Methods of Retaining Fertility

Topsoil Theory

By H. Charles Reed, Apia

AN important discovery has been made, while carrying out experiments with the various green manure crops. A plant has been found that is capable of drawing, from the lower strata of the subsoil, nutrients which are elaborated in its leaves; and as soon as the plant dies, or is cut down, the entire plant dis integrates into rich vegetable-mould or humus.

This is not a matter of a small per centage of haulm or leaf deposit, such as is obtained by many of the small-grow ing Crotalarias, Desmodium, or other cover plants; but a large amount of humus, sufficient to enable the cultivator to continue to raise abundant crops on the same soil, year in year out; with proper crop rotation practised.

It is intended to plant the new subject in single lines between the permanent crops: coffee, tea, rubber, cocoa, and the spices. Already this new source of plant nutrients has enabled a bumper crop of splendid garden vegetables to be grown on land previously rejected by Chinese gardeners as “useless” (and this after about 15 years of continuous cropping).

This alone speaks well for the future possiblities of the humus-producing plant.

It must be borne in mind that the “top few inches of the soil, over and over again, are the most important of all to the crop.” Endless time and money is spent in getting a good tilth, and making the surface soil of such mechanical condi tion that it will readily absorb moisture

on the one hand and retain it on the other. This topsoil is the home of myriads of bacteria, which render the fertilising constituents available to the plant; i.e., in the presence of moisture.

But unless a soil contains a sufficient percentage (about 10 per cent.) of vege table matter (humus) the requisite moisture cannot be absorbed or retained.

Artificial manures have no power of moisture retention; while a stony, sandy soil loses its moisture content in no time, unless a cbver plant, or mulch, is employed.

A large number of plants are surface feeders, and if they are tea, coffee, cocoa, rubber, etc., it is especially important that the surface soil should not be re moved. Deep trenching, “lying fallow” and the turning down of the topsoil (the carpet of nutrients and moisture) under conditions of tropical cultivation, and intense solar heat is, in the opinion of this writer, a misguided practice.

IN lying fallow, a, soil loses its valuable soil bacteria, which perish. In deep trenching (so highly recommended in certain text books) plants often become stationary, dwarfed, or thriftless; and more often than not, fail altogether. For what purpose are the wonderful “tap roots” of plants? Possibly, to draw up the moisture required to elaborate the nutrients provided by the humus con tent of the surface soil. But if the sur face soil is removed, does the plant thrive? I have not found it so in 20 years of field experience. But now real results are made possible by simply grow ing a plant which will enrich the surface soil beyond the wildest dreams of the progressive horticulturist in the tropics.

Virgin soils, soils which have been under natural vegetation for many years, are rich in this natural vegetable humus, and do not require any additional fertiliser.

In fact, the application of a chemical compound to these complete soils is apt to destroy the balance of naturally formed plant nutrients in a soil, until such time as the nitrogen, potash, phos phates, etc., have been partly depleted by crops. The progressive planter will not wait until his soil no longer yields him a satisfactory crop. Millions of planters in the USA put their faith into artificials to restore the soil fertility and dis covered, when too late, that the soil does not respond to such methods.

To-day, crops may be inter-planted with a cover-plant that will restore soil fertility, as it is used up by crops of rubber, coffee, spice, cocoa, or tea. Not alone this; the needed moisture is drawn into the soil from the air and dew, and Is conserved in the retentive vegetable humus the only component in a soil capable of holding moisture, aerating the soil, and preventing sun-scorch to the delicate roots of plants.