7 March 1997

Schedule needed where irrigation tight

WHERE supplies of irrigation water are limited and costly, efficient use can only be achieved by scheduling irrigation properly.

That claim was made by ADAS Gleadthorpe researcher Roger Bailey at a UK Irrigation Association Irrigating potatoes conference at Walford College, Shropshire, last week. Although the comment went unchallenged on the day, the speaker admitted that fewer than 1000 of the 9000 irrigating farmers in Britain seemed to be convinced that scheduling brought financial benefits.

Using Gleadthorpes Irriguide computer model, which has been shown to provide 80-90% accuracy when predicting the effect of any irrigation pattern on yield (Arable, Feb 7), he attempted to prove the sceptics wrong.

Assuming irrigation water for potatoes was limited, profit/ha from scheduling was compared with irrigation at fixed intervals, with or without some allowance for rainfall. In each example scheduling boosted profit, even though the program did not take improvements in tuber quality into account.

Where application was limited to 150mm of water the profit increase from scheduling was £200/ha, and the risks of over watering were avoided.

Mark Stalham of Cambridge University Farm agreed. Unstressed potato crops produced about 0.24t of yield/ha for each mm of water taken up and used. But irrigation response often varied between 0.001 and 0.224t/ha/mm.

"In many cases this type of analysis leads to the conclusion that more water was applied than necessary," Dr Stalham claimed. "This is increasingly wasteful and costly, and must increase the risk of nitrogen leaching." Improved rooting could give crops access to an extra 20-30mm of soil, he added. &#42

Roger Bailey… Urging growers to schedule their irrigation.


WATER WAYS


&#8226 Schedule irrigation for best results.

&#8226 Only 1 in 9 growers using irrigation do schedule.

&#8226 £200/ha extra profit in yield alone. Quality benefits, too.

&#8226 Avoid wasteful over-watering.

&#8226 Boost rooting by avoiding soil compaction.