60 CHOP GROWING AND CROP FEEDING 



free nitrogen of the air combined and stored in the form of organic matter in 

 the soil. We will not enter into a discussion of the exact way in which they 

 do it; the fact is that no one knows just how it is done. But it is enough for 

 the farmer to know that it is done, and that he can, by the growing of these 

 plants, get a supply of material in the soil, that in its decay will give nitrogen 

 to the succeeding crop in abundance. But the very plants that do this nitro- 

 gen catching for him, are the greediest of consumers of the other two im- 

 portant elements of plant-food needed in most soils, phosphorus and potash. 

 While the careful saving and using of the farm yard manures is an important 

 help in the getting of nitrogen in the soil, the manure is always in an insuffi- 

 cient supply, and is poorer in the other elements than is desirable. Therefore, 

 the most important elements which a farmer must buy in order to keep up the 

 productivity of his soil, are phosphorus and potassium in some form. These 

 are essential to the growth of all plants, and are especially serviceable in 

 encouraging the growth of the legumes, and the enabling them to get more 

 of the costly and fleeting nitrogen for us. The various experiment stations 

 have done so much work in the study of the manurial requirements of plants, 

 and the effects of fertilizers, that there has grown up an impression among 

 farmers that for every crop planted, some complete mixture of fertilizers 

 must be applied. There is no doubt that the annual application of commer- 

 cial fertilizers will increase the crop usually grown; but true farming is 

 the getting of good crops at the least margin of expense consistent with the 

 keeping up and improving the condition of the soil. It is nt)t merely growing 

 big crops, but the most profitable crops, too. If a farmer spends $10 for a 

 fertilizer that gives him $10 worth more corn, he is simply buying corn at 

 the market price. He would better have left that $10 worth alone and bought 

 it for less labor. 



