248 HANDY-BOOK OP HUSBANDRY. 



the crops of a life-time; that of the fine bones would probably 

 disappear or grow greatly less after five or ten years ; and that of the 

 superphosphate would probably not be very marked after two or 

 three years. It is the old story of " the nimble sixpence and the 

 slow shilling." In either case the material applied to the soil 

 produces a given amount of effect on vegetation ; that in the 

 superphosphate being developed within two or three years, results 

 in a few large crops which are immediately available, and the extra 

 money which they produce may be in part applied to the renewal of 

 the manure ; the whole bones, on the other hand, produce the 

 same amount of growth, only during a long series of years, while 

 the interest on their cost, and the interest on the value and on the 

 cost of cultivating the land, are constantly running on. The 

 chance for profit is very much greater in the case in which large 

 immediate returns give through the current year a greater amount 

 of increase or profit above the necessary expenses and loss of 

 interest. 



Farmers also speak of superphosphate of lime, Peruvian guano, 

 and other intense manures as being exhausting ; and there is no 

 doubt that in the experience of many districts, as, for instance, 

 those parts of Maryland where, during a few years, the yield of 

 wheat was raised to a very high figure by the use of Peruvian guano, 

 and where it was found that, after these few years, guano failed 

 to produce a beneficial result, they have a good apparent reason 

 for their opinion. Any manures which do not supply all that the 

 plant requires, or all at least of such elements as the soil can 

 furnish in only a limited degree, are exhausting manures. For 

 instance, there may be in the soil a certain amount of phosphoric 

 acid available for the uses of plants, and in the ordinary course of 

 growth without manure a sufficient addition to this supply may be 

 made available by natural chemical processes to constantly furnish 

 fair average crops, that is, to furnish the phosphoric acid required 

 by such crops as grow m the natural condition of the land, of 

 which the capacity may be kept at a low point owing to a defi- 

 ciency of potash, for instance. 



Now, if we apply any manure (such as wood ashes) which supplies 



