Amaiz­ing crop

Farmer’s wife Suzy Sten­nett stud­ies the po­ten­tial for biocrops and anaer­o­bic di­gesters

EADT Suffolk - - Inside - Suzy Sten­nett and hus­band Oliver run an arable farm in west Suf­folk. She chats about the highs and lows of their ru­ral life

FARM­ING seems to be an in­dus­try that is ro­man­ti­cised more than any other, hark­ing back to the by­gone days of heavy horses work­ing the fields, when an en­tire com­mu­nity would be in­volved with the farm, from teams har­vest­ing the fields, no doubt alive with ban­ter and ca­ma­raderie, to black­smiths and wheel­wrights fill­ing the vil­lage with their as­so­ci­ated smells and noises.

Then came the agri­cul­tural rev­o­lu­tion, and the in­tro­duc­tion of trac­tors. The likes of the lit­tle Grey Fergie and the David Brown are now col­lec­tors’ items, as en­thu­si­asts bag them­selves a bit of history to lov­ingly pol­ish. Every in­dus­try must move with the times, and farm­ing is no ex­cep­tion. As world pow­ers strug­gle to find the an­swer to global warm­ing and al­ter­na­tive en­ergy sources, farm­ers find them­selves pre­sented with new op­tions for in­no­va­tive en­ergy pro­duc­tion, from fields of so­lar pan­els and wind tur­bines, to grow­ing crops for fuel.

Maize has his­tor­i­cally been grown in the west coun­try for an­i­mal feed, and in Suf­folk has only re­ally fea­tured in small strips of pheas­ant cover. But over the last five years the agri­cul­tural landscape of Suf­folk has grad­u­ally been trans­formed, as this crop, grow­ing seven to eight feet high and re­sem­bling some­thing out of John Wyn­d­ham’s The Day of The Trif­fids, is in­creas­ingly grown for bio­fuel. Its high en­ergy con­tent and rel­a­tively low in­put re­quire­ments, mean maize (also known as sweet­corn) meets the sus­tain­abil­ity cri­te­ria set by en­ergy com­pa­nies. It pro­duces more en­ergy than is re­quired to grow, har­vest and con­vert it.


Re­quir­ing a rel­a­tively fine seed bed with a good soil struc­ture in or­der to set its roots, maize is drilled in early May once the land has been suit­ably cul­ti­vated. Seeds are spaced every 15cms down the row, with 50cms be­tween each row, gen­er­at­ing a jun­gle of 100,000 – 105,000 plants per hectare, en­sur­ing each plant re­ceives op­ti­mum sun ex­po­sure and is not shaded by the leaves of its neigh­bours.

Maize is a sub­trop­i­cal plant and doesn’t need ir­ri­ga­tion, and, true to its low

main­te­nance crop cri­te­ria, it re­quires only four passes of her­bi­cide and fer­tiliser as the plants shoot up. First leaves form around the stalk, fol­lowed by a tas­sel at the top, which is ef­fec­tively the plant’s flower. The cobs then de­velop within the heart of the plant, form­ing the grain ready for har­vest in Septem­ber and Oc­to­ber. Farm­ers hope for two large cobs of corn per stem for op­ti­mum en­ergy pro­duc­tion. Any more and the cobs would be smaller with a lower en­ergy out­put.

Thea early au­tumn har­vest means maize is cut at a dry mat­ter of 32%, which means that, un­like the cereal har­vest, there’s no wait­ing around in the morn­ing for the dew to dry off, and a rain shower is not nec­es­sar­ily go­ing to stop play. Although sim­i­lar in ap­pear­ance, a for­age har­vester used to cut the maize has a

com­pletely dif­fer­ent style to a re­fined cereal com­bine har­vester. Rather like a hot headed younger sib­ling who en­ters the field to cause to­tal de­struc­tion, the for­age har­vester has two ob­jec­tives – to break open every grain on the maize cobs in or­der to help re­lease the en­ergy in­side later in the process (re­mem­ber, sweet­corn can pass through the body com­pletely en­tire if not thor­oughly chewed), and to chop the giant stalks and leaves into 7mm-10mm slices. This pre­vents them get­ting tan­gled around pumps and mix­ers.

The for­age har­vester chops the maize stalks 7cm-10cm from the ground and passes them through its feed rollers into a drum re­sem­bling one of the many in­tended des­tinies for James Bond. There it meets a set of knives which slash it against a shear bar, then con­tin­ues through the James Bond-style tor­ture cham­ber onto a corn cracker, where two rolls split and crack the grain, pass­ing it into the ac­cel­er­a­tor. The ac­cel­er­a­tor dis­poses of the re­mains by blow­ing the chopped and cracked maize up through a shoot, ex­pelling it into a trailer run­ning along­side. The flow from the for­age har­vester’s spout is con­tin­u­ous, so driv­ers need to work well to­gether to en­sure that all the har­vested maize is col­lected. To en­sure the for­age har­vester can work undis­rupted, thrash­ing through the field, there’s nor­mally a team of about four trac­tors and trail­ers, re­lay­ing to and fro the yard. Other tricks in place to en­sure the chopped maize reaches the trail­ers at all times in­clude an abil­ity to swing the spout around the back of the for­age har­vester by 180°, so the trailer can be po­si­tioned be­hind the for­age har­vester when nec­es­sary.

There’s nor­mally a cam­era fit­ted to the end of the spout, with a feed to a screen in the cab of the for­age har­vester, so the driver can keep his aim ac­cu­rate. If he also has a row finder fit­ted to the front of the for­age har­vester, to guide his ma­chine straight down the rows, he can stay on course with­out hav­ing to look up from the screen.


In the yard the chopped maize is weighed and tipped onto a large walled con­crete pad where the clamp­ing trac­tor takes over, push­ing it up into a clamp up to five me­tres high, con­stantly rolling it to squeeze out the air and start the fer­men­ta­tion process. Silage sheets, like thick black plas­tic bin lin­ers, seal the unit, pre­vent­ing air en­ter­ing and en­abling fer­men­ta­tion to turn the har­vested maize into silage. It’s ready to use for en­ergy pro­duc­tion af­ter six or seven weeks, but it can be stored this way for up to two years.

This silage is the food that feeds the Anaer­o­bic Di­gester (AD), com­monly known in the in­dus­try as a big con­crete cow – fed at one end and re­leas­ing gas at the other, which is now help­ing to fuel the na­tion.

An AD plant is like a huge stom­ach. The in­su­lated con­crete tank houses methanogens, mi­cro-or­gan­isms that pro­duce meth­ane as a meta­bolic byprod­uct in anoxic con­di­tions. The tank, with its heaters and mix­ers, are all cov­ered by a soft dou­ble-mem­brane dome.

Fed every hour by a pro­grammed feed hop­per, the mi­cro-or­gan­isms break down and di­gest the silage. The mix­ers not only help ex­pose the silage to the mi­cro-or­gan­isms, but also help re­lease the bio­gas pro­duced in the di­ges­tion process (ef­fec­tively wind!). The outer mem­brane of the AD plant is con­stantly blown out by a con­tin­u­ous flow of air, while the in­ner mem­brane rises and low­ers ac­cord­ing to the gas pro­duced within the di­gester.

The anaer­o­bic di­gester passes out the bio­gas, which con­sists of 52% meth­ane, 46% car­bon diox­ide and 2% other gas com­pos­ites. It’s then chilled and fed to a gas up­grade build­ing, which strips out the car­bon diox­ide. The re­cov­ered car­bon diox­ide can then be chilled to -35°C and sold in liq­uid form to the food in­dus­try, per­haps reap­pear­ing as bub­bles in fizzy drinks, or used to keep prepacked sand­wiches fresh.

The re­main­ing bio-meth­ane has calorific value of 37 mega joules. It’s en­riched with propane to boost that to 39 mega joules, to meet na­tional grid spec­i­fi­ca­tions, then com­pressed and given an odor­ant (biomethane is odour­less). The gas then leaves the farm and en­ters the na­tional grid.

So are we now in the throes of an­other agri­cul­tural rev­o­lu­tion, this time green and striv­ing to fuel the na­tion as well as feed it? Will we look back in years to come and fondly re­mem­ber farm yards de­void of silage clamps and the oblig­a­tory domed head of the AD plant? Only time will tell.

“Maize (also known as sweet­corn) meets the sus­tain­abil­ity cri­te­ria set by en­ergy com­pa­nies. It pro­duces more en­ergy than is re­quired to grow, har­vest and con­vert it”

Above, the maize har­vest. Be­low, the anaer­o­bic di­gester plant

Above, food for the anaer­o­bic di­gester

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