Researchers in agronomy and soil and crop science suggest guidelines and principles for determining the maximum amount of nitrogen that can be used on the fields without polluting the water beneath. Of interest to farmers and farm managers, the 13 papers were first presented to a 1988 symposium in Anaheim, California. One paper describes the computer applications model, "nitrate leaching and economic analysis package", which is included on a disk in Fortran for IBM PCs. Annotation copyright Book News, Inc. Portland, Or.