EARLY DRILL? CUTRATE…
Early sowing of winter
cereals has much to
commend it. But failure to
adjust seed rates to drilling
date can easily throw away
the potential benefits.
Andrew Blake reviews
recent findings and talks
to a grower with firm views
on the practical adjustments
GETTING winter wheat seed rates wrong can be costly, says John Spink of ADAS Rosemaund. Comments from Cereals 98 suggest many growers sow four times the optimum, and some even six times as much as initial trials show is needed, especially when drilling early, he says.
"The scope for reducing seed rates, especially when sowing early, is massive. In 1996/97, the first seasons work, there was no benefit in sowing more than 80-100 seeds/sq m before Sept 29," he says. "And that was in a year when tillering was quite limited because of the dry cold spring. If anything this season, when crops grew all through the winter, the message is likely to be even clearer."
The replicated field experiments begun in autumn 1996 (Arable Sept 5, 1997) at two sites used four varieties known to tiller quite differently. Drillings were made at 20, 40, 80, 160, 320 and 640seeds/sq m, at ADAS Rosemaund on Sept 29, Oct 25 and Nov 14 and at Sutton Bonington, Notts on Oct 3 only.
At both sites the soil was medium loam. In theory moisture availability means early sowing benefits should be greater on lighter land.
Yields at Rosemaund averaged 8.8t/ha (3.56t/acre) – respectable bearing in mind the range of dates and seed rates used, says Mr Spink. Output fell away from a mean of 10t/ha (4t/acre) from sowing in Sept to 7.6t/ha (3.1t/acre) in Nov. But the figures mask a big seed rate effect, he notes.
At the highest rate the difference by delaying from Sept to Nov was less than 1t/ha (0.4t/acre). But as seed rate fell the yield loss from delaying rose, so that sowing just 20 seeds/sq m in Nov, an extreme treatment to examine tillering, cut output by 4.8t/ha (1.9t/acre).
At Sutton Bonington, where the average yield was 10.7t/ha (4.3t/acre), the highest came from Haven. Its output increased steadily with seed rate to a maximum of 12.9t/ha (5.2t/acre) at 640 seeds/ sq m.
Soissons at 20 seeds/sq m produced the lowest yield at 7.2t/ha (2.9t/acre). "But thats a surprisingly good yield for so little seed," comments Mr Spink.
Soissons and Spark did best at 320 and 80 seeds/sq m respectively, yields tailing off slowly above those levels despite the absence of lodging. Cadenza gave its best – 12.7t/ha (5.1t/acre) – at 160 seeds/sq m, rates above that trimming yield by over 1t/ha (0.4t/acre) partly through lodging.
The results can partly be explained by big variations in development and tillering capacity of the four varieties representing the main UK wheat categories, explains Mr Spink.
Varieties like Haven tiller well but then tend to lose their tillers. Others, like Spark, tiller well and hold onto them. Some, like Soissons are shy tillerers but tend to keep what they produce. Those like Cadenza produce few shoots and struggle to retain them.
The results are from a single year only, he stresses. "We have got to be very cautious." Analysis of last years results showed optimum rates as in the table. "But we wouldnt wish to use them in practice until we have more confidence about what controls tillering."
Taking an average seed rate of 180kg/ha (1.4cwt/acre) and seed at £300/t, mean costs are £54/ha (£22/acre). Applying the economic optima could save £40-43/ha (£16-£17/acre) in Sept, depending on variety, and £14-29/ha (£6-12/acre) if sowing in November.
"If you take yield losses from excessive seed rates into account, particularly where lodging occurred, the benefits could be up to £80/ha (£32/acre)."
Using cheaper farm-saved seed would increase the optima, but not by much, suggests Mr Spink.
The possibility of trimming even further in certain varieties sown early has been highlighted at Rosemaund. Yields from a tillering trial to categorise 17 varieties sown at 320 and 80 seeds/sq m on Sept 23 were compared.
The average cut in output from using the lower rate was 0.3t/ha (0.12t/acre). But the loss is easily offset by seed savings if using bought in material, suggests Mr Spink. "This is despite the 80 seeds/sq m being below the optimum of 83-100 for this sowing date established in the main trial."
Indeed three varieties, Consort, Raleigh and Soissons, all yielded more at the lower rate. But with Abbot losing 0.9t/ha (0.36t/acre) from being sown more thinly, more information on tillering ability is needed before significant reductions can be made with confidence, says Mr Spink.
"But there is plenty of scope. Many people are still sowing 16 stones/acre which is something like 500 seeds/sq m. Even if they go for only 200, given reasonable establishment it leaves a fair margin for error to allow for problems like slug damage. But farmers still need to know their own land. Establishment in the trials was 75%. Sowing in November can bring that down to 40-50%."
SEED RATE RESEARCH
• Big cuts possible in wheat.
lInitial years work only.
• More tillering info needed.
• Establishment warning.
Economic optimum seed rates in seeds/sq m (kg/ha)*
Variety Sep 29 Oct 25 Nov 14
Cadenza 83 (37) 105 (47) 186 (83)
Haven 100 (45) N/A 248 (112)
Soissons 95 (43) 140 (63) 274 (123)
Spark 93 (42) 128 (58) 213 (96)
* Assuming constant TGW of 45g.
Best for barley?
MUCH less work has been done on determining optimum sowing date and seed rate for winter barley, according to Morley Research Centre cereals specialist Doug Stevens. But trials last year suggest sowing appropriate varieties early in the second week of September, in the east at least, has few downsides and may even help crops stand better.
The experiments, drilling Fanfare early in the month, mid-way and late on light land at Docking, Norfolk, highlighted the crops flexibility, says Mr Stevens. "But we have only one years results and June was very wet so it wasnt typical. Id like to see what happens in a dry season, though we arent getting that this year."
"We think that so long as you avoid precocious varieties like Gaelic you can certainly start reasonably early. In East Anglia there should be no disadvantage from sowing as soon as Sept 8-10.
"There was very little difference between the first two sowings, although the yield dropped off slightly at the latest date. It fell 0.24t/ha between the middle and end of September."
Standing power was boosted in the earlier drillings which were shorter, he notes. "There was also less tendency for the straw to brackle."
The main downside of early drilling, increased risk of BYDV, can now be usefully countered with Raxil Secur (imidacloprid +tebuconazole + triazoxide), suggests Mr Stevens.
Weeds, generally encouraged by earlier sowing, are less troublesome than in wheat because barley makes more vigorous autumn growth and tends to be grown where blackgrass is less of a problem.
In contrast to wheat the experiments found no response to reductions in seed rate, notes Mr Stevens. "There is certainly no benefit in going below 200 seeds/sq m. A minimum of 200 plants was necessary for optimum yield from the early sowing." But more work is needed under different autumn conditions to refine the figures, he suggests.