56 ECONOMY OF FARMING. 



" The organic substances contain not all the elementary materials, and their propor- 

 tion of combination is very different. In this consists their more rapid or slower 

 decomposition, and their greater or less facility of affording nutriment. 



" Those organic substances are most rapidly decomposed which are combined from 

 the greatest quantity of elementary substances, and give a perfect, satisfactory and 

 rich nutriment, because all the constituents of the material exist in them, out of 

 which the living bodies are renewed and fashioned. 



"Organic substances, which are combined of only 3 or 4 elementary substances, are 

 harder to decompose, especially if their connexion is firm. Hence it is that flesh and 

 animal substances generally are so nutritious for beasts and plants, as they are com- 

 bined from hydrogen, carbon, oxygen, sulphur, nitrogen, phosphorus, lime, potash ; 

 and hence also the less capacity of nutriment in wood, which is combined only of 

 hydrogen, carbon and oxygen, of alkaline bodies and earths, and besides, is of strong 

 cohesion. 



" As we find silex, alumine and magnesia, iron, manganese, sulphur, phosphorus, 

 lime, alkaline salts, and many other salts in the analysis of the organic substances, 

 we must therefore justly conclude, that these bodies also, since they are essential 

 constituents of the organic substance, are to be considered as directly nutritive. 

 Experience, too, shows that all these bodies do aid the growth of plants. 



" Their efficacy as manures must be much less than of the organic substances, since 

 they contain only one or two materials in themselves which go to the nutriment ot 

 plants. They are also less because, too, these substances only aid plants in a small mass. 



" The organic bodies are divided into two great classes — animals and plants. As 

 animals are consumed in so great a degree by other animals, only a small portion of 

 them goes directly to the benefit of plants as nutriment. Plants afford not only a 

 large portion of the nourishment of animals but of other plants, since the following 

 stock lives on the remains of the preceding one. The nutritious material found in 

 the humus of the soil, or which is brought to the field, consists in a great part of 

 vegetable and only a small portion of animal substances." 



Humus, which, according to Liebig, is the decayed fibre of wood, is characterized 

 by Thaer as " a mould, not properly an earth, but a powdery substance, in a greater 

 or less degree found in the soil. The fruitfulness of the soil depends on its proportions, 

 as likewise it is the only thing in the soil that gives nutriment to plants : it is the 

 remains of vegetable and animal putrefaction — if dry, black and powdery ; if moist, 

 it has a smooth, fatty feeling ; it is different according to the bodies out of which it is 

 formed, but it has certain general peculiarities or properties in which it is essentially 

 alike. Humus is a form of organic power, a combination of carbon, hydrogen, 

 nitrogen and oxygen, and also in lesser quantities of sulphur, phosphorus, and various 

 salts — gives nourishment to organism ; the more life there is, the more humus ; and 

 the more humus, the more life. 



"Humus has less oxygen but more carbon and nitrogen than the plants of which it 

 is composed ; it differs also as there is more or less water or air : as it is in a free or 

 confined state, it is liable to changes, and forms a substance indissoluble in water 

 called extract or extractive matter : if it has not access to air, carbonic acid and 

 extract is produced. Salts exist in a mp.ss in humus — humic acid by itself is unfruitful 

 and injurious to vegetation. Humus differs as it is formed from animal or vegetable 

 bodies. The animal has more nitrogen, sulphur and phosphorus, as is perceivable 

 by the smell it emits when burning." 



ScHWERTZ also, says that " the nourishing substance of plants, to which we give 

 the name of humus, has the appearance of a powdery and usually a brown or dark 

 gray loose substance, in which can no more be discerned its original condition. It 

 burns in the fire, and is soluble in water, especially after an addition of alkali. It is 

 not every decayed substance that is humus, and not every species of humus is in a 

 condition for the fertility of plants. It forms itself from the soil more or less rapidly, 

 according to the organic substances from which it is derived, the firmer or the less 

 firm its texture is, the less or more earthly parts it contains ; and as the circumstances 

 of temperature and soil exert a stronger or weaker influence on the humus." He 

 mentions both the acid and the astringent humus. 



Our Author himself, in Vol. I., under the head of Agrinomie, p. 40, after giving 

 similar characteristics of the appearance, &c., of humus, observes : " It will hold 

 nearly double its weight in water without losing a drop," and says that " Schubler 

 found that 100 parts of humus would retain 190 parts of water. Korte also, of a 

 humus formed from the wild chesnut wood, found it would hold 239 per cent, of 

 water while a loamy clay only held 45 per cent. It loses the water also very slowly. 



