Aspects Of Irrigation

Press, Volume CIV, Issue 30668, 6 February 1965, Page 8

Aspects Of Irrigation

If there were going to be positive developments in irrigation there needed to be an overall national policy on irrigation in New Zealand, Mr W. R. Lobb, the superintendent of the Winchmore irrigation research station, told about 300 farmers and others attending a field day at the station this week. His listeners included farmers from Otago to North Canterbury and city representatives.

Urging planning for irrigation, Mr Lobb said that this needed to be done fairly quickly before areas with a potential for irrigation were subjected to intensive development for dryland farming and other purposes.

volved in laying out an area and developing it for irrigation Mr Lobb said he regarded the progress made as satisfactory. Two of the factors retarding irrigation development were labour and the cost of developing land for irrigation.

Mr Lobb said that if an irrigation rate of 150 acres per cusec of water could be achieved this would mean that a cusec of water applied to agriculture would be worth £lBOO to £3OOO in gross returns. Thus 1000 cusecs of water from the Rangitata would return between £l.Bm and £3m per year if the area was fully irrigated and another 1500 cusecs from the Rakaia river for the proposed scheme between Rakaia and Ashburton would produce another £2.7m to £4.5m, giving a total return of £4.5m to £7.5m, which was the potential of using 2500 cusecs of water in Mid-Canterbury. The irrigation schemes working at present were returning between 20 and 80 per cent on the money invested. There was 1.5 m acres available for irrigation and use of irrigation on this country should have a great impact on national development in the future. Mr Lobb said the introduction of the Valetta irrigation scheme had had the effedt of

Part of the day was Spent looking at automatic irrigation devices and lay-out and a visit was made to the 160 acres automatic irrigation unit on the station. Mr Lobb said that a three fold objective of automatic irrigation investigations was to eliminate labour, to enable irrigation to be practised to the maximum capacity of the land by basing the watering on soil moisture deficit calculations, and to increase the

a 100 per cent or greater increase in land settlement. In Mid-Canterbury and South Canterbury he said that there were now 440 farmers irrigating with 350 of these being in the areas of the three schemes served by the Rangitata river, which was commanding about 230,000 acres of which about 40,000 acres were prepared for border-dyke irrigation. The 350 farmers mentioned had an average of 128 acres prepared for irrigation. Most Developed The most developed scheme in the area—the AshburtonLyndhurst—had about 20,000 acres border-dyked and about 80 per cent of the farmers in the area had land prepared for irrigation. Altogether 50,000 acres was under contract for irrigation. On the Valetta scheme where 6700 acres of land were border-dyked 21 out of 22 farmers had an average of 135 acres of land prepared, on each of the units prepared by the Lands and Survey Department there were 200 acres under irrigation and on the scheme as a whole 17,000 acres was under contract. In addition 9500 acres were prepared for water on the Mayfield Hinds scheme with 95 farms having an average of 95 acres border-dyked, and just under 40,000 acres were under contract.

efficiency of spreading water. On the station he said that by means of alteration of race construction and lay-out it had been possible to increase the rate of irrigation from 2.2 to 3.5 acres per hour, and, of course, it was possible to water for 24 hours a day under the automatic system. When irrigation was developed to the stage where more people wanted more water rosters for supply of water had to operate. All the Valetta farmers were on a roster and this raised the question of reconciling soil moisture deficit calculations with the roster.

Under the soil moisture deficit system if water was available and the deficit was up to an inch irrigation was undertaken, but if it was less than an inch irrigation was delayed until water was next available.

At 3.5 acres per hour, Mr Lobb said that one cusec would water 164 acres and as the automatic unit was supplied with 1 cusec of water to 100 acres this meant that the area could be totally irrigated. This water was available every two weeks but if the water had been insufficient to totally water the unit, then it might have been an advantage to have water weekly.

In South Canterbury on the Levels scheme were were 79 irrigators with a total of 1600 acres prepared for watering and there were 14 irrigators on tiie Redcliffs scheme. Considering the work in-

Mr Lobb suggested that an average number of irrigations for a season was seven but the number could vary considerably depending on when a start was made and he quoted a case where two irrigators under the same scheme started irrigating 15 weeks apart. The sort of level of efficiency of irrigation that they were aiming at was a situation where a 300 acre farm could be watered in five or six hours, and with seven irrigations a year 35 to 42 hours a year would be spent irrigating. With 110 acres in grass Mr Lobb said the automatic unit had been carrying 600 ewes and 120 hoggets and 660 lambs at the peak of the season. At the peak ewes would be set stocked at 10 to the acre with their lambs. Watered under a roster system it had been irrigated once up to Christmas and had up until the present time been watered five times. At 3.5 to 3.8 acres an hour watering for 160 acres would take about 47 hours. Stocking This unit received water and superphosphate, and hay was made dff it and autumnsaved pasture saved. On 160 acres Mr Lobb said that 1200 ewes or slightly more should be able to be carried. To this end the whole 160 acres would have to be topdressed, whereas to carry the same number of ewes on a dryland farm 300 to 500 acres might have to be topdressed. If this type of irrigation could be introduced, Mr Lobb said he felt that some progress would be made. Discussing the extra costs involved in preparation of land and installations for this system of irrigation, Mr A. R. Taylor, a scientific officer at the station, said that the extra costs involved in borderdyking could range from £1 to £2 an acre under favourable conditions to as much as £4 or £5 an acre where lay-out was restricted by existing conditions such as fence lines etc. More cross levelling was required and it was also necessary to build up the race banks so that the water would flow evenly over the sills.

Of the cost of equipment, Mr Taylor said that there would be no extra cost for the sills. The, sheet, pipe support and release mechanism cost £2O and over a 300-acre farm would work out at about 10s per acre.