254 MASSACHUSETTS AGRICULTURE. 



layer extends as deeply as the land has been lately ploughed. 

 That portion of soil immediately underneath this layer is com- 

 monly of the same character as the upper layer itself, except 

 that it is nearly destitute of this vegetable matter. Humus is a 

 compound and very complex substance, made up of various 

 acids and salts, all of which must be rendered soluble before 

 being taken into the circulation of plants by absorption through 

 the roots. It is probable that most of the alkaline substances 

 used as manures, such as those consisting largely of potash, 

 lime and ammonia, act mainly by rendering humus soluble, so 

 that although not in themselves nutriment in the same sense in 

 which humus is, yet by combining with insoluble humus com- 

 pounds, they render them soluble, and then the new soluble 

 compound becomes food. It is important to bear this distinction 

 in mind, that, although all substances included under the gen- 

 eral term manure contribute to promote fertility in the soil to 

 which they are applied, yet humus acts directly and principally, 

 while most others act mainly as adjuncts to that. For instance, 

 the addition of soluble humus to a blowing sand, makes it at 

 once capable of supporting vegetation, while without humus, 

 none of the so called artificial manures would produce a like 

 condition. Ashes would not cause a barren sand, free from 

 humus to be fertile, neither would lime, or in fact any inorganic 

 matter. 



These statements may serve to explain some of the apparently 

 contradictory results arising from the application of special 

 manures. A farmer gives a piece of land a dressing of lime. 

 The effect of lime is to render a portion of the humus in the 

 soil, soluble, and vegetation appropriating it, a large crop is the 

 result. Hence the inference, that lime is a valuable manure. 

 He therefore repeats the application the following season, but 

 neglects to use any humus producing materials in connection 

 with it. The crop in this case falls short of his expectation. 

 A third trial exhausts nearly all the humus in the soil, and the 

 land becomes barren. Hence, lime exhausts the soil. If there 

 had been applied the second season an amount of humus 

 equivalent to the quantity appropriated by the first crop, there 

 would have been little or no falling oif iu the product. 



The practical view deducible from these considerations is, 

 that humus, or vegetable matter, in a state or condition of 



