6. It allows the excrementitious matter thrown out by roots to be carried out of their reach.
All of these actions the soil must be capable of performing, before it can be in its highest state of fertility. There are comparatively few soils now in this condition, but there are also few which could not be profitably rendered so, by a judicious application of the modes of cultivation to be described in the following chapters.
The three great objects to be accomplished are:—
1. To adopt such a system of drainage as will cause all of the water of rains to pass through the soil, instead of evaporating from the surface.
2. To pulverize the soil to a considerable depth.
3. To darken its color, and render it capable of absorbing atmospheric fertilizers.
Name some of the means used to secure these effects.
Why are under-drains superior to open drains?
The means used to secure these effects are under-draining, sub-soil and surface-plowing, digging, applying muck, etc.