PROSPECTS OF AMERICAN AGRICULTURE. 249 



But I have not time to dwell on this part of the subject. I have 

 said that, theoretically, if the normal yield of a soil is lo bushels 

 per acre, if we plow under a year's growth of clover we ought to 

 get 30 bushels, because we have two year's supply of plant-food 

 in the soil. There is a principle, however, which interferes with 

 this result. The soil is very conservative. It is not easy to get 

 out of it all we put into it. A dressing of farm-yard manure or a 

 crop of clover plowed under, is not by any means taken up by the 

 growing plants in a single season. In heavy soils, especially, 

 decomposition proceeds very slowly, and it may be several years 

 before all the plant-food supplied by a crop of clover is given up 

 to the plants. Still the fact remains that when we plow under a 

 year's growth of clover we have accumulated in the soil an extra 

 quantity of plant-food equal to the annual supply rendered avail- 

 able by the processes of agriculture and the decomposing and 

 disintegrating action of the sun and air, heat and cold. And it is 

 this' fact that lies at the basis of all judicious rotations of crops. 

 I cannot but feel that we are on the eve of many important dis- 

 coveries which will enable us to add greatly to the yield of our 

 crops and the profits of our farming. 



We have learned how to make a sheep produce as much mutton 

 from one year's feed, as was obtained from three or four year's 

 feed less than a century ago. We shall learn how to get out of 

 our fa.im-yard manure all, or nearly all, its valuable plant-food in 

 a single year, if we so wish, and consequently be able to raise a 

 much larger crop. We shall have the matter more under control. 



We plow under a crop of clover for wheat, and in this way get 

 two year's supply of plant-food for the wheat. We ought to 

 double our crop of wheat. We ought to get as much wheat from 

 the one crop every other year as from two crops of wheat grown 

 successively on the same land. The advantage of the plan, as I 

 have said, is in saving the seed for one crop and the labor of put- 

 ting in the crop and cutting it. 



But I feel sure that growing a crop and plowing it under, 

 merely to enrich another crop, is not always the most economical 

 plan. It is good as far as it goes. It is far better than growing 

 grain crops year after year on the same land. 



But there is a better way. There is much nutriment in the 

 clover, and this nutriment can be taken from the clover and still 

 leave nearly all the elements of plant-food in the excrements of 

 the animals that have eaten the clover. And what is true of 



