As featured in Arable Farming Magazine
Tools to take cover with
by Arable Farming August 2020
The benefits of cover crops are being explored by many growers, but careful management is needed to ensure residues do not hamper the following crop. Jane Carley gets guidance on destruction principles and looks at tools for the job.
Management of cover crop residues often depends on the drill to hand and the drilling philosophy for the following crop, says agronomist David Felce, whose work for Agrii includes cover crop trials on heavy land at Stow Longa in Cambridgeshire.
“Do you need to move soil and create a tilth, or are you aiming at low disturbance, and is it a disc or tine drill? Drills which move less soil may need help from a cultivation tool,” he says.
Where the cover crop is destroyed by spraying, timing ahead of drilling becomes significant, says Mr Felce.
“Generally, six weeks is needed before establishing the next crop. The results are better if the cover crop is comprehensively removed as it can use moisture needed for the cash crop or create a shading effect if left for too long, which can prevent the soil surface from drying out to create a friable drilling surface in spring.”
Trials have shown a visible difference between springdrilled plots where cover crops were removed earlier and those drilled ‘on the green’.
“Cover crops established in late August should be sprayed off at Christmas, as they will have achieved their purpose by then; those with a good rooting system will continue to offer benefits even when the top is killed off,” says Mr Felce.
“We have found that where the purpose is restructuring, the best results are achieved by a combination of ‘roots and metal’.”
The requirement to work into cover crop residues has become more significant as bigger mixes are used to get the rooting effects – these are more difficult
to kill off than mustard or buckwheat and can return as volunteers.
In order to chop residues or green material without excessive soil movement, a disc must offer a vertical chopping action rather than sliding across the surface,
says Mr Felce.
“Disc drills offer lower disturbance, but can lead to hairpinning and poor establishment in heavy residues.”
For drills with sufficient coulter pressure to cut through trash, such as a John Deere 750A or Sky drill, a crimping tool may be sufficient, either on the front
of the drill itself or front linkage of the drilling tractor.
“This could work where there is a good cover crop canopy, it hasn’t been sprayed off or was sprayed off late and is still anchored in the soil. The tool simply lays the crop down to allow the drill to cut the seed in.”
Tine drills can also work into crimped cover, although the long material can cause them to block up, so good tine stagger and spacing is needed, Mr Felce says.
When working into green cover which will be retained, a grass rejuvenation type drill such as the Cross Slot or T-Sem can work well, ‘stitching’ the seed into friable soil below the cover.
“You can also use a disc drill with good coulter pressure, but those with cultivation elements are not ideal as they will destroy too much of the sward.”
Tools to tackle residues
Where cover crops have created a competitive crop canopy to encourage black-grass germination, allowing the weed to be sprayed off before drilling, it is important to avoid stimulating growth of grass-weed seeds buried in the soil profile at drilling.
That is according to Amazone UK managing director Simon Brown, who says a minimum disturbance drill, such as the Cirrus Minimum TillDisc, the wavy discs on the front of the Cayena tine drill or the Condor or Primera wider spaced tine seeders, move very little soil and are suitable for this purpose.
Mr Brown adds that where cover crops are used to improve soil structure by their root development, breaking up the soil crumb and adding organic matter to feed soil biology, cultivators are useful to chop and mix.
“This can be achieved by the Catros XL or Certos 02 where the disc diameter is bigger, designed to handle more organic matter.
They have much more clearance both between the two rows of discs and between the rear discs and the roller to allow the larger amounts of residue to pass
through and are designed with cover crops in mind.”
An alternative is the new knife roller on the Catros range, he suggests.
“The front knife roller can also be used to bruise the crop rather than mulch it, retaining the cover.
There is a school of thought that we shouldn’t ‘crop the cover crop’ prior to drilling.”
When the requirement is to terminate a standing cover crop, a full cut-out at ultra-shallow working depth provides high capacity and agronomic benefits suggests Vaderstad UK marketing manager Andrew Gamble.
“Working intensively at 0-3cm depth, the CrossCutter Disc crushes and mulches the cover crops without mixing the residues to depth. After one pass, the
cover crops stems are crushed and access points for microorganisms are created.
“By cutting across its entire working horizon, the CrossCutter Disc completely breaks the capillarity of the surface, conserving valuable moisture for the following crop. The ultrashallow working depth ensures a minimum amount of soil is dried out, while the high amount of residues left in the topsoil helps reflect sunlight to further conserve moisture.”
The System Disc on the Rapid drill is designed to create a small amount of tilth in front of the coulter to cover the seed after it is drilled, explains Mr Gamble, allowing the drill to be used in direct or min-till conditions.
“The single disc seed coulter penetrates the soil with a high coulter pressure of 150kg plus, resulting in an exact seed depth, while the aggressive seed disc creates a clean seed slot without straw incorporation, irrespective of soil type or tillage-system.
“For drilling direct into cover crops, we designed a kit which can change the traditional two rows of coulters into a three-row system, increasing the flow of
trash and preventing blocking.”
The Sky drill has been used with success to drill into cover crops in France for several years, explains Opico’s He-Va product manager, Glenn Bootman.
“It will work directly into less advanced cover crops in autumn, and you can also drill into mustard or radish-type mixes in spring, although grass-based mixes will need spraying off. The front rubber roller lays down the crop so the discs work into it.”
He-Va has seen growing interest in its Crimper Roller, he notes.
“The crimper is mounted on the front linkage of the drilling tractor and bruises the cover crop to aid its breakdown rather than cutting into it. It’s ideal for a one-pass no-till regime as there’s no need for soil inversion to destroy the crop.”
Kuhn’s Aurock drill can be equipped with a crimp roller as part of its modular build which can adapt to work in min-till or direct drilling conditions.
Product specialist Will Waterer says: “The optional crimp roller works across the full width of the drill and can be adjusted to apply more or less pressure depending on the density of the cover crop.
“Its action is to roll down the cover crop and produce a mat to drill into, terminating a cover crop without the use of chemicals.
The crimp roller pushes down the cover in the direction of travel, and the length of the drill ensures residues flow through the opener and seeding discs.”
Mr Waterer points out it is not always necessary to chop the cover crop to drill into it, and this allows the cover to be left in place as long as possible, a technique attracting increasing interest, including in zero-till organic crops.
For farms which have committed to cover crops, the Aurock also offers the possibility to drill up to three different crops at once, two at different depths, which could prove useful to establish cover with two sizes of seed, such as peas and mustard, rather than sowing a mix all at the same depth.