3. The proper fermentation of the manure is apt to be interfered with by the loss of that which is its most important agent--viz., the soluble nitrogenous matter--and also by the drying action of the wind. The same objections hold good to a large extent with regard to the setting out in the fields of the manure in large heaps. The risks of loss, in one respect, may be said to be less, owing to the smaller surface presented. On the other hand, they may be greater, owing to fermentation taking place more quickly. Agricultural practice, however, often renders this custom necessary; and if precautions are taken not to let the heap lie too long, and to cover it over with earth, the risk of serious loss may be rendered inconsiderable. With regard to the second method of procedure--viz., the spreading of the manure broadcast over the field, and allowing it thus to lie--Dr Heiden is of opinion that this should only be done when the field is level. In the case of uneven ground the risks are, of course, obvious. It has been affirmed that, by allowing farmyard manure thus to lie exposed for some time, an important loss of volatile ammonia--carbonate of ammonia--is apt to take place. This could only take place where the former treatment of the farmyard manure had been bad. Hellriegel has shown that in the case of properly prepared farmyard manure there is no danger of loss in this way. The absorptive power of the soil for ammonia, it must be remembered, is very great, and the amount of volatile ammonia in farmyard manure is relatively so small that it is scarcely possible that any could escape in this way. Hellriegel's experiments have demonstrated this in a very striking way. He has found that in the case of a chalky soil, and during the summer and autumn months, practically no loss of ammonia takes place. The following considerations may be further urged in support of this method of application, as against immediately ploughing in the manure, viz.:-- 1. That fermentation takes place more quickly. 2. That it results in a more equable distribution of the manurial constituents in the dung, by gradually and thoroughly incorporating the liquid portion of the manure with the soil-particles. Against, however, these undoubted advantages, one serious disadvantage may be urged--viz., that the manure, before being ploughed in, becomes robbed to a large extent of its soluble nitrogenous compounds, which, as we have repeatedly observed, are so necessary for fermentation; and that, therefore, when it is ploughed in, it does not so readily ferment. This being so, it is highly advisable, in the case of light or sandy soils, not to follow such a practice, but to plough the manure directly in.