IRRIGATION IN CENTRAL OTAGO.

Otago Daily Times, Issue 19270, 6 September 1924, Page 7

IRRIGATION IN CENTRAL OTAGO.

TO THE EDITOR. Sib, —The season so far has been fairly dry and the time will soon arrive when irrigation in Central Otago will again be in full swing. I doubt whether the information set forth in the New Zealand Journal of Agriculture is sufficient to ensure the successful irrigation of the various olassses of land contained at present in the Central Otago schemes. The hopes of the Otago Central farmer and also many of the leading citizens of Dunedin who take an active part in the development of Otago have been buoyed up by the magnificent results obtained from the irrigated alluvial deposits in various portions of Central Otago. Apparently all land within the scope of irrigation is to be irrigated. This, I think, will bo a great mistake. Many of the recent projects have been undertaken for the irrigating of a very different class of soil. The ultimate effect of irrigation on this class of land should be thoroughly proved to be successful before schemes of a similar nature are put into operation. I refer to the sedimentary soils such as wo have in Ida Valley. No sedimentary soils in Central Otago have even reached the experimental stage. In some of the foremost irrigation projects in the world, such as in the United States, Canada, or even Victoria, it will be found that the successful irrigation schemes are chiefly operating on what L termed alluvial deposits. Thousands' of acres in the United States that are under irrigation, although termed alluvial deposits, are composed of several feet of decomposed vegetable matter. References to these schemes generally mention feet of soil, not inches, and this class of land therefore offers gome material to work upon.

It seems to be eseantiai that *to bring about success in the matter of irrigation there should bo a great depth of soil, decomposed matter, or deep alluvial deposit such as is usually found in flats which are traversed by very slow-running streams and rivers. The . deposits from fast-running rivers such as the Molyneux are too coarse, the finer deposits being invariably carried away. As percolation on this class of land increases the soil must lose its fertility, and probably a fair percentage of land now under irrigation in Central Otago will after a few years require watering every night and manuring every day. The class of, land that seems to hold out best, is periodically inundated land, the rich sediment supplied to it from time to time compensating for any depreciation brought about by irrigation. The land of this description in Central Otago is practically nil, and the only land that comes anywhere near this mark is .our more recent alluvial deposits. Many years ago irrigation apparently played an active part in the ancient agricultural pursuits of the world. Traces of its uses can be found stretching from Morocco to China, a distance of 7000 miles across the then known world. Deterioration, however, took place; the soil has lost its fertility, and both irrigation and land were abandoned. For countless numbers of years it was a bare, barren waste, but in course of time the soil has again regained its fertility, and irrigation schemes are once more the order of the day. It remains to be seen what time will elapse before history repeats itself. _ Messrs Tennent and Marks state that with our . present knowledge of soil physics and agricultural science there is no need of a recurrence of tlxe destruction of soil fertility by irrigation as in ancient times, provided that the science is properly carried out.” With sedimentary soils such as Ida Valley, how is, this science going to be applied? It will probably take three or four years before irrigation in Ida Valley passes* its experimental stage. By that time the maximum charge for water rentals will have to bo paid. Will tbo settlors t-nen. be in a position to meet the further demands of this scientific knowledge? If the land shows deterioration, it will probably entail the need of an expensive drainage scheme, the expenses of which will have to be borne by the settler. A drainage system for Ida Valley was supposed to have been laid ont in detail when the irrigation commenced, but I think it would be nearer the mark to state that a drainage scheme for the successful irrigating of the sedimentary soils of Ida Valley has not as yet found its way on to paper. ■ • , Probably it would have been more beneficial to Central Otago had the experimental farm been in Ida Valley instead of m Failoway A section from the foothills to the centre of the valley could have been chosen which could have constituted a of the soils contained in the 28,C00 acres under the Ida Valley sclieme. The, altitude would have been about IGOOft higher than that of the present experimental farm, and the site would have contained; a ter percentage of the sedimentary soils which at present show a slight deterioration. If this bad been done the 150 to 200 settlers, when in occupation of the lahd, could have obtained practical information, as their farms would be of a similar nature. The present experimental farm does not permit of the advantages which should be obtained for the furtherance of the successful irrigation of land contained in the Ida I'alley scheme. ■ It is proposed to survey and out up the land into 150-acre blocks, andi as many leading citizens .are so positive that it wiU turn out a veritable Garden, of Eden, I would Suggest that they go one better and ask the Government to guarantee that each section will stand irrigation. Settlers would then find it a safer investment, especially when each sfection would soon carry improvements, including fencing, bousing, implements, ete., well over fo, ir figrires If what Messrs Tennent and Marks state about our present knowledge of soil physics and 'agricultural science is correct, what need is there to go to America for informa. tion as has been suggested? If. there is need, why was it that a thorough investigation of this matter was not attended te, say, 10 years ago? Thousands of pounds have now been spent in Central Otago, and moat of the farmers have now placed a debt on their land equivalent to a perpetual mortgage of from to £l6 per acre, but not one person m Otago can as yet guarantee that 50 per cent, of the sedimentary soils of Ida Valley wall not be a failure inside of 15 or 20 years. It was stated that if Messrs Tennent and Marks visited America, the irrigation authorities of California would be pleased to give information and assistance. Why California? No doubt information on some points is essential, such as methods o. irrigation and drainage of the various classes of soil, but what is probably the greatest controlling agency is topography, the formation of the country and how it came into being, -whether by chemical or mechanical means or bv other means of earth movement, and the further effect on it of climatic conditions, past and present. Central Otago is practically in lat. 45deg S and for similar conditions in America siich States aa Wyoming, Idaho,, Montana, and Dakota would be preferable to California. These States would probably furnish valuable information which would be more beneficial to Central Otago than any procurable from any other State in America. In Cental Otago wo have a fair proportion of alluvial deposits from which wonderful results are, and will be, obtained by means of irrigation. Wo have also a fair percentage of what may be termed old alluvial deposits, and in conjunction with these art. coarser deposits carrying a light soil.. These may or may not hold out. This depends largely on the treatment they receive. Lastly,' we have the sedimentary soils, which I haye previosly commented on. Up to the present time no plan has been proposed that will render this class of land profitable under irrigation.—l am, etc., J. C. Smith. Ixivoll’s Flat, September 5.