Mapping seed rates to boost wheat yields

Nottinghamshire farmer Chris Sheldon knows tailored seed rates are the future. Last autumn his seed rate was twice as high on heavy land as light land. Spring plant counts and harvest results vindicate the change.

“We’d always had a problem with variable soil types, and with clay caps in particular,” explains Mr Sheldon, who farms 400ha of mainly tenanted land with father Mike and brother Jim at Hall Farm, East Stoke, near Newark.

“We know establishment will be poorer on the heaviest ground and in the past we tried to adjust rates manually. But that was never enough, so we ended up with thin patches dragging down overall performance.”

Last autumn all that changed. “Farmacy mapped the whole farm, we sat down and agreed a drilling map, loaded an SD card into the drill and let it do the rest.

“It made a real difference. Crops were far more even this spring and despite the unusual season our harvest results give me confidence we’re heading in the right direction.”

Indeed, yield responses of 0.3-0.5t/ha in wheat, thanks to optimum plant populations across the entire field, mean the service is already being used on 15,000ha, says Matt Ward of Rootplanner Precision, a division of Farmacy, the independent agronomy arm of distributor Hutchinsons.

Manual seed rate adjustments often fail to go either high enough, or low enough, he says. Establishment varied from 54% to 96% in 14 fields on five farms involved with Rootplanner Precision evaluation in 2011. In one zoned field establishment ranged from 57% in the heavy zone to 88% in the lighter loamy zone. “That’s a 31% variation, which is impossible to vary manually on the drill,” Mr Ward explains.

Farmers and advisers are also failing to return to more appropriate seed rates across the rest of the field, creating over-thick crops and a legacy of spring management complications, requiring extra plant growth regulator and fungicide, and fine-tuned nitrogen use. “We don’t want to solve a problem in one part of the field and create another across the rest of the field.”

“We know establishment will be poorer on the heaviest ground and in the past we tried to adjust rate manually. But that was never enough, so we ended up with thin patches dragging down overall performance.”
Chris Sheldon

For Mr Sheldon the biggest variations in soil type are on neighbouring Lady Pitt Farm, which is contract-farmed. The results there look so promising Mr Sheldon reckons the approach will make sense in almost all circumstances.

“I’ve always wanted to plant populations as uniform as possible going into winter, so we can manage the crop as a whole in the spring. I think too many people have been using variable-rate nitrogen to compensate for uneven establishment.”

Variable nitrogen, which he determines using satellite imagery, should be a fine-tuning tool to make the most of an already optimum plant population, he believes.

Cultivations on the predominantly combinable crops farm, with 20ha of sugar beet, are min-till, using a Vaderstad Top Down, followed by double press if necessary. The Horsch Sprinter 6m drill is fully computer controlled, and the drill tractor GPS-equipped. Both milling wheat and malting barley are grown.

Each field was zoned according to soil type (see maps on p27), and seed rates set in conjunction with Farmacy agronomist Gerald Abel. In one 17ha field eight zones were created. Seed rates were varied quite drastically to see what the outcome would be; Gallant wheat drilled on 26 September ranged from 225 seeds/sq m on the lightest ground to almost double that on the heaviest.

The assumption was that despite good seed-bed conditions and low slug pressure, establishment rate could still be as low as 65% on the heavy areas, and as good as 95% on the lightest, explains Mr Abel.

The resulting maps reflected Mr Sheldon’s expectations. “But they put figures to our gut feelings, and probably pushed things a good deal further than we’d have imagined.”

On Mr Sheldon’s farm, like many others last autumn, dry conditions delayed establishment. Slug pressure was not a big issue and a bold home-saved seed sample was used, so there was some concern that the higher seed rate on the heavier land would result in an over-thick crop.

But the reality was a uniform crop by spring. “The crop was definitely more even across the field.” Crop assessments taken in February by Farmacy’s Charles Wright confirmed that, showing 305 plants/sq m in the heaviest zone and 225 plants/sq m in the lightest zone – a surprise, given the doubling of seed rate.

As harvest approached, ear counts showed the different areas of the crop had come even closer together in performance, ranging from 640 ears/sq m in the heavy zone to 656 ears/sq m in the light zone. Finally, the yield-mapping Claas Lexion 570 combine showed just how effectively the adjusted seed rates had worked, with hardly any yield variation across the field, despite the striking differences in soil type and the very demanding growing season.

“With harvesting progressing slowly, early indications are yields are pleasing with the best fields on the farm yielding 9.6t/ha. Mr Sheldon says the crop is much more even in the different soil zones where normally there would be big differences in the thickness of the crop. This shows the variable seed rates have performed well in a difficult year.

“The important thing for us is the consistency,” says Mr Sheldon. “We’ve brought the poorer-performing areas up to the same output as the rest of the field. That’s very good news. Harvesting was a good deal easier too, thanks to the more consistent crop.”

He plans to drill all crops with variable seed rates this autumn. Seed- rate zoning can clearly improve wheat management and final yield. In crops that struggle to compensate after poor establishment, such as winter barley, spring cereals and break crops, it could be even more valuable. The question is whether more growers will pursue the approach this autumn.