Irrigation decisions on Ashley Dene

Press, 15 October 1982, Page 24

Irrigation decisions on Ashley Dene

The new $55,000 irrigation system covering 68ha of the Ashley Dene property of Lincoln College can only adequately water about 30 to 40 per cent of this area in midsummer.

Mr T. D. Heiler, senior principal research officer, Agricultural Engineering Institute, told the Ashley Dene field-day last week that the irrigation system was only

capable of meeting full water requirements on the total area early and late in the season. This was when daily evapotranspiration was around 2mm. When evapotranspiration rose to 4 to 6mm per day, during mid-summer, the total area covered adequately reduced to 30 to 40 per cent of the 68ha. “That is when its use on strategic crops is very important.” he said. The principal of Lincoln College, Professor Jim Stewart, said he had resisted the introduction of irrigation on Ashley Dene because it would change the character of the dry-land farm. But other staff members had successfully argued against him. he said. The irrigation system started last January. Now that it was in, he certainly wouldn’t waste water on ryegrass and clover pastures in mid-summer, said Professor Stewart. The supervisor of Ashley Dene and senior lecturer in farm management, Mr Bob Diprose, said that out of the 68ha under irrigation, 11.7 ha was under rape and Italian ryegrass as a summer forage crop which would extend into winter; B.sha was under Tama ryegrass; 25.6 ha was in established lucerne and 22.1 ha is being sown at present into lucerne out of turnips. The priority order with water during the summer was the rape and Italian followed by the Tama, the old lucerne and then the new lucerne. The new lucerne would get enough to get it established before mid-summer but then the old lucerne would get priority because it would show a better return to water. Mr Diprose said that a few years ago the farm carried 3000 Border-Corriedale cross ewes which were mated to Dorset Down sires. The farm stocking policy was now being changed to include trial flocks of high fertility sheep, such as Booroola crosses. At July 1, 1982, there were 1270 commercial flock Border-Corriedale ewes and 240 ewe hoggets and 1638 ewes in the trial flocks, with 540 replacements. Next year there would be only 1000 Borderdale ewes, with no

hogget replacements kept and the trial flocks would be approaching 3000 including replacements. Professor Stewart said he had stepped down as Ashley Dene supervisor 10 years ago convinced the farm should be 100 per cent lucerne. He had not changed that view. “I can see no other option on dry land',” he said. Mr Heiler was involved in the installation of irrigation to Ashley Dene. He said the capacity of the bore was fixed at 68 cubic metres per hour. “The book would say that only enough area can be watered to ensure a 14-day return with applications of 64mm,” he said. Instead the college authorities had opted for a more typical Canterbury pasture irrigation system and covered 68ha with 34 hydrants at 65m spacings. The length of each run is 300 m on 150 m of hose. The system can apply 38mm gross, or 30mm net on an 11-hour run. It can also apply 80mm gross, or 64mm net on a 23-hour run. With the quicker run the Briggs Roto-rainer model 75 could get round the 68ha every 17 days. With the 23hour run it took 34 days. In practice the farm and college staff were expecting about four or five complete waterings annually. The cost was about $8 per hectare per watering, or up to $4O per hectare per year.