Dave Freeman Archives | ClimateXChange

In 2018, agriculture accounted for 18% of Scotland’s total greenhouse gas emissions (GHG), with a significant share coming from nitrogen fertilisers. One policy approach identified as having potential to reduce nitrogen fertiliser use is through leguminous crops to fix atmospheric nitrogen.

This study assesses the opportunities, challenges and barriers influencing potential production of grain and forage legumes in Scotland. Grain legumes are crops such as beans and peas while forage legumes include lucerne (also known as alfalfa), clover and vetch.

We assess the climate mitigation potential of legumes within arable and grassland rotations and comment on the potential to reduce reliance on imported protein.

Key findings

Current production and trends

There has been a historical decline in the grain legume area in the EU, largely as a result of economic forces. This is matched in Scotland – there is a low level of production (2.3% of the tillage crop area in Scotland).
Use of legumes within forage grazing is an accepted practice in Scotland and large areas of improved grassland benefit from their inclusion. There is little scope for an expansion in the area of legumes in pasture.

Availability of land

There is a large area of land which is theoretically suitable for legume crops growth. Generally, the most suitable land lies in the east of Scotland and the lowlands. However, Scotland’s climate can pose issues for cultivation, leading to a perception among some farmers of poor crop performance.
Climate change is not expected to have a major effect on the area of land that can support legume crops in Scotland.

GHG emissions

The main way to reduce GHG emissions is through crop substitution, increasing the use of leguminous crops. This results in changes in nitrous oxide emission from soil (through changes in nitrogen fertiliser use and crop residue returns to the soil); and lower emissions from manufacture of nitrogen fertiliser (occurring outwith Scotland).
Including legumes in crop rotation, one year in five, could lead to an annualised nitrogen saving of 30.8 kg/ha. This is a saving of 24.1%.
The savings in GHG emissions from including legumes are 107.4 kt CO₂e/yr, rising to 160.8 kt CO₂e/yr when fertiliser manufacture GHG emissions (outwith Scotland) are included. This is equivalent to 1.4% of Scotland’s agriculture emissions, rising to 2.2% when fertiliser manufacture GHG emissions are included.

Market and other constraints and opportunities

The UK is reliant on imports to provide 47% of protein sources used in animal feeds. With greater awareness of the need for sustainable protein, the importance of domestic protein sources is set to increase.
Economic conditions for both demand and supply are key influences on the area of legumes grown. As an ingredient in animal feed, legumes can be uncompetitive with other protein sources.
From a grower’s perspective, the price paid for legumes is too low and other cropping options give higher and more reliable returns. However, new markets for human food ingredients and a growing demand in the fish feed sector could offer opportunities.
There are a range of technical and logistical limitations which depress the market for grain legumes. These may require some intervention but should not be significant, long-term barriers.
Perceived poor performance of grain legumes in Scotland has suppressed the area cropped. However, greater awareness amongst the industry of the potential of legumes to support more sustainable rotations and soil health, and to help manage disease and “regenerate” land, are increasing interest.

Scotland’s Climate Change Plan includes a policy commitment to reduce emissions from the use and storage of manure and slurry.

Agriculture and associated land use account for 24% of greenhouse gas (GHG) emissions in Scotland, with methane the most significant proportion of this at 44%. Methane comes from manure and enteric fermentation. The management of manures is therefore a critical element in mitigating the sector’s GHG emissions.

This study examines the feasibility of developing manure exchanges (slurries and farmyard manures) to reduce these emissions.

Main findings

The arisings of manure in Scotland indicate a total available nitrogen supply of 14,700 tonnes per annum from manure, compared with a total utilisation of applied nitrogen of approximately 152,000 tonnes.
A significant proportion of manures could potentially be part of a manure exchange, with just 6% of manure arisings currently reported as being exported from source.
The potential abatement of GHG emissions by offsetting manufactured nitrogen through the substitution of organic manure is limited. Under the most favourable scenario modelled, the potential saving is equivalent to just 0.68% of annual agricultural emissions.
We found three broad examples of schemes which support the movement of manures and would be relevant within the Scottish context: muck-for-straw, manure exports and movement of livestock.
Requirements for nitrogen are greater in all major regions of Scotland than can be supplied by manure sources.
Compared with other European countries, Scotland does not have a significant oversupply of livestock manures at a regional level.
There are environmental challenges associated with manure and slurry production and storage at an enterprise level, particularly for water quality. The potential for local surpluses has therefore been the focus of this study.
Surpluses of manure can lead to localised environmental impacts if they are not managed correctly. The factors influencing the success of manure exchanges rely on the recognition of costs and barriers and on investment in establishing agreements.
A strategic, regional or national scale exchange model is unlikely to be cost effective for GHG gas abatement. However, there is some potential to support exchanges of manure through improved local distribution (i.e. within a holding or with close neighbours).
The most useful measures are those that focus on the utilisation of manure nutrient value and that form part of an integrated policy alongside other drivers such as water quality (Water Framework Directive), Nitrate Vulnerable Zones, air quality and productivity.

Scotland’s Climate Change Plan makes a policy commitment to reduce greenhouse gas (GHG) emissions from nitrogen fertiliser through improved understanding, efficient application and better soil condition.

This report considers the potential for nitrogen and urease inhibitors to support emission reductions in Scotland, considering Scottish circumstances and conditions, such as soils, crops, rainfall and temperature.

These inhibitors are particularly important for those who are modelling both GHG emissions and air quality. However, while some studies provide consistent messages concerning the evidence of their effectiveness and their impacts on the wider environment, others are contradictory.

Main findings

The evidence indicates that:

There is generally a positive potential impact of inhibitors on GHG and ammonia emissions under Scottish conditions, especially for nitrification inhibitors.
There are no significant concerns over the efficacy of inhibitors in Scotland. Low uptake relates to the niche market; inhibitors are primarily supplied for agronomic benefit with relatively marginal economic gains in most circumstances.
While the efficacy of inhibitors has been confirmed by the review, there remain uncertainties over the magnitude of emissions reductions. There are also questions relating to the environmental risk, trade-offs with potential emission/pollution switching, industry knowledge and practical implementation.
The persistence of the effects for both nitrification and urease inhibitors are likely to be impacted by a warmer climate, although any impact is likely to be minimal. Emissions from unabated fertilisers are expected to increase as climate change progresses. Under these conditions, the role of inhibitors as a tool in mitigating emissions becomes increasingly important.

The evidence for environmental risks includes:

There is little evidence exploring the impacts of N inhibitors on soil health and on impacts to non-target and nitrifying organisms.
Use of nitrification inhibitors can lead to increases in ammonia emissions. However, alongside this, there are benefits for other environmental indicators (particularly GHG emissions and nitrate leaching). The potential increase in ammonia emissions can be mitigated by use of nitrification and urease inhibitors together.
Some research highlights the risk of DCD (dicyandiamide – a nitrification inhibitor) leaching into surface and ground waters. This can have adverse effects on aquatic systems.
There are concerns regarding animal consumption (directly or via traces found on grass/hay) as DCD has been found in dairy products in New Zealand. This led to DCD being banned in New Zealand.
Increased risk of ammonia release from use of nitrification inhibitors will have adverse impacts on ecosystem biodiversity through deposition and increased N loading to sensitive sites.

The main practical/commercial considerations are:

Nitrification and urease inhibitors are not widely used due to poor cost effectiveness under conventional economic analysis at farm gate (i.e. not considering externalities of environmental or societal costs).
In the agriculture industry, there remains significant misunderstanding over the roles and practical application of inhibited fertilisers.
Investment in nitrification inhibitors will not be driven by market pull. Stakeholders feel N inhibitors are not currently attractive prospects for increased investment.
Urease inhibitors are more commercially viable (compared with nitrification inhibitors) and have potential economic benefits due to the potentially high emissions of ammonia losing significant N content. Interest and awareness of urease inhibitors is greater.
Price sensitivity: farmers in the UK are very sensitive to fertiliser price and will seek the most cost-effective source of N. A perception of little or no economic value in inhibited fertilisers will discourage adoption.

Main findings

The evidence indicates that:

There is generally a positive potential impact of inhibitors on GHG and ammonia emissions under Scottish conditions, especially for nitrification inhibitors.
There are no significant concerns over the efficacy of inhibitors in Scotland. Low uptake relates to the niche market; inhibitors are primarily supplied for agronomic benefit with relatively marginal economic gains in most circumstances.
While the efficacy of inhibitors has been confirmed by the review, there remain uncertainties over the magnitude of emissions reductions. There are also questions relating to the environmental risk, trade-offs with potential emission/pollution switching, industry knowledge and practical implementation.
The persistence of the effects for both nitrification and urease inhibitors are likely to be impacted by a warmer climate, although any impact is likely to be minimal. Emissions from unabated fertilisers are expected to increase as climate change progresses. Under these conditions, the role of inhibitors as a tool in mitigating emissions becomes increasingly important.

The evidence for environmental risks includes:

There is little evidence exploring the impacts of N inhibitors on soil health and on impacts to non-target and nitrifying organisms.
Use of nitrification inhibitors can lead to increases in ammonia emissions. However, alongside this, there are benefits for other environmental indicators (particularly GHG emissions and nitrate leaching). The potential increase in ammonia emissions can be mitigated by use of nitrification and urease inhibitors together.
Some research highlights the risk of DCD (dicyandiamide – a nitrification inhibitor) leaching into surface and ground waters. This can have adverse effects on aquatic systems.
There are concerns regarding animal consumption (directly or via traces found on grass/hay) as DCD has been found in dairy products in New Zealand. This led to DCD being banned in New Zealand.
Increased risk of ammonia release from use of nitrification inhibitors will have adverse impacts on ecosystem biodiversity through deposition and increased N loading to sensitive sites.

The main practical/commercial considerations are:

Nitrification and urease inhibitors are not widely used due to poor cost effectiveness under conventional economic analysis at farm gate (i.e. not considering externalities of environmental or societal costs).
In the agriculture industry, there remains significant misunderstanding over the roles and practical application of inhibited fertilisers.
Investment in nitrification inhibitors will not be driven by market pull. Stakeholders feel N inhibitors are not currently attractive prospects for increased investment.
Urease inhibitors are more commercially viable (compared with nitrification inhibitors) and have potential economic benefits due to the potentially high emissions of ammonia losing significant N content. Interest and awareness of urease inhibitors is greater.
Price sensitivity: farmers in the UK are very sensitive to fertiliser price and will seek the most cost-effective source of N. A perception of little or no economic value in inhibited fertilisers will discourage adoption.