232 EXHAUSTION OP THE SOIL. 



lime, magnesia or iron. The amount of potash is also 

 very large, and it is found in combination with silicic 

 acid. 



Take the most careful analyses of the grasses as the 

 basis of calculation, and it will appear that the weight of 

 silicates, phosphates, and potash, removed from the 

 soil in every ton of hay, is not less than one hundred 

 and fifty pounds. Supposing, then, that the crop of 

 hay averages two tons to the acre, and it will rarely 

 fall below this on good soils and under fair cultivation, 

 and it appears that about three hundred pounds of 

 these valuable substances are abstracted from the soil 

 of every acre so cropped, and this course of culture 

 could not long continue without the return of these 

 constituents to the soil. And hence the manures re- 

 quired for these lands are such as contain these sub- 

 stances, such as ashes, lime, and other applications rich 

 in silicates, phosphates, and potash. 



Lime is found in much less quantities than potash in 

 most of the grasses, but the relative proportions differ 

 in different species. In orchard grass, for instance, the 

 lime amounts to only 5.82 per cent., while the amount 

 of potash is 29.52. But in Timothy the lime amounts 

 to nearly 15 per cent., and the potash to over 24. Soda 

 is found in considerable quantities in some species, and 

 is wanting in most. 



No one of the grasses appears to be better adapted 

 to supply the wants of animals than Timothy. Its 

 amount of phosphates is larger than that of any other. 



The amount of water in the stem is greater than in 

 the leaf, so that the percentage of nutriment is greater 

 in the leaf and flower stalk or panicle than in the stem. 

 It has been found, by actual and often repeated experi- 

 ments, that grass loses more than half of its weight of 

 water in curing; and it never becomes so dry, by any 



