SOIL SESSION. 123 



-of these legumes, we must know that the soil contains the proper bacteria 

 (the same bacteria will not produce nodules upon all legumes) and we 

 .must know that these bacteria will not develop well in a sour or acid soil ; 

 indeed, some of them will develop scarcely at all under these conditions. 

 If the soil is sour, an application of fine ground limestone or air-slacked 

 burnt lime must be made to destrov this sourness. Limestone is here 

 not a food for the plant, but it makes the conditions such that the bac- 

 teria can develop and supply the plant with nitrogen, which will be added 

 to the soil in the crop residues or in the crop which is turned under. The 

 other two elements, phosphorous and potasium, are both mmeral ele- 

 ments coming from the soil itself, and no rotation nor the growing of 

 any particular plant can increase the total stock of these elements. The 

 most that may be done is to bring about a transformation which will 

 make them more available to succeeding crops. The only way in which 

 we can increase the existing supply of either of these elements is to buy 

 some material which contains the element and apply this to the soil. 



We know that when we grain farmers remove one hundred bushels 

 of corn from an acre of ground, leaving the stalks on the ground, we are 

 taking away from that acre one hundred pounds of nitrogen, seventeen 

 pounds of phosphorous, and nineteen pouds of potassium. We cosider 

 it good farming when, by means of improved seed, good rotation, and 

 good cultivation, we can take off one hundred bushels of corn from an 

 acre; and so it is, but we want to go a step farther; we want to know 

 if this system is always going to maintain itself ; will it always be pos- 

 sible to get, annually, such amounts of plant food out of an acre of 

 ground? Let me say that two-thirds of the nitrogen, three- fourths of 

 the phosphorous, and one-fourth of the potassium necessary to produce 

 the whole corn plant are in the grain, the part sold from the farm in 

 ■grain farming. 



We have seen that a rotation including sufficient clover or other 

 legumes will solve the nitrogen part of the problem for us. This rota- 

 tion does still another important thing. It is the means of keeping the 

 supply of organic matter or decaying vegetable matter in the soil. Chop- 

 ing up and turning under corn stalks, as well as getting back into the soil 

 3.\\ of the oat and wheat straw, aid in this respect. This organic matter 

 is one of the things which are most easily worked out of the soil by a 

 system of grain farming in which cereals alone are grown, and in which 

 stalks and straw are burned. At the same time, it is a most important 

 factor in the productive power of a soil. It keeps the soil porous and 

 well aerated, in a good workable condition, it improves its moisture 

 holding capacity so that it will not suft'er from drouth to the same extent 



