THE manipulation of plant population is of key importance in achieving maximum yield potential, Agrovista’s Chris Martin told delegates at a recent event organised by Northeast Bioresources at Eryholme, near Darlington, in County Durham.

The target is to build a canopy with a green area index of about 3.5 at flowering. This is best achieved with a plant population of about 30 plants per square metre.

At this level, the crop can photosynthesise with maximum efficiency, when the seed number is being set at the end of flowering.

Mr Martin said: “It is tempting to go for higher seed rates, in the hope of achieving better establishment, but our trials have shown this policy to be counter-productive.

“The main problem associated with over-crowded plants is competition.

We have come to this conclusion after collating information from our eight experimental sites around the country.

“Our findings have been borne out by research in Germany, which had discovered that as soon as oilseed rape touches another plant, it becomes competitive in its search for light.

“It tends to grow taller, rather than exploiting a more natural, prostrate growth habit, with lateral branching. The taller, weaker plants are more susceptible to lodging and disease, with fewer leaves for utilising sunlight.”

COMPETITION

He said the first point of competition comes from within the sowing row, which is why the number of seeds sown per linear metre has been found to be more important than seed rate or row spacings.

It is thought that about 15 plants per linear metre is the maximum number of seeds permissible, before inter-row competition reduces yield.

Mr Martin said: “At traditional 12cm-row spacings, there won’t be too much inter-row competition, unless excessively high seed rates have been used, but as row width increases, it’s vital to reduce seed rates, to prevent overcrowding.

“It is particularly relevant where rape has been established with a sub-soiler type machine, with row spacings likely to be in excess of 30cms.

“This was a lesson learned last year, when many crops established this way lodged as early as April and suffered significant yield penalties.”

SEEDBED NITROGEN

Information gathered from the trial sites over the years has indicated that applying seedbed nitrogen and phosphate improved the establishment percentage and increased the green area index in the autumn.

In all cases, it produced a positive yield response, with a benefit of 0.3t/ha this year at the Eryholme site.

FUTURE PLANS

Plans for the future included the sowing of companion plants, such as vetches and clover mix, alongside the rape.

Mr Martin said: “This theory is applied in France, to help reduce the weed burden associated with wider row spacings.

“The vetch and clover mix is selected for its early prostrate growth habit and sown between plant rows. It is also chosen for its frost sensitivity, so the companion plants die off naturally over the winter.

“As they have a very low carbon: nitrogen ratio, the decomposing material acts as a green manure. In France, spring chemical nitrogen inputs have been cut by about 30ksg/ha, where companion plants have been used.”

Another area for further research was the use of amino acids, said Mr Martin.

He said: “Amino acid treatments have been shown to produce consistent yield benefits in trials. The plant is capable of producing its own amino acids, but this can be a very energy-intensive process.

“The purpose of a supplementary treatment is to provide an immediately available source to the plant, liberating energy for other essential processes.”

In previous trials, amino acids have been applied in spring at about the green bud stage, with the intention of reducing stress during the peak growth period.

“However, last season we tried applying amino acids in the autumn. On all the sites except one, they produced better rooting, with an average 20 per cent increase in root mass. The most effective application timing was the four true-leaves stage.

“At the Eryholme site, a combined autumn and spring application of amino acids led to an increase in yield of more than 0.5t/ha.

“This is some of the most exciting technology we have seen for some time with oilseed rape and will be evaluated further this season.”