Wait…before maize under-sowing
With rising soil temperatures and drying soils offering ideal maize-drilling conditions, grass breeder Barenbrug has reminded growers of the soil-health value in under-sowing with grass.
Retention of important nutrients, reduced topsoil loss and improved harvestability are just some of the benefits, but timing and species selection are crucial, says the company’s agriculture commercial manager David Linton.
“We all recognise that maize is a high-risk crop for soil health,” he explains, “and a cover crop like grass is probably the single best move a grower can make to reduce that risk. Yet it remains something of a niche undertaking.”
Water quality is potentially the biggest ‘win’, David points out, because the grass will help retain recognised ‘problem’ nutrients such as phosphorus and nitrates, which water companies regard as potential pollutants along with excess sediment.
“Of course, it’s a grower benefit too. Retaining those nutrients in the soil makes them available for the following crop. Trials have shown how under-sowing maize provides a greater reduction in nitrate leaching than autumn-established cover crops after maize.”
Another concern that David thinks may be stunting growers’ adoption of the practice is a perceived penalty on yield or quality, but trials have proved that under-sowing has no significant effect on yield, ME or starch content. He attributes this concern to inappropriate species selection for under-sowing. “There’s been a tendency to recommend Italian ryegrass, but that can be absolutely the wrong choice, particularly if sown too early,” he warns.
“Think about it. It’s one of the fastest-growing grasses; that’s why farmers like it. But those same attributes – rapid germination and swift establishment – present a competition problem for maize, particularly during the first six weeks post-emergence.
“There’s also the consideration, especially where arable farms have added maize to the rotation – for example for AD – that IRG is a weed species. You want to avoid purposely introducing what may become a weed burden.”
David’s suggestion is two-fold: let the maize establish first without grass and avoid the ‘Italian mistake’ by sowing alternative varieties when the maize has reached 6-8 leaves.
“There’s further benefit from a species like tall fescue,” David continues, “because of its deeper, branched rooting system. This provides a much bigger boost to soil structure and health post-harvest, as well as being able to ‘soak up’ nutrients from a far greater volume of soil.”
What’s more, David says fescue’s branched rooting also improves the soil’s ‘bearing capacity’ – essentially allowing the soil to take a greater load without damage, a worthy consideration if conditions turn wet before or during harvest.
Barenbrug has developed a ‘maize-friendly’ green cover option, utilising the company’s proven tall fescue genetics. David says it’s been selected for a combination of traits – those that favour fast germination, to get the seedling out of the soil quickly, but also slower growth post-germination to avoid presenting competition for the growing maize crop.
“Our recommendation for Proterra Maize is to wait until the maize has reached the 6-8 leaf stage, then sow at 12kg/ha with an inter-row drill.
“Proterra Maize presents a better option than Italian ryegrass, especially for fields in an arable rotation, and assures the grower that – rather than ‘any old grass’ – this is a cover crop that won’t rob the maize of sunlight, moisture or nutrients,” David says.
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