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Under-sowing maize can boost output – and be good for the environment, says Phil Billings. Big benefits from protecting watercourses by under-sowing maize

Under-sowing maize can boost output – and be good for the environment, says Phil Billings.

The uptake of under-sowing maize is on the rise and an establishment technique that more farmers are exploring. Doing it successfully is a fine art so careful planning is required to achieve optimum results

Timings are key to the success of under-sowing maize, so close attention is needed. The timings of under-sowing very much depend on the maize maturity rating, weed profile and soil type.

Most people choose to under-sow with grass once the maize is established as otherwise, if drilled at the same time, it can cause weed management complications and outcompete the crop, taking energy away from cob development.

The size of the maize cob is determined up until the eight-leaf stage, so it’s essential that the crop gets off to a good start, as this is what affects the ME or metabolisable energy, and protein in the silage.

It’s also best to select hardier grass varieties, such as fescues or perennial grasses, as they’re likely to better withstand the harsh conditions they could be exposed to.

There are two different under-sowing options:

  • 1) If you are planting an early maturing maize variety and planning to harvest in September, apply a post-emergence herbicide before the four-leaf stage so the grass seed can be planted around the six-leaf stage. This allows the maize to become well established before the grass emerges. It may mean the grass is slower to establish, but it will grow out well after harvest.
  • 2) If you’re planning to harvest in October and plant a late maturing maize variety, drill the grass seeds once the maize is around the four-leaf stage. However, before planting the grass seed, apply any herbicides that are required. The post-emergence herbicide should be applied before the four-leaf stage, so the grass seed can be planted, and emerging weeds don’t ‘rob’ yield from the maize crop.

A disc coulter is the most reliable way to plant the grass. It allows for a firm seed bed and good soil-to-seed contact, which is key for optimum establishment. If wet weather is expected drill the grass before the rain if possible, to avoid soil compaction when travelling over the ground.

Optimum timings

Another top tip is to not under-sow your entire maize crop in year one. Planting a small area initially will allow growers to understand the optimum timings for drilling the maize and the grass, before rolling it out across the whole farm.”

I’d always advise farmers to ‘hope for the best, but plan for the worst’ when it comes to the weather and growing maize, that way they’ll be better prepared to deal with unexpected changes.

Harvesting an under-sown maize crop should be no more difficult than a traditional crop. If the timings are right from the outset, the grass should not have outcompeted the maize and grown tall enough to interrupt the harvest.

Once you’ve cut the crop, you’ll be left with a layer of grass biomass on the surface protecting the soil from rainfall. But below the ground, the root mass will have grown considerably, resulting in a high level of microbes and rhizosheath around the root, improving soil structure, infiltration, and carbon storage.


Live roots in the soil allow microbes to thrive, which is fundamental for the storage of carbon and nutrients such as nitrates, potassium, boron and many more, whereas bare soils cannot capture the sunlight and therefore prevent these processes from happening.

An under-sown crop will store these nutrients in the soil, making them readily available for uptake by the following crop. It’s key to keep the workforce of microbes and worms in the soil thriving, so they can benefit future crops in the rotation.

On top of the beneficial carbon and nutrient capture an under-sown maize crop brings, there are also major environmental benefits such as reduced run-off, soil erosion and leaching.

They can also provide financial benefits for farmers in that the nutrients captured in the soil can help fund the next crop, as producers don’t need to replace lost nutrients with slurry or fertilisers. Alternatively, the leftover grass can provide valuable grazing for sheep or cattle.

Phil Billings is an agricultural adviser at Severn Trent. If you are interested in under-sowing maize on your farm, contact your local Severn Trent agricultural adviser or visit for advice and funding.