d, second, because of
the readiness with which nitrogen may disappear from the soil under
improper management, either through nitrification and leaching or by
denitrification and passing back into the air.

Assuming a given type of management, the question is, How much of the
required nitrogen will be obtained from the legumes in the cropping
system, how much from the manure, and how much must be purchased in
commercial fertilizers? No satisfactory cropping system can be devised
at the present prices of farm products and cost of fertilizers for the
production of the ordinary cereals and hay that does not include the
production of some legume. Assuming a legume in the cropping scheme,
the fertility of the soil may be maintained by yard manure alone or by
commercial fertilizers alone. Illustrations of both methods are to be
found in actual practice. Generally speaking, however, the use of yard
manure supplemented with commercial fertilizers will be found more
scientific and in the end the most economical.

A factor entering into this problem will be the amount of purchased
feed. If considerable amounts of purchased feeds are used and the
resulting manure carefully preserved and judiciously applied, the
commercial fertilizers required will be reduced to the minimum.

A concrete illustration may bring out the philosophy underlying farm
schemes better than abstract problems.

The following outline shows a five-course rotation with the method of
fertilization which the results of the Pennsylvania Station indicated
would be advisable, at least on limestone soils in eastern United
States.

1. Maize yard manure, 8 tons per acre.
2. Oats nothing.
3. Wheat acid phosphate, 350 lbs.
muriate of potash, 100 lbs.
4. Clover and timothy nothing.
5. Timothy nitrate of soda, 150 lbs.
acid phosphate, 150 lbs.
muriate of potash, 50 lbs.

This rotation is suggested for the purpose of maintaining a farm that
is already in a fairly fertile condition and one on which there is no
considerable amount of purchased feed. Where concentrates are
purchased liberally, yard manure should be available to use on the
timothy and meadow in place of the commercial fertilizers.

Where there is plenty of manure and it is desired to increase the
amount of maize and hay and reduce the amount