*T424, 425, 426, 427J humus— ammoniac a l manures. 225 



ingredient, ready to be delivered to the roots of plants, whenever called for. 



424. When we consider the great importance to vegetable economy, of the 

 properties of humus just referred to, it cannot be surprising that its presence 

 should, as a general rule, exercise an influence so decidedly favorable on the 

 productiveness of soils. Yet it is incontestably true, that humus alone, with- 

 out mineral matter, will not support vegetable growth ; while on the otJier hand, 

 examples of very fertile land almost destitute of humus are common, and par- 

 ticularly so in our own State. The fertile "red lands" of Pontotoc and 

 Chickasaw, for instance, and some of the best yellow loam lands of Holmes, 

 Madison and Hinds, are so poor in vegetable matter, as to render its amount 

 almost inappreciable; and yet these lands are justly considered as being among 

 the best upland soils in the State. It is nevertheless true, that a perfectly 

 healthy development of cereals or any useful cultivated plant, is rarely attained 

 in soils destitute of humus. 



425. Clay a Substitute for Humus. — It will be observed, however, that only 

 soils containing a considerable amount of clay, can be permanently fertile in the 

 absence of vegetable matter. We must conclude, then, that clays must, to 

 some extent, pjssess the same properties as humus; and such, in fact, experi- 

 ment prove-; to be the case. It has been stated above, that clays are powerlully 

 retentive of moisture; and in like manner we find, that clays will absorb 

 ammonia from the atmosphere — not to the same extent as humus, it is true, 

 but still sufficiently for the purposes of vegetation (IT 378). The presence of 

 humus or vegetable matter, therefore, is more essential to sandy soils than to 

 those of the opposite character ; to both, however, it is highly beneficial ; for it 

 must be borne in mind that while clay may replace humus so far as its reten- 

 tive and absorbent powers are concerned, it does not exercise the stimulant 

 action resulting from the decay of vegetable matter (H/422). 



426. Green Cropping. — It must be recollected, that inasmuch as all vegetable 

 matters ordinarily at the disposal of the agriculturist, contains fixed mineral 

 ingredients (i. e., ashes), their application to the soil is useful not only with ref- 

 erence to the formation of humus, but also as introducing into the soil import- 

 ant nutritive elements. If the vegetable substance thus used has not been 

 obtained on the same soil, we shall thus add to the stock of fertility ; but when, 

 as in the case of turning down green crops, the material used has itself been 

 raised on the soil, then in reality we add nothing to the latter except the vege- 

 table matter itself, which in its decomposition forms humus, and has been 

 derived from the air. At the same time we thus return to the soil in a more 

 available condition, the mineral ingredients which the crop obtained from it. In 

 both these causes united, we have the rationale of the good effects which follow 

 the procedure in question. We must remember, however, that this is merely a 

 stimulative process ; and that it can be practiced only at the expense of dimin- 

 ishing the duration of fertility — being eminently exhaustive. 



427. Ammoniacal Manures — It may be proper to introduce in this place, 

 some considerations on the subject of ammoniacal manures, such as now occur 

 in commerce under various denominations, such as "ammoniated guano," 

 "ammoniated marl," etc.; together with the impure sulphate of ammonia, 

 which is now manufactured on the large scale, for agricultural purposes, from 

 the offal of the manufacture of coal gas. For the present, I shall speak of the 

 effects of ammoniacal salts alone, independent of any substances with which 

 they may have been mixed. Ammonia (,^361) is necessary to the nutrition, piop- 

 erly speaking, of plants. It is absorbed into the vegetable organism both 

 through the roots and leaves, and serves for the formation of. the nitrogenized 

 substances contained in plants, such as gluten, vegetable albumen, casein, etc. 

 Whether plants are capable of assimilating directly the nitrogen of the atmos- 

 phere for this purpose, is still an open question; although it appears most likely 

 that they cannot, and are dependent upon ammonia alone for their supply of 

 nitrogen. 



K— 15 



