The Green Food Project

The Green Food Project - HGCA/AHDB report for the Wheat Sub-Group

Increasing the production of wheat in the UK– Essential actions to meet wheat’s potential by 2050

Pete Berry, Sarah Clarke, Neil Paveley,James Clarke & Roger Sylvester-Bradley, ADAS

Key Points

• Analysis shows farm yields could double to ~15 t/ha. Yields haven’t improved beyond 8t/ha for the last 15 years, but could be increased to 9 t/ha using current best practice.
• Progress is needed in logistical, mechanical and chemical technologies to improve yields in conjunction with genetical technologies.
• Achieving 15 t/ha will depend on innovations to: (i) prolong the crop’s yield-forming period, (ii) increaseits water capture, (iii) improveits photosynthetic efficiencyand (iv) protect yield-formation from disease, pest and weed effects.
• High yields will have an effect on the environment – less drainage to water courses, more nitrogen pollution, and more greenhouse gas emissions per hectare (but less per tonne of grain).
• Policy should encourage higher output, and knowledge exchange should be energised through a ‘yield enhancement network’ where scientists, support industries and growers can develop methods to enhance productivity.

Summary

UK wheat production may be increased by expanding its area and by increasing its yield per hectare. The limit to area expansion is about 10%. However, physiological analysis showsthat farm yields could double to ~15 t/ha, from the current UK farm average of 8 t/ha, if the net effect of climate change isnear neutral.

Plant breeders continue to improve wheat variety yields by 0.5 t/ha/decade, and have done so for 50 years. But there has been no on-farm yield improvement beyond 8t/ha for the last 15 years. Thus an immediate need is to realise existing genetic potential. The rate of yield progress must also be simultaneously quadrupledto achieve 15 t/ha by 2050.

Large investments in biotechnology have not, as yet, enhanced wheat yield progress. Resource analysis shows that the technologies required to effect yield improvement are logistical, mechanical and chemical,as much as genetical. Longer term genetic advances must be anticipated and enabled by other technologies, so that potential synergies are properly developed and exploited. Wheat yields could be increased by ~15% (to 9 t/ha) through comprehensive adoption of current best management practices. Further progress to 15 t/ha will depend on innovations to: (i) prolong the crop’s yield-forming period, (ii) increaseits water capture, (iii) improveits photosynthetic efficiencyand (iv) protect yield-formation from disease, pest and weed effects. Yields could decline if the rate of evolution of resistant pests, pathogens and weeds outstrips the rate of introduction of new genetic and chemical controls.

Environmental repercussions of yield enhancement must be anticipated so that additional adaptation and mitigation technologies can arise concurrently. The main environmental implications of achieving potential yield include less drainage to water courses and aquifers, more nitrogen (N) pollution and more GHG emissions per hectare (but less GHG per tonne). Water supplies must be sustained either by adaptations in the water supply industry or by shifting wheat cropping westwards, whilst N pollution may be mitigated by reducing crop N demands and by improving crop N use.

Meeting these unprecedented challenges for UKfarming depends on a paradigm shift in aims and attitudes in the industry towards innovation: industry must become confident that their profits will be enhanced through higher output more than through reducing costs. However, yield is the prime driver of profit from cropping, and efficient business structures have evolved in recent years (with larger farming units, fewer and more technical staff, more sophisticated support industries, greater mechanisation and automation)hence much faster innovation appears feasible. It is crucial that a policy environment for farming is created which instigates and fosters this transformation. We proposethe initiation of a ‘yield enhancement network’ with ‘maximum yield sites’, where scientists, support industries and growers could discuss, integrate and test ideas;to energise knowledge exchange and enablesustainable, high wheat productivity to be realised in the UK through coming decades.

Introduction

Global food security depends on increasingcrop production by 50% in 20 years and by 70% in 40 years[1]. The UK is better placed than most countries to respond, because it has a high yielding environment which is less threatened by climate change than most, atechnically proficient farming industry, with a comprehensive and skilled R&D infrastructure. However, there are constraints on expansion of cropping in the UK and wheat yields have shown no improvement since the 1990s, so the challenges appear considerable, and may require some stimulus.

Despite recent price surges, real wheat prices over recent decades have decreased to an all time low[2].At the same time environmental and safety constraints on development and use of crop inputs have increased, and due to cross-compliance, farm management has focused more on environmental services. Farming businesses have survived mainly by diversification and by reducing fixed costs, with fewer staff and greater areas farmed. Growers have also specialised, so that the frequency of wheat in the rotation has increased. For enhancement of productivity, the industry has largely relied on plant breeding rather than targeting innovations in growing systems and practices. However, wheat is a true-breeding crop, for which growers may save their own seed; this constrains the ability of plant breeders to extract full value from their improved varieties, hence investment in wheat breeding worldwide is only a tenth of investment in maize breeding.Maize has equivalent production and end-use value to wheat but its largely hybrid seed allows the breeder to extract value annually from each variety. Most wheat breeding companies are thus less able to take risks and invest ininnovation.

Wheat production may be increased by expanding cropping and by enhancing yield per hectare. In 2009 we showed[3] how the UKwheat area could expand primarily by replacing 10-20% of temporary grassland (<5 years old) and by increasing the proportion of wheat in arable rotations. After adjustment for the significant reduction in set-aside since 2009 and the increase in temporary grass (<5 years old)[4]we estimatehere that the current wheat area of ~1.9Mha could expand by 0.21 to 0.24Mha. Thus wheat production could increase by 10-13% assuming similar yields on the new wheat land.Environmental implications of this expansion would be modest, arising largely through greater nitrogen (N) use on wheat compared to grass or the other crops it replaces. However, such area increases would clearly be far from adequate in meeting the increase in wheat production required by 2050.

Thus this review analyses the potential for increased wheat yield per hectare on UK farms, itidentifies research opportunities and describes the knowledge exchange conditions required to realise this potential;it then assesseslikely impacts on the environment and suggests appropriate additional adaption or mitigation measures.

Potential of wheat in the UK environment

There are gaps between different yield estimates (Figure1)6: a large ‘Technology gap’ between estimated potential yields and yields currently achieved in research trials, a ‘Practitioner gap’, thought to be small, between yields achieved in research trials and yields of the most efficient farmers, and a ‘Systems gap’, often large, between the most efficient farmers and the mean or typical farm. Part of this Systems gap is due to factors which are difficult to overcome, such as soil type.

Figure 1. Defining yield estimates and gaps between them.6

Current achievements

UK average farm wheat yields are 7.8 t/ha, and have been at this level since the mid-1990s. Similarly staticfarm yields have also been observed elsewhere within Europe and further afield. Farm wheat yields appear to be far from their potential because farm yield variation remains normally distributed –as many yieldsexceed the national averageas are less than average. A new record field yield for UK wheat of 14.3 t/ha was recorded in Lincolnshire in 2011. There is a large and increasing Systems gap;average yields in HGCAvariety trials (underpinning the Recommended List) are currently 10.8 t/ha, 3t/ha more than average farm yields. Furthermore, this gap is widening. Since the mid-1990s, Recommended List trialsand other recent research[5] show variety yields have been increasing by at least 0.5 t/ha/decade[6] for 50 years, contrasting with the recent static farm yields (Figure 2). These trends indicate that crop management currently employed by growers is preventing the increasedproductivity of modern varieties from being realised.

Potential yield

Based on light energy and water potentially available to wheat (as a species) in the average UK arable environment (under research trial conditions), potential wheat yield has been estimated at 18 to 19 t/ha1,[7]. This is based on a potential whole crop biomass (grain plus straw) of about 27 t/ha, assuming that wheat could intercept up to 60% of the annual incident light energy (constrained by the need for time to ripen, harvest, re-plant and re-establish a full green canopy) and that this could be converted with the maximum efficiency observed for wheat in temperate climates. Of this crop biomass, at least 2.6t/ha is needed for leaves, 6t/ha for the stems, and over 2 t/ha for floral organs (chaff), giving a potential grain yield of 18-19 t/ha at 85% dry matter7.

Figure 2.Yield trends for (a) winter wheat: □ UK farm yield and ■ UK Recommended List yields (RL).

Due to inherent differences between research plots and whole fields (i.e. the Practitioner gap), this research potential translates to an average on-farm yield potential of at least 15 t/ha, about double the current national average farm yield of 7.8 t/ha. Thus greater scope for increasing wheat production in the UK lies in increasing the yield per hectare rather than in crop expansion and, with both, UK annual wheat production could exceed 30Mt. However, assumptions underlying the 15 t/ha estimate indicate that its realisation will require as yet unknown combinations of wheat traits and wheat culture, thus will require initiatives to energise innovation, along with significant and targeted investment in research and development.

This estimate of yield potential applies for average soils receiving the average rainfall for the main arable areas of England, and for irrigated crops. However, if wheat is grown on soils such as sands, with a low water holding capacity, or in the drier east of the country, potential yields would be reduced by around 2 t/ha6, and they would be reduced by 4 t/ha if both conditions applied6. Conversely, if more wheat were grown in the wetter west, potential yields would increase by around 2 t/ha.

Effects of climate change

There are several effects of climate change that are likely to affect potential yields. An increase in atmospheric carbon dioxide (CO2) concentration to 550 ppm will have a fertilising effect; 11% yield increases are estimated for crops such as wheat[8]without increasing water use. However, increases in atmospheric ozone may prove damaging[9] and warmer temperatures are likely to be negative: they will tend to shorten wheat’s life cycle (hence reduce overall growth), increase respiratory losses, and inhibit grain set. Greater evapotranspiration and less summer rainfall will also reduce yield in some regions, andthe area of the UK where yield potential is restricted by water availability will expand7. The overall effects of climate change on potential yield are thus uncertain,but at least in the South and East it seems probable that yield potentials will decline. A recent review[10]and the Government’s Climate Change Risk Assessment[11] both illustrated large differences in predictions of the effects of climate change on wheat yields due to different climate scenarios and modelling approaches.

Research and Technology to enhance wheat yields

Immediate opportunities to enhance yield

Improved crop management.Input choice, rate and timing may match crop requirements less precisely now than in the late 1980s due to reduced staffing and tighter margins. It has been suggested that improved crop management could increase wheat yields by 10%3. Although it was also estimated that this might take 10 years to achievethrough knowledge transfer and training3,as will be explained below, new conditions for technology exchange such as existing ‘precision farming’ technologies to automate crop monitoring and input application,might enable and enhance the pace of improvedcrop management with the current reduced labour-force.

Irrigation. Although itwould theoretically be possible to increase wheat yields by 15% using irrigation, economic and environmental constraints would make irrigation difficult to justify for such an extensive, low-value crop. A maximum realistic yield increase of 5% might be achieved by irrigation3, but this would only become economically viable with higher grain prices.

Fertilisingin excess of current economic optimacould cause modest (2%) increases in wheat yields3. However, without new technology to target these at nutrient deficient areas, theywould also require price changes to become economically viable, and they would also cause increases in GHG emissions per tonne of grain (~120 kg/CO2e/t additional to 400 kg/CO2e/t at present).

Overall, we estimate that knowledge exists to increase farm yields by ~15% (from 7.8 to ~9t/ha) assuming each of the above effects is additive. However, economic changes and substantial knowledge transfer initiatives will be required to realise this increase.

Yield enhancement through innovation and targeted research

The potential wheat yield of 18-19 t/ha estimated aboveassumes an extendedyield-forming period (from the start of stem extension to the end of grain filling), increased efficiency of light energy conversion to biomass, increasedsoluble biomass in stems(for relocation to the grain) and deeper rooting (unless irrigation is provided), as quantified in Table1.

Table 1. Crop characteristics for potential wheat yield6.

units / Current research trials / Potential research targets
Start of stem extension / date / 10 April / 28 March
Start of grain filling period (GFP) / date / 19 Jun / 14 June
End of GFP / date / 29 July / 1 Aug
GAI at start of stem extension / ha / ha / 2.0 / 2.5
GAI at start of GFP / ha / ha / 6 / 7
Light energy intercepted in GFP / proportion / 0.83 / 0.88
Efficiency of energy conversion† / g/MJ / 1.2 / 1.4
Soluble stem biomass / tonnes /ha / 2.3 / 5.0
Rooting depth / metres / 1.2 / 1.8
Seed yield (at 15% moisture) / tonnes /ha / 10.5 / 18.5

†Efficiency of light conversion is the grammes of biomass formed per megajoule of light energy intercepted by the crop’s green canopy.

In 2009, a comprehensive exercise was carried out to establish the research and development priorities required to achieve the potential yield for the UK3,and the resulting detailed list of research requirements is set out in Appendix 1, together with estimated timescales to impact and potential effects on yield and GHG emissions.

Following on from the 2009 report3 technologies and targets likely to be appropriate in achieving the potential wheat yield have been suggested (Table2)[12]. These technologies are categorised as Biotechnology and Plant breeding, Chemistry, Engineering (including IT), and Farm system design and management. The conclusion isthat progress will depend on co-ordinationof geneticadvances with the other enabling technologies. It is proposed that traits for research and development to realise the potential yield must embrace four main aims:

Prolonging the crop’s yield forming period

Increasing water capture and conversion efficiency

Increasing the crop’s conversion of light energy

Protecting yield potential from disease, pests and weeds

However, the large environmental impacts of increasing conventional fertiliser use to support potential yields are such that a fifth area of ‘Improving the crop’s N efficiency’ must be added. These five areas then are summarisedin the following sub-sections.

Table 2.Technologies required to achieve potential wheat yield adapted from Sylvester-Bradley (2010): Traits and technologies in bold are regarded as priorities.

Target / Technologies
Biotechnology & plant breeding / Chemistry / Engineering & IT / Farm system design & management
Life cycle adaptation / Daylength & temp. responses; frost tolerance / Growth regulators / Cultivators and drills; Harvesters / Sowing logistics
Biomass partitioning / Soluble stem biomass / N / Seed rate management
Nutrient capture / Rooting & nutrient assimilation / Loss inhibition & fertiliser formulation / Soil, seed and foliar targeting and precision location / Rotation design; sowing methods
Water capture / Rooting / Growth regulators / Soil management, and irrigation / Rain harvesting & water storage
Longer green canopy lifespan / Leaf no. & life-span. Low grain N / Prolonged nutrition & protection / Fast combine harvesters / Rotation design to accommodate later harvests
Better photosynthesis & water conversion / Canopy form, sink capacity, C4 metabolism, CO2 pumps / Anti-transpirants / Wind breaks
Nutrient conversion / Nutrient storage in canopies & grains / End-use processing & marketing
Lodging resistance / Shortness, stem material strength / Growth regulators / Rotation, seed rate and sowing date
Weed control / Herbicide resistance / Herbicides / Cultivations / Control opportunities
Disease control / Resistance to & tolerance of pathogen / Fungicides / Monitoring & forecasting / Rotations, crop choice
Pest control / Resistance, push-pull / Pesticides / Cultivations, monitoring & forecasting / Rotations, farm habitat design
Waste minimisation by harvest efficiency / Synchrony of ripening / Harvesters

Prolonging the crop’s life cycle and yield forming period

Extending the total life cycle of a wheat crop should significantly improve yields by maximising light capture during a season, the three targets being: earlier stem extension, earlier canopy closure, and delayed canopy senescence (death).

An earlier start to stem extension in early spring should release feedback-inhibition of photosynthesis by creating a demand (sink) for photo-assimilate. However, understanding of wheat development is inadequate to achieve ‘designed’ earliness at present so appropriate breeding approaches must be enabled through quantitative phenotyping of those genes influencing the key aspects of crop development including; vernalisation (requirement for cold period), photoperiod (sensitivity to daylength) and earliness per se. Work was initiated through recent BBSRC and Sustainable Arable LINK projects (e.g. LK0992[13]), and methods developed, but further work is needed to reach a position where plant breeders can make progress.