Permaculture Designers Manual
CHAPTER 8 – WATER IN PERMACULTURE
Section 8.7 –
The Distribution of Elements in the Soil Profile in Permaculture
There seem to be two important determinants of the concentration of elements or nutrients through the soil profile (that vertical column of soil from the surface to 2 m or so deep).
The first is the penetration of water. Water is a universal solvent, enabling compounds to dissociate into ions, and transporting them, firstly, to various deposits at microsites in the soil.
This effect works in three dimensions:
Water travels by infiltration to varying depths, soaking in from the surface down.
Water can also rise from the soil water table upwards, either by flooding, by capillary action (soaking), or by being pressured upwards by an aquifer now in permeable sediments.
Water travels by through now, traveling by the effects of gravity downslope in the profile.
This latter effect produces soil types called catenas specific to slope, drainage, rock type, and landscape (Figure 8.3).
INFILTRATION effects are most marked in soils where, for very long periods, a succession of light intensity rains have alternately wetted and then dried out in the soiL
At the wet-dry boundary we find concentrations of easily soluble salts and deposits of minerals and nutrients (sometimes in over-supply).
The second set of effects on element transport is biological. Elements are actively sought out or selected, and either concentrated or dispersed by living organisms.
These effects are myriad in total, but some of the ways this is known to happen are:
CONCENTRATION BY SELECTIVE SPECIES of fungi, bacteria, and invertebrates which can seek out, assemble, and change specific compounds to stable new forms as concretions or nodules. Iron iron-manganese, calcium, phosphate, zinc, nickel , copper, selenium, cadmium, phosphate and nitrogen are all so selected and concentrated by one or other form of mycorrhiza (root fungi), bacteria, molluscs, or algae.
CONCENTRATION BY ACCUMULATION OF DETRITUS. Diatoms, swamp peats, whole forests, sponges (and their spicules of silica), molluscs, and vertebrates are at limes buried by volcanism , sedimentation, or deposition in oceanic deeps to form specifically concentrated sediments, and eventually ore bodies or rock types (coal. rare earths, or manganese deposits).
DISPERSAL BY TRANSPIRATION. Many water plants seem to be able to dissociate and transpire a great variety of substances to atmosphere. Reeds do this with mercury, hydrogen, and other elements from phosphates to chlorine. Not all of these are vaporized to drift off in the winds; many are deposited in special leaf repositories, or evaporated to a wax, dust, or efflorescence on the leaves and stems of trees, from where they are washed down again to earth by rain throughfall.
In this way, both major plant nutrients and minor elements are concentrated in the top 4 cm (1-2 inches) of soil below trees. Metals, oxides, halogens, acids, alkalis and salts are also concentrated.
CONCENTRATION BY METABOLIC PROCESSES
We build our bodies up by ingesting a large range of complex foods, as do all living things. From these ingested bodies, materials are selected to build our bones, flesh, blood, and brain tissue or organs, nails and hair, fats and milk.
Thus, our own bodies and those of other animals are complex storages of elements; even our faeces package very different concentrations of potash, nitrates, and pollutants from the different concentrations of foods that we eat.
And, by our behaviors, these are variously disposed of in a personalized, culturally-determined, or species specific way in the environment.
Plants and animals ceaselessly ingest and defecate, refect and exude over their whole lifetimes, thus altering the concentration of nutrients in their immediate environment.