Part article taken from Crop Production Magazine
Written by Lucy de la Pasture
Black oats and vetch mixtures are popular, with vetches supplying N fixation while the oats are reported to have an allelopathic effect on some weeds. Where clovers and vetches are included in the cover mix then destruction with glyphosate may not be as reliable –– legumes are one of the few weeds poorly controlled by glyphosate. Peter Cowlrick points out that full control may not be necessary depending on the following crop and chemistry available. “An effective alternative to glyphosate for cover destruction are products containing 2,4-D plus glyphosate, which should give better results on vetch and clover.” On its trials site at Lamport, Agrovista has been looking at the role cover cropping can play in the rotation to manage difficult blackgrass. Niall Atkinson is the man with his feet on the ground at Lamport and stresses that minimal soil disturbance is absolutely vital when drilling into a cover crop. The reasoning is simple, he says. The cover crop (which has to be established by Oct 1 under the Basic Payment Scheme rules) allows a healthy population of blackgrass to establish underneath the canopy, depleting the seedbank, he explains. The main objective is to kill this off and not stimulate further blackgrass germination when drilling the following spring crop. “The idea is to collapse the canopy to gain access to the blackgrass and other weeds lurking underneath. You generally need to burn off the cover about six weeks before the planned drilling date, so to establish a spring cereal crop you’ll be looking at a glyphosate (2 l/ha plus adjuvant, such as Companion Gold) application in early Feb. “If the cover contains black oats, these could be knee height by the time the first desiccation timing is reached. A second application of glyphosate, ideally seven days before the target sowing date, will be needed to take the blackgrass out,” he explains. One of the major benefits a cover crop brings is soil conditioning, believes Niall Atkinson. “Compared to ground which has been left fallow or winter ploughed, the surface layers of the soil will be damper because the cover holds the moisture. Practically this means drilling may potentially be a few days later but it’s important to wait until surface conditions are right and not force the crop in,” he stresses. “What you’ll find is that where the fallow and ploughed land has a dry crust on the surface, it’s still wet underneath. The cover crop is the opposite, damp on the surface and drier underneath, and has structure which will benefit the spring crop being planted.
Drill setup key to cover crop success
When it comes to crop establishment after cover crops, drill setup is extremely important, says Agrovista’s Niall Atkinson. “Although direct drilling is preferable, it’s not essential. Much of the work at Lamport has been done with the Great Plains Spartan, but conventional drills can do a good job, provided they’re adjusted to minimise soil disturbance. The cover crop has been restructuring and working the soil so you don’t necessarily need to direct drill, though a disc drill is preferable to a tine drill,” he notes. “To adapt the Väderstad Rapid to drill into cover, lift the System Disc clear of the soil. If you have GPS then keep the bout markers up, make sure the track eradicators and rear scratcher tines are also lifted out of the ground. On the Väderstad Rapid there are different coulter settings against the disc and this is factory set on the middle setting. You’ll probably need to adjust this to the top setting so that the disc is cutting the slot and the coulter sits above, placing the seed.” For the Claydon hybrid drill, the standard setup has too much soil disturbance, he advises. Either change to the wet weather setup or to the low disturbance option using the disc to cut through the trash. Dale has also developed a modification for their Ecodrill especially for use in cover crops, replacing the opening tine with a disc instead. One of the things growers will find really noticeable is that the seedbed will always look scruffier than normal, warns Niall Atkinson. “The cover crop is still fastened to the ground by its roots and the drill will just comb through the material on the surface. That means drilling will probably be slower than usual to avoid soil disturbance, more likely 8-10km/h instead of 12-14km/h. On the plus side, the roots of the cover crop hold the soil, minimising soil movement and therefore blackgrass germination.” Getting the seed rate right is another key to successful establishment into a cover crop. “At Lamport we’ve been using up to 500 seeds/m2 –– you don’t want to be in the conventional region of 250-350 seeds/m2 ,” he advises. As far as fertiliser application goes, he prefers combined application at drilling if available. If not, apply fertiliser just ahead of the drill, with 50% of planned nitrogen applied to the seedbed,” he suggests. Another point to be aware of is that you may not get full closure of the drill slots when surface conditions are slightly damp. “It’s preferable to run a set of rolls over 24 hours after drilling when the surface has dried a little to complete closure of the drill slots and maximise soil-to-seed contact,” he adds.