EFFECTS OF SAWDUST USED AS A MULCH AND AS A SOIL AMENDMENT ON SOIL TEMPERATURES UNDER IRRIGATED AND UNIRRIGATED CONDITIONS

Soil temperature readings were taken at 7.30 a.m., noon, and 5 p.m. over a 3-year period (2 years without and 1 year with irrigation) at a point 4 inches below the surface of sawdust-mulched, sawdust-incorporated and check plots. The effect of blackened sawdust mulch on soil temperatures was also studied. Marked differences between soil temperatures in the various treatments were found, the greatest being during July when the difference between the average maximum and minimum air temperature was also greatest. Soil temperatures were lower in the sawdust-mulched than in the check plots, except at 7.30 a.m. under irrigation when readings were higher throughout the season in the mulched plot. After August under irrigated conditions and after October without irrigation a reversal took place, and the soil temperatures became higher under the mulch than in the check due to the slower heat loss from the mulched soil. Incorporating sawdust had only a slight effect upon soil temperatures, but blackening the mulch markedly reduced the soil temperature differences between mulched and unmulched treatments.