If different soils have different potential to get a
crop going and support its early growth, why use a blanket seed
rate? That was the rhetorical question Peter White answered for
himself four years ago when the purchase of a new drill gave him
the opportunity to use different seed rates within fields, not just
from field to field.
"It's something I'd wanted to do for a while and in some fields,
where soils were different on one side of a field to the other, we
did adjust the rate accordingly," he says. "But with some fields
containing up to five variations of our Keuper Marl silty clay
loam, GPS technology was the only way we could do it with any
precision."
This autumn, as in the past four, fields will be sown with as
many as five different rates, typically ranging from 90% to 125% of
the "base" rate and, on the best soils in perfect conditions, down
to 85% of that figure.
"The objective isn't to save money by using less seed; we're
still using about the same in total," Mr White explains. "But we'd
always struggled to get even plant counts and when I saw satellite
plant density images that closely matched some familiar soil type
patterns on the farm, I felt precision seed rate adjustment was the
way to go."
Leyfields extends to 800ha (1975 acres) at Kneesall near Newark.
This year, winter oilseed rape and first wheats accounted for about
70% of the arable area in roughly equal proportions, with the rest
down to second wheats and 100ha (250 acres) of spring malting
barley - a newcomer to the rotation on the lighter land to help
tackle blackgrass and spread the workload.
Five-year average yields are running at 10.13t/ha (4.1t/acre)
for wheat - with 2008 results coming in a bit better than that -
and oilseed rape at 3.6t/ha (1.45t/acre).
A devotion to minimum tillage managed with the help of a spade
and penetrometer has brought clear improvements in soil structure
and general well-being so all straw is chopped on the combine and
stubble tackled by Simba and
Horsch
cultivators that prepare the way for a Sprinter ST tine drill.
This arrived on the farm in 2005 complete with electric drive to
the Horsch seed metering system and a GPS package from
Farm Works comprising a
hand-held PDA with GPS receiver and Track Mate, Site Mate and Guide
Mate software, plus the Farm Track and Farm Site laptop computer
software.
The first challenge was to create the seed rate maps: "I'm
fortunate in having a good knowledge of the soil type distribution
having farmed here for more than 20 years; it would be more
difficult on unfamiliar ground," says Mr White. "We're also
fortunate in having soils that are quite distinct."
For some fields, it was a case of simply sitting down with the
laptop and drawing the different soil zones; in others, running
around on a quad bike using the PDA as a GPS plotter provided the
application map.
But the most effective method, it seems, has been to put
on-the-go rate adjustment in the capable hands of drill operator
Adam Swan, record his inputs and, after a bit of tweaking and
smoothing here and there, use that data for the following year's
seed rate map.
"Sitting high on the tractor gives you a good perspective;
differences in colour and physical characteristics show the
boundaries between one soil type and another very clearly on
freshly cultivated soil," he says. "And, of course, you're covering
the whole field. It brings a lot more precision to the broad-brush
approach you get from using your own knowledge of fields or walking
them at ground level."
A typical rate of 170 seeds/sq m for sowing in the third week of
September are shifted upwards on heavier, poorer soils to
compensate for likely germination and drainage issues, and in
anticipation of a higher slug population.
"The higher rate also offsets the tendency for these soils to be
colder and slower to warm up in spring, resulting in plants that
don't tiller as well," Mr White explains. "We'll trim the rate on
better and more fertile soils where we expect a higher germination
percentage and better tillering - and to avoid lodging, because
that's the last thing we want with a minimum tillage system."
Rates may be adjusted season-to-season to some extent, based on
how fields performed the previous year, but he warns against making
frequent changes that may confuse the interpretation of crop
performance.
"If you've a good reason to expect a heavier slug burden in a
particular field or you've had lodging in some areas, then fine,"
he says. "But I think you've got to be wary of constantly making
changes when you don't know what the season ahead is going to
bring."
One limitation of the current set-up is that once the data has
been recorded to an SD card and that has been slotted into the
drill's control box there is no opportunity to make further tweaks
- to compensate on the day for a cobbly seed-bed, for example. That
would only be possible if the in-cab control unit could run the
mapping software.
Precision farming sceptics will also point out that it is
something of an act of faith to accept that what the drill terminal
says is being sown is what is actually being sown. In this case,
reassurance comes from the Farm Works software totting up the total
amount of seed required to sow each field in often quite complex
seed rate patterns.
The next step will be to use yields maps to further analyse the
causes of variations in crop performance across individual fields.
Results from the difficult 2007 harvest are being disregarded, so
it is hoped that yield contour maps from this year's campaign can
be looked at alongside those from last year to start picking out
areas for investigation.
While Mr White is excited by the rewards of precision farming
technology he readily admits to being 'pretty clueless' when it
comes to the software technicalities. But Adam Swan has taken to it
with enthusiasm - preparing and manipulating the maps and sowing
crops at variable seed rates has added a new dimension to his job
and one that he enjoys.
Nor does it take up an inordinate amount of management time, as
some sceptics fear precision farming technology is bound to do:
"It's a good way to make productive use of wet days," says Mr
White.