No. 6. DEPART.MENT OF AGRICULTURE. 471 



time the weather is often very dry, usually very hot; the tempera- 

 ture of the soil is raised to the point which reduces the activity, 

 if not destroying altogether the soil organisms, and because of the 

 absence of these the changes that take place later are very ma- 

 terially reduced. Rotations should be adopted which will permit 

 the continuous covering of the soil by regular crops, or such catch 

 crops as will keep the land covered between the seeding of the 

 different ones in the rotation. A discussion of the crops adapted 

 for this purpose will be found in subsequent pages. 



There are also losses of mineral elements, which may be prevented 

 by keeping the ground covered by the growing crops. For example, 

 lands that lie bare during the late fall, winter and spring are liable 

 to be washed and gulleyed, and the finer particles on the surface 

 carried either away from the land or to such points as to make it 

 impossible to utilize them in the growth of crops. This loss may 

 be avoided if the above suggestions are followed. 



Improvement Due to Soil Amendments. 



Another method of improvement, which is partly chemical and 

 partly physical in its character, is the addition of lime. This can 

 hardly be regarded as a natural method of improvement, because 

 additions have been made to the soil of substances not before pres- 

 ent; still it differs from the addition of manures or fertilizers, which 

 contain the essential fertility constituents, nitrogen, phosphoric 

 acid and potash, as the improvement is due, not so much to the 

 direct action of the substances added as to their effect upon the sub- 

 stances already in the soil. That is, the function of the lime is 

 to increase the active fertility of the soil by action upon the sub- 

 stances there, and thus causing a greater absorption by the plant 

 of the nitrogen, phosphoric acid and potash already in the soil, and 

 without adding thereto that which was not there before. The three 

 main ways that lime may improve soils are : First, hy attacking the 

 vegetable matter^ thus assisting in the change of the combined 

 nitrogen into active, and by the reaction of the lime with certain 

 phosphate and potash compounds, rendering them available to 

 plants. This function of lime, however, is only largely valuable on 

 soils already rich in vegetable matter and mineral constituents. 



The second function of lime is to change the physical character 

 of the soil; for example, on heavy clay soil, whose particles are finely 

 divided, and whose texture is so dense and compact as to prevent 

 the easy penetration and movement of water, the lime helps to coagu- 

 late the fine particles of the soil, thus making it more open and 

 porous, and permitting the penetration and free circulation of air 

 and water. While upon the sandy soils, which are too loose and 

 open and texture, and which permits a too free movement of water, 



