What would be the best manures to apply to a light sandy soil in order to make it more moisture-retentive?
Manure as a term implies:
Bulky organic matter usually applied in large quantities (as against fertilisers which are mostly of a concentrated mineral nature). Only large quantities of lignified material (grassare not woody or lignified) will supply humus. Humus is the dark organic substance resulting from the breakdown of plant or animal tissues. Its benefit in most soils is in its water-holding capacity, its natural aeration (when freely drained), its support for the microflora and microfauna agencies which contribute greatly to the soil’s fertility, arid its ability to improve the soil structure into aggregates of soil particles or crumbs, which aid soil fertility enormously.
Farmyard manure – cow manure
Of the organic manures available, this is, perhaps, the best for light sandy soils, owing to its moisture-retaining qualities; it will also supply significant quantities of N, P and K, and of minor elements. Any other organic manures that are well-rotted would be suitable, their main function being to ,supply humus. Humus has been described as decomposed vegetable matter that has lost its original shape and form. Its presence in light sandy soils is of the utmost importance, as it has a cementing effect on these soils, binding them closely together and thus improving the water-holding capacity. Moreover, it possesses the special characteristic of absorbing moisture. Hence, a light sandy soil well-supplied with humus is better able to withstand drought. (Soil depth may then be the limiting factor).
Other humus-forming materials include wool_shoddy (now only available in certain parts of the country,) seaweed, spent hops, and well-decayed garden refuse (). Only bulky wastes are suitable for the formation of humus.
On a small area the proprietary brands of hop manures are useful, as in addition to supplying small amounts of the humus-forming spent hops, they also contain nitrogen, phosphates and potash.
In the ordinary sense of the word, one would hardly call peat a manure, yet when applied to light sandy soil it is of considerable benefit in improving the moisture-holding capacity. This is only usually possible on a small scale because of its cost. However, responsible gardeners are now turning away from the use of peat as the ecological repercussions of stripping peat bogs become more widely known. An alternative which is rapidly becoming popular is composted coconut fibre, which has even greater moisture-retaining properties than peat.
Well-rottedmould is of considerable benefit to light soils in areas where it is obtainable.
All bulky organic manures to be dug in are best applied in early spring. Oxidation of organic material is very rapid in sandy soils, and if applied in autumn a good deal of the material will be broken down before the next growing season, and some of the nitrates produced would be lost due to leaching.
The digging or ploughing-in of green crops in autumn is of considerable value. The growth of these crops may be stimulated by application of suitable inorganic manures. Potash is usually deficient in light sandy soils, and could be incorporated in the form of sulphate of potash in the compounds or mixture used.
In addition to the direct application of manures, it is helpful in many instances to lay some well-rotted organic substance on the soil surface around the base of plants, (but not touching theas this may cause rotting) to conserve soil moisture. This practice, .known as mulching, is of special benefit to surface-rooting crop s such as raspberries. Well-rotted farmyard manure, spent mushroom , peat moss litter, grass cuttings, (but not after treatment with weedkiller) or spent hops are commonly applied for this purpose.
Generally speaking, sandy soils require much more generous manuring than clay soils, and both organic and inorganic materials should be used.
Soil Particles much enlarged
The soil water is held by surface tension to the surface of the particles, as well as by colloidal materials such as organic matter and clay particles.