LAND AND DRAINAGE.

New Zealand Herald, Volume LXIV, Issue 19720, 20 August 1927, Page 18

LAND AND DRAINAGE.

SMALL AREA TREATED.

SCOPE FOR IMPROVEMENT.

LARGE TRACTS. BY H.B.T. In comparison with the extent of both cultivated and pasture land in New Zealand, the amount of systematic drainage which has been undertaken is almost negligible, and yet, with, the exception of free lime-stone land, soil which has a shingle foundation, and that with pumice underlying it, there are very Jew soils in the Dominion which can be classed as well drained. Most of these would be distinctly benefited by scientific artificial drainage.

It is only natural that work in a young country, the first land to be drained, has been that which was obviously waterlogged —swamps, flat land which has an underlying strata of hard-pan, low-lying lands bordering on lakes and streams, •where the fall is insufficient to allow the water to escape rapidly, and the bottoms of valleys which lack an adequate outlet. As a rule, all such land, with the exception, perhaps, ot hard-pan land, is exceptionally rich, and if the draining operations are thorough, they quickly repay the amount expended. Vhe first effect of draining is to raise the temperature of the soil. This does not appear to be a very great accomplishment, but in reality it has more to do vith the fertility of the land than has anything'else. To gain some idea of this, just suppose you could transport land from an altitude of about 2000 ft. down to sea-level. Naturally one would anticipate that it would be much more .productive at the lower level than on the bleak uplands, and yet this represents only a difference of about ten degrees in soil temperature. Such a rise in tempeiatuie is very frequently secured in drained land over its undrained state. Effects of Continued Saturation. It is a scientific fact that .it requires much more ■ heat to raise tne temperature of water than it cloes of soil, and in undrained land this rise of soil heat is glower owing tc tile fact that evaporation of surplus j moisture, which must taKP place before the soil commences to warm, causes a further lowering, instead of a rise in temperature in the soil. This accounts for the fact that swamps and badly-drained pastures are slower 111 com ing away in the spring than well-drained hillsides.

One of tho worst effects of continued saturation, is the fact tfiat it prevents , the development of the micro-organisms which we call soil-bacteria. In their absence, the acids of decaying vegetation remain unaltered in the soil. The mineral salts dissolve in the water, but do not .take on a form in which they are available as food for the plants. ' The eoil thus becomes " dead:." A poorly-drained field, however well it is tilled, and 'however lavish the application of artificial lertiliseis, will ' nevei respond liberally l'he land, if ploughed j when damp, bakes into hard lumps, which are difficult to break down to a fine sou mulch, and left too iong. turning over and working becomes an impossibility. During the growing season, the struggling plant is subjected to alternations of riiown \ and baking, with the result that the \ only plants that really thrive are weeds ) which can' survive the unkindly conditions. Retention of Moisture in Summer. Owing to its poious " live" condition, ■well-drained soil actually retains more moisture during the summer than undrained soil, but this is held in suspension in the subsoil from whence it rises slowly by capilliary action to noui ish the plant growing in the warm soil - mulch above. A great many of the swamps in the North Island are of peat formation, and the usual practice of draining and laying these down in pasture _has , not proved entirely satisfactory. The reasons for this are that the soil, being very porous and spongy, holds a great deal of water in the wet, winter season, but. when summer arrives, there being lio subsoil to retain a part ot this moisture within reach of the plant roots, they EiJffer from drought conditions, unless the rainfall is fairly frequent. In the United States ol America, a scientific method of utilising this peat land has been evolved which is entirely satisfactory, and which has made these rich peat svamps the most sought-after of any of eir agricultural land. First the land is thoroughly drained, and di rectly it has reached that stage of dryness when it will support agricultural implements, the ploughs are put in and drawn backwards and forwards across the boggy surface by means of ropes and pulleys, and a stationary engine. Other cultivation j follows, and while the soil is still moist, a thick, quick-growing crop is sown to smother all weed growth. When this crop has reached maturity, the ground is. sufficiently firm to permit of harvesting operations, and when these are completed the whole area is trenched {or sometimes banked), to allow of irrigation. Much might be done in New Zealand with similar areas were this procedure adopted. Drainage and Science.

Drainage, generally, is a more scientific business than the average farmer imagines. It is not sufficient to run a deep drain through the centre of a swamp area and imagine the land will thereafter come into; profit. Central drains are necessary, but drains must also be provided round the margin of the wet area to catch this soakage and carry it off before it reaches the land being drained. The best method of bringing in such drained swamp lands is to utilise it for two or three seasons for the groV'ing of grain crops, such .as rape, barley, oats, maize, eta This gives the land time to sweeten and aerate before being laid down in permanent pastures, and aids also in the / eradication of weeds. Stiff clay pasture lands, and sometimes hard pan land, can be satisfactorily treated with shallow tile or mole drains, and machines can now be procured which will do- this work quickly and cheaply. Hard-pan land on the fiat presents a more difficult problem, and where the strata underlying the pan is porous, sat isfactorv drainage has sometimes been secured by a combination of tile-draining and blasting, or breaking uri the pan in the depressions toward which surface ■water and soakage will naturally drain. Frequently with comparatively small outlay in drainage, the productiveness of both agricultural and pastoral land can be doubled, and wherever indications of excessive water can be detected from the class of growth or the condition of the soil, serious consideration ehould be given by the farmer to the possibilities of efficient drainage.