Orchard floor management utilizing soil-applied coal dust for frost protection Part II. Seasonal microclimate effect

Abstract

Orchard floor management has been found to affect the microclimate on radiation frost nights; however, long-term effects of management on the seasonal microclimate have not been studied. Comparisons were made of microclimatic factors in the spring of 1986 between two adjacent 1.4 ha peach ( Prunus persica (L.) Batsch) plots in the Shenandoah Valley of West Virginia. The orchard floor of one plot had grass maintained in both the 3-m-wide tree row and 3-m-wide grass alley (grass plot); the floor of the other plot was similar except that coal dust was applied to the soil surface of the tree row (coal dust plot). Net radiative ( R n), soil heat ( G), and sensible heat flux were greater during the daytime in the coal dust plot. Averaged over the 55-day period of this study, the daily R n and G was 7 and 2 W m −2 greater in the coal dust plot, respectively. Thus, G accounted for 30% of R n on a daily basis. Daily average tree-row air (to 195 cm) and soil (to 5 cm) temperatures were ∼ 0.2 and 2.5°C higher, respectively, in the coal dust plot. The cumulative differences found at the end of this study indicated that the coal dust plot absorbed 32 MJ more net radiant energy than the grass plot. Cumulative G differences accounted for 9 MJ (30%) of the R n difference, with a greater heat flux into the soil in the coal dust plot. An approximate difference of 130 growing-degree-hours (GDH), which represented a 1% difference, was found at the end of the study. However, at the time of bloom, which required 4000 GDH, only a 40 GDH difference was found. These results indicate that microclimatic differences between management systems are cumulative and that differences for the site studied can develop by late spring. In years with greater cloud-free days, even larger microclimatic differences could develop than those reported in this study.