146 Report on Trials of Plows. 



Successive crops of corn have been annually taken from the soil 

 ever since, but the average product has run down to about forty- 

 bushels to the acre. In the year 1862 a large field was plowed 

 with the sod and subsoil plow to the full depth of eight inches. 

 The result of this experiment was that the land produced one hun- 

 dred and twenty bushels to the acre, while the skim plowed land 

 contiguous to it yielded but forty bushels. 



These facts show an additional answer to the question, "How 

 does plowing increase the fertility of the soil ?" They tell us 

 very clearly that it is by aifording facilities to the extension of 

 the roots, and thus extending the range of pasture for the plants. 



The answers already given by no means exhaust the question. 

 There are still many important uses of plowing which are yet 

 undescribed. The germination of seeds requires seclusion from 

 light; they must therefore be placed beneath the surface. They 

 also require the presence of atmospheric air; without it the radicle 

 will not enter the soil nor the plumule jDrotrude into the air; nor 

 Avill the starchy matters stored up in the cotyledons be trans- 

 formed into sugar for the nourishment of the young plant. Pul- 

 verization of the soil is therefore essential, that the seeds may be 

 regularly secluded from the light; but in such a way that the air 

 can penetrate very freely to them. These conditions are com- 

 pletely fulfilled when the land is properly plowed. 



Stagnant water in the soil, by cutting off the access of air to 

 the roots of plants, prevents their nutrition and consequently 

 their growth. Deep plowing diminishes this evil by permitting 

 the water to penetrate deeper into the ground. 



Warmth of the surface soil is essential to the growth of crops. 

 When water lies upon the surface, it is taken up again into the 

 air by evaporation, which causes the absorption of an immense 

 amount of sensible heat which it renders latent. The cooling of 

 surfaces by evaporation is made practically familiar to us when- 

 ever we wash our hands or wet our heads. Deep plowing and 

 thorough pulverization, by permitting the water to sink into the 

 ground, diminishes the amount of evaporation from the soil, and 

 thus prevents the temperature of the surface from being lowered. 



The exhalation of moisture from plants into the air is very 

 great. In the experiments very carefully made by Hales, he found 

 that a sunflower threp and a half feet high, with a superficial area 

 of 5.616 square inches, perspired at the rate of from twenty to 

 thirty ounces in twelye hours, or seventeen times more than a man 



