1. P. E. Rasmussen, U.S. Department of Agriculture, Agricultural Research Service, Columbia Plateau Conservation Research Center, Pendleton, OR 97801, USA. K. W. T. Goulding, Institute of Arable Crops Research–Rothamsted, Harpenden, Hertfordshire, AL5 2JQ, UK. J. R. Brown, Department of Soil and Atmospheric Science, University of Missouri, Columbia, MO 65211, USA. P. R. Grace, CIMMYT–International Maize and Wheat Improvement Center, Lisboa 27, Apdo Postal 6-641, 06600 Mexico DF, Mexico. H. H. Janzen,...