206 MASSACHUSETTS HORTICULTUEAL SOCIETY. 



makes humus, or vegetable nionkl. This common ingredient of all 

 arable soils is not necessar}' for plant growth ; for, on a small scale, 

 in pot culture good crops have been obtained in a soil as white as 

 snow, and therefore quite free from any humus, but containing all 

 the real plant nutrients that have been mentioned. But tliat this 

 humus is an important ingredient of a fertile soil no one can doubt. 

 Given two soils equally' rich in nitrogen, potasli, phosphoric acid, 

 lime and all such mfi^ters, but of which one is poor in humus and 

 the other rich in it, but 3'et not so excessively rich as a bog or a 

 muck bed, there is not a farmer or gardener who knows soils who 

 would not give more for the soil rich in humus than for the other. 

 In the course of the deca}' of these vegetable matters several acid 

 substances are formed, and chiefly carbonic acid. These acids act 

 on the large quantit}- of difflcultl}^ soluble plant food in every arable 

 soil of fair quality, and aid in bringing it into solution, and thus 

 within easy reach of the plant. Few farmers realize what a large 

 native stock of crop food they have in their soils. In the case of 

 a fertile soil from a Western State, analyzed some time ago in Ger- 

 many, there would be, by calculation from the analysis, in one acre 

 of it, and within a foot from the surface, 2,400 pounds of phos- 

 phoric acid and 7,000 pounds of potash. But nobod}' in New 

 England has a Western prairie soil on his farm ; nevertheless, 

 judging from analyses of twenty-five ditferent soils of average 

 quality by tlie same chemist, we may sa}' that an average good 

 soil will contain, within twelve inches from the surface, and there- 

 fore accessible to the crops, and fit for plant food if any means can 

 be provided for bringing it into solution, 1,500 pounds of phos- 

 phoric acid, 1,500 pounds of potash, and over 1,750 pounds of 

 lime. Compare these amounts with those that a crop takes up, 

 and one can realize more full}' the native value of a good soil. The 

 quantities of phosphoric acid and potash in pounds, per acre, re- 

 quired l)y some of the more common crops are shown in the follow- 

 ing table : — 



These native supplies, then, so verj- much larger than the 3'early 

 demands of the crops, if we can bring them into use only a little 



