226 PLANT-FOOD AND AGRICULTURE. 



When OUT land is already at its maximum fertility, if we apply 

 to this land annually the plant-food elements in the quantity re- 

 moved by our crops, and in that form in which they can be appro- 

 priated by the crops, and in the form in which they will retain 

 their appropriability, then we shall annually obtain the maximum 

 crop from our land, and in this sense we can apply a given quan- 

 tity of fertilizer for a given amount of crop, and expect that 

 amount of crop at harvest. 



If our land is agriculturally barren, by the application of a com- 

 plete fertilizer once, we may obtain a crop ; but it may not be that 

 amount of crop which we would figure from the proportionate 

 elements supplied, because the elements would not be so distrib- 

 uted throughout the land as to be available, in their whole effect, 

 to the plant. Yet the continued application of the complete fer- 

 tilizer would, in the course of time, bring this land to its maximum 

 fertility, and then we should expect to obtain a given increase from 

 a given application, the given application being all along grad- 

 uated to the agricultural capacity of the land. 



If the land be in an intermediate state, as most of our land is, 

 the same principles apply. 



We thus see that, whether we use dung or a complete fertilizer, 

 we may expect satisfactory results, provided we claim only those 

 results which are justified by reason. 



It may be interesting to some to know how far experience cor- 

 roborates these claims, which are the logical deduction from our 

 tabulated facts. We are pleased to state that they are in exact 

 accordance, and confirm our results at every step. The careful 

 and exact experiments of Mr. Lawes, at Rothamstead, continued 

 now for thirty or more years, show that on the dunged and chem- 

 ically-fertilized plots, side by side, there is do difference in the 

 amount of crop, but both alike produce the maximum capacity of 

 the land. The same facts are indicated in the farm practice of 

 Mr. Prout, at Sawbridgeworth, England, a practice which has 

 now been continuous for many years. The experience on Wau- 

 ehakum farm. South Framiugham, although limited to two years, 

 is also strongly confirmatory. 



It is certain that our reasoning is correct, thus confirmed by 

 experience, but it is equally certain that to obtain the best results 

 from either dung or fertilizer, some knowledge must be used. Let 

 us consider the subject further, then, and see upon what principles 

 our using of fertilizers must be based. 



