"In case of horses, the manure can be kept buried for several weeks if some means are used to prevent the escape of ammonia. Cattle produce what is called a 'cold' manure, while it is called 'hot' from horses because it decomposes so readily. One of the best substances to use for the prevention of loss of ammonia in horse stables is acid phosphate, which has power to unite with ammonia and hold it in a fixed compound. About one pound of acid phosphate per day for each horse should be sprinkled over the manure. Of course the phosphorus contained in the acid phosphate has considerable value for its own sake, and care should be taken that you do not lose more phosphorus from the acid phosphate applied than the value of all the ammonia saved by this means. Porous earth floors may absorb very considerable amounts of liquid from wet manure lying underneath the dry bedding, and the acid phosphate sometimes injures the horses' feet; so that, as a rule, it is better to clean the horse stables every day and supply phosphorus in raw phosphate at one-fourth of its cost in acid phosphate." "Before we leave the nitrogen question," said Mr. Thornton, "I want to ask if you can suggest how we can get enough of the several million dollars' worth we have in the air to supply the needs of our crops and build up our land?" "Grow more legumes, and plow more under, either directly or in manure." "That sounds easy, but can you suggest some practical system?" "I think so. I know too little of your conditions to think I could suggest the best system for you to adopt; but I can surely suggest one that will supply nitrogen for such crop yields as we have considered: Suppose we change the order of the crops and grow wheat, corn, oats, and cowpeas, and grow clover with the wheat and oats, plowing the clover under in the spring as green manure for corn and cowpeas. If necessary to prevent the clover or weeds from producing seed, the field may be clipped with the mower in the late summer when the clover has made some growth after the wheat and oats have been removed. Leave this season's growth lying on the land. As an average it should amount to more than half a ton of hay per acre. The next spring the clover is allowed to grow for several weeks. It should be plowed under for corn on one field early in May and two or three weeks later the other field is plowed for cowpeas. The spring growth should average nearly a ton of clover hay per acre. In this way clover equivalent to about three tons of hay could be plowed under. Clover hay contains 40 pounds of nitrogen per ton; so this would supply about 120 pounds of nitrogen in addition to the 173 pounds possible to be supplied in the manure. This would make possible a total return of 293 pounds, while we figured some 200 pounds removed. Of course if you save only 100 pounds in the manure the amount returned would be reduced to 220 pounds."