Post-harvest cover crop choices 

With harvest well underway, now is the time to think about soil condition and quality, and improve its productivity. Limagrain UK has used results of its trials on a range of cover crops to develop seed mixtures that can fulfil these roles.

“Overall, our results showed that the benefits of a cover crop such as biomass production and nutrient capture, that reduces leaching, can easily cover establishment costs,” says Limagrain seed specialist John Spence. “And further benefits are possible from selecting specific mixtures.”

Trials were carried out in 2015/16 on sites in Lincolnshire with varying land types. Two single varieties and four mixtures were each drilled directly into 0.4ha stubble plots using a Sky Easy drill or a Dale drills Eco drill. Samples were taken at regular intervals and measured for biomass and nutrient retention.

“Oilseed Radish and mustard were compared with four Limagrain catch and cover crop mixtures all with specific attributes,” adds Mr Spence.

Limagrain’s John Spence

These mixtures, Lift ‘N’ Fix – a rye and vetch mixture, Sprinter – a black oats and vetch mixture, Soil Improver with oats, oilseed radish, phacelia and mustard and Green Reward with rye, oat, oilseed radish, tillage radish, mustard, vetch and phacelia, all yielded between 2 and 2.5 tonnes of dry matter per hectare in a 12 week growing period, with the mixtures Green Reward and Soil Improver producing more than 17t/ha of green organic material.”

Based on N, P and K found in the green material after eight and 12 weeks, Limagrain has calculated a nutrient value for each mixture and showed that each can uplift significant quantities that would potentially have been lost if the land was left fallow.

“Lift ‘N’ Fix was the most successful – designed specifically to capture nitrogen – with more than 100kg of N being captured by the mixture, which, with the value of P and K based on current fertiliser prices (ammonium nitrate £210/t, triple superphosphate £275/t, muriate of potash £240/t) is worth £126.85 a hectare.

“If we include the value of the nitrogen fixed by the vetch and £15 worth of sheep grazing we have a crop value for Lift ‘N’ Fix of £152/ha. This outweighs the growing cost of Lift ‘N’ Fix of £138/ha.”

Based on the trial results, Limagrain calculated the value for Soil Improver to be £156/hectare. “This mixture includes species with a variety of different rooting depths which help to relieve compaction through the soil profile,” adds Mr Spence. “It is the mixture we recommend when soil compaction is the main priority.”

Sprinter, a fast growing mixture that supresses weeds and is ideal where blackgrass control is a priority, had an estimated value of £148/ha. All three mixtures satisfy EFA criteria. Green Reward, the final mixture in the trials is a premium multi species mixture which covers all bases as a cover crop giving high biomass, soil conditioning and compaction alleviation as well as blackgrass control.

“The cost of growing a single species cover crop may be covered by short term benefits like weed suppression and nutrient capture, but, for the same growing costs, farmers can reap additional benefits by using specially designed mixtures that fulfil specific roles.

“A poorly designed or poorly established cover crop will bring few benefits above leaving the land fallow and may cause more problems than it solves. And simply selecting the cheapest crop that is EFA compliant could be a missed opportunity whereas mixtures designed to meet specific requirements will bring additional short term benefits and the longer term use of these well designed cover crops will also lead to improvements in soil health and organic matter.”