riety of
weeds. Now the result of the application of different manures tends
respectively to foster the different kinds of grasses. Thus when one
kind of manure is applied, grasses of one kind tend to predominate and
crowd out grasses of another. It has been found that _the more highly
pasture-land is manured the simpler is the nature of its herbage_ (that
is, the fewer are the different kinds of herbage growing on it).
_Unmanured pasture, on the other hand, is more complex in its herbage._
The result is, that the application of manure to pasture-land is
attended with certain dangers. To maintain good pasture it is desirable
to effect a proper balance between the different kinds of grasses. For
this reason permanent pasture may be said to be, of all crops, the least
commonly manured. As a rule it is only manured by the droppings of the
cattle and sheep feeding upon it.

_Influence of Farmyard Manure._

It is found that the influence of farmyard manure upon the composition
of the pasture does not tend, to the same extent, to the undue
development of one type of herbage over another; and in this respect it
is probably to be preferred to artificial manures.

The same reasons, however, do not hold with regard to rotation seeds,
where an abundant growth is desired, and complexity of herbage is not so
important. A further reason which exists for the manuring of meadow-land
is the greater impoverishment of the soil taking place under such
conditions. As illustrating the influence of different manures on
different kinds of herbage, it may be mentioned that in New England
wood-ashes, a manure commonly used there, have been observed, when
applied to pasture, to bring in white clover, and that the application
of gypsum had the same effect. An explanation of this fact may be found
in the influence of potash on leguminous crops. The chief value of
wood-ashes as a manure is due to the large percentage of potash they
contain, while the value of gypsum is probably to be accounted for by
the fact that it has an indirect action, and sets free potash from its
inert compounds in the soil. In the Rothamsted experiments this point
has been verified, and potash has been shown to increase the proportion
of leguminous plants on a grass-field. Nitrogenous manures, on the other
hand, more especially sulphate of ammonia, have been found to increase
the proportion of grasses proper, and to diminish the proportion of
leguminous plants. The effe