With subsoil compaction difficult to quantify at field-scale, PhD student Joseph Martlew of Cranfield University has been working with NIAB TAG to investigate methods to quantify and alleviate it in arable soils.
Discussing his results so far in the Horsch-sponsored Soil Hub he highlighted the influence of cover crops in the rotation.
“Repeated use of cover crops in the rotation had a small positive impact, improving subsoil structure and reducing subsoil compaction in the field,” he said.
But in a laboratory experiment, the bio-drilling action of cover crops had a limited impact on subsoil compaction and crop performance following a single season.
“However, this is perhaps not surprising as it was a tall order to expect a single plant to modify compaction in a single season,” said Mr Martlew.
Image analysis software (x-ray CT images) captured benefits of cover crop rotation to subsoil structure that were overlooked by traditional field and laboratory methods, he added.
“In some ploughed plots, it looked as though there was a compacted pan. But on closer inspection, using x-ray CT image analysis, porosity was fairly good, and perhaps indicated a functional pan where water, nutrients, roots and gases could pass through. In fact, the pan may have been protecting the deeper subsoil from damage by vehicular traffic. It shows we should not rely on a single method to characterise subsoil compaction, or compaction, more generally, to get a true idea of what is going on.”
Also speaking in the Soil Hub, Mike Harrington, director and senior agronomist at Edaphos, explained how soil regeneration using practices such as growing cover crops, can help growers move to a lower-input system.
It is possible to reduce nitrogen applications by building natural capture of nitrogen through cover crops scavenging and retaining nitrogen in the system, said Mr Harrington.
“We are having to look at changing the way we manage N applications in these systems. With two wheat blend crops in 2020 harvest, yield average was 7.8t/ha and we applied 100kg/ha of nitrogen. Last year the yield was 9.4t/ha with 120kg N/ha applied and just one fungicide at flag leaf.”
Reducing inputs such as artificial N which may increase the susceptibility of plants to disease, could help reduce reliance on chemicals, suggested Mr Harrington.
“The way we manage crops will be hugely different to the considerations we have at the moment from RB209. We are beginning to reduce N application but we also need a safety valve such as tissue testing.”
Taking account of nutrients in cover crops and their availability is already influencing crop nutrition programmes.
Mr Harrington gave an example of a mustard cover crop and the nutrients it had captured. “The mustard captured 270kg N/ha, 143kg K/ha and 30kg P/ha in the top growth.
“Not all the N is available, it depends on when the cover crop is taken out, how long it takes to be digested and recycled and when the following crop is drilled as to how N comes into system. But no doubt it is a fantastic way of collecting nutrition we would potentially have lost.
“Many farms are moving from K Index 1, or even 0 to 3s and 4s through reallocation of nutrients from deep down being brought up to the surface. It means we have to look very carefully at how we introduce information on managing crops going forward. Farms able to drop P and K need to be able to manage accordingly as stresses and strains come in.”