Undersowing maize with grass can provide a valuable green cover crop after harvest to reduce damaging soil erosion and nutrient loss often seen in over-wintered bare stubbles.
Ongoing trials led by Agrovista in partnership with Reaseheath College and Pottinger UK, have confirmed that provided the right species are sown at the right time and in the right place, the
technique does not negatively affect maize yields and can even enhance them.
“Growing maize and grass together is gaining favour in Europe with farmers who need to keep in line with tightening environmental legislation,” says Agrovista agronomist John Ball.
“It is a technique we’ve been keen to examine here to help future-proof the crop. Concerns over the environmental impacts of maize are increasing. Leaving bare maize stubbles may soon no longer be allowed.”
Two years of large-scale in-field trials at Reaseheath College, Cheshire, based on several years of earlier small plot work are producing new recommendations to help growers achieve optimum results, says Mr Ball. Sowing the grass at the same time as the maize has produced the most consistent performance but maintaining a 15cm gap between maize and the companion plant is key.
“In both years we used a Pottinger Aerosem seed drill to establish the maize in 75cm row widths and sow grass in three rows spaced equally between the maize. This achieved the all-important 15cm gap between the different species, to prevent the grasses from smothering the crop.”
To help further, the maize variety Pioneer P7326 was chosen for its good early vigour.
In 2016 a range of grass-based mixtures were tried, but tall fescue produced the best results in terms of cover and also produced the best yielding maize crop, at just over 21t DM/ha.
“The other grasses were not far behind in terms of maize yield, and overall we saw a small uplift from sowing companion mixtures with the maize. However, these grasses were nowhere near as good as tall fescue in terms of providing cover once the maize had been cleared. The ryegrass grew too rapidly and ran out of steam in mid-August, so there was much less green material present after harvest while creeping red fescue was mulched by harvest traffic. The tall fescue had a much bigger root system and grew more steadily, so was able to pick up quickly once the crop was gone.”
The increased maize yield was probably due to the grassroots improving soil condition, allowing the crop, which is a weak rooter, to exploit more of the soil profile, says Mr Ball. The tall fescue was also good at smothering weeds.
In 2017 the mixtures were fine-tuned, based on two Agrovista Technisward mixtures.
Soil Max is a combination of tall fescue and Advanced tall fescue.
The Advanced component of the mix is a tall fescue/ryegrass cross with good persistence and stress tolerance - important under maize where moisture and nutrients can be scarce.
Enviro Max is a mixture of late perennial ryegrass and Advanced tall fescue.
Soil Max produced the best maize yield of the two grass mixtures, at 18.5t DM/ha and produced the best over-wintered cover crop by far, says Mr Ball.
Although including vetch to the mix increased yields, the resulting cover crop was poor and thin.
“It brought nothing to the party but added to the seed cost,” says Mr Ball.
“As a result of these trials, we are now recommending Soil Max as the companion crop of choice when drilled at the same time as the maize. As well as providing the best yield/cover combination, the slow-growing tall fescue and Advanced tall fescue help to suppress weed emergence and retain residual nutrients post-harvest, thanks to a large and deep root structure that also benefits the soil profile.”
The mixture also offers good grazing for sheep, an added benefit of this technique, says Mr Ball.
Standard herbicide treatments can be used successfully with the one-pass establishment technique.
In 2016, a post-em strategy was employed using mesotrione, which generally worked well, although control was less effective in some areas.
In 2017, a pre-em treatment of pendimethalin followed by mesotrione + pyridate at the three-to-four leaf stage was used. “We achieved better weed control and the grass came though well – we didn’t see any adverse effect in terms of establishment,” says Mr Ball.
Growers without access to a Pottinger drill could adapt other maize drills to sow grass between the maize rows and preserve the 15cm gap, he adds.
“However, the key is to drill the seed or at least ensure it has good seed-to-soil contact, rather than using a seeder box where establishment can suffer, and you lose the gap between the maize crop and grass, so competition and shading losses increase.”
Over-sowing grass
Further work during 2016 showed it is possible to establish the grass post drilling of the maize crop.
In 2016, several grass and legume mixtures were over-sown when the maize had four to six leaves, using an Aitchinson direct drill.
“It produced some good results, but it was more difficult to maintain the maize/ grass gap and shading of the companion mixtures was more of a problem at this stage,” says Mr Ball.
“The perennial ryegrass/tall fescue mix achieved the best results. The ryegrass established more quickly and, because it was sown at a later date, did not suffer from early senescence. The mixture produced a good carpet of grass post-harvest.”
However, maize yields can be reduced by up to 7% using this later technique, probably due to disturbance of the young maize roots at drilling, and the fact that the less developed grass roots provided less benefit for the maize roots. Herbicide application can be tricky, as it can clash with the sowing date of the grass seeds, but minimal effects were seen on the companion crop even when vetches and clovers were included. Although a further overseeding trial had been planned in 2017, the narrow drilling window was missed.
“The maize had been drilled into a dry seedbed, but took off when rain arrived,” says Mr Ball.
“It rushed through the 4-6 leaf stage and we would have ended up causing more harm than good.”
Mr Ball recommends growers planning to establish grass at this stage should use the Enviro Max mixture.
This has the best chance of establishing before the maize canopy develops fully, enabling it to produce excellent ground cover with a fibrous root system for soil stabilisation that is also suitable for grazing.
Further work in 2018 will look at developing the potential of over-seeding, examine the suitability of new companion crop varieties and investigate further mixtures.
Potential undersowing benefits:
• Reduced nitrate leaching
• Allows earlier applications slurry/ digestate applications
• Improved slurry/digestate utilisation
• Improved soil structure
• Reduced soil erosion
• Improved organic matter levels
• Winter grazing for livestock
Trial summary
Sowing grass with maize:
• Pottinger Aerosem drill can establish companion plants consistently
• No detrimental effects on crop yield
• Grass selection needs to account for early vigour and persistent growth
• Fescue seem to have best mix of vigour and persistence
• Pre-em herbicide showed no effect on establishment
• Clovers and vetches not effective with this system
Over-sowing when maize at 4-6 leaves
• Additional operation requiring man and machine increases costs
• Tall fescue gives best growth and deeper rooting
• Herbicide timings can be a problem
• PRG gives best ground cover and fibrous roots stabilise soil