27 February 1998

FIELD TESTS FOR N PROVE WORTH

TESTING soil samples on an individual field basis for nitrate levels brought a 28% reduction in the amount of nitrogen applied to brassica crops on one fen farm last year.

That meant a total saving of 280t of N fertiliser, with no adverse effects on crops.

David Walker, farm manager for L W van Geest at Spalding, Lincs, is one of almost 100 larger farmers who have been trying the Solomon system developed by Independent Agriculture consultants, Vince Dempsey and John Haywood. Environmentally and economically he is well pleased.

Reflectometer readings of soil nitrogen reserves enabled the customary first 100kg N/ha top dressing on the 1619ha (4000-acre) vegetable growing farm to be missed out completely on some cabbage crops. Total nitrogen use was cut from 200kg/ha to 75kg/ha and even 50kg/ha in some cases.

This year he intends to extend soil testing to include cereal land.

No one-year wonder

Mr Walker confesses to having early fears that using up soil nitrogen reserves would make the potential to save on fertiliser a one year wonder. But it doesnt seem to work like that, he says. He was still able to cut back on fertiliser on second brassica crops.

The £550 Solomon kit is used to take reflectometer readings of nitrate levels in soil water through the use of suction lysimeters in soil probes. It can also be used to check N levels in growing plants through sap testing.

Each reflectometer test uses an indicator strip costing 25p. Mr Walker has cut that cost by taking five core samples for every 2ha (5 acres) and combining them, to give a single test reading.

Project manager for Solomon Systems, Vince Dempsey, says the purpose of the kit is to optimise nitrogen use and encourage the development of field-specific farming. Test results do not always lead to a reduction in nitrogen use, he notes. In some cases the recommendation could be for higher rates.

Using a standard nitrogen policy gives a reliable crop response in 10 years out of 10. But in six of those years nitrogen is over applied, he suggests.

Testing for available nitrogen prior to application is a better way forward, he says.

Test readings taken on farms are put through a computer model, which makes allowances for varietal variation and produces a nitrogen recommendation.

Growing importance

Testing for soil nitrogen reserves is of growing importance, says Mr Dempsey. "It is important environmentally, it is being built into supermarket protocols and it is important economically as margins tighten," he says.

Nigel Sanderson, Bothal Farm, Morpeth, has been trying out suction lysimeters on his 174ha (430-acre) mainly cereal growing farm and has found them accurate in the field, easy to use, but a little time consuming.

Initial difficulty in getting satisfactory readings at 30cm and 60cm (12in and 24in) depths, particularly on some of his heavier fields, were eventually overcome.

Light fields in cereals for the third year were showing 45kg N/ha in Dec 1996, whereas the reading in a field of first wheat after rape averages 30kg N/ha.

But, he said, the 30kg was still there in the spring when the plants began to grow, whereas on the lighter land the nitrate was being taken up more rapidly by the crop and was moving down the soil profile &#42

Solomon soil N testing saved growers money last year by helping them match fertiliser rates, soil supply and crop need more closely.

SOIL N TESTS

&#8226 Solomon system tests soil N reserves and sap contents.

&#8226 Kit costs £550.

&#8226 Helps optimise N rates.

&#8226 Big cost savings possible.

&#8226 100 farms evaluating in UK.

&#8226 Solomon system tests soil N reserves and sap contents.

&#8226 Kit costs £550.

&#8226 Helps optimise N rates.

&#8226 Big cost savings possible.

&#8226 100 farms evaluating in UK.