SOIL FERTILITY. 623 



fertilizers as applied to the growing of crops as to any other single thing 

 that farmers have been so hostile to ' scientific ' farming and to scien- 

 tific agricultural institutions. 



The physical conditions of the soil in regard to fertility are as 

 important perhaps to the farmer as all the others put together, because 

 they are more directly under his control. Yet this has never been fully 

 understood by the farmer, nor has it been developed with agricultural 

 students as it should have been. Air and moisture are the two most 

 important substances in the soil. The conservation of these and the 

 bringing of them to the roots of the plants is, therefore, one of the 

 chief problems. It is merely the management of these two substances, 

 for they are always present, that the farmer should concern himself 

 with. Timely and suitable cultivation, then, for the development of 

 crops is of the highest importance. Indeed, manuring of soil resolves 

 itself largely into a question of supplying moisture and placing soil in 

 such a condition that the air and moisture are in the best situation for 

 use by the plant. In fact, when a farmer plows under a crop of rye 

 he does not add any material to the soil excepting what the plant 

 obtained from the air, and this is always available from the air. The 

 other substances contained in the rye are simply restored to the soil. 

 There is no addition. The rye is, therefore, not a manure in the proper 

 sense, but a means by which the farmer improves the physical conditions. 



It is not difficult to see, therefore, that the artificial manures in 

 powder form can not contribute to any very great extent to fertility, 

 if fertility is so largely a physical question. There are conditions of 

 soil, such as size, shape and arrangement of particles, which have to do 

 directly with the air and the water content. The arrangement of the 

 particles can be controlled largely by the farmer. 



There is one other force called physical affinity, which is of the 

 highest importance because it is largely through the interaction of 

 this force among the various substances in the soil that plants are 

 capable of extracting solids in solution from it. This physical affinity 

 is exercised among the various soil constituents, each one exerting an 

 influence over the others. Now, if some substance (not in the soil) 

 be added to it, the whole equilibrium may be disturbed by the affinity 

 this may have for the substances already there. A chemical analysis 

 can not determine this. The soil yields up to chemical analysis all that 

 it contains, no matter what the relationship may be among the con- 

 stituents. To the plant, however, which depends upon a form of phys- 

 ical affinity for its soil food, all the soluble substances will probably 

 not be given up. Therefore, it is a question of physics, as well as one 

 of chemistry, which will determine soil fertility. 



When the farmer summer-fallows a field he does not add anything 

 directly by the way of a fertilizer to the field, yet it is much more fertile 

 the year after the summer-fallowing has been done. One benefit of 



