46 Elementary Principles of Agriculture 



(c) By applying substances which act chemically 

 or physically upon the particles. These are called amend- 

 ments, or indirect fertilizers. Lime is a familiar example. 

 It renders many stiff clay soils mellow, and cements or 

 binds together the particles of a sandy soil. Fertilizers 

 are also amendments, because they act to modify the 

 texture of the soil as well as to supply mineral plant 

 food. Evidence is not wanting that the good effects of a 

 fertilizer are sometimes much greater than the amount 

 of mineral food supplied would allow us to expect. This 

 is probably due to the effect of the fertilizer on the 

 texture of the soil particles. It is especially true of 

 composts, for they serve not only to supply plant food, 

 but also to improve the texture of the soil. 



74. The Texture of the Soil affects the yield of crops 

 to a striking degree. To improve the texture is often 

 equivalent to an application of a fertilizer. One farmer 

 will raise as much on twenty-five acres as another will 

 raise on forty acres. A gardener will raise as large a 

 plant in a small pot of soil as a farmer does in a yard 

 of soil. It seems that the surface exposed to the action 

 of the root-hairs in the pot of soil may be equal to the 

 yard of imperfectly prepared soil in the field. 



75. A Soil is in Good Tilth when the particles are small 

 enough for all the root-hairs to find a surface upon which 

 they may act. A soil in good tilth exposes a large sur- 

 face to the slow action of water, air and roots. (Fig. 30.) 

 A coarse, lumpy soil may contain an abundance of plant 

 food, but still make poor crops. If we take a cube and cut 

 it into halves, we increase the surface exposed by one-third ; 

 we add two sides. By dividing again, we increase the 

 surface in the same ratio. It will be seen that a lump of 

 soil, when sufficiently fined to be in good tilth, exposes a 



