100 THE PEOPLE'S FARM AND STOCK CYCLOPEDIA. 



defects of both sand and clay soils. Added to sand it makes 

 it more retentive of moisture and elements of fertility. Added 

 to clay, it makes it more porous and more easily worked. By 

 the use of green crops plowed under to increase the proportion 

 of humus, or by cultivation and use of lime to decrease its pro- 

 portion, the farmer can thus change the character of his soil, and 

 to a considerable extent make such a soil as he needs. 



What Constitutes a Fertile Soil ? A fertile soil is one 

 that is capable of yielding, under favorable conditions of season, 

 large crops. The requisites of fertility are 



1st. A sufficient supply in the soil of plant food that is, of 

 the material which the plant draws from the soil. In practical 

 estimates we may consider this plant food to consist of nitro- 

 gen, phosphoric acid, and potash. There are other substances, 

 such as lime, magnesia, sulphuric acid, and iron, which are 

 equally essential for the growth and health of the plant, but as 

 these are almost always present in sufficient quantity the real 

 question of fertility rests on the first three named. 



2d. The plant food in the soil must be in such a state of 

 combination that the plant can use it. This is a point of the 

 utmost importance. Many soils contain plant food in abun- 

 dance, yet are infertile, because the material is in forms that the 

 plant can not use. Where one piece of soil will be found that 

 is unproductive on account of lack of plant food, a hundred can 

 be found which produce but poor crops, though containing plant 

 food in abundance, because the food is in forms which the plant 

 can not use. It is not uncommon to find soils containing in the 

 upper twelve inches from five thousand to ten thousand pounds 

 of nitrogen to the acre, and which yet show greatly increased 

 crops by the addition of thirty or forty pounds of nitrogen to 

 the acre. Of course, such an addition would make no appreci- 

 able difference in the actual amount of nitrogen the soil con- 

 tained, but the benefit was due to the fact that the thirty or 

 forty pounds of nitrogen contained in the manure was in form 

 that the crop could immediately use, while nearly all of the ni- 

 trogen originally in the soil was in unavailable forms. 



3d. The fertile soil must contain sufficient moisture to supply 



