130

LIQUID MANURE.

be preserved in proper receptacles, sheltered from thesun and rain, so that the volatile products of its decay-may neither be lost by the heat of the former, nor washedaway by the latter; and lastly, by the action of waterit should be softened, and as much as possible reducedto a fluid state, so that it may be easily and uniformlyapplied to the land. The formation of liquid manuretanks deserves the most serious attention of the farmer.

404. In the application of these kinds of manure, ithas to be remembered that although carbonic acid andammonia are the principal food of plants, yet that thereare limits to the quantity of these substances theycan absorb, and that too great a supply of such food isnot only useless, but even objectionable, being highlyinjurious. It is useless to give a plant abundance ofcarbonic acid and ammonia, if we do not at the sametime give it those earthy and saline substances which itrequires (364). Even if both are supplied to plants, itis impossible for them to absorb more than a limitedquantity. Excess does harm.

405. As animal matter is either directly or indirectlyformed from vegetable substances, it is natural to expectthat animal substances must contain, in addition to thefour elements of organic matter (58, 221); the same earthysubstances which plants contain, and this is really thefact (278). The phosphate and carbonate of lime of thebones is obtained from plants, and the alkaline and othersalts found in the various parts of the animal body arederived from a similar source.