THE cultivators are out and the seed drills going – but all might not be as it seems.

Many of these machines will actually be cultivating ground for catch crops, or cover crops grown for reasons other than just to be cropped. The machines have to be fast and work big areas to make the job worthwhile.

The process is becoming popular in England, but now ground breaking research trials into the impact of green cover crops in Scotland, have demonstrated notable benefits for spring barley yields, soil and water quality, biodiversity and soil resilience.

Conducted by the James Hutton Institute and Kings Crops, a division of Frontier Agriculture, the three-year trial assessed ongoing soil conditions and compared yield results from Concerto spring barley. The crop was grown on plots previously planted with either green cover crop mixes or control stubble from another barley crop.

As well as improved organic matter and overall soil conditions, the seven cover crop options led to barley yield increases of up to 0.6t/ha by the third year. In particular, Defender oil radish showed the most impressive results, followed closely by the radish mix (oil radish and tillage radish) and the Kings Soil Vitality and Soil Structure mixes. The impact from the over-wintered stubble was minimal in comparison.

This trial took place at the James Hutton Institute’s Balruddery Farm, in Dundee, with the first cover crops drilled in September, 2015, following the spring barley harvest. Kings’ technical advisor for Scotland, Alan Johnson, explained: “The conditions for planting and growing cover crops in Scotland are different to the rest of the UK. Cooler temperatures and later harvests mean the window for successfully establishing green cover is much smaller than in other areas, which can make some growers reluctant to grow it.

“As a result, it was important that this trial replicated realistic conditions and timings so we could gather accurate results, assess the outcomes and identify the benefits. We see plenty of examples in other areas where cover crops improve the outputs of cropping and bring about significant environmental benefits, so it’s important to better understand the options available to growers in Scotland so they can capitalise on these benefits too.”

Cover crops are fast-growing annuals which, when planted between two cash crops, play a significant role in harvesting and recycling valuable nutrition, improving soil structure, reducing erosion and benefitting farm biodiversity. Hence, their inclusion can form part of a cropping strategy to advance ‘natural capital’ and safeguard soil, boosting yields and delivering financial savings.

The options used in the trial comprised Jupiter turnip rape, Kings Structure Mix, Defender oil radish, radish mix (oil radish and tillage radish), Kings Vitality mix, vetch and rye and Kings EFA mix (mustard and oats).

For the duration of the trial, each crop was repeatedly sown after the barley harvest in the same field alongside a control stubble with all plots GPS fixed. They were drilled in 200m by 6m strips over a block of 6.9ha. Fertiliser was applied alongside the seed, comprising 30kg nitrogen (N), 5.4kg of potassium (P) and 19kg of potash (K) per ha.

The cover crops were ploughed in April and the fields drilled with Concerto spring barley shortly afterwards. In the first year, tests showed that the soils were already more resilient. The risk of erosion had reduced and there was an increase in organic matter content where a cover crop had been.

In the second year, these benefits continued alongside differences to the following Concerto barley crop, with the mean yield increased by more than 450kg per ha between 2016 and 2017.

While barley yields were slightly lower in the third year due to the dry season, they were still much higher than the strips that were left over as winter stubbles.

Additionally, the consistency of nitrogen levels within the harvested grain samples was better. Previously, there had been a general concern that improving soil fertility may bring nitrogen levels up in the barley and cause it to miss malting specifications, but this was not the case.

Dr Blair McKenzie, soil scientist at the Institute said the crops faced three very different winters. “The 2015-16 year was one of the wettest, while 2016-17 was nearer average and 2017-18 had a very cold finish with the ‘Beast from the East'. This meant that the state of the cover crops into March also differed between years. Despite this, the soil conditions and barley yield were consistently better under the cover crops than in soil that had been left with cereal stubble over-winter.”