g the
eight years. In 1865 the plat, last manured in 1863, gave over double
the yield of the unmanured. In the following ten years its yield was a
half more than that of the unmanured. In the next ten years the yield
was a quarter more. In the next ten years it fell to 6 per cent more
than the plat that had received no manure in the beginning of the
experiment. In the following ten years it rose to 15 per cent. Here is
a lasting effect of manure for over forty years where grass was grown
continuously.

CHAPTER XV

CROP-ROTATIONS

The Farm Scheme.--Notwithstanding some of the theorizing that does not
commend itself to the practical man, farm management is taking on the
form of a science. It involves the organization of a farm for best
results, and in the scheme that should be worked out for any particular
farm the most important feature is the crop-rotation. The selection of
crops is controlled by so many local considerations, including the
personal likes and dislikes of the farmer, that very rightly the kinds
of rotation are innumerable. The order in which crops may be grown with
most profit is less variable, and yet even here local conditions may
quickly derange the scheme of a theorist. There is, however, such right
relation of facts to each other that we are getting a working
philosophy, and the individual farmer can bend practice to his own
liking in considerable degree, and yet not compel plants to do their
part at a disadvantage. He has much liberty in the order of their
growing, without endangering profits materially. Theoretically, this is
not true, and the factors of production on any farm are such that the
largest return is obtainable in only one scheme of farming. Practically
there is rather wide liberty.

Value of Rotation.--Experience has shown the benefit of variety in
crops grown on land. Among the advantages of crop-rotation are the
following:

1. It enables the farmer to maintain the supply of organic matter
in his soil. The roots and stubble of a grain crop are insufficient
for this purpose, and the introduction of a sod or cover crop is
helpful.

2. It permits the use of legumes to secure cheap supplies of
nitrogen.

3. Some plants feed near the surface of the ground, and the use of
other plants which send roots deeper adds to the production.

4. Some crops leave the soil in bad physical condition, and the use
of other crops in the rotation s