Maximising the greenhouse gas savings in biofuels produced from wheat will require a change in attitude towards nitrogen use in the crop, and a £15/t premium to make it viable for growers, ADAS‘s Roger Sylvester-Bradley said at HGCA‘s “Arable Cropping in a Changing Climate” R&D conference.
From 2010 the government intended that the rewards for biofuel use should be related to the amount of greenhouse gases they save, which would cause feedstocks to be valued in the same way, he said.
“EU biofuels must save greenhouse gases. Growing UK feed wheat as we do now saves around 40% of the emissions associated with petrol.”
The vast proportion of GHG produced from growing wheat was attributable to nitrogen fertiliser, he said. About 38% came from N fertiliser manufacture, while a further 38% was from its use in the field. “The rest is mainly diesel (10%) and drying (8%).”
Reducing that to produce the optimum amount of greenhouse gas savings would require growers to think very differently in terms of nitrogen, he said.
Optimised alcohol wheat
Minimum greenhouse gas wheat
Optimum N (kg/ha)
Gross margin (£/ha)
Ammonium nitrate £150/t; Feed wheat £145/t; Alcohol £0.27/litre
Analysis, using a typical nitrogen response curve, suggested the optimum N required to maximise GHG savings was only 91 kg/ha, compared with 236 kg/ha for feed wheat as grown now. The optimum for alcohol (or starch) production – which processing plants could pay a premium for soon – was 184kg/ha, he said.
Given current prices, that would result in a £131/ha lower gross margin for wheat grown to maximise GHG savings, he pointed out. “The premium required to compensate growers would be significant – in the order of £15/t or £130/t CO2 equivalent saved. It remains to be seen whether future accreditation arrangements and market mechanisms will support that.”
Wheat for biofuel made sense under the RTFO rules due to take effect in April, which assumed the same GHG savings for every wheat crop, he said.
But when savings were calculated at a farm or field level, which would be necessary when biofuel use would be rewarded by how much GHG it saved, innovative ways of reducing the amount of N required could be needed, he suggested.
In the longer term, genetic modification could help. Canadian researchers had discovered an enzyme that increases nitrogen assimilation in plants. Transferred into oilseed rape using GM technology it had halved the N fertiliser requirements, he said.
Of more immediate help would be a change in varietal testing regime. Recommended List trials were set up to find high yielding varieties under high inputs, including nitrogen. But for biofuel wheats it would be better to know which were high yielding under low N conditions. “To bring progress we need to test varieties with no N, as well as ample N at some sites. That would give the motivation for breeders to do the same, and select varieties for their N efficiency as well as yield.”
Reducing that to produce the optimum amount of greenhouse gas savings would require
Eight attributes of biofuel wheat
- High yielding (to reduce land requirements)
- Requires little or no N fertiliser
- Be established with minimal cultivations
- Harvested dry (no drying)
- Large straw yield (sequesters carbon or when burned replaces fossil fuels)
- High content of fermentable starch and sugar in grain
- Minimal grain protein and low non-starch polysaccharides (bad for processing)
- Easily demonstrable attributes to verify GHG value
HGCA R&D conference
The two-day HGCA conference “Arable Cropping in a Changing Climate” in association with Farmers Weekly and Crops covered the potential impacts climate change could have on UK agriculture, how growers might adapt and the opportunities that could occur. For more coverage see www.fwi.co.uk and the next issue of Crops out on 9 February