Defining soil quality for a sustainable environment : proceedings of a symposium sponsored by Divisions S-3, S-6, and S-2 of the Soil Science Society of America, Division A-5 of the American Society of Agronomy, and the North Central Region Committee on Soil Organic Matter (NCR-59) in Minneapolis, MN, 4-5 November 1992 / editors, J.W. Doran ... [et al.] ; organizing committee, J.W. Doran, J.A.E. Molina, and R.F. Harris ; editor-in-chief SSSA, J.M. Bigham ; managing editor, Susan Ernst