Annual Report

FOOD EQUIVALENTS.

BY SIR J. B. LAWES, BART., LL.D., F.R.S.

Two years ago the British Parliament passed an act by which tenant farmers were entitled to receive compensation for unexhausted manures on leaving their farms. Before, however, the claim could be established it was necessary for them to satisfy arbitrators or judges that such manures not only existed in the soil, but also that they possessed the value claimed for them. Of the claims made, so far as my, experience has gone, the result has been by no means satisfactory to the tenants, and an opinion generally prevails that the benefits to be derived from the act are very much less than what was anticipated when it was passed.

The science of Agriculture will have to pass through several generations of progress before it will be in a position to pronounce with any certainty as to the locality and the value of the various substances applied in manures to the soil. The fond belief which once prevailed, that if the manures applied were not taken up by the crops they must still exist in the soil, has been rudely disturbed by the discovery of nitrification. That the annual amount of organic matter nitrified each year is more or less a measure of the soil's fertility would appear to come under the head of a general law. It cannot be an accidental circumstance that all the cereal crops grown with mineral manures on my land have declined in yield, more especially when analyses of the soil have proved with certainty that its organic nitrogen has also largely declined. Nor would the fact that mineral manures in certain localities have produced largely increased crops be sufficient to disturb the above conclusion, as their application may have had the effect of inducing more active nitrification.

It is true that the experiments on corn which have been tried in the States do not give much encouragement to the idea that this magnifi

cent cereal feeds in a similar manner to that of its more humble brethren; still, I should require more careful and longer extended experiments to satisfy me that plants of the same natural order had different modes of taking their food from the soil.

While nitric acid has no permanent resting place in a soil, and ammonia is rapidly converted into nitric acid, organic nitrogen-or, in other words, nitrogen in combination with carbon-has a durability which may be measured by days or by centuries. It is the uncertain degrees of durability in the manures from cattle foods which are employed by the British farmer that, on the one hand give him an equitable, as well as a legal claim for compensation, but on the other hand place serious obstacles in his way when he attempts to enforce his claim. It was with the hope of rendering some assistance to the farmer that we recently wrote a paper on this subject, and although the subject generally has only a local interest, still there are some parts which may, I hope, possess a certain interest to the farmers of the United States.

It must be evident that whenever a food is consumed by stock a certain portion of it must be retained by the animal, and that this portion will vary with the composition of the food. It was therefore necessary to construct a table to show, first, the chemical composition of the various foods in use; secondly, their feeding properties, and the amount of ingredients which the animals consuming these foods were likely to retain in their system; while the third part of the table gave the amount of manure ingredients which might be expected to pass through the animal, and on these we place a value calculated from the prices at which they could be purchased in the form of artificial manures. The table referred to will be found on pages 116 and 117.

It is quite obvious that in the construction of a table of this description we lay ourselves open to criticism of various kinds. The chemist may call the figures in question as not being in accordance with the chemical composition of the foods; while the practical farmer may say that he knows much better than we do that such results cannot be obtained in his feeding sheds. To one and the other we can give but one and the same answer, which is to this effect: that we know ourselves-perhaps better than they do the imperfections which are to be found in the table, but that its construction is the result of the best data at our command, and that as knowledge and experience advance the various items can be corrected and amended.

In making use of food equivalents, or in other words in selecting from the table the number of any of the foods required to produce one pound of increase, it is necessary to understand that the results can only be obtained by a judicious use of the various foods. An ox could not be kept alive on linseed alone, and if fed upon straw alone a ton of this substance would be more likely to produce no increase than the amount of pounds given in the table. Therefore now to give a few illustrations of increase upon foods, to show how the figures are applicable to the ordinary practice of farming.

Many years ago we conducted a series of experiments upon various breeds of sheep, thirty of each breed being in most cases selected, and the system of feeding was such as any ordinary farmer would employ when fattening his sheep for market. For each experiment the foods were carefully weighed, and a fixed amount of cake, or meal and hay, was supplied, but the animals were allowed to eat as many Swedish turnips as they liked. The following table gives the amount of food consumed by each breed of sheep to produce 100 lbs. increase in their live weight, as given in the table published in 1861, and also the amount of increase which the same amount of food should give, if calculated according to the present table :