Research offers insight into managing lush OSR

Article taken from Agronomist & Arable Farmer

Recent Agrovista Growcrop Gold research, coupled with two ADAS projects, have helped the company better understand how oilseed rape crops build yield and what’s needed to manage lodging.

The conclusions from this research are that high crop density has a number of yield suppressing effects – fewer leaves for photosynthesis, reduced lower branching, poor light penetration to leaves and fewer pods.  Putting it simply, dense canopies are lower yielding.

The principles of Agrovista’s development work revolve around concentrating seed rates per linear metre, which result in a short plant and not seeds per square metre.

We are looking for a plant with an optimum of eight to nine primary branches – these are crucial for seed set, pod fill and yield.  In addition, strong secondary branch development is essential and can deliver yield gains upwards of one tonne per hectare.  Often growers increase row widths but do not adjust plant density ‘up the rows.’  As we progress, the ability to correlate seed rates/row widths and new plant growth regulators gives us the opportunity to change the crop architecture of OSR.

Dramatic Underestimation

ADAS research has highlighted that the impact of lodging in oilseed rape is dramatically underestimated in the UK.  In field surveys undertaken by Dr Pete Berry, on average 35% of the crops he surveyed we lodged but, because lodging occurs in the centre of fields, on many farms it often goes unnoticed.

Changes to seed rates will hopefully change the plant architecture and contribute to less lodging.  Dr Berry identified that lodging losses result from the collapsed canopy’s reduced ability to intercept light, coupled with difficulties in general crop management and harvest.  These losses result from reduced seed set, poor seed fill and pod shatter.

The magnitude of yield losses depends on when lodging starts and its severity.  Lodging at flowering will reduce seed set and seed weight.  If lodging occurs at early pod fill, it is most damaging for yield loss – averaging 52% when the crops is 70° to the ground.  The report also calculated that lodging caused a 2% loss in oil (calculated £10t/t at £350/t) and increased glucosinolate levels.

Metconazole Useful

Added to this piece of work, ADAS has also identified that metconazole is very useful for manipulating crop canopies, diverting growth from leaf biomass into seed and oil yield.   It does so by reducing the apical dominance of the plant whenever it is applied.  How it performs depends on the growth stage of the plant at application.

Spring applications of metconazole have been shown to increase root length density by 25% at a 40-100cm depth.  Because oilseed rape may produce insufficient adventitious rooting in the 40-100cm zone, this finding may be useful if soil moisture becomes low during the season.  This 40-100cm zone is important for water uptake in May and June during seed-fill.

A combination of agronomy practices, lower seed rates, delaying applications of nitrogen and applying Caryx (the new plant growth regulator product will be essential.  Growth-regulating fungicides – metconazole or tebuconazole – are valuable for this, but the most effective product on the market to manipulate canopy architecture (and to reduce the risk of lodging) is Caryx.

Caryx, the first plant growth regulator (PGR) for use on oilseed rape, was launched last spring.  It contains metconazole and mepiquat chloride.  These actives give complementary modes of action, consistent performance – even in low temperatures – and deliver positive rooting effects and very good crop height reduction.

The timing of application for Caryx is growth stage 31-59, stem extension to yellow bud.  BASF’s recommended dose rate is 1.4 litres per hectare.

Agrovista has already proved that there is an optimum plant number and an ideal plant canopy shape which is best achieved at 25-30 established plants/m² in the spring.  The knowledge that a plant’s seed numbers are set in the two to three weeks after the end of flowering is valuable in addressing the challenge thereafter – to ensure that seeds fill well by keeping plants healthy and maximising photosynthesis.  Trials point to achieving this with a green area index (GAI) of 3.5-4 at flowering.

The Green Area Index (GAI) app

March is the best time to measure GAI, even if you intend to apply fungicides in April.  For best effects, metconazole should be applied between a GAI of 0,8, flower buds visible at start of stem extension (March) or of 2.0 or above, late green bud/yellow bud (April).

The GAI tool which can be found at gives you an accurate and consistent assessment of an OSR crop’s green area index (GAI) from a digital photograph taken with your phone.  The size of the OSR crop canopy is a critical indicator for several management decisions regarding nitrogen and growth regulation applications.


17 March 2014

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