SOILS AND ALKALI. 
9 
Cultivation conserves soil moisture. It must be remem¬ 
bered that this water contains soil ingredients in solution. 
Hoffman has estimated that the quantity of matter dis¬ 
solved from the soil by water varied from .242 to .0205 
per cent, of the dry earth. The experiments of 
Humphrey and Abbot have shown that about 
one-sixtli of the total sediment of the Mississippi 
river is soluble in water. Another important fact is the 
relation between the soil and heat. The heat comes from 
three sources: Solar heat, as the sun’s rays ; heat of 
chemical decomposition within the soil, and the original 
heat of the earth’s interior. The latter cannot be of any 
value to plants; the heat of chemical decomposition is 
not of any value, except in a few special cases. The sun, 
therefore, remains the only source of heat of practical im¬ 
portance in relation to the production of crops from the 
soil. Dark-colored soils, absorbing most and radiating the 
fewest rays, must attain the highest temperature. 
Schubler’s classical researches on soil temperature, show 
that there is a difference of over 7° C. between white and 
black soils, all other conditions being alike. The ease 
with which a soil receives and retains solar heat is largely 
due to the specific heat of the soil. The specific heat of 
a body is expressed by a number which shows the amount 
of heat necessary to raise a given weight of the body one 
degree (0° to 1° C.) of temperature, as compared with the 
amount necessary to raise the same weight of water one 
degree. The specific heat of the soil is usually between 
.20° and .25° ; while that of water is taken as the stand¬ 
ard, or 1°, or four or five times as high. It must follow 
that the moisture of the soil possesses great influence on 
the soil temperature—so much so, that a dry, light- 
colored soil may attain a greater degree of warmth than 
a moist, dark-colored one. The action of water in reduc¬ 
ing soil temperature is easily explained. In our latitude, 
we see the water in all its forms—solid, liquid and gase- 
