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LAMMA 2021

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Undersowing maize: What, when and how to undersow to get the best results

With concerns over soil and water quality following the harvest of maize, a charitable organisation and a group of farmers are making use of dedicated undersowing drills to combat the problem. Alex Heath finds out more.


Maize is a valuable crop which an increasing number of farmers are benefiting from growing, whether to feed livestock or the rising number of anaerobic digesters across the country. However, due to the growing and harvesting seasons of the crop, it poses a number of challenges for growers.


Harvested in the autumn, when conditions are often less favourable for field work, both getting the crop off the fields and subsequent reinstatement of the land are both issues. One solution a group of growers in Herefordshire and Monmouthshire are taking advantage of is undersowing the growing maize crop with grass, filling in the areas between the plant rows that would otherwise lie bare.


The Wye and Usk Foundation is a charitable organisation focused on the ecology and water quality along two of the country’s major rivers of the same names. Kate Speke-Adams, the foundation’s head of land use, says: “Around 10 years ago, the amount of land put down to maize in the rivers’ catchment areas rose significantly, leading to an increase of soil finding its way into the rivers.


“We had to find pragmatic ways of reducing the risk posed by maize stubble left over winter. Because our climate is becoming more unpredictable, we were finding farmers were struggling to get on the land after maize to establish a new crop.”


After exploring a number of options, Mrs Speke-Adams says the foundation and local seed supplier Field Options teamed up.


“Field Options had seen and experienced a lot of undersowing in Denmark,” she says.

Liking what they saw, the foundation built a prototype with parts from cultivation and drill manufacturer Weaving. The aim was to see if the principle of sowing a second crop a month after the maize has been planted was feasible.


“It worked well,” says Mrs Speke-Adams. “Weaving then took the design and started building it themselves.”

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The foundation now runs two of Weaving’s Inter Row IM6001M drills, with another two on order. It offers the service to farmers who otherwise could not afford the machine or would not bother undersowing, as a way of stopping run-off entering the river.


“As the drill is only used on a farm for a few days each year, it is an expensive machine to own, however, with us offering the service to multiple farmers the cost is drastically reduced,” she explains.


The area covered by the two machines is growing, hence the addition of another pair. Currently about 200 hectares per year is undersown, across 15 farms. She adds that weather patterns, time of planting and the distances covered on the road complicate logistics and affect the annual output of the drills. The service is supported by Field Options, which also provides the seed mix as specified by the farmer.


Mrs Speke-Adams says the run-off has been noticeably reduced.


“The cover is already a month ahead of anything that could be planted, conditions permitting after the harvest, so soaks up excess water and traps any erosion caused during heavy and prolonged periods of rainfall.


“Last October we had a severe storm with torrential rain. We saw run-off in all types of stubbles, including maize that had not been undersown. However some of our farmers who had undersown were able to travel on the fields two days later, with minimal disturbance to the soil,” she adds.


Not only is sediment run-off an issue, but nutrient leaching into the watercourses is also causing problems in the area, especially phosphate. This is causing eutrophication in the surrounding streams and rivers says Mr Speke-Adams, and consequently impacting on the health of the flora and fauna of the watercourses.


The project has spread by word of mouth by neighbouring farmers, as well as open days showing not only the environmental benefits, but also the advantages in terms of soil health and its use as an extra feed source for livestock.

In the field: Chris Norman

In the field: Chris Norman

Chris Norman, The Leen, Pembridge is one farmer which has used the service offered. The family farm were winners of the Gold Cup in 2017 with its herd of 600 autumn calving cows. The winter ration for the herd revolves around maize and grass silage served in equal measures. The farm is also home to a 500kW AD unit.


Having previously been run as an organic unit, the farm is no stranger to dealing with maize as it grows, says Mr Norman.


“We were previously dealing with weeds in standing maize between the two- and four-leaf stage using an Einbock grass harrow,” he explains.


Grass was also put down in between the maize crop using the harrows, as far back as eight years ago, but with mixed results, says Mr Norman.


“The aim is to keep the soil in the same place by having a living plant binding it together,” he says.


Having confidence that the maize would withstand being drilled alongside, he took up the option to use the foundation’s drilling service, which he says has transformed the germination rate.


The farm grows about 40 hectares of maize each year, either in house, or with other farmers, all of which is undersown, conditions permitting.


Undersowing is done mid-June, when the maize is just under knee height, and after the last weed spray.

When the maize is harvested, Mr Norman says there does not appear to be much volume in terms of grass, however, a dose of digestate post-harvest and it grows well throughout the winter, allowing for a flush to be grazed once or twice by the cows in the spring.


He says the biggest advantage is to the soil health. “The advantages are significant. When you put a spade or cultivator in the ground the earth smells sweet, otherwise the soil is pretty inert if nothing is growing in it,” he says.


“We farm light loam over gravel. The worm activity is enhanced, and the soil structure is a lot better. Plus, when we turn the cows on in spring, they turn the grass into muck which is easily available to the subsequent maize crop.


“Tractors also travel better come harvest, even after last year’s wet weather.”


Interestingly the farm has not ploughed its maize land for six years, instead using a Mzuri direct drill where possible, although last year the crop was established with two passes of a cultivator and then drilled with a precision seeder. The grass sward is sprayed off prior to planting.


Having tried various seed mixes, including plantain, chicory and vetch, Mr Norman has concluded an Italian ryegrass sward is best, and comments there is no adverse effect on maize yield.

What to plant and when?

What to plant and when?

Francis Dunne of Field Options says most farmer’s stick with Italian rye grass (IRG) as the species to fill in between the maize rows, as a reliable choice. He says some have tried winter vetch/IRG mixes with differing success rates, while this year there will be some trials using berseem clover.


Diploid varieties of IRG are typically best he says, due to a larger seed count per kilogram, with less vigour in the early stages than tetraploid varieties. Where IRG is thought to have too much vigour and likely to compete too much with the growing maize plants, a perennial ryegrass can be used instead he says.


Mr Dunne says the opportune time to undersow is when the maize plant is showing six to eight leaves, typically mid-June, when the maize is just under knee height, and a week after the last post emergence herbicide spray.


Seed rates for IRG are generally between 17.2 and 19.7kg per hectare says Mr Dunne, around half of a normal grass seed rate, as only the ground in between the maize rows is sown. He says the success rate for establishment is 90 per cent, only encountering persistent problems when undersowing the 2018 crop, as conditions were exceptionally dry.

The machine

The machine

Weaving IR drill specifications

  • Working width: 6.4 metres
  • Number of rows: Eight
  • Number of coulters: 27
  • Coulter bank spacing: 750mm
  • Coulter to coulter spacing: 187.5mm
  • Hopper capacity: 300 litres
  • Power requirement: 80hp
  • Weight: 1,500kg
  • Price: £19,800 plus VAT

Weaving officially started making the IR drill four years ago, but has recently given it an overhaul, making it sleeker and easier to use. Now only available in an eight-row guise, the two outer coulter sets can be removed if needed to act as a six-row machine. Although it is classed as an eight-row machine, it actually seeds nine ‘gaps’ between the plants.


In its standard format each bank of seeding units is made up of three coulters spaced 187.5mm apart from one another within each bank. The centre coulters are spaced 750mm apart, centre-to-centre. A total of 27 coulters are present, made up of a double disc opener with a rubber press wheel.


Row widths can be adjusted using a rack and pinion system on the main frame, as opposed to bolts used on previous models. It now also features a hydraulic side shift system to keep in rows.


The drill also features the firm’s Magnum seeder, with a hydraulic fan and Accord-type metering system.

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