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Energy Maize – Sustainable approach pays off for Biogas

17.7.17

Energy Maize – Sustainable approach pays off for Biogas

Article courtesy Jon Myhill Future Biogas , written by Wendy Short

Several thousand acres of maize are grown each year, to produce fuel for the AD (anaerobic digester) plants managed by Future Biogas, which has four sites in the county of Norfolk. The company’s regional feedstock manager, Jon Myhill, offers some pointers for growers.

Formed in 2010, Future Biogas uses about 50% maize to produce gas at a total of nine AD plants in Eastern England. The fuel, or ‘feedstock,’ requires careful management and in return, growers can expect to receive a payment, calculated on a price per tonne, that is agreed 12 months in advance. In Norfolk, maize growers are generally found within a 10-mile radius of each plant and crop management can present some challenges, with erosion at the top of the list of issues to tackle, says Mr Myhill.

Soil Erosion

“There have been some links made between maize production and soil erosion, so it is advisable to take some precautionary measures, such as avoiding the planting of the crop on steep slopes,” said Mr Myhill. “A large acreage of our maize is followed by winter cereals and this practice will limit soil erosion. We ask our contractors to use low pressure tyres on their trailers and that is also helpful.

“We are currently investigating the potential for reducing erosion by under-sowing maize, possibly using tall fescues. This technique is used widely in Germany, but there may be a risk that herbicide applications could be compromised and that yields might suffer, due to increased competition.”

The over-working of light soils was another contributing factor, he added.

“The plough and the power harrow have their places, but over-worked soils are easily damaged, especially if we get a heavy summer downpour. The rain can degrade the soil structure, preventing it from holding together.”

Cover Crops

Cover crops may have a role to play, in meeting environmental requirements, said Mr Myhill.

“The rooting systems of cover crops grown before maize will remain after the plants have been desiccated and will promote water infiltration, as well as increasing soil organic matter levels. We are looking at vetch, phacelia, mustard and oil radish.

“The cover crop must be sprayed off or mulched into the surface, to allow the maize to be drilled into a moist seed bed. †This practice will also ensure that the primary crop does not have to compete with the cover crop. †If it is left in the ground for too long, the cover crop will take up valuable soil moisture, leaving †the †maize in a dry seedbed, which could be detrimental to establishment rates.

“Planted after maize, oats and rye are cheap options for cover crops and we also have tried mustard and oil radish. However, the system is in its infancy and it is too early to make a decision on which species have produced the best result.”

Mr Myhill suggested that cover crops planted after hybrid rye or other cereals will grow more rapidly and capture greater levels of soil nutrients, if liquid digestate (the by-product of the AD process) is applied to the land at sowing. The plants will release the nutrients slowly, making them available to the following maize crop. This fits in well, as maize has a high demand for late summer nitrogen, he said.

Drought Management

The effect of even short spells of drought, which have been experienced by Norfolk growers on light sandy soils in recent years, can be mitigated to some extent, by choosing later-maturing varieties with an FAO of 230-260. Mr Myhill favours Ricardinio (KWS), as well as Amagrano (KWS), a new variety for 2016. †

“These varieties are reliable, high-yielding and have the potential to achieve our target dry matter at harvest of 32-36%,” he said. “If drilled first, the later-maturing varieties are in the ground for longer and therefore have a greater ability to withstand periods without water.

“Another way to drought-proof crops is to use lower seed rates. The standard figure is 100,000-105,000, but we recommend 80,000-90,000, in areas prone to drought. A lower plant population means that each plant will have access to more water; this approach has adopted successfully for the past two years.”

Mr Myhill pointed out that soils in some parts of Norfolk contain as little as 2% organic matter and that the diminishing number of livestock in the county has left growers with little access to slurry or farmyard manure.

“The application of digestate can lift soil fertility and encourage microbial activity,” he said.

“Our digestate comes in two forms; one is a liquid, which can be applied either by shallow

injection, or as a top dressing. The other is a solid, applied by a standard muck spreader.”

Growers have been bombarded with advice on minimising soil compaction, but Mr Myhill

issued a word of warning.

“It is advisable to dig down with a spade in several areas of the field, to establish the depthof

any suspected compaction. Coarse, sandy soils are not prone to compaction and if the

problem is limited to the top few inches, it can be removed with minimum tillage operations.

The sub-soiler may only need to work at a shallow depth, if at all. Working too deep can

create more problems than it solves, by damaging the soil structure. It also increases fuel

usage and wear and tear on machinery. “

Maize for biogas is a crop which fulfils all the requirements of a sustainable nutrient cycle, he

noted.

“When maize enters the AD, it releases methane and carbon dioxide. The methane is

burned in a gas engine, to produce electricity, or injected into the national gas grid. All of the

other nutrients are returned to the land in the digestate, which in turn requires less artificial

fertiliser.† Maize is good break crop and an excellent feedstock for AD, because it is high in

energy and provides bulk, “ he said.

Typical Digestate Analysis

Solid Digestate††††††††††††††††††††††† Nutrient†††††††††††††††††††††† Total kgs/tonne†††††††††††††††††††††††††††††††††† *Available Year One†††††††††††††††††††††††

N†††††††††††††††††††††††††††††††††††††††††††† 4.73†††† ††††††††††††††††††††††† 28%

P††††††††††††††††††††††††††††††††††††††††††††† 2.88†††††††††††††††††††††††††††† 60%

K††††††††††††††††††††††††††††††††††††††††††††† 5.11†††††††††††††††††††††††††††† 90%

Liquid Digestate†††††††††††††††††††††

††††††††††††††††††††††††††††††††††† Total kgs/cubic metre

††††††††††††††††††††††††††††††††††† N†††††††††††††††††††††††††††††††† ††††††††††††† 3.42†††††††††††††††††††††††††† 50%

††††††††††††††††††††††††††††††††††† P††††††††††††††††††††††††††††††††††††††††††††† 1.16†††††††††††††††††††††††††††† 60%

††††††††††††††††††††††††††††††††††† K††††††††††††††††††††††††††††††††††††††††††††† 5.01†††††††††††††††††††††††††††† 90%††††

*Dependent on analysis†††††††††


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