SOIL EXHAUSTION AND ROTATION OF CROPS. 155 



any other crop. This, of course came from the soil. All 

 these shallow-rooted plants, when they succeed clover, find 

 ready to their hand, in the upper eight or ten inches of the 

 soil, material brought up by the previous clover crop from 

 twice that depth, or more. The clover not only furnishes to 

 the succeeding crop these mineral matters that were in the 

 upper portion of the soil, but it takes them up from a depth 

 where they would not be directly accessible to other plants, 

 and puts them where they are wanted. The clover plant 

 leaves in the surface soil, as the table shows, a much larger 

 quantity of all those materials than any other crop. The only 

 apparent exception is that of soda, and soda is a substance 

 which is not, as the best information we have upon the subject 

 tends to show, essential to any cultivated plant. We have 

 of magnesia, 46 lbs. in clover, against 14 in rye. Of potash, 

 77 lbs. in clover, against 30 lbs. in rye. Of sulphuric acid, we 

 .have 24 lbs. in the case of clover, against 12 in the case of rye. 

 Of phosphoric acid, which is, on the whole, the most precious 

 mineral substance in the soil, because it is the most costly 

 when we have to supply it by purchase to our fields, we have 

 71 lbs. in the case of clover, against 24 lbs. in the case of rye. 

 Now, the point comes in here again to which 1 referred 

 yesterday ; namely, the ratio of root to top and of foliage to 

 seed. In the rye crop, when ripe, I have nearly 14-15ths of 

 the vegetable matter above ground, (and the same is probably 

 true of all the grains,) and when I get off my crop, I get off 

 14-15ths of the whole. (See table, page 96.) Fourteen- 

 fifteenths of the vegetable matter is carried away in my grain 

 and chaff and straw, if I cut close to the ground. In the ob- 

 servations whose results are given in this table, there was no 

 stubble. If I leave stubble on the ground, I reduce the pro- 

 portion of removed substances. When I take off the clover 

 plant close to the ground, for every fifteen pounds I take off, 

 I leave ten pounds in the soil ; whereas, in the case of rye, 

 for every fourteen pounds I take off, I leave only one in the 

 soil. That is a great difference. When I cut the grain 

 crop low, I take it nearly all away ; but when I mow off my 

 clover hay, I leave two-thirds as much as I take. The 



