Land Drainage

Hawke's Bay Tribune, Volume XVII, Issue 208, 17 August 1927, Page 7

Land Drainage

Scope For Improvement in N.Z. Methods Employed and Benefits Received ' By “Sundowner' ’ (Written for the Tribune. All Rights Reserved.)

In comparison with the extent oi both cultivated and pasture land in New Zealand, the amount of systematic drainage winch has been under taken is almost negligible. And yet, with the exception g>f free limestone land, soil which has a shingle foundation, and that with pumice underlying it, there are very few soils m our Dominion which can be classed as well drained, and most of these would be distinctly benefited by scientific artificial drainage. As is very natural in a comparatively young country, the first land to be drained has been that which is obviously w'aterlogged. In this category we have swamps, that land which has an underlying strata ol hard-pan, low-lying land bordering lakes and streams where the fall is insufficient to allow the water to get rapidly away, and the bottoms ol valleys which lack an adequate outlet. As a rule all such land, with the exception perhaps of hard-pan land, is exceptionally rich, and if the draining operations are thorough, quickly repays the amount expended in the work. There is. however, an immense area of land, both flat and undulating which still remains undrained and which would well repay the money such work would cost. THE BRITISH EXPERIENCE. In older countries, such as Great Britain, this subject has received the attention which it merits, for it is realised that good, drainage is the foundation upon which agriculture is built. New Zealand, also, is now rapidly reaching that stage in its history when this subject must he studied more seriously, and with the experience of other lands, and much scientific data to guide us. we should be enabled to accomplish vast improvements at a minimum of expense INCREASED SOIL TEMPERATURE The first effect of draining is to raise the temperature of the soil. This does not sound any very great accomplishment, but in reality it has* more to do with the fertility of the land than anything else. To gain some idea of this, first suppose you could transport land from an altitude of about 2000 feet 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 temperature is v»ry frequently secured in drained land over its undrained state. It is a scientific fact that it requires much more heat to raise the temperature of water than it does of soil, and in undrained land this rise of soil heat is slower owing to the fact that evaporation of surplus moisture, which must take 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 in coming away in the spring than well-drained hillsides, further, when land is in a waterlogged condition, there is no opportunity for air and sunlight to penetrate the soil and introduce the nitrogen which means so much to the growth o£,the plant. In land which is regularly waterlogged each winter, and from which the drainage is slow in spring and summer, the absence of plant food to depths in the soil where it is unavailable to the plants, is very considerable. Most of the minerals and humus in the soil are soluble to the extent that they are readily held in suspension in water, and as this latter drains away, it takes with it this available nourishment, leaving the land impoverished. WET SOIL IS DEAD SOIL. One ot the worst effects of con tinned saturation of soil, however, is the fac| that it prevents the devel’opmen 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 they do not take on a form in which they are available as food fo r the plants, and tire soil becomes “dead." “Dead” soil, when wet, is slimy and cold, when dry, hard and cracked. from observing the behaviour of your land under these varying conditions, therefore you can be guided as to whether drainage s required or not. WHERE WEEDS THRIVE. A poorly-drained field, however well it is tilled and however lavish may be the application of artificial fertilisers, will never respond liberally. Tlie land, if ploughed when damp,, bakes into hard lumps which are difficult to break down to a fine soil mulch if left too long and turning over and working becomes an impossibility. During the growth season the sruggling plant is subjected to alternations of drowning and baking, with the result that the only plants that really thrive are weeds which can support the unkindly conditions Owing to "its porous, “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 capillary action to nourish the plant growing in the warm soil-mulch above

DRAINING PEAT SWAMPS. A great many of our 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 spono'- holds a gisat deal of water in the wet winter season, but when summer arrives. there being no subsoil to retain a part of this moisture within reach, of the plant roots, they suffer from drought condition unless the rainfall is fairly frequent. Further, this peat land appears to lack in mineral and organic constituents, and while the growth, under favourable weather conditions, is luxurious. animals grazed on it for anv length of time scour and if not medically treated or moved to other pasture waste away and ultimately die in the midst of plenty. SCIENTIFIC TREATMENT. In the United States of America a scientific method of utilising this peat land has been evolved which is entirely satisfactory, and which has made these rich peat swamps the most sought-after of any of their agricultural land. First the land is thoroughly drained, and directly it has reached that stave of drvness when it will support agricultural implements. the ploughs are put in and drawn backwards and forwards across the boggy surface by means ot ropes and pulleys and a stationary engine. Other cultivation follows, and while the soil is still moist a thick, quick-growing crop is sown to smother all weed growth. When this crop hag 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. With the possibility of applying irrigation water in such quantities and whenever the soil may require it. enormous crops are grown on this rich land, and it is thereafter kept entirely for agricultural purposes Much might be done in New Zealand with similar areas were this procedure adopted. THE ART OF DRAINING Draining, generally, is a more scientific business than the average farmer imagines it. It is not sufficient to run a deep drain through ihe centre of a swampy area and imagine the land will thereafter come into profit. Although central drains are necessary, if they alone are depended upon, it means that the soakage from the hill faces surrounding the area must slowly percolate through all the swamp to reach this get-awijw. Drains must also be provided round the margin of the wet area to catch this soakage and carrv it off before it reaches the land being drained. Springs must be looked for and tapped bv branch drains, and the whole system must be so laid out n s to interfere as little as possible with subsequent cultivation. THE BEST METHOD. The best method of bringing in such drained swamp land is to utilise it for two or three seasons for the growing of green crops such as rape, barley oats maize, etc. This gives the land time to sweeten before being laid down in permanent pasture, and aids also in the eradication of weeds Stiff clav pasture land, and sometimes hardpan 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. Hardpan land on the flat presents a more difficult problem, and where the strata underlying the pan is porous, satisfactorv drainage has sometimes been secured by a combination of tile draining and blasting or breaking up of the pan in the depressions towards which surface water and soakage will naturally drain. Each drainage problem presents special features, and for each a separate plan must be carefully tried out. But plan there must be if the work is to be successful. Frequently, with comparatively small .outlay in the 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 should he given by the farmer to the possibilities of efficient drainage.