Focusing on five key management areas can help ensure arable growers get more from maize produced for AD plants.
Wilson Hendry of Grainseed shares his top tips...
With a direct link between gas production and energy content fed in, maximising energy yield per hectare should be the primary objective of all maize growers looking to produce as much gas as possible from crops.
While livestock producers may choose varieties taking into account starch content and maturity, this is not the case for biogas growers.
Freshweight yield can be largely ignored as well, as this is mainly a factor of how much water maize contains.
The two parameters which really do matter are dry matter yield/ha and the metabolisable energy (ME) per kilo of crop produced as these will give you an indication of total energy production and gas yield from your land.
For example, in the new 2018 British Society of Plant Breeders (BSPB) Descriptive List for maize for anerobic digestion on favourable sites, the variety Bonnie achieves a dry matter of 31.9% and the highest ME at 11.54 MJ/kgDM, producing an energy yield of 208,000 MJ/ha.
But to establish which of the varieties available will maximise energy production in any particular situation requires a good understanding of land and resources available.
Maize is much more influenced by its immediate growing environment than cereals and oilseed rape and it is not just about geographical location either.
Soil structure, gradient, field aspect and microclimate can all influence how a crop will perform.
One of the most common problems arises when growers over-estimate the heat units available in a particular location and compound this by selecting a later maturing, higher yielding variety in an attempt maximise production.
The earliest maize needs at least 1,200 heat units – average day temperatures above 6degC on an accumulative basis from May 1 to September 30 – and the best management decision you can make is to be realistic about whether your location will achieve this.
If it will not, think again. The all-important energy production is largely based on cob maturity and this will only occur if there are enough heat units available for the plant to mature properly.
‘Bred for Britain’ varieties are selected specifically to achieve early cob ripeness.
Soil type is important too. The optimum soil pH for maize is 6.5-7.0 and the availability of key nutrients can be affected either side of this.
Always go for a more expensive soil test than a basic one as this provides a lot more data.
Maize agronomy is much simpler than it is for conventional arable crops, with few performance-enhancing interventions possible once the crop is established. The choice of variety is therefore critical.
A later maturing group (below 7) might look encouraging in terms of potential yield, but without sufficient heat units for it to fully finish, you will be losing a lot of its potential.
Outright field yield is much less important than achieving a minimum of 30% dry matter and high energy yields to maximise gas output.
Selecting a maturity group one higher (earlier) than you feel appropriate is often a good idea as modern early varieties can fully mature in most conditions with consistent high yields too.
In the 2018 BSPB descriptive list for maize for anerobic digestion on less favourable sites, top-five varieties such as Ardent, Lovely and Remington, still achieve starch contents of more than 30% and deliver total energy yields of up to 183,000MJ/ha – within 10% of top performers on favourable sites (see table).
A 500kW maize-fed biogas unit requires about 200ha/year of crop so a range of maturity dates is beneficial with harvesting, but sticking with earlier maturing, high output group 7-11 varieties is usually the safest option.
Ultimately the aim is to match the variety choice to every field to maximise dry matter without taking unnecessary risks with maturity.
Good seedbed preparation and effective early weed control can affect final maize yields by up to 30%.
As well as helping crops get away strongly, which is essential for high yields, a good, even tilth helps all plants achieve the same growth stage at the same time which results in easier harvest and more consistent energy production.
Ideally, a maize plant needs to put down as much depth in roots as there is growth above the ground, so any soil compaction is bad news.
A compaction pan is usually visible at about 12-18in of depth, so getting a spade out and checking if you have a problem before planning your cultivations is always beneficial.
Maize also provides an opportunity for arable growers to carry out effective grass-weed control and, with the crop also susceptible to early weed competition, it is an important management area.
With maize being late spring drilled, there is a good opportunity to use glyphosate pre-cultivation.
Furthermore, the grass-weed herbicide used in maize crops is nicosulfuron (commonly called Samson), which is a sulfonylurea and is useful in providing a different mode of action on black-grass.
After all the hard work of growing the crop, many less experienced growers lose a lot of the crop’s full potential at harvest.
Most maize crops will increase in dry matter by about 2-3% per week in September and October, but in good weather this can increase to as much as 5% in a single week, so growers need to be careful if they want to get the best quality material in the digester.
Target dry matter for harvest is always a minimum of 30% with a firm cob and only a small amount of moisture which can be squeezed from the grain.
If grains are still clear or milky, whole plant dry matter is likely to be less than 25% and harvest probably three to four weeks away.
If starch is gritty, dry matter will be about 25-28% and harvest probably around a week away, depending on dry matter target.
A good indicator is when the ‘milk line’ can be seen 50% up the grain.
Cutting higher up the stem to improve overall digestibility can result in higher methane yields per tonne fed, but this decision can only be made at harvest based on the current availability of feedstock and potential yields.
Early maturing maize varieties such as Ardent, Lovely and Remington, in the top five of the 2018 BSPB descriptive list for less favourable sites, can produce total energy yields within 10-15% of top performers on the list for favourable sites, such as Bonnie – the variety with the highest combination of harvest dry matter and ME overall.