SOIL EXHAUSTION AND ROTATION OF CROPS. 



197 



case of clover, 10:16, 10:19, 10:23, and lastly 10:15, which may be 

 an error of observation. 



Here you have another capital fact brought out — the greater 

 relative quantity of roots in the ripe clover plant. You have half 

 as much roots as top, in the clover plant, whereas you have almost 

 fourteen times as much top as roots in the ripe rye plant. These 

 plants, then, are very different in the way in which they act upon 

 the soil, and therefore in the way in which they leave the soil. 

 When you reap r} 7 e close to the ground you take away one hun- 

 dred and thirty-six out of one hundred and forty-six pounds, and 

 thus leave very little in the soil. When you cut clover you may 

 leave half as much in the ground as you take off'. That, is a point 

 of great importance in considering their relative bearing upon the 

 question of exhaustion, and shows that you may expect a very 

 different result from leaving clover roots and clover stubble in the 

 soil than from the roots and stubble of rye. 



Mr. Lyman. If we cut the rye low we take very nearly the 

 whole of the plant off from the land, and it requires five times as 

 much put back to bring the rye field up to an equality with the 

 clover field, as it stands cut, with the roots in the ground. There- 

 fore we cannot look for a crop that would be equal to what clover 

 would bring us unless we restore this ratio. 



Prof. Johnson. You are right. 



Mr. Lyman. What is the difference if we plow the two crops 

 under? 



Prof. Johnson. The total weight of your rye crop is 272 ; the 

 total weight of clover is 246 ; so that in this case the clover has a 

 somewhat less absolute mass of vegetable matter. 



Question. There are two or three other important questions. 

 We want to know if the plants take from the soil a certain amount 

 of mammal constituents of saline matter? 



Prof. Johnson. They do, of course. That is one of the first 

 principles of agriculture. 



Question. Do these roots left in the soil create any thing ? 



Prof. Johnson. Nothing whatever. 



Question. Then they take from the soil manures to grow them, 

 the same as what you take off7 



Prof. Johnson. Certainly. They take manures or equivalent 

 nutritive matters. 



Question. It took all these manurial matters to make this crop, 



