Oilseed rape growers must pay more attention to crop nutrition if they are to increase future yields, according to UAP.

Average on-farm yields have plateaued over the past decade, but better balancing of crop nutrient requirements and removal will play a key part in future yield improvements, says the firm’s Will Foss.

This season some growers may have cut back on applied nitrogen rates due to higher soil N, but in many cases where N:S fertiliser was used, sulphur rates could also have been reduced below crop requirement, he says.

A 4t/ha crop needs about 80kg S/ha, although applied rates will depend on soil availability and target yield, he says.

“You need to plan fertiliser strategy before booking fertiliser to allow flexibility, in case you need to adjust rates in the spring.”

Growers also need to consider total crop nutrient uptake throughout the season.

Typically, many oilseed rape crops receive around 200kg/ha of nitrogen (depending on soil type, previous cropping, etc), but N uptake can peak at around 240kg/ha in June, he says.

“Lower nitrogen rates may well be one of the factors for the plateau in yields.”

Variety will affect yield response to nitrogen and trials in Germany suggest modern, high yielding varieties, such as hybrids will show a greater response to N compared to conventional varieties, he notes.

Mr Foss goes on to highlight the importance of phosphate and potash.

“The removal of P and K [in the harvested crop] is very similar, but you need to look at total uptake throughout the season and ensure sufficient P&K is available for peak uptake.”

For example, a 4t/ha crop has a peak potash uptake in June of 290kg/ha, yet 1t of seed only removes 11kg of potash – the remainder goes into the soil profile, he notes.

“It may well be worth looking at an N:P:K compound.”

Trace elements

Of the trace elements, boron is the most important and deficiency can lead to extended flowering, poor seed development and stem splitting, he says.

“While sugar beet growers may be more aware of boron, oilseed rape also has a very high requirement at 320g/ha [compared to 480g/ha in beet].”

Soil or tissue testing during the main spring growth period can be used to identify any deficiency and he suggests applying Opte B at 2.0-2.5litres/ha, possibly repeating during late autumn, stem extension or early flowering if there is a high deficiency risk.

paul.spackman@rbi.co.uk