Irrigation Development In Valetta Area

Press, Volume CIV, Issue 30919, 27 November 1965, Page 9

Irrigation Development In Valetta Area

When the Lands and Survey Department completes settling about 8200 acres of country within the district of the Valetta irrigation scheme by 1968 Mr R. M. Maclean, senior field officer of the department in Timaru, believes that the carrying capacity of the block will have been raised from 2800 ewes, 1500 ewe hoggets and 300 dry sheep in 1950 to about 30,000 ewes and replacements.

Mr Maclean made this forecast at a field day held this week by the Valetta-Tinwald Irrigation Association on one of the department’s farms yet to be settled where an area of 109 acres has been set out for automatic irrigation under the supervision of Mr A. R. Taylor, an agricultural engineer of the Department of Agriculture’s irrigation research station at Winchmore.

Mr Maclean said that the department had held 8200 acres within the scheme, and due to uneven topography and topsoil, subdivision had been planned for the irrigation of 5/Bth of the area with 25 units each having 200 acres under irrigation. Under the manual system of irrigation then operating and based on a weekly roster of eight cusecs of water for 36 hours this gave a coverage of 4 inches an acre over 72 acres, or once round the 200 acres each three weeks. The average construction cost an acre under this system, including dams and headgates, was about £9 10s over the area actually border dyked, or £6 an acre over the total area of the farm.

“At this cost the farming potential is doubled and on parts of Valetta increased possibly fourfold,” said Mr Maclean. “I do not claim that this increase is all due to irrigation, for improved farming techniques together with lime, superphosphate and certified seed have also played their part.”

In 1950 Mr Maclean said that the block of 8200 acres was carrying 2800 ewes, 1500 ewe hoggets and 300 dry sheep. In 1957-58 with some improvement done under dryland farming the country was carrying 4200 ewes, 1600 ewe hoggets and 400 dry sheep. With the advent of irrigation development, by 1961 stock numbers had increased to 9750 ewes, 3500 ewe hoggets, and 600 dry sheep at which date settlement had been started. To date 17 sections had been settled each having an average area of 325 acres and carrying between 1100 and 1200 ewes and replacements. At present the block was carrying about 25,000 ewes and 6500 ewe hoggets. “When the block is finally disposed of in 1968 I would envisage that the 25 sections will be carrying about 30,000 ewes and replacements,” said Mr Maclean.

With development now aporoaching its final stages, Mr Maclean said he wanted to thank Mr Bush of the Minis-

try of Works, Mr R. L. Lindsay, . the Ashburton County engineer, and members of the staff of his own department for their co-operation. In the spring of 1964-65 a request had been received from the Valetta-Tinwald Irrigation Association for automatic irrigation to be developed on a farm scale and the lay-out for this system on the area still to be bordered had been handed over to Mr Taylor, of the Winchmore irrigation research station. To date it appeared as though the cost involved in this system was £l2 10s an acre. This involved an improvement in headrace construction and precise levelling within checks giving a considerable rise in the rate of watering. The whole question, he said, revolved around the most efficient use of water available and if rates of four acres an hour could be achieved this would enable the fanner to apply water at 10-day intervals instead of at three weekly intervals under the old manual method. Differences Mr Taylor said that in developing a system for this country they had been faced with some differences from conditions on the station at Winchmore where automatic irrigation had been practised. Everyone had said that a great deal more water would be used on the Valetta country, and that the rate of watering of 3| acres an hour achieved at Winchmore would never be realised. For the automatic system on this country borders each 34ft wide had been grouped in sets of three, but in the light of experience now obtained it was recommended that groups of four should be used with a reduction in the number of headrace structures needed. If four borders were watered at a time he said that this would cover just under three acres. Mr Taylor said that the system involved raising the banks of headraces, also the sills over which the water flowed, and also raising the head of water.

In preparation of the country for this sort of system Mr Taylor said that as well as a grader a motorised scraper had been used, and this had enabled the construction of a race that would not have been possible otherwise.

Mr D. S. McCormick, irrigation superintendent of the Ministry of Works in Ashburton, said that farmers could facilitate land preparation by having their land well ploughed beforehand and having a grubber on hand while land preparation was in progress. Once checks had been completed, he said, they should be grubbed immediately. Grubbing up of some of the coarser material resulted in the country holding better if there was a strong wind soon after. (That this is a windy area was very apparent as a roof was recently blown off a woolshed on this farm.) On the automatic area at Valetta concrete structures, including sills, are being

used, with metal dam gates operated by alarm clocks. Mr Taylor said that wooden as well as concrete sills had been used. The concrete sills, he said, were more costly and more difficult to put in. They worked out at about 25s each compared with 14s for the wooden ones, but with a mould recently developed for putting the concrete sill in on the site the cost was reduced to about the same as for the wooden sill. He could not stress too strongly the sowing of the headrace as soon as it had been cut, said Mr Taylor. He indicated a race where some subterranean clover had been sown in addition to the pasture mixture being used in the paddock. Mr W. R. Lobb, superintendent of the Winchmore irrigation research station, said that they should be sowed with the standard mixture of ryegrass, clover and crested dogstail. Mr Taylor suggested that an electric fence might be used to protect races from cattle. It would also be desirable to keep lambs off them if possible. Mr Taylor said that the 109 acres could be irrigated under the automatic system in 21 hours which was of the order of 5 1/6 acre an hour. He said that the average rate would be about 4| to 5 acres an hour.

For the Lands Department’s Irrigation development on the Westerfield country, Mr Taylor observed that development of automatic irrigation had come about 10 years too late. Asked by Mr B. A. Lauder, of the Department of Agriculture, how this system could be applied to the 40,000-odd acres border dyked on present schemes, Mr Taylor said it would take more men in the field. However, he felt that a lot of old races could be converted to the system or they could plough up a chain in from a fence line and construct a headrace there..

Mr Lobb complimented Mr Maclean and the Lands and Survey Department on what they were doing. He said his listeners would be aware what this country could look like in a dry season. They would not be deluded by the current conditions.

Under dry land farming he

said that the carrying capacity of this country could be raised from a quarter of a ewe to the acre to something like one to one and a half, but for the expenditure of an average of £9 IQs an acre, to take Mr Maclean’s figures, carrying could be raised from lj to 3} ewes to the acre and this latter expenditure would be the lesser figure in the overall development cost. Certainly the degree of subdivision would not have been obtained without the exploitation of the potential of irrigation. Mr Lobb said that automatic irrigation had now reached the stage where it was worth consideration by farmers and anyone embarking on irrigation should consider nothing less than automation. He said that the aim was use of eight cusecs of water to irrigate about one acre per man per minute. He said he was surprised that they were achieving such a good level of efficiency under automatic irrigation at this stage. He said ability to irrigate the total irrigable area of a farm within a todays interval would mean that moisture levels were maintained at good levels and a good level of efficiency of water usage would be obtained. Even allowing that the Valetta country was slightly drier than Winchmore, it did not have as good moisture holding capacity and evapotranspiration was a little higher, this sort of level would not really be necessary. It was anticipated that with eight to 10 waterings a year not much production would be lost. The aim, he said, was to devise a system that would enable irrigation to be done on a soil moisture deficit basis within the roster period. If it was possible to get round the whole of an irrigable area in that time it would be possible to think in the terms of such a system.

Mr L. Tarbotton, chairman of the association, said that it was obvious that automatic irrigation had got beyond the experimental stage. Even the most doubtful critics must agree that it was workable.