RYE MULCH CHARACTERIZATION FOR THE PURPOSE OF MICROCLIMATIC MODELING

In a field experiment conducted at two locations in Southern Ontario, Canada, during 1989 and 1990, we monitored several rye mulch character istics including mulch amount, residue area index (RAI), percentage co ver, reflectivity and transmissivity of solar radiation. Changes in mu lch surface and soil temperatures, and soil water content induced by t he presence of a rye mulch were also measured. Empirical functions wer e obtained to describe (a) initial-mulch amount and mulch reduction ra te, (b) mulch amount and RAI, (c) change in percentage cover over time , (d) change in short-wave reflectivity over time at various percentag es of ground cover, and (e) change in transmissivity with RAI. By obta ining the area of straw per unit dry matter of straw (A(m)) and the sl ope of the linear regression between mulch reduction rate and initial mulch amount, functions were derived to describe the change in mulch c haracteristics over time. Mulch temperatures differed with mulch amoun t, warmer at the top and cooler at the bottom of a thicker mulch. Sinc e mulch amount decreased faster for larger mulch rates this difference changed over the season. Soil maximum temperatures in the surface lay er were lower under the mulched treatments when compared to the no mul ch plots. This difference decreased more quickly over the season for t he initially heavier mulch. Soil water contents were higher under the mulched than the no mulch treatment in 1990, with differences decreasi ng after rainfalls.