THE pressures on to cut inputs even further – and seed is the first in line. But when do you start to spend more on other inputs, than you can save on seed?
CWS Agricultures project manager for Focus on Farming Practice, Alistair Leake has, in the past, erred his seed rates on the side of caution: "If you are short of plants, you cannot turn back the clock."
However, last year he experimented with lower seed rates on the ICM fields at Stoughton near Leicester.
Using a direct drill for an early winter wheat sowing of 9 September he used a rate of 110kg/ha. This represents a substantial reduction compared with rates of 160-180kg/ha on the conventionally farmed areas, and as high as 250kg/ha on the organic system.
In retrospect, 110kg/ha was probably a little low, he reckons. "Sowing that early and with a direct drill, the crop is at greater risk of pest attack. I learnt a lot about slugs last year," he adds ruefully.
"With slug pellets costing £10/ha at a reduced rate, and the spreading operation adding another £7/ha, I feel inclined to bring the seed rate back to a level around 130kg/ha."
There are so many tradeoffs when you reduce seed rates. Slug control is just one. Weed control in a less competitive crop is another. At what point do you start to spend more on herbicide than you save on seed, he asks.
A comparison by CWS of wheat sown at different seed rates and on different dates turns the question around (see table 1).
Under the treated regime, yield was sacrificed by later drilling. But the weed suppression achieved by the combination of delayed drilling and higher seed rates is illustrated by the yield results in an untreated situation.
This suppressive effect should be enough to allow cost savings from reduced herbicide rates, argues Mr Leake.
He does concede that lower seed rates provide an opportunity to produce a cheap crop of wheat where the rotation allows a good degree of weed control ahead of drilling – after grass or set aside for instance. He also points out the value of glyphosate, at £4-5/litre, in reducing the weed seed bank.
"If you are using reduced rates of seed, for goodness sake protect it," pleads Mr Leake. His choice of seed treatment last year on the low rate Reaper was fludioxonil (Beret Gold).
But the upside of a thinner canopy was a reduced disease pressure, he adds. The first fungicide spray didnt go on until flag leaf.
Lower seed rates also tend to produce stands of big, well-tillered plants that tend to stand very well compared to lots of closely spaced individual stems. But Mr Leake advises great caution before dispensing with plant growth regulators in the light of this years lodging.
Seed rate trials in 1995/96 by Profarma have gone further toward identifying situations where low seed rates can make a positive contribution to yield.
"For early drilling – 31 August – we tested rates for Brigadier from 39 to 183kg/ha," says technical manager Craig Morgan. "And, yes, the highest yield did come from the lowest rate." But that, he stresses, disguises all sorts of factors – lodging at higher seed rates because of freak summer storms at the Goole site, the three BYDV sprays that were necessary and the hand weeding of oilseed rape volunteers on the lower rate plots.
"The dose response curves for herbicides go out of the window at low seed rates. Thinner canopies allow almost continual germination of weeds, especially oilseed rape."
But, curiously, disease levels didnt vary significantly between the different seed rates.
For later drillings, using the same variety, the yield differential between seed rate narrows to just 0.4t/ha (see table 2).
"On high yielding moisture retentive fertile soils where lodging is a perennial problem with early drilling, there is a chance to reduce seed rate, but you do increase the BYDV threat and you do need to steer as far away as possible from earlier rape crops," concludes Mr Morgan.
On lighter soils the benefits of lower seed rates are more universal. Trials at the light land site at Weston Hall in Cheshire compared six varieties, each at two dates, with and without fungicide, and at two rates – 78 and 183kg/ha. Almost without exception, the lower rate outyielded the higher.
"On heavier land the biggest saving from low seed rates is seed cost. But on lighter soils, especially those prone to spring drought conditions, the crop sustains itself better so theres an additional agronomic benefit," suggests Mr Morgan.
David Stormonth, newly appointed director of the Brown Butlin group, summarises: Seed is the starting point for a crop and an obvious place to look for economies. But, beyond a point, low seed rates becomes a false economy.
To find that balance you need to take account, not only of the varietal characteristics, but also seedbed conditions, drilling dates, possible winter kill, weed species present and the known risk of pest attack.
"The formula is the same at any grain price – but when grain price falls the need to look at the detail becomes greater," says Dr Stormonth. The mechanism, he adds, is to sow by seed number, not weight.
"Seed is still a relatively low variable cost. If plant populations are too high, then theres been a nominal waste of capital. But the danger is getting them too low and feeling the effects at harvest. A good plant population gives the basic foundation of a potentially high yielding crop, which may withstand low levels of attack before the need to resort to chemical methods of crop protection."
Lowering seed rates is on every growers mind as input costs come under fresh scrutiny. Tia Rund seeks expert advice.