An Agricultural Testament by Albert Howard

The transformation of soil fertility into a crop is only possible by means of oxidation processes. The various soil organisms--bacteria and fungi in particular--as well as the active roots need a constant supply of oxygen. As soon as this was recognized, aeration became an important factor in the study of the soil. In this matter, however, practice has long preceded theory: many devices such as sub-soil drainage, sub-soiling, as well as mixed cropping--all of which assist the ventilation of the soil--have been in use for a long time.

The full significance of soil aeration in agriculture has only been recognized by investigators during the last quarter of a century. The reason is interesting. Till recent years most of the agricultural experiment stations were situated in humid regions where the rainfall is well distributed. Rain is a saturated solution of oxygen and is very effective in supplying this gas to the soil whenever percolation is possible. Hence in such regions crops are not likely to suffer from poor aeration to anything like the same extent as those grown in the arid regions of North-West India where the soils are silt-like and most of the moisture has to be supplied by irrigation water low in dissolved oxygen. Such soils lose their porosity with the greatest ease when flooded; the minute particles run together and form an impermeable surface crust. Only when the humus content is kept high can adequate permeability be maintained. Long before the advent of the modern canal, the cultivators of India had acted on this principle. The organic matter content of the areas commanded by wells has always been maintained at a high level. Irrigation engineers and Agricultural Departments have been slow to utilize this experience. Canal water has been provided, but no steps have been taken simultaneously to increase the humus content of the soil.