28 



If we have by this time made good our contention that the injurious 

 action of fresh farmyard manure observed by the German experimenters 

 is due to the fermentable organic matter which it contains and is generally 

 in proportion to its amount, we have next to ask : What proportions of 

 manure to soil were used in German experiments. If these proportions 

 were the same as those employed in ordinary agriculture, then our 

 farmers may expect to meet with the same results when they em- 

 ploy farmyard manure under similar circumstances. If, however, far 

 more of this manure was applied to the soil in the German pot experi- 

 ments than is used in practical agriculture, we must clearly take the 

 German results simply as illustrations of the properties of farmyard man- 

 ure, and not as examples of what we have to expect in practice. Organic 

 matter in the soil acts, in fact, in an injurious manner only when it is of 

 such kind and quantity that it changes the character of the soil from an 

 oxidising to a deoxidising medium. 



For our present purpose we may assume that the depth of soil 

 turned over by the plough — the quantity in fact with which a dressing of 

 farmyard manure would be mixed in practice — will weigh, when dry, 

 1,000 tons per acre. It follows that an ordinary d re-sing of 10 tons of 

 manure per acre will amount to 1 per cent, or the soil. A farmer may 

 now and then double this proportion, but 2 per cent, will very rarely be 

 exceeded. In the experiments which Wagner first describes, each pot 

 held 7,000 grams of soil, and the quantity of dung employed was about 

 500 grams, or 7 per cent, of the soil, representing, therefore, 70 tons per 

 acre. In his main series of experiments the pots contained 18,500 grams 

 of soil, but the manure was only incorporated with the upper portion, 15 

 cm. in depth. The surface area of the soil is mentioned in this case ; we 

 are thus able to state that his ordinary dressing of dang, 500 grams, was 

 equivalent to 40 tons per acre, incorporated with about six inches of 

 soil • this amount was doubled in a few instances. In experiments on 

 denitrification, in which no crop was grown, the dung employed 

 amounted to 10, 18 and 20 per cent, of the soil. Maercker does not 

 ffive the details of his experiments so fully as Wagner, but from one 

 sentence it would appear that his pots held 6,000 grams of soil. His 

 unit of nitrogen is larger than Wagner's so that about 600 grams repre- 

 sents his ordinary application of dung, which thus amounted to 10 per 

 cent, of the soil, or 100 tons per acre. In some of his trials with farm- 

 vard manure the dressing was three times this amount. 



It is, then, quite evident that the quantities of dung mixed with the 

 soil in the German experiments were far in excess of the amounts com- 

 monly employed by a farmer and that a great delay of the process of 

 nitrification, and a production of actively denitrifying conditions, was 

 only what might naturally be expected under the circumstances of the 

 experiments, and is no proof that the same actions will occur to the 

 same extent in ordinary arable farming. 



That the farmyard manure was used to great disadvantage in the 

 pot experiments we have just described is indirectly admitted by Wag- 

 ner for at the commencement of his paper he tells us that his former 

 experiments have shown that, under the conditions which occur in prac- 

 tice 251b. of the nitrogen contained in farmyard manure may be expected 



