INFLUENCE OF VARYING SOIL CONDITIONS ON NIGHT-AIR TEMPERATURES

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SYNOPSIS A relation shown to exist between the temperature of the soil and the ensuing minimum temperature of the air immediately above, as affected by the varying conditions of the former—constituent character of the soil, moisture content, and the amount and character of the vegetal cover. Low night-air temperatures in gardens and truck farms may often be prevented in the first place by the selection of soil in which there is sandy component, as sand and sandy laoms are warmer than other soils and give off heat in the nighttime by conduction to the air above, thus diminishing the probability of critical temperatures and the formation of damaging frosts. Secondly, the land in use should be well drained of surplus moisture, as wet soils are invariably cold soils and more susceptible to frost damage. Lastly, any soil, whether it be sand, loam, or clay is warmer when it is clean and free from weeds and unnecessary vegetation, as bare soils are productive of higher night-air temperatures than those covered with a rank growth, form which the heat received in the daytime is lost at night by radiation to space. Finally, there may be several reasons why frost forms on one side of a street and not on the other, or in one section of a level farm and not in another. If there are contrasting soils, one productivity relatively high night-air minima and the other relatively low readings, or if the land differs even slightly in the amount of moisture, or in the kind and extent of the surface covering, or amount of insolation received, frost will appear in the sections which have wet, colds soils, covered with heavy vegetation or uncultivated, while, on the same night and under the same meteorological conditions, frost may not form on other ground close by where the soil is relatively dry, warm, and clean.