Establishing an overwintered green cover on continuous maize field stubbles is becoming increasingly important to reduce soil erosion and to improve soil health. RAGT’s David Ramdhian assesses the options.
Leaving maize stubbles bare overwinter is no longer tenable. The heightened risk of soil erosion, nutrient loss and damage to soil health is too high a price to pay, and not only for affected farms.
Run-off from fields is also coming under increasing scrutiny from water companies and environmental pressure groups, and unless steps are taken to prevent it, maize growing may be severely restricted or even stopped in some areas in the not-too-distant future.
Where a following winter crop is not an option, the most effective way of avoiding these problems is to establish a green cover that will put on enough bulk to adequately protect soils over winter.
Such a cover will bind soils together while keeping them friable and aerated, improving their structure and supporting soil biology. They will also take up nutrients for release into subsequent crops.
One way of establishing a cover, particularly on heavier ground with late-maturing maize varieties that may not be harvested until late October, is to undersow with a grass mix.
However, maize is very sensitive to early competition so if the grass is sown with the maize, it is vital to choose slow-growing mixtures, such as fescues, but even then it is not an exact science.
Experience suggests that to avoid compromising yield it is better to wait until the maize is established with 4-6 leaves before undersowing. This does mean a second pass with a drill that is set up to sow grass between maize rows, which may mean employing a contractor, and there is always a risk that you damage the maize at this point.
The best species choice at this timing is probably a fescue/perennial ryegrass mix that establishes rapidly and can grow in shade, but is not so aggressive that it holds back the maize.
I believe a much simpler and more reliable approach is to choose an early-maturing maize variety such as RGT Duxxbury, RGT Agiraxx or RGT Pixxon and establish a green cover after the crop has been removed at the end of September or the first week of October.
There are plenty of cover choices – in some cases a simple black oat or grass cover that can offer an early bite before the field is returned to maize the following spring will do the job.
Sometimes more is needed. RGT Maize Expert is a mix of brassicas, oats and ryegrass specifically formulated as an effective overwinter break crop in maize rotations.
As well as protecting the soil surface, its intensive rooting system occupies different horizons of the soil, effectively repairing and improving structure.
The plethora of roots also captures nitrogen efficiently, a key benefit at any time but particularly given current fertiliser prices. The captured nitrogen will be released into the following crop as the cover material breaks down.
Given that soil conditions should still be good when the maize is cut, creating an adequate seed-bed for any of the above cover crops should be relatively simple; simply scratching seed in can often work well for minimal cost.
I believe the potential benefits of choosing an early early-maturing maize variety outweigh the perceived advantage of growing a later one – ie bulk.
Early maturing varieties have come a long way in recent years, narrowing the yield gap on their later counterparts and offering high quality, highly digestible forage that can be gathered in good conditions with minimum hassle, while leaving plenty of time to protect soils over winter.