Author: Geoff Porter, OVA Natural Environment Co-ordinator

For many years, Government and environmental groups have raised concerns about the increased growth of maize in this country. As a result, multiple pieces of legislation and guidance focused on good farming practice have been produced. A significant change in the amount of maize grown took place with the development of Anaerobic Digesters, AD’s, that produced power from waste. Government supported this ‘green’ energy by providing producers with subsidies which still continue. Power plant owners found that adding vegetation to waste increased power output and that maize was ideal; it was no longer only grown as a foodstuff.  

Government statistics show that in 1973, 8,000 hectares,(ha) of maize were grown; by 2000 this was 98,000 ha. At this point, almost all was grown as animal feed. Between 2008 and 2014, hectarage increased by 20% and significantly, 20% of that was produced for use in AD’s. Ten years ago, 171,000 ha were grown in England of which 17% went to digesters. By January 2015, there were 174 AD’s. Just 2 months later that had risen to 185.

What has driven this rapid increase in maize production and what are the repercussions? AD plants initially used waste food, treatment work waste and animal slurry which when broken down by microorganisms produces ‘green’ methane. This is used as gas fuel or to generate electricity. Adding plant material such as grass, cereals, sugar beet or maize produces more methane. Maize has become the preferred option because its high levels of biomass and basic starch make biological digestion easier. When the crops go to AD’s it results in additional maize having to be grown for animal feed. Anecdotally, this is happening locally. 

Government supported using waste materials to produce ‘green power’ with subsidies for producers under the Feed-in-Tariffs (FITS) scheme in April 2010 guaranteeing a fixed price for A.D. generated electricity. The following year, the Green Gas Certification Scheme (GGCS) was established by the Renewable Energy Association, with quarterly payments for generators based on production along with capital investment for AD’s. The Renewable Heat Incentive (RHI) was also introduced. These subsidies fuelled the growth of maize for use in AD plants rather than as a food plant. 

By 2016, AD producers were receiving £50 million in Government subsidies. In June that year, the Soil Association said that growing maize for sole use in AD’s was a threat to food production. Using public money to subsidise AD plants regardless of what they were using to produce their power should stop. Primarily, they should be fuelled with slurry and other waste products as originally intended. They concluded that ‘double subsidies for maize use in anaerobic digesters was counter-productive to managing soil sustainability and should be withdrawn.’ In 2021, the Governments Green Gas Support Scheme, (GGSS), administered by Ofgem was introduced, bolstering the UK’s commitment to environmental sustainability and ‘green’ energy. It incentivised biomethane gas production. The scheme was to end on Nov. 30th 2025 but has been extended to 31st March 2028. GGSS does though expect that AD plants will reduce the use of ‘organic’ material to under 50% by increasing the use of food waste for fuel production by 2026. Extending the scheme underlines the Governments longer term commitment to AD’s.

In order to increase the productivity of maize, seed growers have developed new varieties specifically for AD’s. At harvest, these ideally constitute 32% dry matter and a high level of starch, perfect for biogas production. There are both early and later maturing varieties. Many of those favoured by AD’s and farmers mature later. All have a narrow harvesting window when energy content is optimal. In 2024, total maize growth was 237,000 ha, an almost 30 fold increase in just over 50 years. It’s estimated that over the next 3 years, 30% of that total (71,100 ha) will be grown for AD’s.

Maize seed is usually planted along with diammonium phosphate, (DAP), a granular water soluble compound containing nitrogen and phosphorus. This encourages early plant growth but also temporarily increases soil pH and can result in increased soil acidity. 

The Soil Association, a charity that promotes organically sustainable farming are concerned about AD maize production. Their focus is on environmental protection and encouraging ‘farmers and growers to adopt sustainable practices, improve soil health and enhance biodiversity on their land’. Maize crops are seen to increase the risk of soil erosion and compaction. In 2016, the Environmental Audit Committee also heard concerns about more maize crops with the likelihood of erosion as climatic change increases the likelihood of  extreme weather events, especially heavy rainfall. A study by the National Trust in South West England showed that the soil in ¾ of fields under maize was so damaged that rain was unable to penetrate resulting in run-off into watercourses and rivers.

The Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency (EA) published The Reduction and Prevention of Agricultural Diffuse Pollution (England) Regulations 2018 and the Sustainable Farming Incentive Scheme. Both detail guidance to maize growers.

It says they must:

• focus on reducing soil erosion and water pollution
• choose appropriate fields for crops
• manage soil compaction
• use cover crops to minimise bare ground
• harvest early to prevent soil damage and run-off
• use fields that have good drainage
• avoid fields with steep slopes and
• light unstable soils most prone to erosion 

The Environment Agency echoed the above adding:

• crops should not be harvested in wet weather as this compacts soil resulting in run-off.
• early maturing maize varieties are preferable
• farmers should be vigilant when harvesting late crops
• soil should be loosened following harvest to enable water penetration
• wheel ruts can develop into water channels and should be removed post harvest
• high risk fields should be avoided. (Alternative crops should be used)
• steep slopes and sandy soils should also be avoided
• crops should be harvested before the end of September to enable a cover crop to be grown
• cultivated fields should have buffer strips near water courses
• seed should be sown along contours not up and down slopes

In September 2023, the E.A recommended to Devon and Cornwall farmers that they should consider crops ‘other than maize’ due to the increased likelihood of climate change, extreme weather events and increased likelihood of pollution incidents from soil erosion and run-off. The EA can take enforcement action if pollution prevention is not taken. The Agriculture and Horticulture Development Board (AHDB) advise that crops should be under-sown in June to aid soil and nitrogen retention and reduce the impact on the water environment. It says that the costs of under-sowing maize are balanced off by nutrient saving. This guidance equally applies to farmers growing root crops in light soils on hillsides.

At a time when farm subsidies are unreliable, growing maize for biogas must seem to be a good option to cash-strapped farmers. Government appears to be giving out mixed messages to growers, on the one hand underlining its commitment to AD green energy by extending subsidies to 2028 whilst, along with the EA producing advise not to grow maize in Devon and Cornwall. A.D. plants that Government are encouraging require fuel. The result is arable land producing fuel rather than food. 

Heavy rain falling on bare compacted ground after late harvests has serious environmental impacts. Rain cannot infiltrate the ground and runs off hillsides. Soil, containing nitrogen fertilisers and insecticides is carried down roads, ditches and into watercourses. This leaves mud on roads, silt and chemicals in brooks and rivers and as witnessed locally, in severe circumstances it floods properties. Heavy agricultural machinery not suited to narrow Southwest lanes and roads often travel miles between field and A.D. plant causing structural damage, congestion and the consumption of large quantities of diesel. This has both an environmental and financial cost.

Poor agricultural management - planting up hillsides, single access above a watercourse, no under-planting

The River Otter is graded poor due to constant high phosphate levels. Whilst evidence shows that the majority of this comes from SWW treatment works rather than farming, the impact of soil run-off into watercourses can still be significant. Not only does the cocktail of previously mentioned diammonium phosphate, herbicides and insecticides used on crops damage aquatic life, silt also smothers riverbeds. Nutrient enrichment caused by high levels of phosphorus (and nitrogen) results in entrophication, causing excessive algal and plant growth, This in turn blocks sunlight hindering plant photosynthesis and depleting oxygen levels. 

Equally concerning as deposited topsoil is its removal from fields. In 2005, Good Agricultural and Environmental Condition (GAEC) standards were aimed at ensuring farmers protect soil, water habitats and landscapes underlining the importance of soil protection. In Sept 2009, DEFRA published Safeguarding our Soils – A Strategy for England and in 2018, a second that included Farming Rules for Water stating that Farmers and Land Managers should minimise the risk of pollution by not using excessive nutrients and fertilizers. More recently in Jan 2024, they published Guidance, Code of Good Agricultural Practice (COGAP) focused on soil protection, water and air. Soil was described as ‘a vital recourse for food production, water management, habitat support and carbon storage.’ All of this legislation and guidance suggests ongoing Government concern about poor land management and pollution avoidance. 

Soil runoff through rutted gateway from Maize & root-crop farming resulting in soil erosion and village flooding

The John Innes Centre states that it takes between 200 and 1,000 years to produce 25mm of topsoil. In human timescales, soil is not renewable. One episode of heavy rainfall can rapidly wash that away.

In conclusion, much of East Devons hilly landscape once comprised multiple dairy farms with small grass meadows, hedges and ditches that helped prevent water run-off. Some of these meadows have become large open arable fields unsuitable for maize and root crops. Hedges and ditches have been removed. 

Many tenants now use contractors, paid to sow, harvest and transport who have no investment in the land. This third tier increases the likelihood of poor land management, ignoring good farming practice; crops sown up hillsides, seldom under-sown and harvested regardless of weather conditions left with bare compacted soil. Poor land management threatens the viability of future food production and negatively impacts water courses. When things do go wrong, it’s too easy for owner, tenant and contractor to simply blame each other for the resulting pollution.

Despite all the concerns about the environmental impacts of maize growing in Devon and Cornwall, its production for AD’s through financial incentives continues. Lessons are not being learnt and additional maize is being grown. Guidance is being ignored. Hillside arable fields of sandy soil are still being planted with maize. Producers fingers are being crossed behind backs that it won’t rain when crops are harvested and that should there be run-off and pollution the penalties will be lenient.

All this evidence questions whether power generated by maize really is ‘green’, so are ongoing subsidies warranted? Will producers that ignore guidance resulting in environmental damage be held responsible and made to pay more than the crop’s worth? Shouldn’t both land and AD owners be made ultimately responsible for ensuring that maize is being grown in accordance with Government guidelines?

What can you do?

If you see pollution resulting from poor agricultural management or the threat that that could happen,

contact the Environment Agency on 0800 807060.