The total N mineralized in soils amended with plant materials ranged from 0 in 3 soils amended with sawdust to 983 mg N kg^–1 for Webster soil amended with alfalfa. Expressed as a percentage of total organic N added to soils, the N mineralized ranged from 1 to 58% for sewage sludges and from 13 to 67% for animal manures. The percentage of organic N mineralized in plant materials ranged from 3% for soybeans to 97% for alfalfa. Addition of corn residue or sawdust resulted in decreases in N mineralization ranging from 3 to 687%. Soil types have marked effects on the mineralizable N (N_o) pools and firstorder rate constants (k).

Key Words: N_o • N immobilization • sewage sludges • animal manures • crop residues

¹ Journal Paper no. J-11988 of the Iowa Agric. and Home Economics Exp. Stn., Ames, IA. Projects 2112 and 2274. Presented before Div. S-4 Soil Sci. Soc. Am., Detroit, MI, 3 Dec. 1980.

² Postdoctoral Research Associate and Professor of Soil Chemistry, respectively, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011.

Received for publication August 12, 1985.