Work at Agrovista’s cover crop trial site at Blagdon, Northumberland, reveals benefit of using roots and cultivations to better soil structure and crop establishment.
Abby Kellett reports.
While traditionally, cultivation has been a common way of breaking through soil compaction, improving infiltration and creating soil tilth, more recently, cover crops have proven a useful tool in improving soil structure. But the combination of both roots and steel together provide an even greater benefit, according to Agrovista.
The company’s technical manager, Chris Martin says: “Unless you have perfect self-structuring soils, you are always going to need a combination of roots and metal, you will never get away with just one or the other.
“Our trials have shown that where we just use metal, in the form of subsoiler legs, we are able to lift the soil but nothing more. Where we use cover crops alongside metal we get good soil fracture and the roots colonising the remaining soil clods.”
See also: AHDB funded review uncovers cover crops
In a comparison of 16 cover crop varieties at the site the extensive root network of black oats proved particularly effective in breaking up soil aggregates and in retrieving immobile nutrients from the soil.
“Black-oats have lots of fibrous roots, which can reach parts of the soil that other roots cannot. Its roots are able to gather tightly bound nutrients like phosphate, making it available to the next crop.”
Because of this, he suggests black oats are a key cover crop component.
Where there is a need to remove compaction, cover crops with deep, aggressive tap roots such as berseem clover and radish should also be considered, according to Mr Martin.
Results from 2016 trials, which looked to evaluate the use of April-drilled berseem clover ahead of OSR establishment, also highlights numerous benefits – predominantly in aiding soil workability as well as by improving the growth of OSR.
“We looked at using berseem clover with and without a subsoiler and found that where we had used a subsoiler leg, the drilling tractor used 9.26 litres less fuel, the draft was reduced by 31 per cent and the engine torque was reduced by 23 per cent – so significant tractor savings.”
But the berseem clover made a notable contribution in aiding OSR establishment and growth. “When we measured the size of the crop in November, where we have no berseem clover and no subsoiler, the crop canopy contained only 30kg of nitrogen and 6t/ha of fresh weight.
“Where we put the berseem clover with no subsoiler used, we doubled the nitrogen and fresh weight in the crop canopy and encouraged the crop to establish significantly better.
“However the best results were recorded where we put the berseem clover and the subsoiler together – showing the real benefit of using roots and metal together.”
Going forward, Mr Martin sees cover crops, such as berseem clover, as a means of reducing cultivation depth. “The more we move soil, the more we weaken it. If we could move less soil with metal, it is going to be more efficient on the tractor and it is going to do less damage to the soil.
“You will also get less surface slippage and so less surface compaction. I think that is the real future of OSR growing.”
By reducing reliance on metal, Mr Martin said growers could boost the biological activity of their soils. “Where we used cover crops as opposed to leaving land fallow, there was a significant increase in bacteria, protozoa, earthworms and, in particular, soil fungi.
“When you put a tool in the ground you are always going to interrupt that fungi so it is important this is compensated with roots,” he says.