12 June 1998

Sap test &foliar

feed are route to root success…

Monitoring the nutrient

status of a crop throughout

the growing season is

helping two growers correct

any nutrient deficiencies or

imbalances as they occur.

Louise Impey reports on the

use of sap testing with foliar

nutrition to improve both

yields and quality

BORON deficiency in spring-drilled onions first persuaded Lincolnshire grower Ted King to use sap testing.

"We grow onions on rented land because there is a white rot problem in this area," he explains. "So when we find a clean field, we try to use it for onions two or three times."

In 1996, a deficiency problem showed up in part of a rented field. Although a soil test had been done in the autumn, no particular shortages were apparent and the cause of the poor crop growth was a mystery.

"We did a sap test at the end of May and immediately identified that boron was low in the affected part of the field," he recalls. "The aluminium content was high, which may have indicated a lower pH in that area and that phosphorus was also low."

Recommended

Testing was done by Omex Agriculture, which recommended Mr King apply both boron and phosphorus in a tank mix, followed by an application of manganese.

"The foliar application of boron pulled the crop round and it went on to yield as well as the other part of the field," says Mr King.

"We had another sap test on June 18, which showed phosphate, potassium, magnesium, calcium and molybdenum levels were lower in the poor area. But by then they were not felt likely to affect yield.

"It also showed that the high aluminium level might be restricting phosphate uptake, because we had made the recommended phosphate application in May yet levels were still low."

As onions were grown in the same field in 1997, Mr King had it sap tested as a precautionary measure at the end of May.

"This time it showed phosphate, calcium and boron were low. Omex suggested a mix containing all three, which we used to safeguard yields," he says.

As well as onions, AG King and Sons grows sugar beet, potatoes, cauliflowers, cabbages and wheat at Swineshead, near Boston. Sap testing has only been used on the onions as Mr King considers it too expensive at £90 a field to be used routinely.

"We only use this technique if we can see there is a problem and are unable to solve it for ourselves," he says.

"The only routine application we make to the onions every year is seaweed extract. Sap testing allows us to add any other nutrients the crop may need."

CAMBRIDGESHIRE potato grower Andrew Cade has used sap testing for six years.

He grows 61ha (150 acres) of Sante, Fianna and Maris Piper near Whittlesey for various markets and the test has highlighted different trace element shortages every year according to the growing conditions and potato type.

"I used to make a blanket trace element application, putting on manganese as a matter of course, but it was based on guesswork, rather than on meeting the crops requirements," he says.

Having discussed the sap-testing service with Omex, he decided to use it on all the potatoes. Three samples were taken from the crop at planned intervals during the season, the results were analysed and a recommendation given.

"What it has shown us is that the nutrients do get out of balance, which affects the uptake of certain trace elements," explains Mr Cade. "Both aluminium and molybdenum can cause problems on this farm, so its a case of keeping the balance right."

He points out that the cost of having a tailor-made foliar solution varies with the mix required and variety in question.

"It costs us £20-25/ha (£8-10/acre) for each application and we usually make three treatments in one season. We just add the mix provided by Omex to a blight spray, as we are going through the crop anyway."

Mr Cade says the test results are easy to follow as the nutrients in surplus or shortfall are shown in different colours.

"The recommendation comes with the results, so we can take corrective action quickly," he adds. "We have always seen a benefit from this approach where weve left a spray width and done some test digs.

"As most of our crop is down to Maris Piper, the challenge is to get a good-sized tuber. Since we have been using sap testing, we have never had a problem with small tubers."