IRRIGATION.

Otago Witness, Issue 2734, 8 August 1906, Page 20

IRRIGATION.

(Contracted.) Several meet interesting papers -were read £t the recent meeting of the Victorian Institute of "Engineers on "Irrigation." The p&pexs have a special value to tb in view of the determination to develop farming by irrigation in Central Otago. The papers were somewhat technical but, even to the non-expert, highly' interesting. It appears to be generally conceded that the difficulties in establishing irrigation are very muoh greater in countries' where people t»n get along in a fashion without it — in -certain parts .of Victoria, for example, rad California— that is to say, . where fair crops can occasionally be raised without any irrigation, and where people are content with small yields. The chief point made by all those who took part in the discussion was that far better and move «yen results were by irrigation, which takes the pi*oe of s rainfall . necessary for the' sowings., growth, and development «oi the crops. ' For example, one often hears in certain districts a farmer complain that the ground U too hand to -plongfc— irrigation before ploughing e» as to get xn early sowing has been proved to be successful, xdA bo ice irrigation in » dry *pr»g;. In brief, jt appears to me *b«t in a district like the Otsgo -Central,- vrc ,^m tibe Gamaru district, where, semi-drought* are hot unknown, if water for irrigation is and the ccuntry admits oi being irrigated, a former can, ma it -were, «onnzßsd the equivalent of a rainfall and ensure tihe growth and ripening of his crop. In Uew Zealand we have abundance of water, and .sometimes I daresay the irrigable area available would not warrant the necessary expenditure ; but in Victoria, Kew South Wales, and South .Australia there are 43 million acres of irrigaUe land, and it is impossible, owing to shortage, .to supply water to more than a saiaH portion of this area; but nevertheless, even with our small area, it must not bo forgotten that in Central Otago we have a. very large extent of summer hill country, which is practically valueless unless supplemented by winter lood-preducing areas. The latter axe not available in the majority of instance* tmless irrigable land ia utilised. "Beopfe <lo not .thoroughly realise the benefit that would ite derived from irrigation, even in the wetter parts. Very often delayed autumn tshm led to late etwxng' with the accompanying results of i»a crops, -and there was no wonter grass for the cattle." The possession of a rmodeaite Tainfall is, of course, advantageous, as it lessens the cost of irrigation, and m this connection it is important to note that tp« opinion is almost universally held that under -an irrigation «cheme the farmer should only pay for the water he consumes. Rigid economy cannot be expected under • system of charging independently of the amount used. In JLmerioa, when the system <rf «J® <* irrigating water was initiated, it -effected a Bavmg of from ZD to 25 per cent, of water used. Mr Garsen, engineer for 1&e Mildum Trust, who controlled the distribution of water, said that there was not a man in Mildura wiio would not contradict him when he said, "You have had sufficient water; we will shut it off." He expressed the opinion that the only way to educate irrigators in the proper use of water was to charge them for what they used. "He had seen as much as 2ft in a" field where 6in would have given a better result. And the president stated that he bad iound very much more water used in irrigation than was required — sometimes three or four times more, — leading to an impoverishment of the soluble constituents oi the soil. This iB an important consideration, as there is always considerable loss of volume in delivering water. In America the amount of water diverted, inoluding losses in main channels, is 5.47 f t; including losses in laterals only, 2.37 ft; supplied at margin of fickle, 1.34 ft. In Victoria a very simple submergefl weir gauge is used, so that the exact evfpply to each consumer can be recorded. It appears to me that the policy of sale by meter will have to be adopted in this country. As to what irrigation will do, the results are- most interesting. From -returns published by the U&. Department in 1901, tbe average increased yield «rf various crops by irrigation is given as follows: — Barley, 95 per cent. ; oats, 49 per cent. ; potatoes, 141 per cent, ; Wheat, 131 per cent. In Queensland Messrs Drysdale Bros, put down a pumping, phuit on fcheir Burdokin Estate of a total capacity of 57 million gallons per 24 hours, costing .£9OOO, which resulted an «.n all-round increase -of 50 per cent, oa *heir -crops. Messrs Gibson and Howe, y on the Burnett, spent £22,000 (lift 250 ft), 'Vid got an ioc»e*se -of -75 per cent, ia iheit -

yield; and private -enterprise in other loraltties Iras given -similar results. It appefis, however, irrigation inta-odueee a novel -set t>f conditions into agricultural methods. Money lias to be -spent (that, towever, is not a novelty to our tanners), land has to he graded, cultivation carried <m without cessation on a scale oi thoroughness, and it is evident that to gain the "best resurts^irom irrigable land a very liigh standard of farming has to be maintained. That appears to he universally admitted, and* as farmers are naturally conservative it will probably be a little difficult to oerstiade them of the necessity of specialising for this class of agriculture. It is a great pity that we have not a very much larger ai«ea oi irrigable land. In the colony we reverse the problem that^ faces £he expert in xyther countries. There he ties to ask liimself what amount of water he has available. In New Zealand -the question has to be asked, Wthat area of irrigable land is available, for -we have water in abundance, and where we cannot get a gravitation supply we can wHo&b with either <&cap coal or ■eteotriofty as a power-, and ac a pump has only to work -at intervals the cost is not prohibitive. The island of Hawaii is an illustration of what can be done by pumping, even with costly fuel and unaided private enterprise. The total water pumped at Hawaii *or irrigation to an average VMj-igirt -of 200 ft is no lee£ tkltn 600 million gallons in 24 hours. It k well -worth whiie considering whether there arc not certain areas in Otago~" which would be cheaper served by an intermittent system of pumping than by gravitation -supply, and whether or not the future of the interior is dependent -upon -the intelligent use of electricity, for the -volume of urateT -necessary to irrigate a l»rg« a*ea is very much -greater than one would assume. Perhaps some of our friends in the Centra! who -farm by irrigation will give the result of thedr, Practical experience. For ■example in Victoria, "for rather yoonjr fruit -trees, a depth of 2in over all is found Jieoeaeary, for older trees 3in. Three inches is allowed fox watering before ploughing. Irrigation by one' good soaking ie -deemed very mncb preferable to two ox three light irrigations, and irrigation by funrow is universally recommended. How does that compare with irrigation in "the Central? It may ako interest orohardiste to know that Mr M'Caug'bev tried the follow, ing method of making an orchard, and the result was a. conspicuous success: — He -excavated the land to a depth -of sft, and -out 18in of -river eand on the bottom. The oarfch was then replaced and the oroha/rd completed. Surface irrigation was not .permitted, the moisture being supplied to the sand beneath ihe orchard. This method -was probably adopted owinsr to the shortage of -water and in orcW to avoid lose by . ■evaporation. I frankly admit that I know little about the subject of irrigation, but I got so interested in tbe article I have mentioned that I noted a few -points in the hone of inducing a discussion by those who -understand the subject. T r ndoubtedlv the irrigation -engineer will bulk largely -in the near fnto-re. and the sooner -we -collect our data and make -observations the better. "Victoria is adnaittfdlv in its rnianey as fa* as irr-igatJon is concerned, but we are scarcely alive, and #»enefore we naturaflr turn to Victoria a\nd the State* -for information on flic subject, as their conditions of life are similar to our own.