Humus in the soil has seldom been taken at its full worth. The mission which it fulfills is second in importance only to that which is fulfilled by the presence of plant food in the soil. Humus is helpful in keeping soil in proper physical balance, in binding soils that are much prone to blow, in in-creasing the power of soils to absorb and hold moisture and in making more effective the action of fertilizers.
When the humus is exhausted the physical condition of the soil suffers. The soil becomes more impacted, less easily aerated, and less easily penetrated by the roots of plants. Some soils so light as to lift with the wind can be kept from blowing, at least in a great measure by simply keeping them stored with grass roots or other vegetable matter buried in the soil. The increase in the power of soils to hold moisture is very great when well stored with humus. When commercial fertilizers are sown on land they will fail to respond properly unless the land is supplied with humus.
Such being the case, every effort should be made to store the soil with humus. It would not be impossible to have excess of humus, but in practice this seldom happens. Humus may be put into the soil in the form of clover roots and of grass roots, of buried catch crops and barnyard manure.