AGRICULTURAL AND FOREST METEOROLOGY ELSEVIER Agricultural and Forest Meteorology 78 (1996) 67-81 Rye mulch characterization for the purpose of microclimatic modelling C. Wagner-Riddle a,,, T.J. Gillespie a, C.J. Swanton b a Department of Land Resource Science, University of Guelph, Guelph, Ont., Canada NIG 2W1 b Department of Crop Science, University of Guelph, Guelph, Ont., Canada N1G 2W1 Received 4 November 1994; accepted 12 March 1995 Abstract In a field experiment conducted at two locations in Southern Ontario, Canada, during 1989 and 1990, we monitored several rye mulch characteristics including mulch amount, residue area index (RAI), percentage cover, reflectivity and transmissivity of solar radiation. Changes in mulch surface and soil temperatures, and soil water content induced by the presence of a rye mulch were also measured. Empirical functions were obtained to describe (a) initial mulch amount and mulch reduction rate, (b) mulch amount and RAI, (c) change in percentage cover over time, (d) change in short-wave reflectivity over time at various percentages of ground cover, and (e) change in transmissivity with RAI. By obtaining the area of straw per unit dry matter of straw (A m) and the slope of the linear regression between mulch reduction rate and initial mulch amount, functions were derived to describe the change in mulch characteristics over time. Mulch temperatures differed with mulch amount, warmer at the top and cooler at the bottom of a thicker mulch. Since mulch amount decreased faster for larger mulch rates this difference changed over the season. Soil maximum temperatures in the surface layer were lower under the mulched treatments when compared to the no mulch plots. This difference decreased more quickly over the season for the initially heavier mulch. Soil water contents were higher under the mulched than the no mulch treatment in 1990, with differences decreasing after rainfalls. 1. Introduction Mulch can be defined as any material on the soil surface through which continuous liquid water films from the soil are not present. The traditional mulch consists of a " Corresponding author. 0168-1923/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSD10168-1923(95)02242-2