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richer the ration is in nitrogen, phosphoric acid and potash, the more valuable will be the manure produced by the animal. The next question to determine is what proportion of the fertilizing content of the food is recovered in the excrement.
No Loss of Plant Food With Mature Animals.Let the reader imagine that a matured animal (a steer for instance) is confined in such a manner that all of the excrement, both liquid and solid, can be preserved, and that the animal is kept on a maintenance ration. If now the total dry matter in the materials fed is determined, and likewise that voided in the excrement, it will be found that the dry matter in the excrement is just about one-half the amount that was present in the food consumed, the greater part of the other half having been given off from the lungs as carbonic acid gas. If, on the other hand, the food is analyzed to determine the nitrogen, phosphoric acid and potash it contains, and the excreta are also examined, in the same way, it will be found that the entire amount of these constituents is voided by the animal in the solid and liquid excrement. While the excreta, therefore, contain only half of the total dry matter which was present in the ration, they contain all the constituents that are generally considered to have fertilizing value.
Young Animals Retain Part of Plant Food.While these figures would hold good for a matured steer that was neither gaining nor losing in weight, they are not correct for young and growing animals. The latter retain a certain proportion of the nitrogen and phosphoric acid for use in building up their bodies. The amount thus retained depends primarily on the age of the animal, and also as will readily be imagined, on the rapidity of its growth. Recent experiments indicate that calves during the first three months of their lives retain in their bodies about one-third of the fertilizing value of the food consumed, or in other words, the excrements from such animals contain two-thirds of the fertilizing ingredients of the ration. For the first year of their existence they use in body growth an average of about one-fifth of the nitrogen, phosphoric acid and potash that was present in the food, and the amount gradually diminishes until practically not any of these materials are retained. It may be noted here that where matured animals are gaining in weight during fattening there is no drain on the fertilizing value of the manure, provided the gain in weight is all in fat. This is due to the fact that fat contains only carbon, hydrogen and oxygen, and hence its production does not remove any of those constituents which are considered in calculating the fertilizing value. Although the steer and calf have been used by way of illustration, the remarks regarding them hold true as well of the other classes of animals such as swine, sheep and horses, and the age of the animal has the same effect on the value of the manure.
The Milk Contains Some Plant Food.—In the case of the cow another factor is introduced, as a certain proportion of the nitrogen, phosphoric acid and potash is removed in the milk. Milk contains on an average about 0.53 per cent of nitrogen, 0.19 per cent of phosphoric acid and 0.175 per cent of potash. A cow giving an annual yield of five thousand pounds, therefore, removes in the milk fertilizing materials amounting in
value to $4.89. If the milk is sold this amount of fertility is removed from the farm. If, on the other hand, butter only is sold practically none is carried away, as all the valuable ingredients are found in skimmilk; the fertilizing value of three hundred pounds
Butter removes a smaller quantity of the elements of fertility than any other pro
duct which is sold from the farm. The fertilizing value of one ton of butter amounts to only 44 cents.
of butter, for instance, amounting to only 61/2 cents. Even where the milk is removed fully 85 per cent of the manurial value of the food is recovered.
Eighty Per Cent of the Plant Food Recovered in Manure.--It will thus be seen that a very large part of the elements of fertility contained in the ration fed is recovered in the excreta, and that the age of the animai is the principal factor in determining the amount that is removed. The fertility removed in the milk when it is sold from the farm is also of considerable importance, and should not be ignored. Taking into account the relation between matured and young stock, milch cows and non-milk producing animals, as found on the average farm, it is conservative to assume that at least 80 per cent of the nitrogen, phosphoric acid and potash, present in the materials fed on the farm, is voided by the animals in the solid and liquid excrement. This takes into consideration the amount removed in the milk, that retained by the young animals during their growing period, and, consequently, the fertility removed from the farm by the sale of the animals produced thereon. In order, then, to determine the fertilizing value of the excrement produced from a ton of any of the feeding stuffs mentioned in the table given above it is only necessary to find eighty per cent of the fertilizing value therein stated. It will thus readily be seen that the composition of the feeding stuff really determines the value of the excrement. That produced from one ton of wheat straw being worth only $1.74, while the excrement from one ton of corn meal, wheat bran, linseed meal or cottonseed meal would be worth $4.53, $9.84, $15.49 and $20.93 respectively.
Nitrogen the Most Valuable Constituent of Manure.—By referring to the table it is seen that the most important factor in determining the fertilizing value of a feeding stuff, or the manure produced from it, is the amount of nitrogen that it contains. This is due to the fact that nitrogen is usually present in larger proportion than phosphoric acid or potash, and is much more costly when purchased. Nitrogen is also used by the animal body in much larger amounts than the other substances, and the difference in fertilizing value between the food and the excrement is largely due to the retention of nitrogen. It will be shown that the losses in manure fall more heavily on its nitrogen content than on the other elements, so it again becomes evident that the most expensive material to furnish is also the one most readily lost. This but confirms a previous statement that the problem of the profitable maintenance of fertility is largely a question of an economic method of supplying the plant with nitrogen.
Effect of Ration on Value of Manure Per Ton.While the total value of the excrement depends almost entirely on the composition of the ration, it does not follow that the value of the manure per ton is proportional to the fertilizing value of the substances fed. Cattle fed on highly nitrogenous rations drink more water than those kept on a ration low in nitrogen, and experiments have shown that the excrement contains a larger per cent of water in the former case than in the latter. The cattle fed on the narrow ration will produce more tons of excrement at a greater total value, but the value per ton will not be very different from that resulting from a wider ration. The following table adapted from a Cornell bulletin gives results with two lots of pigs, Lot I, having been kept on feeds extremely high in nitrogen, while Lot II, were given a ration containing a much smaller proportion of nitrogenous materials.
EXCREMENT FROM 1,000 POUNDS LIVE WEIGHT OF PIGS
Weight per Value per Value per day, lbs. day
ton Lot I . . . . 108.9 $0.2106 $3.86 Lot II . . . . 56.2 0.104
It is noteworthy that while the total value of the manure produced per 1,000 pounds of live animal in