should be applied to the particular crop which will give the most profitable returns for their use.

Résumé.-In Part I the reader was reminded that continuous cropping without the use of fertilizers finally results in practical exhaustion of the soil. The food of the plant, and the history of the formation of the soil were briefly considered, and the conclusion was evolved that to maintain the fertility of the land two things were necessary; first, to make more of the potential food available; second, to add something to take the place of the materials removed in the crop.

Part II has been devoted to a discussion of the first proposition. Tillage, drainage, irrigation, fallowing, green manuring and rotation are distinctly methods of changing potential plant food into available forms and, with the exception of the nitrogen gathered by the legumes, add no plant food whatever to the soil. Although, as has been previously stated, it is claimed. by some that by an intelligent use of these processes alone a profitable yield can be obtained indefinitely, it is the common experience that even with the use of the best methods of culture known in the past, it is impossible to maintain the fertility of the land without the use of some form of fertilizers. As it is obviously impossible to return the crop to the soil, the next thing that suggests itself is to feed the crop to the farm animals and use their excrement as a fertilizer. The subject of barnyard manures is of sufficient importance to justify its discussion at some length as Part III of this treatise.

PART III

BARNYARD MANURE

Effect of stable manure on growth of corn.

The plot on the left was manured with stable manure, while the one on the right received none. Stable manure is the best and safest of all fertilizers

CHAPTER XI

FACTORS AFFECTING THE VALUE OF FRESH MANURE

Importance of Barnyard Manure.—Barnyard manure is the oldest and is still undoubtedly the most. popular of all fertilizers. It has stood the test of long experience, and has proven its position as one of the most important manures. The fact that the applica

tion of the excrement of animals to the soil results in increased crop production, is mentioned by the early Roman writers, and from that time to the present, the majority of farmers have placed their main reliance on this class of manures for maintaining the fertility of the land.

"A well kept manure heap may be safely taken as one of the surest indications of thrift and success in farming. Neglect of this resource causes losses which, though little appreciated, are vast in extent. Waste of manure is either so common as to breed indifference, or so silent as to escape notice.

"According to recent statistics there are in the United States in round numbers, 19,500,000 horses, mules, etc., 61,000,000 cattle, 47,000,000 hogs, and 51,600,000 sheep. Experiments indicate that if these animals were kept in stalls or pens throughout the year and the manure carefully saved, the approximate value of the fertilizing constituents of the manure produced by each horse or mule annually would be $27, by each

head of cattle $20, by each hog $8 and by each sheep $2. The fertilizing value of the manure produced by the different classes of farm animals of the United States would, therefore, be for horses, mules, etc., $526,500,000; cattle $1,220,000,000; hogs $376,000,000; and sheep $103,200,000 or a total of $2,225,700,000.

"These estimates are based on the values usually assigned to phosphoric acid, potash and nitrogen in commercial fertilizers, and are possibly somewhat too high from a practical standpoint. On the other hand, it must be borne in mind that no account is taken of the value of manure for improving the mechanical condition and drainage of soils, which as subsequent pages will show, is fully as important a consideration as its direct fertilizing value." (Farmers' Bulletin 192).

If it is assumed that one-third of the value of the manure is annually lost by careless methods of management, and this estimate is undoubtedly conservative, the total loss from this source in the United States is about $750,900,000; a loss the more unfortunate because practically all of it could be prevented.

Composition of Manure From Different Animals. —The manures produced by the various classes of animals differ greatly in their composition and in their physical properties. The table on the next page gives the average percentage composition of the fresh manures (including solid and liquid excrement) from the more common farm animals.

By reference to this table it is seen that the difference in the value of the manures as given is due, to a large extent, to the variation in the amount of water present in the excrement of the different classes of animals.