Humus. — The word humus is a general term, and includes the decayed remains of animal and vegetable matter of all kinds. This is the material which, when mixed with sand and clay, gives richness and fertility to the soil, and as decay proceeds the valuable ingredients it contains are liberated for the benefit of the crops. Humus also has the power of absorbing and retaining moisture and heat in a wonderful degree _it improves the texture of a soil, rendering it more friable and easy to work, and is the medium in which there lives an immense number of minute organisms so essential to the production of available plant foods. Lime.-this is essentially a transitory substance constantly being removed by crops and percolating water, and absorbed by combination with acids from decaying. Vegetable matter, fertilisers, etc. Period ical dressings of lime are very necessary, but this will be fully discussed in the chapter on manuring. Soils may be simply classified as a clay soil when this material predominates to any great extent; a sandy soil when sand is present in excess; a black organic soil when it contains an excessive amount of humus, as all peaty soils do, and sometimes, though to a less degree, old garden soils which have long been heavily manured and as a loamy soil. Loam is the best kind of soil, being very fertile, easy to manage, and well adapted for the successful cultivation of vegetable crops. Loams vary somewhat in texture.
