Ground Cover Affects Frost Penetration

Abstract

Many phases of the relation between low atmospheric temperature and the soil have been studied and data or observations recorded. These records show that the soil freezes from the surface downward; that the soil constituent which actually freezes is the soil water; that the water which first freezes is that in the soil interstices, followed by that which surrounds the soil particles as molecular envelopes; that this water freezes in the form of long, needlelike crystals, and that these may coalesce to form ice masses, sometimes several inches in diameter. That these ice crystals and ice masses exert tremendous crystallizing force has long been known. Lyon, Fippin and Buckman in Soils state that when one cubic foot of water changes to ice the crystallizing force is about 150 tons. This freezing and the subsequent thawing break up soil masses and have a granulating effect on the soil particles, through which the physical condition of the soil is improved for crop production. If repeated frequently the alternate freezing and thawing of the surface soil may do much damage to crops and seedling trees through heaving. Low temperatures in the soil may also cause severe root injury to fruit plants. In fact, this is among the important environmental factors which determine the adapatation of the various kinds and varieties of fruit in the temperate zone. The above sketch indicates part of the background which led to the studies recorded in this atricle. Beginning in the winter of 1934-'35 data regarding frost penetration into orchard soils under various methods of surface treatment have been collected. The general story told by these studies was consistent for the years 1935 and 1936 even though the more severe weather of the second year forced the frost to much greater depths than in 1935. Reports of frozen water pipes in 1936 indicate that not for many years had the soil been frozen so deeply. The record for the winter of 1936'37 varied in several ways from that of other years and will constitute the present report.