Caution urged with computer forecasts

3 July 1998

This "pocket laboratory" from ADGEN accurately detects potato viruses X, Y and leafroll on-site in about 15 minutes. "These products will be of tremendous help to growers, advisers and diagnostic laboratories," says Stephen Holmes, ADGENs general manager. "Real-time results mean that prompt action can be taken to cut pesticide usage and minimise losses". Tests cost from as little as £4.25.

Caution urged with computer forecasts

FINE-TUNING input use can help protect crop profits. But where computerised predictions are involved much may depend upon the system used.

That is the picture emerging from trials at the Scott Abbott Arable Crops Station at Thornhaugh, Peterborough.

The work is conducted against a background of wheat worth £70-£73/t. "We have our purchased inputs under control at £24-26/t," says John North, an SAACS trustee. "The only way forward now is with higher yields achieved with the aid of new technology and input forecasting."

The brash land has more stone than soil and needs adequate summer rain to meet or exceed a realistic wheat yield of 7.4t/ha (3t/acre).

Five nitrogen prediction systems are being compared with the figure from the MAFFs RB209 advisory booklet. Further plots had N rates rising in 50kg/ha steps from 0-250kg/ha.

RB209 advised 190kg/ha. Four prediction systems suggested different splits totalling 120-160kg/ha, while the fifth advised only 57kg/ha – probably because it assumed an estimated 40kg/ha of N supply from the 30-60cm soil profile – which was solid limestone. Plot combine results are awaited with interest.

"Prediction, split application timing and nitrogen rate will be important in combating the Green Tax proposals. We want to reduce autumn leaching by ensuring there is less than 60kg/ha of N left in the soil in the autumn," says Mr North.

Further input cost comparisons based on SAACS trials show 95% blackgrass control cost £31/ha, but 100% control was £87-95. "Cost cutting here could be risky if you have a significant blackgrass infestation," points out Mr North. But 100% cleavers control was achieved for £29 or £49/ha. "I prefer £29/ha."

Margins over fungicide sprays of £81/ha for one spray, £95/ha for two sprays and £31 for three sprays show the need to tune according to risk based on variety, weather and target grain quality. &#42

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