Manures and the principles of manuring

by Charles Morton Aikman

We have already referred to the manuring of crops of the leguminous class in discussing the manuring of meadows and permanent pasture. It was there pointed out that the tendency of certain manures was to encourage the growth of the leguminous plants of the herbage, while other manures had the effect of encouraging those of the gramineous class. It was pointed out that a manure which had this effect was potash, or any manure which owed its characteristic action to the fact that it supplied potash to the soil or set it free in the soil.

Leguminous Plants benefit by Potash.

This is one of the most important points to notice in manuring leguminous plants. Just as we can say that nitrogenous manures are specially beneficial to cereals, and phosphatic manures to roots, so potash is the special manure for leguminous crops.

Nitrogenous Manures may actually be hurtful.

But we have, further, an even more striking characteristic of leguminous crops to notice. We have seen that, with regard to the crops already discussed, while there are cases in which a fertilising ingredient may be of no value, or may positively exert a hurtful action on the crops, such cases are only exceptional. With regard to leguminous crops, however, we find that almost invariably they derive little or no benefit from the use of artificial nitrogenous manures. And this is all the more striking since they contain large quantities of nitrogen in their composition—twice as much as the cereals. The fact, which has long been noticed with regard to certain members of this class of plants, such as clover, that not only do they contain a large amount of nitrogen, but that by growing them on a soil the soil is largely enriched in this valuable fertilising constituent, has long waited for a satisfactory explanation, which at last has been forthcoming. The discovery that leguminous crops can draw on the boundless store of nitrogen present in the air has done much to clear up the mystery. There are, however, other problems with regard to the growth of leguminous plants which still await solution.

Clover-sickness.

One of these is the fact that land on which a leguminous crop like clover has been growing for a number of years becomes unfit to support its growth any longer. Such a soil is termed "clover-sick"; and many have been the theories put forward to explain the phenomenon, but none of them can be regarded as satisfactory.

The knowledge that leguminous plants have the power of deriving their nitrogen from the air, furnishes us with an economical means of enriching our soils in nitrogen. By growing leguminous crops alternately with cereals, for example, the air should be made to furnish the necessary nitrogenous manure. As a matter of fact, modified forms of such a practice have long been in use—indeed the ordinary rotations of crops are, to a certain extent, adaptations of this practice.

Alternate Wheat and Beans Rotation.

An interesting experiment carried out at Rothamsted may be here cited which illustrates in a striking manner the truth of the above statement. Wheat and the leguminous crop beans were grown alternately. It was found that almost as much wheat (containing nearly as much nitrogen) was yielded in eight crops of wheat so grown as was yielded by sixteen crops of wheat grown consecutively in an adjoining field.