16 February 1996

Keep an eye on whats in water

ACCOUNT needs to be taken of the nutrient analyses of irrigation water as potato growers seek to fine tune their fertiliser programmes, David Kirkham, technical director of the Nottinghamshire based Field Care, told the FSCconference, in Wetherby .

Presenting a table of typical analyses of irrigation water, Mr Kirkham pointed out that water drawn from lagoons carried 60ppm of potassium compared with just 2ppm in water from becks and boreholes and 5ppm for mains water.

Six applications of 25mm (1 inch) of lagoon water would equate to a seasonal application of 108kg/ha (96lbs/acre) of potash.

Failure to take account of that could result in excessive potassium levels, which would depress dry matter and leave crops more susceptible to internal bruising.

Bryan Pickles, FSC arable specialist, said the use of both phosphate and cytokinin growth stimulants as foliar sprays at the correct growth stage could have a significant effect on number of tubers produced and on tuber size.

But it must be decided in advance at which point tuber manipulation would start and this would depend largely on the end market.

Varieties which naturally set low numbers of tubers would benefit from manipulation at tuber initiation. Other varieties would benefit from manipulation at the bulking stage to maximise ware yield within tight contract specifications.