Poultry Manure.--The value of poultry manure often is overestimated. Its content of plant-food is one half greater than that of horse manure, ton for ton. The availability of the nitrogen is so great that returns from applications are immediate, and give the impression of greater strength than is possessed. Its availability makes it excellent for plants that need forcing. For such use it needs reenforcing only with acid phosphate, but as a general manure it should have the addition of potash. Acid phosphate should be used in the poultry-house to prevent loss of nitrogen, which escapes quickly on account of rapid fermentation, and to supply phosphoric acid. Thirty pounds of acid phosphate to each 100 pounds of the manure gives a mixture containing one pound of nitrogen, three pounds of phosphoric acid, and two fifths of a pound of potash. The addition of four pounds of muriate of potash makes the mixture a well-balanced and effective fertilizer when used at the rate of 500 to 1000 pounds per acre. Dry muck or loam should be mixed with it to serve as an absorbent and to give good physical condition. CHAPTER XIV THE USE OF STABLE MANURE Controlling Factors.--The farm supply of stable manure is a carrier of plant-food, returning to the soil four fifths of all the fertility removed in the crops fed, but it is much more than this. Land which receives only plant-food, as may be the case when fertility is supplied in commercial fertilizers, loses good physical condition. Organic matter is needed for maintenance of physical condition, the retention of soil moisture, the freeing of inert minerals in the land, and the promotion of bacterial life in the soil. No small share of the value of a ton of manure is due to its organic matter. This is a factor in the problem when deciding what disposition of the manure will pay best. One field may be in condition to respond fully to the use of commercial fertilizers, while another is too deficient in humus for best results. Some crops are more insistent upon supplies of organic matter than others. Again, the disposition of the manure depends upon the supply. If most crops are fed on the farm, the manure is a leading source of fertility for all fields and crops, and may be used once or twice in the crop-rotation on every field. If the manure is in small amount, due to a scheme of farming involving the growing of crops for market, the function of the manure may be only to encourage the starting of sods, in which legumes are a leading factor.