27 February 1998

Trickle tapes give big boost to Dutch GM…

Making better use of limited water supplies is every root

growers desire. Here, we relay the experiences of UKand

Dutch growers who have tried drip irrigation

DUTCH grower Arjan Janknegt reckons trickle irrigation – even in last years wet summer – increased his potato crop gross margins by nearly £800/ha (£325/acre).

Farming in the Polders, near Zeewolde, Mr Janknegt has trickle irrigated his potatoes for two years. If UK growers want to boost profits by satisfying the most lucrative specialist potato crop contracts, they too should take a serious look at the technique, he suggests.

At the heart of Mr Janknegts system is T-Tape made from a new polymer, TSX.

"When we used to reuse pipes, cutting and joining could be a real headache. And worn pipe wrecked application accuracy," he recalls. "We now use a 4mm diameter pipe with 30cm emitters at the cost of less than £200/ha every year."

Mr Janknegt lays the T-Tape at 50mm (2in) depth within each ridge at the same time as ridging up with a rotary ridger.

"While labour requirements at planting to cut and join the laterals and the mains increases by 10-15%, this is a small price to pay. In fact we probably save money later in the year compared to moving reel-hose irrigators to get round crops," he suggests.

"The whole system is incredibly accurate and provides a very uniform wetting zone throughout the season. Monitoring is critical though, and you have to build up a knowledge of how much each variety needs and when and where it will get its water from within the soil profile."

Last season he used 7mm of water early on – enough to get seed roots emerging properly. "If we had used overhead irrigation wed probably have had to apply at least 25-30mm or waited for a 20mm shower of rain," he suggests.

Analysis of soil moisture levels by Enviro-Scan confirmed that three weeks of steady drip irrigation in June, topped up by regular rainfall events in July and August, kept moisture deficits low.

However, similar measurements on his unirrigated potatoes showed that while rain in July topped up reserves in the topsoil, roots at 50cm (19.7in) were always short of moisture.

Prior to harvest, Mr Janknegt uses a haulm topper to remove the strong growing tops. Two reels operated by the tractor hydraulics then rewind four laterals at a timeup to 4.3mph (7km/hour).

"While we were concerned that this operation could damage the ridges and lead to greater tuber greening, we tend to get in and harvest within a couple of days, so this is not really a problem."

Last year, Mr Janknegt used the technique on three potato varieties, comparing the results against adjoining crops that had not been irrigated.

On Santana, a long tuber variety grown for chipping, trickle irrigation improved marketable yield by over 7.5t/ha (3t/acre) raising profits by 38% or around £778/ha (£315/acre). The inclusion of fertigation through the T-Tape system added a further £44/ha (£18/acre).

"This was almost solely a response to better nutrient use and the use of drip irrigation for just a three week period in June to keep the soil moisture deficit low at 50cm depth."

Trickle irrigation also improved marketable sample quality on Mr Janknegts Bintje, providing 11.4t/ha (4.6t/acre) more potatoes in the 50mm plus bracket – a 17% increase.

"While it is early days for us with fertigation, we monitored the nutrient content of our Santana and Bintje crop leaves throughout the exercise and found the technique to be much more accurate."

"By applying nitrogen on to soil around the roots, uptake was more targeted and we saved around 20-30% on nitrogen needs," he says.

DUTCH TRICKLE TIPS

&#8226 Potato GM up nearly £800/ha.

&#8226 More labour at laying, but less during season.

&#8226 New T-Tape each season.

&#8226 Lay-flat main hose allows sprayer access.

&#8226 Fertigation boost yield further.