34 Nature-Study Agriculture 



tween particles as the mineral elements of the soil do, 

 but the water enters its very substance and saturates 

 it like a sponge. Great quantities of water are held 

 in this way if humus is abundant, and such water is 

 easily given up to plants. Keeping the ground well 

 stored with humus is, then, one of the most important 

 of all good farm practices. 



Where Alkali and other soils. In all soils there is a continual 



comes from weathering or decomposition of the soil grains, and 

 soluble substances (one of which is common salt) are 

 always being formed. Where the annual rainfall is 

 large, these substances are washed out, conducted to 

 streams and rivers, and carried to the sea. (That is 

 why the sea is salt.) In those regions where the annual 

 rainfall is small, as in parts of the West and the South- 

 west, the salts that form are left in the ground. When 

 abundant, they are spoken of as " alkali " and the soil 

 is called " alkali soil." In some places there is so much 

 alkali that crops will not grow at all. 



The cause In the Central and Eastern states, sour soil is often 

 tti^remedy met with- Sourness is due to acids that accumulate in 

 the soil when it lacks lime. Lime neutralizes the acid 

 as soda neutralizes the acid of sour milk used in cooking. 

 So adding lime is the remedy for a sour soil. In some 

 sections where the heavy rainfall has dissolved the natural 

 lime and washed it out of the ground, liming will some- 

 times double the crop. 



Color of soil A black or very dark soil is universally regarded as a 

 good soil, and it usually is such, the dark color being due 

 to an abundant supply of humus. A light-gray soil in- 

 dicates a deficiency in humus. - 



