THE BENEFITS OF SUMMER CULTIVATION. 189 



everything that could be gained by the working of the bare 

 ground was secured by the cultivation of a growing crop; 

 and more; for the shading of the land preserves the moisture, 

 and chemical action goes on more effectively in the moist 

 soil than in the dry. Thus the gain resulting was found to 

 be a profitable crop and the improvement of the soil to as 

 great, or nearly as great, an extent as though no crop was 

 taken and the labor was spent on the bare ground. 



No farmer dreams of summer fallow now. He prepares 

 the land for corn, potatoes, beans, mangels, or some crop 

 which can be thoroughly worked during its growth; and 

 thus gains all the benefits which can result from this thor- 

 ough working. What then are these benefits which result 

 from this summer cultivation of the land ? 



It has been shown in previous chapters that the soil de- 

 rives a considerable amount of valuable plant food from the 

 atmosphere, and necessarily these contributions are greater 

 in proportion to the quantity of air which passes through, 

 or into and out of the soil; by circulation. It is known that 

 the soil gathers from 7 to 10 Ibs. of nitrogen every year, in 

 the form of nitric acid and of ammonia from the atmosphere. 

 But this result was proved by experiments made in the cool 

 climate of England and not upon cultivated soil. It is well 

 known that heat is a most active agency in developing ni- 

 tric acid and ammonia; and that if nitric acid is produced 

 in the atmosphere by the action of lightning^ and if ammon- 

 ia is produced by the decomposition of organic matter, that 

 in our hot summer climate, when electrical disturbances are 

 most active, and when decomposition is most rapid, we may 

 expect the fullest and most effective results of these agencies 

 and a correspondingly large product of these forms of com- 

 bined nitrogen. Thus the contribution of these forms of 

 plant food are more copious during the summer season than 

 at any other. 



But these contributions are brought down by the rains 

 and by the air which circulate in the soils. It is evident 

 and obvious that the more the air can be made to circulate 

 through the soil, and the more water that passes through it* 



