Being able to variably apply seed according to identified soil zones and expected establishment rates has increased wheat and barley yields by an average of 0.2t/ha on a Hampshire farm.

For farm manager Tim Walters, the agronomic benefits have been just as important as any economic gains, and he admits that the use of precision farming technology across 600ha of combinable crops has made his life easier.

“Although it does allow me to manage the various zones within fields differently, variable seed rates have actually simplified our agronomy and day-to-day crop husbandry,” he says. “An even plant stand is so much easier to manage.”

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The very chalky, flinty soils that predominate at Upton Park Farms, Old Alresford mean that it is vital to get the required plant numbers, especially as the farm grows a sizeable area of spring malting barley.

Matching seed rate to soil type and seed-bed quality allows him to deal with much of the variability at the outset rather than trying to rectify things later on in the growing season.

Even establishment

Mr Walters aims give the crops the best possible start to achieve an even establishment, which leads to better efficiency with inputs.

While lodging caused by over-thick crops is less likely to be an issue on the estate’s chalk soils, thin plant stands are at risk from weed competition.

“There’s very little in the way of effective grassweed herbicides that can be used in spring barley. So we need to make as much use of crop competition as we can, as well as cultural control, to beat blackgrass.”

With this in mind, he is able to combine the establishment and seed rate calculations produced by the system with his own blackgrass maps – allowing him to up the seed rate where bad weed patches have developed.

“I can make modifications if I need to,” he says.

“It is soil texture and seed-bed orientated, but there may be pressing agronomic reasons for increasing or decreasing seed rate.

“So there is flexibility within the system, despite it sometimes being described as prescription farming.”

Precision farming technology

Having first ventured into precision farming in the 1990s with variable P and K fertiliser applications, based on GPS soil analysis maps, Mr Walters continued to assess precision farming techniques and look for ways to fine-tune input use – using on-farm trials by precision farming specialists SOYL to help with some of his decisions.

As a result, he has since moved on to variable rate nitrogen applications, as well as seed, and has John Deere’s Greenstar guidance and control on the tractors, plus an RTK signal. A Horsch Sprinter drill completes the line-up.

“We have bought into the technology,” he acknowledges. “Of course, it is much cheaper now than it used to be, and much of it comes as standard on new machinery. The compatibility problem that existed before has also been dealt with.”

Mr Walters describes variable applications of P and K as a no-brainer. “On this farm, we moved from making annual blanket applications of 0.24.24 NPK or Fibrophos to using straights every other year, targeted accurately to where they were needed.

“The savings were huge. We now have one artic load of TSP (triple superphosphate) and muriate of potash delivered, plus a bit of Kieserite if magnesium is required.

“Not only have the costs come down, our purchasing requirement has been simplified and we have achieved more uniform soil indices.” 

Starting point

Variable seed rates were first experimented with in 2009, when a drill with the ability to alter seed rates on the move was purchased.

The first step was to have soil electrical conductivity testing done, so that different soil zones could be identified. These were then ground-truthed, or verified, by a SOYL specialist, before expected establishment maps were produced.

From this information, seed maps were created, with drilling rates matched to the soil type and potential.

Tim Walters

“There was quite a range of predicted establishment across individual fields,” recalls Mr Walters.

“It went from around 60% to 80%, which reflects the variation in landscape and soil type that we have here.”

The visual effects of more even crops were obvious, but a trial conducted by SOYL in one field comparing flat and variable rates confirmed a 0.2t/ha yield benefit. That has since been repeated in commercial crops, with yields steadily increasing.

“We’ve committed to variable seed rates across all of our wheat and barley, but they’re not being done in our oilseed rape, as we use a different establishment system,” he adds.

Spring barley nitrogen trials

Tim Walters is now working closely with SOYL to see if he can use variable rate nitrogen on his spring barley crop.

“The issue with spring barley is that there’s very little crop biomass at the time that nitrogen is applied,” he says. “So using remote sensing technology to measure canopy development, as you do in winter cereals, isn’t appropriate.”

He has been applying 145kg/ha of nitrogen on the crop for last few years and would like to be able to use higher rates to increase yields, without affecting the all-important grain N% with maltsters have an upper limit.

As a result, Simon Griffin of SOYL has been using previous yield and soil maps to come up with a variable nitrogen plan. In a trial conducted last year, the rate went up to 175kg/ha and down to 116kg/ha, with yields recorded at 10t/ha and grain N at 1.6%.

“Our farm average spring barley yield is just over 7.0t/ha, so it looks like this has potential,” says Mr Walters.

Variable seed rates – getting started

Growers considering the use of variable seed rates should start by looking at their existing farm machinery, to see whether it has the capability to alter rates according to a treatment plan, advises SOYL’s technical manager Simon Griffin.

“Most people start by doing one area of the farm, so that they can see what it has to offer,” he says. “That approach also helps to spread the cost, as you only pay for the area done.”

The first stage is the conductivity survey, which looks at clay content, soil depth, stoniness and moisture content. This information is then used to conduct a physical soil survey, so that areas of similar conductivity values can be zoned and assessed.

“Armed with potential seed rate zones, we can then calculate seed rates for each one,” he explains. “That’s done by taking the potential seed-bed quality and any plant loses that may occur over the winter.”

The final stage is to create a variable seed rate application file, which is compatible with the seed drill controller, he adds.

There is a £15/ha charge for the scanning, ground-truthing and zoning, and a further 50p/ha charge for the production of maps, he reveals.

“If a farmer just wants the scanning done, there’s a charge of £8/ha.”