Maize has been blamed by environmentalists for flooding and soil damage. Chloe Palmer finds out if maize can be grown sustainably.
When George Monbiot blamed the Somerset flooding on the dramatic increase in maize growing upstream, an alliance of environmental charities echoed support for his arguments.
Mr Monbiot argued soil loss from harvested maize fields left bare over winter was the cause of the silting up of rivers and ditches, thus exacerbating flooding problems.
Ross Cherrington, senior farm adviser with the West Country Rivers Trust, agrees there are examples of bad practice in catchments where he provides advice, but acknowledges there are good reasons why maize is grown.
Mr Cherrington says: “Maize is an excellent crop for cattle and, grown well, it can make a positive contribution to a farm business. Selecting the right field in the right place with a suitable soil type is critical.
“Farmers must always have a plan B, so if the weather breaks, they have the correct machinery and a strategy to sort out potential damage to soil during and following harvest.
Choosing a field which does not drain directly to a river or stream, is not too steeply sloping and is accessed via a gate at the top of a hill, will significantly reduce the risk of sediment and nutrients reaching watercourses.
Using maize fields as a ‘dumping ground’ for slurry over winter has also added to problems of diffuse pollution and Mr Cherrington says it is a waste of valuable nutrients.
The correct management immediately after harvesting is essential, he says, arguing ‘if farmers can harvest a maize crop, they must be able to rough cultivate the field afterwards to limit soil erosion’.
Mr Cherrington has observed first hand the impact of increased sediment in rivers in the South West as a result of soil erosion.
He says: “Sedimentation of rivers and streams leads to swamping of gravels used by fish for spawning and can kill fish eggs and insect larvae. When suspended in water, sediment inhibits fish vision so they cannot see what they are trying to catch and eat.
“Sediment transports phosphate which results in eutrophication of our inland and estuarine waters. Pesticide residues are carried on sediment which can cause damage to aquatic life.”
Mr Cherrington believes farmers must think more carefully about how and where they grow maize.
He says: “There are some farmers who do not see the impact of their operations outside their farm gate. Wherever there are visible examples of environmental damage, campaigners will continue to be vocal and push for more regulation and enforcement.”
John Morgan of the Maize Growers Association concedes there are some examples of ‘inappropriate maize growing’, but says ‘maize as a crop is beneficial’.
He cites a number of advantages gained from growing the crop.
“Maize is very high yielding when grown in the right place, so this frees up other areas of the farm to be managed more extensively.
“It is a good utiliser of organic manures, as it grows right through late summer when other arable crops are slowing up or dying back. It is also efficient at converting sunshine into biomass, compared to grass and cereals, and so it is no coincidence it is the major crop grown globally.”
Mr Morgan compares maize to other late harvested crops where there is an inherent risk of heavy machinery causing soil damage during wet conditions.
He urges farmers to consider a range of methods which, if implemented, can substantially reduce the risks to soils.
He says: “Selecting the best variety for the site is critical, so where the field presents a higher risk because of slope or soil type, an early harvesting variety is preferable. Drilling as early as possible is desirable, based on soil temperature rather than a fixed date.
“Maize ripens following a certain number of days of heat and sunshine. If the crop can accumulate as many days of warmth as possible during early summer when days are long, it will mean it does not need to stay in the ground late into October when days are shorter and cooler.”
Establishing maize under biodegradable plastic is another method of securing extra growing days early in the season, according to Mr Morgan.
“Using a biodegradable plastic film means maize can be drilled 10 days earlier. Then for the first four to six weeks, the crop will grow more quickly because of the increased temperature and shelter.
“The use of film is particularly helpful in the more marginal maize growing areas to facilitate earlier harvesting.”
Most farmers are dependent on contractors for harvesting their maize which can worsen problems in wet years as some fields cannot be harvested at the optimum time.
Mr Morgan says: “Paying contractors promptly and having a conversation regarding harvesting dates and practice will help ensure the best job is done.”
He highlights the importance of post-harvest management of maize, stating ‘no maize stubbles should be left unmanaged over winter’.
Bare compacted soil is at high risk of erosion, so rough cultivation with a chisel plough or similar is vital, he says.
Other options for managing maize post-harvest have been trialled as part of a Defra-funded research project.
Led by Dr John Williams of ADAS, the research has focused on effects of contrasting cultivation and ground cover management practices on diffuse pollution and maize yields and quality.
Dr Williams says the use of late-sown cover crops with maize is rarely successful.
He says: “Traditional cover cropping is not practical after maize, because the harvest date is too late for satisfactory establishment.
“Our research shows strip tilling before maize is drilled into grass or a cover crop does not work either, because maize is out competed and yield penalties are significant.”
Dr Williams says maize has advantages over other late harvested crops, because it is possible to over-sow it with grass to create a cover crop which can be retained after harvest.
He says: “We recommend farmers plant maize and when it reaches the four to five leaf stage, broadcast grass seed over the crop.
“This will provide green cover underneath the crop and, allowing maize to establish first, means grass should not significantly affect growth.”
Dr Williams believes the environmental benefits of this approach are substantial.
“Once maize has been harvested, grass will grow well. Over winter, grass cover will mean reduced nitrate leaching losses, as well as significantly lower phosphate and sediment run-off.”
If the field is to be returned to maize, Dr Williams advises the grass sward is sprayed off because of potential competition with establishing maize plants.
He says: “When grass is ploughed in, it will return some nitrogen to the next crop and will provide additional organic matter.
“There is the cost of additional operations, but some farmers may be able to utilise grass by grazing over winter. Alternatively, there may even be an opportunity to take a silage crop before planting maize in May.
Dr Williams says another option is to sow winter wheat or a hybrid rye, as they only require a rough seedbed. Both crops will establish and grow rapidly in autumn, thus providing good cover, and their deeper roots help stabilise soils.
One farmer who has demonstrated maize can be grown responsibly is Graham Duke, South Bridgetown.
Farming 162 hectares (400 acres) and milking 250 Holstein cows near Launceston, Mr Duke has grown maize for 10 years and by his own admission, has ‘never caused soil damage’.
This year, he has chosen to move to a predominantly grass-based system, but 2014 was a bumper maize harvest, so he is still feeding some of previous year’s crop.
Mr Duke ‘never tills before May 1’, but always chooses a moderately early harvesting variety without compromising yield.
Participating in variety trials for Mole Valley Farmers since 2008 gave him an insight into which varieties suit his land.
He says: “We are on favourable land for growing maize. I found trials helpful, because varieties perform differently from one field to the next. Ukon did well here and we typically expect yields of 50-62 tonnes/hectare.”
Mr Duke selects his fields for maize carefully, avoiding steeply sloping fields and those lying closest to the River Tamar. Mr Duke says most importantly, his management post-harvest is key to minimising impact on the environment.
He says: “I always plough and drill a crop of winter wheat the same day we harvest maize. We usually harvest by mid-October, so this allows time for establishment of wheat before winter.
“I always create tramlines around the contour of the hill, because if tramlines run down the slope, they create a pathway for water which takes soil with it.”
Although Mr Duke is now aiming for more milk from grass, he thinks maize will always form part of the diet for cows.
“Maize is a wonderful feed for energy and condition and I will continue to include some in the ration, even if I have to buy it in.”