FOR POTATOES…
1 September 2000
DRIBBLE IRRIGATION JUST THE JOB
FOR POTATOES…
BETTER control of tuber set leading to higher yields of more evenly sized tubers, scab control in vulnerable fields, lower blight risk, better targeting of water and less lost by evaporation.
Those are the claims being made for automatically controlled drip and trickle irrigation systems, monitored by in-crop sensors.
To demonstrate those benefits the technology is being used in a late-planted crop of Nadine in testing soil and field conditions at Cound near Shrewsbury.
Potatoes need adequate water at tuber initiation, and lay-flat disposable plastic tape placed at 50mm (2in) from the top of each ridge dribbles water into the top 30cm (1ft) of soil, just where it is needed, says Dick Hewitt of Oakleys Irrigation, Shrewsbury.
"The conventional rain gun often does not put the water where it should be, especially in irregularly shaped fields."
The 5ha (12.4-acre) field at Cound received 175.2mm (6.8in) of rain during March and April, which delayed planting into a declodded but still lumpy seed-bed until May 5.
A further 69mm (2.7in) to mid June followed by a later 39mm (1.5in) kept the crop above stress level until mid-July. But soil monitoring across a 50cm (19.5in) profile showed the crop nearing stress level by mid-July.
Regular monitoring is done with a Diviner 2000 portable probe inserted into tubes placed in the crop after planting. This is attached to an EnviroSCAN data logger and reads the moisture at 10cm levels using electrical capacitance. Resulting graphs monitor water availability.
"The readings led us to apply 1190cu m of drip irrigation, equivalent to 26mm or 1in over the site between July 14 and 24," says Peter White of Peter White Water Management. Cost of a Diviner system with 20 tubes, training and support costs £2500, he notes.
The data is used to decide and download water volume and timing requirements to the automated Rainbird control units which activate solenoid valves controlling each 1ha (2.4-acre) block of T-Tape, says irrigation specialist Mark Hodkinson of Field Fumigation.
"That avoids a lot of manual labour in-season." It also ensures the water is around the roots in the critical 20-30cm (7.8-11.7in) area during tuber initiation, especially in cloddy ridges, he says. Those tend to dry quickly and the water from conventional irrigation tends to run off the clods.
Trickle benefits
A moist ridge enables even tuber initiation, benefiting tuber yield and even size as well as limiting scab risk and avoiding foliage wetting which can increase blight risk and the need for spraying, while also minimising soil capping, he adds.
"Twenty percent better yields have been achieved with drip irrigation. This may mean that planting rate and distance have to be adjusted to control tuber size and shape to meet market demands. We also found that fertigation, the addition of nutrients to the irrigation water, gave us a better cook quality with a crop of Maris Piper grown for chipping last year," he adds.
• Results from the demonstration field will be reported in a forthcoming issue of farmers weekly. *
Above left: Mark Hodkinson of Field Fumigation Ltd, using a portable datalogger to download volume and timing requirements to a Rainbird unit which controls the solenoid valve supplying water to the T Tape header feed. Above right: Peter White of Peter White Water Management, Leiston, Suffolk, using the Diviner 2000 portable electrical resonance probe in an in-crop tube to monitor soil water at 10cm intervals to 50cm with the results downloaded to an EnviroSCAN data logger.
WATER WISE
• Drip water in ridge where needed.
• Monitor water levels in soil profile.
• Target water to need, avoid stress.
• Less evaporation loss.
• Improve yield, size, shape.
• Limit scab risk.
Nadine tubers produced in cloddy ridges from a May 5th planting following heavy rain in March and April. The T Tape drip irrigation tube placed 50cm below the ridge top at planting is clearly visible.