Imagens das páginas
PDF
ePub

great sources of loss in the decomposition of farmyard manure is due. If the temperature of the manure-heap be permitted to rise too high, the carbonate of ammonia volatilises. It is probable, also,' that a not inconsiderable portion of the nitrogen escapes into the air in the free state. The last of the most important gaseous products of decomposition are sulphuretted and phosphoretted hydrogen. It is to these gases that much of the smell of rotting farmyard manure is due.

2. The second class of substances formed are soluble organic acids, such as humic and ulmic acids. The function performed by these acids is a very important one. They unite with the ammonia and the alkali substances in the mineral portion of the manure,. forming humates and ulmates of ammonia, potash, &c. It is these ulmates that form the black liquor which oozes out from the manure-heap.

In very rotten farmyard manure traces of nitric acid may be found, but it must be remembered that the formation of nitrates is practically impossible under the ordinary conditions of active fermentation of farmyard manure, except perhaps in its very last stages.

3. The third class of changes taking place have to do with the mineral portion of the manure. The result of the formation of so much carbonic and other organic acids is to increase the amount of soluble mineral matter very considerably.

Analyses of farmyard manure.—It is chiefly to the valuable researches of the late Dr Augustus Voelcker that we owe our knowledge of the composition of old and fresh farmyard manure. All interested in this important question should peruse the original papers on this subject contributed to the 'Journal of the Royal Agricultural Society' by Dr Voelcker. Typical analyses illustrating the variation in the composition of farmyard manure at different stages of decomposition will be found in the Appendix.1 From what has been already said, it is obvious that the composition of farmyard manure is of a very variable nature.

The quantity of moisture naturally varies most, and this variation will depend on the age of the manure, and the conditions under which it is permitted to decay. It may be taken at from a minimum of 65 per cent in fresh, to 80 per cent in well-rotted manure. The total organic matter may be taken at from 13 to 14 per cent; containing nitrogen, .4 to .65 per cent. The total mineral matter will range from about 4 to 6.5 per cent, containing of potash from .4 to .7 per cent, and of phosphoric acid from .2 to .4 per cent.2

As Mr Warington 3 has pointed out, one ton of farmyard manure would thus contain 9 to 15 lb. of nitrogen, about the same quantity of potash, and 4 to 9 lb. of phosphoric acid. These quantities of nitrogen

[blocks in formation]

and phosphoric acid, calculated to (95 per cent) nitrate of soda, and (97 per cent) sulphate of ammonia, and (25 per cent) superphosphate, give respectively 57.25 to 96 lb. nitrate of soda, 45 to 75 lb. sulphate of ammonia, and 35 to 79 lb. superphosphate. That is, in order to apply as much nitrogen to the soil as is contained in one ton of nitrate of soda, we should require to use from 23 to 41 tons of farmyard manure; similarly one ton of sulphate of ammonia contains as much nitrogen as 30 to 50 tons farmyard manure. In the same way one ton superphosphate of lime contains as much phosphoric acid as 28 to 64 tons farmyard

manure.

The value of rotten manure is, weight for weight, greater than that of fresh manure. This is due to the fact that, while the water increases in amount, the loss of organic matter of a non-nitrogenous nature more than counterbalances the increase in water; the manure, therefore, becomes more concentrated in quality. The loss on the total weight, according to Wolff, in the rotting of farmyard manure, should not exceed in two or three months' time 16 to 20 per cent—viz., a sixth to a fifth of its entire weight. Not only, however, does the manure become richer in manurial ingredients, but the forms in which the manurial ingredients are present in rotten manure are more valuable, as they are more soluble. These statements must not be taken as proving that it is more economical to apply farmyard manure in a rotten condition than

[blocks in formation]

in a fresh one. The distinction must not be lost sight of which exists between relative increaseincrease in the percentage of valuable constituents -and absolute increase. The increase in the value of the manure by the changes of the manurial ingredients from the insoluble to the soluble condition may be effected at the expense of a considerable amount of absolute loss of these valuable ingredients. This is a point which is probably too often left out of account in discussing the relative merits of fresh and rotten farmyard manure; and it is important that it should be clearly understood. In the words of the late Dr Voelcker: "Direct experiments have shown that 100 cwt. of fresh farmyard manure are reduced to 80 cwt. if allowed to lie till the straw is half rotten; 100 cwt. of fresh farmyard manure are reduced to 60 cwt. if allowed to ferment till it becomes 'fat or cheesy'; 100 cwt. of fresh farmyard manure are reduced to 40-50 cwt. if completely decomposed. This loss not only affects the water and other less valuable constituents of farmyard manure, but also its most fertilising ingredients. Chemical analysis has shown that 100 cwt. of common farmyard manure contain about 40 lb. of nitrogen, and that during fermentation in the first period 5 lb. of nitrogen are dissipated in the form of volatile ammonia; in the second, 10 lb. ; in the third, 20 lb. Completely decomposed common manure has thus lost about one-half of its most valuable constituent." While, of course, a very great amount of absolute

loss of the valuable constituents-the nitrogen and ash constituents-of farmyard manure may take place through volatilisation and drainage, by taking requisite precautions this loss may be very much minimised. As regards the total loss, this, in two or three months' time, should only amount to 16 to 20 per cent or one-sixth to one-fifth of the weight.1 The use of fixers, to which reference has already been made, will greatly minimise this loss. The application of fixers is best made to the manure when still in the stall or byre. The health of the animal benefits by so doing, while the manure is at once guarded against loss from this source.

As to the relative merits of covered and uncovered manure-heaps, much difference of opinion exists. It is one of these questions which does not admit of final decision one way or another, as it depends so largely on the individual circumstances of each case. That manure produced under cover is more valuable than manure made in the open is readily granted. The question, however, is as to whether the increase in its value is sufficiently great to warrant the extra expense involved in building covered courts. This depends on the individual circumstances of each case, and cannot be decided in a general way. For experiments on the relative value of manure made under cover and in the open, see Appendix.2

The method of applying farmyard manure to the 1 See Appendix, Note XIII., p. 62. 2 Note XIV., p. 63.

« AnteriorContinuar »