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LAMMA 2021

LAMMA 2021

Reducing runoff with undersown maize

Trials show undersowing maize can help protect water without adversely affecting yield.

Initial results from undersown maize trials conducted by water company Severn Trent on the Sherwood sandstone in north Nottinghamshire are promising, despite an unseasonably wet year. This is according to Phil Billings, catchment officer with the firm, who designed and managed the trials.




The findings show maize yields from the undersown plots were comparable to control plots. Mr Billings set up the trial to investigate the effect of undersowing maize with different species on the amount of nitrate leaching from the soil.


He says: “Maize is now grown across large areas of land overlying the Nottinghamshire boreholes and nitrate leaching from soils here represents a major cost to Severn Trent. We wanted to observe the effect of a variety of different undersowing treatments and to ensure there was no impact on yields of maize.”

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The environmental benefits of the trials have not yet been fully quantified as monitoring of water samples from the trial field will be ongoing over the winter months.


“We set out 49 plots which were 100 metres long and 36 m wide. We established a range of undersown species using different sowing techniques, dates and rates, applied pre-emergence herbicide to certain plots but not others and also compared different row widths when drilling the maize.


“Digestate was the main nutrient source and this was applied with and without nitrate inhibitors and at different timings.


“We wanted to gauge the degree of flexibility with sowing date and rate for the undersown species and to measure the cost of the different treatments to help us identify factors which might limit uptake of this approach by farmers,” says Mr Billings.


Early results from the trial indicate that drilling date, row spacings, the use of pre-emergence herbicides and applications of digestate to the maize crop all have the potential to improve yields and crop quality.


“We found disc drilling the undersown seed is the best way of achieving good seed to soil contact. Where we broadcast the seed and then harrowed it we saw nothing but fat hen and I think this is not a reliable option on the soils we have in this part of the country.



“Drilling the seed up to the four leaf stage is preferable as a lower seed rate of 7kg/ha can be used so it reduces the cost of establishing the sward beneath the canopy. Later drilling necessitates increasing the seed rate up to 15kg/ha proportionately to the eight 8 leaf stage.


“The use of a pre-emergence herbicide made a significant difference to yield and using a contact herbicide earlier and before weeds appear under the maize leaves is important.


“We applied two grades of mycorrhizal inoculant to some plots because we think these products may help on farms where there is a high phosphate index but the phosphate may not be available to the crop. No significant benefit has been seen in this case,” Mr Billings adds.


The trials also experimented with different methods and timing of applying digestate and Mr Billings hopes the judicious use of this source of nutrients and organic matter may remove the need to apply di-ammonium phosphate (DAP) to maize crops in the future.


“By using precision techniques to apply the digestate, it can be applied during the summer months when weather conditions are right. We looked at the option of dribbling the digestate into the maize canopy and this can reduce early nitrate leaching and result in better capture of nitrate by the crop,” he explains.


Mr Billings said comparing the results from the plots where the maize was drilled at widths of 30cm using a Horsch TD, at 50cm with a MaterMacc and at 75cm with a Tempo suggested wider widths reduce disease incidence.

“It was striking to examine the cobs from the plants drilled with the Horsch TD because many were going mouldy, even though yield from these plots was good. I think this is because there was poor airflow between the plants and little light reaching them.




“Conversely, I detected very little disease in the cobs from the 50cm and 75cm spacings and there were only minor differences between these plots. These findings point to precision drilling as the best technique to use where quality is critical,” Mr Billings says.


He estimates the cost of drilling the undersown sward at £20/ha excluding seed. Of the seed mixes used, the Westerwolds ryegrass was the cheapest at £30.50/ha based on a 10kg/ha sowing rate. An Enviromax tall fescue and perennial ryegrass mixture was £43.90 at the same rate. The most expensive post-harvest sown mixture was vetch and rye, costing £169/ha at a seed rate of 140kg/ha.


“If the seed is drilled early before the maize reaches the four leaf stage, the lower seed rate means costs are reduced but if drilling is delayed, the costs escalate due to the need for a higher seed rate. If drilling is delayed beyond the eight leaf stage, it is probably better to consider a cover crop after harvest.




“The benefits of undersowing to the environment are clear. It means there are fewer issues with runoff meaning less sediment entering watercourses.


“Because of the mining history of this area, there are subsidence fractures in the sandstone. So even where there are no ditches or streams, it is important to prevent runoff and leaching of nutrients because it can lead to ponding and leachate seeping down to the aquifer.


“If you are in a Severn Trent priority catchment, we can help with the costs of under-sowing by providing a grant to support up to 50 percent of the cost. We can also provide grants to support using precision techniques for applying digestate and slurry,” Mr Billings adds.


Looking ahead, Mr Billings is keen to trial varying applications of digestate, incorporated to different depths so in the future it may be possible to move away from the use of DAP.

Top tips for under-sowing maize

  • Adopt a sensible approach to the choice and timing of pre-emergence herbicide
  • Apply contact herbicide early to avoid an umbrella effect from weed colonisation
  • Based on findings from the trial plots on sand land in north Nottinghamshire and dependent on crop maturity and canopy structure:
    • Drill early at a low rate – circa 7kg/ha up to 4 leaf stage
    • If drilling later increase seed rate to c.10kg/ha at four to six leaf stage and c.15kg/ha at six to eight leaf stage
  • If planning to drill after the eight leaf stage, consider a post-harvest cover crop unless yield is likely to be low

Source: Severn Trent

Treatments and operations


The previous crop on the field was sugar beet.



April 1

Pre-digestate cultivation

April 9-11

Digestate from REL

April 14

Digestate worked in

May 15

Light cultivation

May 15-16


July 15

Second application of digestate



Seed rates and drilling



10 row Tempo 7.5m – 75cm spacing

12 row MaterMacc 6m – 50cm spacing

20 row Horsch TD 6m – 30cm spacing



Target seed rate 117,500 per ha

Maize variety: LG31211 (FAO 220)


Feed quality:

  • Metabolisable energy (ME) values consistent at around 12 ME across all the plots per kg of dry matter (DM)
  • Crude protein figures similarly constant across most plots with the highest values recorded for undersown chicory and Enviromax
  • More variation in starch levels; the plots with maize undersown with chicory has the lowest starch values at below 25 per cent. The highest starch level of 38 percent was recorded from the plot undersown with Enviromax and clover and a similar figure found on the plot treated with a nitrogen inhibitor
  • Dry matter (DM) was relatively consistent across all the plots – the Enviromax plot showed the highest level of DM and the clover/chicory the lowest
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