THE POTENTIAL PLANT FOOD 85 



The contribution to the store of available ingredi- 

 ents. Nature is at work, constantly, changing the un- 

 available stores of plant-food ingredients into available 

 forms : every sort of soil maker is at work. Hence, we 

 may conclude that the crops (included in our rotation) 

 have not only for use the supply that was available at the 

 beginning, but they have, also, an additional supply that 

 is being contributed constantly by the soil-making agents. 



It is not unreasonable, then, to suppose, that when wise 

 farming is done, manure added to the land, thorough 

 tillage performed and a good tilth maintained, this contri- 

 bution to the store of available food ingredients will keep 

 pace with the outgo through the crops removed. 



In this connection attention should be called to the fact 

 that soils are running out rapidly under the present sys- 

 tem, due to loss of available food by constant removal of 

 crops, and to the loss of humus, and the consequent in- 

 jury to physical condition. 



The return of ingredients to the land. There is sel- 

 dom observed a system of soil cropping that removes 

 the entire crop growth away from the land : always some 

 part of the crop is returned to the soil, from where it 

 originally came. With cotton, leaves, stalks, and often 

 the seed find their way back ; with corn, the entire stalk 

 or else the main stem, with the leaves, in the resulting 

 manure; with wheat, always the stubble and often the 

 straw ; and so with the most of our crops : some parts of 

 them go back to the soil. In this way, the annual re- 

 moval of plant food is lessened and a complete exhaustion 

 is, in every way, quite out of the question. 



The increase of nitrogen due to the legumes. In the 

 cycle discussed previously, during the entire term, clover 

 occupies the land, more or less, for twenty years. Consid- 

 ered in connection with this discussion, it is clearly evi- 



