1 November 1996

Minimum-pass system can do the business…

Minimum pass wheat husbandry is the subject of the latest in our series bringing HGCA levy-funded researchers face to face with growers. Andrew Blake reports

HOW many times do you need to travel through a winter wheat crop to achieve a decent margin? Answer: Less than you might think.

That is the thought-provoking background to a three-year project undertaken by the Arable Research Centres and Scottish Agronomy using £120,000 of growers levy cash.

Conceived when pundits were suggesting that the grain price would soon be as low as £85/t, the work remains valuable under the threat of CAP reforms and changing farm structures, maintains ARCs technical co-ordinator, Nick Poole. "Even now prospects do not look so rosy as they did recently."

A common grower response to a financial squeeze is to expand operations over more land so spreading fixed costs, he explains. But there comes a point, which varies for individuals, when doing so makes it increasingly hard to justify multiple passes. It is then that the new work may offer reassurance that going through less often can still provide good returns.

Not to be confused with work on minimum cultivations, the HGCA idea explores the outcome of applying different levels of specifically timed inputs using three, five or seven passes. Key backing comes from access to new agrochemicals and a better understanding of crop structure which allows them to be used more precisely, says Mr Poole. "We have now got some of the most effective fungicides and herbicides ever employed."

The trials, on five English sites and one near Perth, have already generated 1728 plots-worth of information in the past two years and highlight the potential of the minimum pass concept.

Two varieties have been sown – Brigadier and the more disease-resistant Hunter – to see if one is more suited to the approach than the other. Four seed rates, each early and late drilled, have been tested mostly in a first wheat slot. "To date we have not had a lodging year to test the effect of seed rate."

Three-pass system

During the growing season the three-pass system employs a single autumn herbicide, one spring nitrogen dressing and a flag leaf (GS39) fungicide. For the five-pass test the N (same amount) is split and an extra fungicide used at second node (GS32). Seven passes brings in a stem extension (GS30) growth regulator and an ear-emergence (GS59) fungicide.

Seven passes is already relatively economic compared with some farms where 10 is the norm, observes Mr Poole.

Mean yield advantage of seven passes over three was quite marked in 1995 but less so in 1996. "But we need to interpret that broad overall view," he says. Differences were distinctly regional – three passes in Scotland and on fertile land at Wye in Kent coming closest to the seven-pass results.

"At Wye, where yields were very good over the past two seasons, the mean difference between three and seven passes was only 0.21t/ha."

Provided the number of passes is not exceeded the system permits whatever pesticides are required at the time to be applied. The scope to tank-mix a summer aphicide in the seven-pass system offers a flexibility that was particularly valuable at one site last year, he notes.

So what is the bottom line so far? The crunch question is how often the gross margin from three passes outdoes that from seven.

Much depends on the figures used to cost each pass and the grain selling price, says Mr Poole. "We have put each pass in at £5/ha, which is a reasonable farmer charge." That makes seven passes £20/ha (£8/acre) more expensive than three purely for application.

Over two years the worst scenario was at Biggleswade in Beds. There, even with grain at £85/t, the gross margin from three passes rarely matched that from seven after a bad aphid attack in 1995. By contrast at Wye three passes equalled or bettered the results from more frequent applications more than 90% of the time – even at over £100/t.

Couldnt you be getting away with fewer passes, asks the ARCs Nick Poole (right) of barometer grower Andrew Hebditch (left) and agronomist Arthur Hulls. Careful timing of new chemistry could provide the key.