Dorset grower John Martin, together with Kings Seeds, has designed his own cover crop mix, which provides the maximum benefit to his calcareous soils while also being cost-effective.

He was first encouraged to use cover crops on Deverel Farm, in Milborne St Andrew, in 2007 by Wessex Water to help reduce nitrates leaching into drinking water, as a borehole is located on the edge of the farm.

Being in a drinking water catchment area, Mr Martin receives £60/ha to grow his cover crops, which is covering his costs while also increasing the organic matter content of his soil, and feeding the bacteria.

See also: Practical tips for establishing cover crops

Since 2007, the soil organic matter content has increased by 1.5%, building in extra moisture-holding capacity into the chalk soil, which has some clay cap.

Spring cropping

After getting out of dairy in 2000, Mr Martin now grows 300ha of combinable crops on a rotation of winter wheat then spring barley, followed by alternate breakcrops of oilseed rape and large blue peas.

Mr Martin is happy to have about two-thirds of the farm in spring cropping if it means that the organic matter of the soil can be lifted.

“There is no silver bullet to improving yields, it has got to come from the soil.

The chemical experiment is coming to an end – we can’t get all the answers out of a spray can.

“Whatever we grow as our main combinable crop is not necessarily good for the soil, so for six months I grow for the combine, and the other six months I grow something for the soil,” he says.

Soil bacteria have varying needs, so Mr Martin tries to grow as much of a mix as possible, but cost is an important factor.

About 80ha of cover is grown for the Countryside Stewardship’s mid-tier scheme, which pays £114/ha.

A further 40ha located close to the borehole is funded through Wessex Water to reduce nitrate leaching.

When funded through one of the two schemes, Mr Martin budgets to spend £30/ha on cover crop seed, but if he was funding it entirely himself, he would only spend £15-£20/ha.

© Tim Scrivener

“The price that Wessex Water pays does cover the costs of growing the cover crop if you are efficient.

“If you are going to make multiple passes it won’t, but if you are going to make one pass with  seeder mounted on the cultivator then it will,” Mr Martin says.

Comparing options

Conscious that the cover crops farmers in water catchment areas are being encouraged to grow also need to be cost-effective, Wessex Water has been running a trial of different mixes with varying costs on Mr Martin’s farm.

Different combinations of oil radish, phacelia, linseed, lupin, buckwheat, vetch, burseem clover, red clover and spring oats were drilled at various seed rates to give a seed cost ranging £10-£30/ha, so that growers can compare effectiveness against cost.

Despite holding the trials for Wessex Water, Mr Martin is happy with the mix he has been growing for the past couple of years (see “Crop seed costings”, above), which includes buckwheat for phosphate, and sunflowers for biodiversity.

© Tim Scrivener

He also adds a bit of oil radish into the mix to ensure there is good growth if the cover crop is sown later, as the oil radish will successfully establish later than some other components of the mix.

In June, he orders £30/ha worth of seed with the hope that if the cover can be drilled in August, the seed rate can be lowered and some seed held back for the following year, reducing the cost.

Mr Martin aims to have all of his cover crops sown by 4 September, but last year due to the early harvest he was finished by 15 August, so he has some seed saved over for next year.

Case study: Jake Freestone. Gloucestershire

Cover crops play an integral role in Gloucestershire farmer Jake Freestone’s no-till system, helping to lift the organic matter content of his soils from 1.1% to 2.5%, alongside a policy of chopping and retaining straw.

Establishment costs on the 900ha arable unit have been slashed from £169/ha before 2004 when the farm was plough-based, to just £52/ha now.

However, cover crops are an additional cost and Mr Freestone warns that growers can spend a fortune on them if they want, but by home-saving seed, like he is with buckwheat and vetch, costs can be reduced.

Growing companion crops and grazing covers are also ways Mr Freestone is increasing the cost-effectiveness of his cover crops.

For a seed cost of £30/ha, he is growing vetch and burseem clover in with his oilseed rape, and reaping a net financial benefit of £35/ha in reduced herbicide, fertiliser and insecticide costs.

This excludes any benefit to the soil or nature.

His 1,200 ewes are also being fattened on a mix of turnips with vetch to host mycorrhizal fungi and increase nitrogen.