Significant benefits from growing companion plants alongside oilseed rape have been observed in a series of trials based in the UK
Significant benefits from growing companion plants alongside oilseed rape have been observed in a series of trials based in the UK. Farmers Guide examines the result.Establishing companion plants in oilseed rape crops is a well-established practice in parts of France, primarily to help growers reduce nitrogen losses through the winter to meet tight environmental restrictions.However, the technique has also been shown to benefit growers’ pockets, delivering extra yield and reducing crop demand for bagged nitrogen in the spring. Speaking at a recent Grow Crop Gold technical meeting held at Morley, Norfolk, Agrovista technical manager Mark Hemmant (left) said: “We thought it was time to see if the practice could produce similar yield benefits and fertiliser savings in the UK.”Companion planting was introduced to the national network of Grow Crop Gold oilseed rape trials sites last season. A mix of frost-intolerant species is grown alongside the crop during the autumn, mopping up nitrogen that would otherwise be lost. Companion plants then die or are sprayed off in winter, allowing captured nitrogen to be released gradually in the spring.French trials have shown this typically reduces the need for bagged N by 30kg/ha and, together with improvements in weed control, soil structure, crop rooting and pest control delivers 0.2-0.3t/ha of extra yield, said Mark.Plots were sown between 15th August and 7th September 2012 depending on site. OSR was sown at three rates – 10, 15 and 28 seeds/m length of row at 55cm spacings – and companion plant seeds broadcast at 20kg/ha between the OSR rows using a second seed hopper.A blend of common and purple vetch and berseem clover was used to ensure an ideal combination of growth characteristics, rooting depths, frost tolerance and N release.”Establishment was good at all the sites except Stoughton (Leicestershire), in areas with high surface trash, and Brechin – it was too far north for the plants to establish,” said Mark.Companion plants had only a minor effect on crop establishment, with an average of 42 per cent plants establishing where they were present, just four fewer than on OSR-only stands. There was also a significant increase in top growth, especially at lower seed rates, with OSR growing alongside companion plants hitting a fresh weight of 4.78t/ha compared with just 1.78t/ha on OSR-only plots.
“What was really surprising was the massive impact companion planting had where growth and establishment was poor,” said Mark. “At Croft in North Yorkshire OSR plant weight was three times greater on companion plant plots by 6th March at the lower two seed rates.”All sites tested showed companion plants encouraged autumn rooting. Root neck diameter assessed in March was about 20 per cent bigger, suggesting much improved winter hardiness.Why companion planting encourages bigger, stronger crops remains unclear, said Mark. “It could have been due to rhizodeposition – the release of beneficial organic compounds into the soil – or companion plant roots improving soil drainage and aeration or providing an alternative food source for slugs.”At Morley plots had significantly more biomass and plants captured an average of 29kg/ha of N over winter, the equivalent to 50kg/ha of bagged N. However, even at Croft where plant growth was much more restricted 23kg/ha of N was captured.The net effect of companion planting was carried through to yield in most cases. At Croft, given the significant uplift in crop growth, yield jumped regardless of crop seed rate, averaging 0.30-0.55t/ha more across companion-planted plots, said Mark.At Morley in Norfolk, using the optimum seed rate, the inclusion of companion plants with oilseed rape lifted yield by 0.5t/ha.At Morley where crop growth was more normal, at the high OSR seed rate the effect was neutral, and at the low seed rate there was a slight yield penalty, probably due to a swamping effect. However, at the optimum 15 seeds/m length of row, the inclusion of companion plants lifted yield by 0.5t/ha.
Given the 60/ha cost of seed, further work is needed to assess when the technique is most likely to generate positive returns, said Mark. Trials in 2014 will assess seed rate and establishment methods as well as herbicide screening.Life after neonics
Life after neonicotinoids is one of several new projects being introduced to the 2013/14 Grow Crop Gold trials. It is the fifth year these trials have been running, aimed at developing establishment and agronomy techniques to improve OSR yields and margins.Agrovista’s national trials co-ordinator Niall Atkinson says flea beetle damage will be a major concern for many growers next season after the ban on neonicotinoid seed treatments.Seedbed application of nitrogen and phosphate is likely to become more important, he said. “To reduce flea beetle damage the crop needs to grow away quickly, so this is something to think about.”
Rolling to ensure good seed to soil contact is also vital. “Flea beetle damage is always worse in dry, cloddy seed-beds where the crop is struggling to get away.” Other new projects include evaluation of a novel soil polymer/fertiliser granule and pollinator strips designed to improve OSR yields as well as the environment, says Agrovista.Restructuring benefits OSR rootsRunning a restructuring tine through the ground just ahead of planting oilseed rape is showing real benefits on the Doncaster site included in the Agrovista trials.
Great Plains mounted a Simba ST bar ahead of a Yield-Pro Planter when planting crops in late August, and the combination is already showing clear benefits by producing stronger, better rooted plants, says UK sales director David Holmes. “Yield-Pro planters achieve highly accurate seed placement, which raises yields of crops like maize by ensuring every plant has a dedicated rooting zone and can develop to reach its full potential. We are keen to see whether these benefits can be realised in oilseed rape.”But with OSR being recognised as a ‘lazy rooting’ crop, the company decided to test whether using a tine working to a 200mm depth to restructure the soil directly below the crop rows would provide any benefits.”Sample plants taken from the rows planted by the ST Bar and YP planter show bigger, stronger rooting systems, which is important, as we know that the bigger the root the plant has before the winter shut down the better it is likely to yield.”The better soil structure produced by the ST Bar is a great insurance policy against the vagaries of the weather – whether it turns wet or dry.”If the winter turns wet then the water will be able to drain away freely, avoiding the threat of water-logging which risks drowning the roots.”And, if conditions become dry next summer, we know the plant has a robust root structure that will enable it to seek out any available moisture and so maintain its full yield potential,” he comments.