Vol. XIII. No. 309. 



THE AGRICULTURAL NEWS* 



77 



SOIL INVESTIGATION. 



STUDIES IN SOIL TEMPERATURE. 



The following article constitutes part of a lengthy 

 abstract published in the Experinvnt Station Record 

 (November 19 1"!). It embraces the results obtained 

 by C. J. Bouyouios in America frum the systematic 

 study of the factors icHuencing soil temperature. 

 Readers of the Agricultural JVevjs who are directly 

 interested in soil chemistry and physics should obtain 

 the author's puper {Michigan Sta. Tech. Bull. J 7), as 

 several original methods are described therein: — 



It was found in general that the specific heat of different 

 types of soil, gravel, sand, loam, clay and peat, in dry con- 

 dition, did not differ very materially. This was true both 

 by equal weights as well as by equal volumes. The specific 

 heat of peat was about half as great as that given to it by 

 other investigators. The moisture content of these different 

 soils in their natural condition varied very greatly, and 

 since water has such high specific heat it made a tremendous 

 difference in their final specific heat. 



'The heat transference in the different soils was 

 measured (1) in their dry condition, ("2) in their natural 

 state under laboratory conditions, (3) under field conditions. 

 It was found in all these three states that the order of heat 

 conductivity was the same. Gravel possessed the highest 

 heat-transmitting power, followed in order by sand, clay, 

 loam, and peat respectively. Convectional currents, molec- 

 ular diffusion, and distillation influenced very greatly the 

 rate of flow of heat, and consequently the values obtained 

 do not represent the true heat-conducting power of these 

 different types of soil. 



'In field conditions the solar radiation tended to travel 

 with greater rapidity and facility vertically than horizontally. 



'The study on radiation showed that color had no effect 

 upon radiation, which is contrary to the common belief, but 

 it had upon absorption: that the different types of soil 

 tended to radiate differently when dry, about the same and 

 more when well moistened and in their natural condition, 

 and that a dry surface or mulch reduced the radiation. In 

 the dry state, sand exhibited the highei^t radiating power, 

 followed by gravel, clay, loam, and peat, respectively. The 

 water, however, had by far the highest radiation capacity of 

 any soil either in the dry or moist state. 



'When the temperature of the different types of soil (all 

 covered with a thin layer of the same kind of soil in order to 

 eliminate the factor of color and other factors) was studied 

 under field conditions, it was found that they all cooled and 

 froze about the same time in the upper (1 inches, but in the 

 spring they thawed and warmed up at different rates. This 

 was attributed to their different specific heats and to the 

 downward and upward trend of air temperature in the fall 

 and spring respectively. The gravel and sand thawed first, 

 followed by clay one day later, loam two days later, and peat 

 ten days later. The temperature of the fir.'-t two soils rose very 

 rapidly after thawing, while that of the others rose very 

 slowly. When the lower depths of the latter soils had thawed, 

 however, their temperature rose also quite rapidly and finally 

 reached the same degree of magnitude as in the former or 

 lighter soils, and all continued to have almost the same 

 temperature from then on throughout the summer, autumn, 

 and winter. 



'This equal degree of warmth of all the different types 



of soil during the warm part of the year and especially during 

 the summer season was believed to be due largely to the thin 

 layer of the same kind of soil with which they were all 

 covered. This thin layer of soil tended to equalize the 

 amount of heat that penetrated into these different kinds of 

 soils by eliminating the differences of their colour and by 

 equalizing, to a large extent, the amount and rate of 

 evaporation of their moisture. 



'Of all the different types of soil, sand showed the 

 greatest amplitude and was followed by gravel, clay, loam, 

 and peat, respectively. The greatest monthly fluctuation for 

 all soils occurred in June and the least in February. 



'The different meteorological elements played a great 

 part in the temperature of the soils, but on account of the 

 complexity of their behaviour it was dithcult to trace the 

 direct influence of all of them. 



'The results from the investigation on the effect of organic 

 matter on soil temperature showed that the rate of thawing was 

 about proportional to the amount of organic matter present, 

 but that after thawing the temperature of the soils con- 

 taining '201, 3 32, 5-47, and 6 95, per cent, organic matter 

 was higher throughout the summer than the temperature of 

 the white sand and of the peat. The temperature of these 

 last two soils w.as about the same during the warmer part of 

 the year, but during the cold seasons the peat had a higher 

 temperature. The magnitude of the amplitude of all these 

 soils behaved in the same order as the average temperature. 



'The conditions of cultivation, non-cultivation, and sod 

 had a very distinct effect upon the soil temperature. During 

 the winter all three plats had about the same temperature 

 with a small difference in favour of the sod. In the spring 

 the sod and uncultivated plats thawed first and the cultivated 

 plat about one day later, at the "inch depth. The temperature 

 of the sod plat rose several degrees above that of the other 

 two plats and continued to be in excess until the plants had 

 made a considerable growth, and then it dropped below that 

 of the two bare plats, and remained so throughout the 

 summer months; but when the cold period came the order 

 was reversed, the temperature of the bare plats fell below 

 that of the sod plat and continued to be lower throughout 

 the second winter. The temperature of the cultivated plat 

 rose slightly higher than that of the uncultivated, after thaw- 

 ing, and continued to be slightly higher than during the 

 early part of the spring season or up to about the middle of 

 May, and then the uncultivated plat became the warmer and 

 remained so throughout the whole summer. During the fall 

 both plats had about the same temperature with a slight 

 difference in favour of the uncultivated plat. The ditference 

 in temperature between these two plats was explained upon 

 the following general facts: (I) IJifferent rate of evapora- 

 tion, (2) dift'erent rate of heat conductivity, (3) difference in 

 temperature at the lower depths, and (4) the effect of the 

 dry mulch of the cultivated soil. 



'Salt solutions had a very marked influence on the rising 

 and lowering of soil temperature. Different salt solutions of 

 the .same density or the same solution of different densities 

 raised the soil temperature considerably. Their influence 

 was also very pronounced on the rate and degree of lowering 

 of temperature, as well as on the rate of thawing. 



'The different kinds of manure raised the soil temper- 

 ature differently — horse manure the most, sheep manure the 

 least, and the cow manure intermediate. In every case the 

 greatest rise took place in the first three or four days. The 

 rise increased with the increase in quantity. The degree of 

 rise is probably insignificant for practical conditions.' 



