lb. Old spruce-wood 1/2 Old poplar-wood 3/4 Old oak-wood 1-1/2 Corn-stalks 17-1/2 Bean-stalks 20 Grape-vine twigs 40 (Storer, 'Agricultural Chemistry,' vol. ii. p. 108.) PART III. MANURES CHAPTER VII. FARMYARD MANURE Farmyard manure is the oldest, and is still undoubtedly the most popular, of all manures. It has stood the test of long experience, and has proved its position as one of the most important of all our fertilisers. It is highly desirable, therefore, to make a somewhat detailed examination of its composition, and to see on what the variation in this depends; and, finally, to examine into the mode of its action as a manure. That it should prove a valuable manure is scarcely to be wondered at, as it is originally formed from vegetable substance, and as it therefore contains all the elements present in the plant itself. Its composition is very variable, and probably no two samples would yield exactly similar analyses. In this fact lies one of the chief difficulties of the treatment of the subject, and all statements made in the following pages as to its chemical composition must be taken as only _approximate_. We may divide its constituents into three classes. 1. That portion due to _solid excreta_. 2. The liquid portion, largely made up of dilute _urine_. 3. The _straw_, or other material, which is used as litter. The composition of the manure will vary according to the proportion in which these three substances are present, as well as according to the composition of the substances themselves. It will consequently tend to a clearer apprehension of the subject if we first examine briefly the chemical composition of the solid excreta and urine of the farm animals. 1. _Solid Excreta._ The manurial value of the solid excreta of animals--_i.e._, the proportion they contain of _nitrogen_, _phosphoric acid_, and _potash_--depends on a variety of conditions. The solid excreta of horses, sheep, cows, and pigs, are well known to possess different properties, as well as to vary in their composition. What, however, has a still greater influence is the nature of the food. This is owing to the fact that the solid excreta are made up of undigested food. We can scarcely expect the same quality of solid excreta from an animal fed on poor diet as from an animal fed on very much richer diet. Again, the percentage of the food voided in the solid excreta varies in the case of different animals.[131]