Switching from spring-applied ammonium sulphate fertiliser to autumn-applied N:P:K plus elemental sulphurhas helped one Nottinghamshire grower improve yields and cut nitrogen requirements.

Dean Broadberry of Roewood Farm, Winkburn, switched to autumn-applied Omex suspension fertiliser six years ago. He believes the move helped boost wheat yields by about 1.2t/ha (0.5t/acre) and oilseed rape yields by nearer 0.7t/ha (0.3t/acre). With wheat at about £130/t across 210ha (520 acres) and oilseed rape at £330/t over 93ha (230 acres), this has resulted in useful extra profit, he says.

Also, spring nitrogen requirements were reduced by about 40kg/ha and better utilisation of available nitrogen by increasing sulphur levels led to a further saving of £24/ha (£10/acre) across the cereal acreage.

Improved labour efficiency by spreading workload from the spring to the autumn has also had a significant impact on the business, although financially it is difficult to quantify, he adds. “Arable farmers can always argue for and against going down an autumn-applied fertiliser regime, but in my case the switch to Omex suspension makes total sense.”

Chris Pacey and Dean Broadberry

Using an autumn-applied fertiliser mix instead of spring ammonium sulphate is one reason behind
Dean Broadberry’s (right) better wheat and oilseed rape yields (pictured with Chris Pacey)

In addition to 323ha of combinable cropping, Mr Broadberry runs a 1214ha (3000 acre) stubble-to-stubble and part-contracting operation, an on-site cereal cleaning enterprise on contract with Gleadell Agriculture for drying, cleaning or grading up to 1500t of grain per month, and a 7000t storage facility. Workload pressure is therefore significant most of the year.

“Switching to Omex suspension fertiliser significantly reduced the workload because most of the fertiliser required for the oilseed rape and wheat is now delivered by the company and applied in the autumn by an Omex contractor.

“Applying fertiliser in the spring doesn’t actually help the crop for that season, more likely the next one, provided the nutrients have not been leached out by that stage,” he says. “The advantage of using Omex P:K suspension plus elemental sulphur in the autumn is that the sulphur in this form is released slowly over the critical growing period. This is particularly relevant for rape. Because elemental sulphur is also stable in the soil there is virtually no leaching.”

Mr Broadberry used to apply sulphur as ammonium sulphate along with the nitrogen in the spring, but the sulphur has a diluting effect on the nitrogen product, which means that to provide the appropriate levels of nitrogen for the crop, he would have to put higher rates on in the first place.

“Now with autumn-applied elemental sulphur wehave reduced our spring-applied nitrogen requirement by 40kg N/ha,” he says. “This saves money and physically reduces the amount of material and associated storage andhandling issues and Ihave increased use of sulphur above the normal levels.”

Crops dry

Well-timed fertiliser applications canhave big benefits for crop establishment

Improved rooting

Mr Broadberry says that autumn-applied P:K plus elemental sulphur improves rooting, which gives the crop the best chance of establishing, which ultimately benefits yield and quality.

Last year, better rooting helped wheat yields average 3.25t/acre, compared with a normal average of 3t/acre, he says. “We put on double the amount of sulphur on both rape and wheat, which means 40kg/ha and 20kg/ha respectively.”

Better oilseed rape establishment in the autumn also helped reduce grassweed herbicide use through crop competition. For example Kerb (propyzamide) usage for controlling blackgrass in oilseed rape has been slashed by nearly three-quarters, saving an estimated £3,200, he says.

“For autumn application to be effective, it is important to use the correct elemental sulphur particle size too small and there can be too much conversion in the autumn, leading to potential losses through the winter too large and the sulphur will not break down quickly enough in the spring,” says Omex district sales manager Chris Pacey.

“Omex uses 50 micron elemental sulphur, which starts breaking down after a lag in the autumn and rapidly releases sulphate sulphur in the spring. The elemental sulphur converts to plant-available sulphate according to soil temperature, providing a small amount for autumn growth and most of it is released from February to May.”

He says that conversion slows significantly at temperatures below 10C and restarts in the spring as soils warm up. The autumn application stimulates numbers of the thiobacilli bacteria that break down the sulphur, leading to a rapid flush of sulphate in the spring, so the remaining sulphur is rapidly oxidised once soil temperatures increase following the winter.

Spring applications still preferred

Mark Tucker

Yara’s Mark Tucker reckons applying N:P:K fertiliser in the spring is better than autumn applications.

Think carefully before moving away from spring-applied ammonium sulphate, representatives from two leading fertiliser manufacturers advise.

“The majority of products in the UK are ammonium sulphate-based and all the work I’ve seen suggests spring ammonium sulphate is still the most reliable, efficient and cost-effective form of sulphur for UK arable crops,” GrowHow’s central and south adviser Ross Leadbeater says. Elemental sulphur needs much more time to become available to crops and applying it in the autumn is not when crops need it most, he reckons.

Many oilseed rape growers using liquid fertilisers may also find that they cannot get enough sulphur onto oilseed rape, and will often have to top up with a solid product, such as DoubleTop, or ammonium sulphate, anyway, he says.

Yara’s Mark Tucker says elemental sulphur generally needs about 6-8 weeks to break down and get into a readily-available form within the soil solution, so will have to be applied well before the crop needs it. By contrast, sulphate products are more readily available, but also more leachable, therefore need to go on when the crop needs sulphur most – the spring, he says.

As for P&K, Mr Tucker advocates moving from autumn to spring applications. He believes this allows growers to better target fertiliser to peak crop requirement and also to reduce the need for separate passes in the autumn. “Generally, if your soil’s Index 1 or 2, there will be enough P&K to establish the crop. If it’s Index 0, you’re certainly going to need P&K in the autumn.

“Phosphate in the soil is constantly moving between available pools in soil solution to unavailable pools. If you put more on than is needed in the autumn, the soil will naturally balance this out and take phosphate out of the available pool,” he explains.

Where possible, waiting until the spring means growers can easily apply P&K with first, second or even third nitrogen applications through combined products, with exact rates depending on specific crop requirement, he says.

“There’s still a lot we don’t know about phosphate in the soil, which is something we all need to better understand.”