142 Bulletin 129. 



gen, 5,000 of potash and 3,800 of phosphoric acid. These quan- 

 tities are from 50 to 500 times greater than those sold off the farm 

 in any crop. There is at least 50 times as much nitrogen in such 

 a soil as is sold in any part of any crop, and much oftener 100 or 

 even 200 times as much. There is at least 100 times as much 

 "potash as is carried off the farm in any part of a crop sold, and 

 oftener 500 times as much. Similar figures might be given for 

 phosphoric acid. Why, then, must we fertilize our soils, in one 

 way or another ? 



The one most important reason is that these plant-foods in the 

 soil are for the most part in an insoluble, or as very commonly 

 said, unavailable form, and that they usually become available 

 only little by little each year. That they do thus become gradu- 

 ally available, is clearly shown by some of the experiments of 

 Lawes and Gilbert, of England ; some of their plats have yielded 

 crops of wheat and other cereals now for fifty years and more, 

 without any manure. 



It may be, however, that one of these foods does become avail- 

 able year by year in large enough quantities to contribute its 

 share towards a good yield of some crop, provided that there is 

 enough of the other two, but that there is in fact not enough of 

 the other two ; or it may be that enough of two of the foods will 

 become available fast enough each season for a good crop, but that 

 the other one will not ; there will be only a poor crop in either 

 case. 



There are cases in which it would be only folly, with some thou- 

 sands of pounds of the one or the two foods in the soil, and in 

 such a condition that the crop grown on it can get all it needs for 

 a good yield, (at least for one year, and probably for the next year, 

 and even for a few years more), to buy these foods in commerojwj 

 manure ; nor would it be the height of wisdom to keep putting 

 them on the soil year after year in stable manure, since that also 

 contains the three foods under consideration, as well as other use- 

 ful substances. 



There are therefore two ways of using manures of any kind, 

 ^(fable or commercial. One may he called the blind and unbusi- 

 ness-like way, the other the sharp and business-like way. We 

 will consider only the second way . 



