SOIL EXHAUSTION AND ROTATION IN CROPvS. 99 



the total weight of clover is 246 ; so that in this case tlie clo- 

 ver has a soiueuiiat less absolute mass of vegetable matter. 



Question. There are two or three other important ques- 

 tions. We want to know if the plants take from the soil a 

 certain amount of manurial constituents or saline matter? 



Prof, .Johnson, They do, of course. That is one of tlie 

 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 otf ? 



Prof. Johnson. Certainly. They take manures or equiva- 

 lent nutritive matters. 



Question. It took all tliese manurial matters to make this 

 crop, and if you carry it off you carry off those manurial 

 matters ; whatever you leave restores what it took to make it, 

 and no more ? 



Prof. Johnson. Yes. 



Mr. Gould. Ought it not to be said that in its previous 

 condition the manurial matter was in an insoluble condition, 

 not adapted to the plant ; whereas, what you leave is in a 

 soluble condition, and assimilable ? 



Prof. Johnson. During the growth of a crop, plant-food 

 in the soil does pass from an insoluble into a soluble form, 

 and being taken up by the crop remains in that part of the 

 crop left in tb.e field in a state adapted for immediate use. 

 The deep-rooted clover also, in this case, brings up, from 

 an average depth of sixteen inches, matter which remains 

 in part within the range of shorter-rooted grain crops. 



Adjourned to two o'clock. 



