The state of site-specific management for agriculture : invited chapters and the proceedings of a symposium sponsored by Divisions S-6, S-4, S-8, and S-5 of the Soil Science Society of America, Division A-3 of the American Society of Agronomy, and the North Central Regional Committee on Site-Specific Management (NCR-180) in St. Louis, Missouri, 31 October 1995 / editors, F.J. Pierce and E.J. Sadler ; organizing committee, F.J. Pierce ... [et al.]