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Spring OSR Management

Date Added: 13/02/2012

Forward OSR crops require careful spring canopy management to attain desired yields.

Following near perfect conditions for oilseed rape crops to establish during the autumn of 2011, many arable farmers will need to deploy a careful canopy management strategy to ensure that crops which have grown too far forward don’t suffer reduced seed yields at harvest.



That is the cautionary advice from Richard Elsdon, technical manager for United Oilseeds, who warns that history proves the UK farmer is not good at managing forward crops of oilseed rape.


“The exceptionally cold conditions last winter ensured that growth rates of crops which had got too far ahead were curtailed, resulting in plants of a more manageable size going onto the spring,” Mr Elsdon describes.  “The ensuing dry spring limited growth further, so that crops in many areas were typically 30-35cm shorter than normal.  This reduced growth, and a thinner canopy, ensured that light could penetrate the canopy and keep leaves lower down the stem green while flowering took place.


“After flowering, plants with an optimal amount of canopy were able to photosynthesize to a far greater level than those with extensive canopy growth, enabling them to produce more energy.  This in turn allowed the development of a greater quantity of oil-rich seeds.  As a result, last year’s harvest gave some exceptionally high yields.”


In contrast, the 2006-07 season produced one of the poorest yielding crops of the last ten years.  As was the case last year, crops grew vigorously in the autumn producing huge plants going into the winter.  However, a relatively mild winter meant that crops continued to roar away into the spring, producing a massive top canopy and poor yields.


“With weather patterns becoming increasingly unpredictable we simply cannot depend on nature to come to our rescue again this season,” Mr Elsdon warns.


“Last autumn was characterised by a prolonged period of conditions that were well suited to vigourous establishment and excessive plant growth,” he adds.  “By late November many current crops had already achieved a Green Area Index (GAI) of 3.4, whereas the ideal for that time of year should typically be much lower at around 1.5.”


Mr Elsdon warns these large crops will need very little in the way of nitrogen prior to the spring, but will still need their full allowance of sulphur if they are to yield well.  “Work carried out for HGCA by Dr Steve McGrath from Rothamsted Research has shown that 70-80kg per hectare of sulphur as SO3 can be applied as late as April without compromising yield.


“As most farmers apply sulphur as ammonium sulphate, a later than usual application will reduce the nitrogen growth surge as the crop will by then be 30cm or so tall.”


In an ideal world, Mr Elsdon believes that forward crops should receive sulphur as magnesium sulphate so that nitrogen calculations and applications can be carried out separately.


Mr Elsdon also states that no matter how large crops have grown, all should have their GAI measured in late February – just before the spring growth spurt takes place.  This can either be done using a digital camera and downloading the image to a GAI website, or by using a dedicated smart phone application which can give instant results from the field.  A more accurate, but more onerous method of calculating GAI, is to measure the weight of crop growing in a square metre.  The weight in kilos multiplied by 0.8 gives the actual GAI of the crop.


“At the end of February, a GAI of up to 2.5 is fine and shouldn’t give cause for any alarm bells to ring.  Above this, farmers will need to think carefully to ensure their spring nutrient strategy doesn’t provide too much nitrogen to already advanced crops.”


For Philip and Gareth Watkins of Gillow Farm, Harewood End, Hereford, the problem of forward crops is a very real concern this year.  In some of their 118 hectares of oilseed rape, some fields had reached a GAI of 3.46 by mid-December.


“We have chosen to grow two Pioneer varieties again this year because they produced such high yields for us last season,” Philip Watkins describes.  “Typically we’ll achieve something like 3.2 to 3.5 tonnes per hectare, but last year our PR46W21 yielded an average of 4.2 tonnes.  Likewise our dwarf PR44D06 – which we grow so that we can get on and off some rented land as quickly as possible and get into our contracting work – reached 4.0t/ha.”


This season the two varieties were drilled between 21st August and mid-September, with the PR46W21 sown first.  “Both varieties were planted in near perfect seedbeds that allowed easy establishment.  If anything, some of the land was a little too dry, but the autumn brought just enough rain to ensure the crops got off to a rapid start,” Philip explains.


Concern over the rate at which their oilseed rape was growing started to creep in to Philip and Gareth’s minds by late November when many fields had grown to knee-height.


“We think the excessive growth is a result of a combination of factors,” Gareth explains.  “The dry summer meant that there was a lot of residual nitrogen left in the soil, while the mild autumn gave an unusually long window for growth.  Added to that, the young plants put down huge tap roots during the dry early autumn, which meant they were able to scavenge extra nitrogen when the rains finally came later in the year.”


In order to ensure that their crop of oilseed rape still yields well, Philip and Gareth have taken steps to adapt their usual spring management regime.  “This year we will be putting a lot more time and effort into treating each field on an individual basis,” Gareth describes.  “In previous years we have been guilty of treating each large block of land as a whole and adopted a blanket approach to fertiliser applications.  It is evident that this strategy won’t work for us this year so we will be treating each field according to their individual GAI score.”


The Watkins are also using a GPS based auto-steer system to minimise fertiliser overlap.  “So far we have only subscribed for a basic GPS package, but I can envisage us embracing full precision farming in the future to provide even greater fertiliser accuracy,” Gareth predicts.


“We have also ensured that the fertiliser spreader is accurately calibrated to ensure optimum application and we are in regular dialogue with our agronomist and with Richard Elsdon to ensure that we get the best advice available.  We have been growing wheat, barley and oats long enough to have a good understanding of what we’re doing, but oilseed rape is much more of a specialist crop to grow.  For that reason we aren’t afraid of taking specialist advice to make sure we have a logical strategy in place.”


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