A system for applying liquid fertiliser when planting potatoes is also proving successful for applying seed-bed fertiliser when establishing oilseed rape. Peter Hill reports.

A Lincolnshire grower who started applying fertiliser with rapeseed at sowing almost by accident has become a convert for the technique.

“I was a bit sceptical at first,” says David Armstrong at Abbey Farm, Bardney. “But there have been such obvious visual differences where some of the crop has missed its dose of fertiliser that I now wouldn’t want to sow rape without an early dressing of nitrogen and phosphate.”

The main objective when establishing around 140ha of oilseed rape within the 566ha arable rotation at Abbey Farm is to get the seed in the ground as soon as possible after winter wheat has been harvested.

Variable soil types ranging from heavy clays and light peaty fens to blowing sand has made it a challenge to achieve good oilseed rape gross margin at the best of times. The crop used to be sown using a disc drill after subsoiling.

“But apart from involving two operations, if conditions were a bit tacky you could see the re-compaction effect of going in with the drill,” says Mr Armstrong. “That’s when we decided to sow off the back of a subsoiler – to save costs, reduce the workload at a busy time and avoid undoing the work done by the subsoiler.”

Planting potatoes

Adding fertiliser to the operation was first tried two years ago after a Chafer Quickstart system was selected for applying fertiliser when planting potatoes.

“Using the same technique for oilseed rape was being talked about a lot at the time, so it made sense to have the equipment usable for both crops,” says Mr Armstrong. “It caused a few pump difficulties because of the big difference in volumes – 1,000 litres/ha for potatoes compared with 120-150 litres/ha for rape.

“But the return-to-tank arrangement used for the lower volume application will hopefully have solved that issue,” he adds.

The 16.5% nitrogen, 33% phosphate liquid compound is put on via single stream jets positioned in front of each leg of a Cousins V-Form five-leg subsoiler. With the fertiliser spread and worked in by the action of the leg moving through the soil, so the seed is broadcast in 15cm bands from a drop tube and “splash plate” positioned behind each leg and about 40cm above the ground.

“In my experience, it’s important not to drop the seed too close behind the leg, especially on lighter soils that close up easily,” says Mr Armstrong. “I’ve heard the argument for putting it on in front of the crumbler roller, but this incorporates the seed and I’ve never had success broadcasting on to the surface when patching up a thin crop.”

Whenever conditions allow, the subsoiler also tows a roller for maximum moisture conservation and to make this a one-man, one-pass operation as often as possible during the busy harvest period.

On-farm evidence

On-farm evidence of the effect of applying fertiliser at sowing is limited to observations made when some of the crop has failed to get its dose – if the “on” switch is forgotten for a few metres into the field, for example.

“It’s difficult to pick out any difference in the crop through autumn and winter, but come March/April, the effect has been quite visible both years,” says Mr Armstrong. “Where the crop has been stressed, due to compaction, wet conditions or a nutrient issue, we’ve seen as much as a foot difference in plant height.”

Oilseed rape is grown across all the different soils on the farm, but on some of the heavier clays, where phosphate lock-up is a recognised problem, the soils record very low phosphate indices, below 1 and as high as 5 on the sandy loams.

“Placing liquid fertiliser close to the seed at sowing means phosphate is readily available to the plant after the seed germinates,” Mr Armstrong adds. “We’ve seen a marked effect at yellow bud stage thanks to a missed strip right across one field, even on more fertile ground.”

The one-pass approach also saves costs – by eliminating a separate autumn application and by cutting total fertiliser use from the 30kg/ha applied overall to the 20kg/ha applied down the seed row.

Lifting yields

In combination with other measures, such as soil structure improvement, the technique is credited with helping to lift yields by about 10% to an average of 3.9t/ha.

The Chafer Quickstart system comprises a glass reinforced fibre (GRP) or stainless steel tank of 1,000-litre, 1,500-litre or 2,000-litre capacity, mounted on a frame that also carries the equipment needed to make it a self-contained unit.

This includes a hydraulic-drive self-priming centrifugal pump of up to 450 litres/min output, an automatic rate control system using a GPS speed sensor, a pressure filter, and all essential valves and pipework.

There are also fast-filling and emptying ports, a pressure-monitoring system and an electric on/off valve that can be rigged up to operate automatically when the implement is lifted and lowered for a headland turn.

Mr Armstrong’s 1,000-litre Quickstart package has a “plain” frame carried on the front linkage of his 345hp tracklayer. For smaller power units needing front-end ballast, an extended frame capable of carrying a weight block is available – as are numerous cultivator-mounted options.

“We went for the front-mounted option because putting the big tank on the subsoiler would have been too much,” he says. “Besides, this arrangement suits the potato planting application better.

“It takes a bit of time connecting at all up and making sure everything is working OK, and it certainly doesn’t come off the tractor until the rapeseed is all done,” adds Mr Armstrong. “But having looked at systems from other suppliers, it was the build quality of the Chafer equipment that was decisive in our choice.”