SOILS AND FERTILIZERS 75 



mulch. Loose straw or any other coarse mulch will 

 also prevent surface evaporation. 



Oversupply of Water in the Soil. --The growth of 

 vegetation is retarded by too much water as well as 

 by an insufficient quantity, for, as stated on page 72, 

 an oversupply of water, by filling all the spaces between 

 the particles, will exclude the air, which is as necessary 

 to the life of the plant as is water, and is also necessary 

 to the microscopic vegetable life of the soil, a life that 

 is very beneficial to plant growth. 



Too much water will reduce the temperature of the 

 soil, and thus hinder growth. 



Another harmful effect is the failure of roots to strike 

 deep into overwet soil, for the plant has little chance 

 for life if the topsoil later becomes dry. 



Soil that is too moist cannot be cultivated as it should 

 be, and thus weeds have free growth, and every weed 

 grown deprives a useful plant of food. 



Effects of Cultivation on Soil. Cultivation, or 

 tillage, is the breaking up or crumbling of the soil by 

 means of the plow or other implement, either before or 

 after seeding. There are five beneficial effects of cul- 

 tivation : 



1. It crumbles and mellows the soil. 



2. It causes more rapid and greater formation of 

 soluble plant food. 



3. It lessens evaporation of soil water. 



4. It kills weeds. 



5. It makes possible better aeration of the soil. 



(1) When the soil is thoroughly crumbled, roots can 

 find their way through it with ease ; thus tillage will 

 help to form an extensive root system for crops. 



(2) This stirring and breaking up of the soil allows 



