The vegetable garden in the tropics - Journey to Forever

Most of the roots of vegetables concentrate in the topsoil and, to a lesser
extent, in the subsoil, but there are differences between vegetables. Pigeon
pea roots, for example, grow much deeper than those of lettuce.
Soil tillage should not change the relative position of the soil layers: the
fertile top layer should stay on top and each layer should stay in place as
much as possible.
The first tillage of the soil, especially if the soil is compact after clearing,
should be done two spits deep, to at least 30cm. Work with an open
furrow. At the bottom you turn the spadeful, and on top of that you
throw the first spadeful from the next furrow etc. When working with a
hoe you also work with an open furrow. Remove the earth from a narrow
strip, loosen the bottom layer and cover it up again with the earth of
the top layer from the next strip, and so on.
Figure 6: A soil profile
Deep tillage is especially recommended for soils that are compact and
less permeable (often clayish soils). For normal maintenance, a depth of
one spit will do (see fig. 7). After several tillages (while working under
manure) the layer of topsoil, suitable for cultivation will become thicker
and looser.
22
The vegetable garden in the tropics