Farm Carbon Cutting Toolkit


05.10.15 Investigating the effect of pH and fertiliser on Nitrous oxide production from farm soils

So for the last blog of the month looking at Nitrous oxide here is a piece of research conducted by Theo Platts-Dunn at Lancaster University as part of a Masters programme. Some of the data that informed the study is based on Adam's farm, so this is a great opportunity to see some research in action (which also fits nicely into our theme).

Our thanks to Theo for allowing us to publish it here.

What's is all about?

This project aimed to assess the effectiveness of how nitrification inhibitors work, in conjunction with common inorganic fertiliser (Ammonium Nitrate and Urea), to reduce nitrous oxide emissions from soil after fertiliser application. As the well as the effect of inhibitors on N2O production I was also interested in the effect of the pH on N2O as I had found some lack of clarity regarding its influence in prior research. I designed a laboratory experiment to investigate these themes.

What did it find?

The results of the experiment showed that the nitrification inhibitors drastically reduced the N2O production when applied together with fertiliser compared to fertiliser applied which contained no inhibitor (Up to a 90% reduction). With regard to pH, a slightly more acidic soil generally results in lower N2O production. This was true with the ammonium nitrate treated cores and the control cores. This is likely due to the enzyme inhibitory effects of a lowered soil pH. Soil cores treated with urea did not show a statistically significant difference between ambient and lowered pH suggesting that urea increases the pH of soil when applied.

What does it mean?

The findings of this report highlight some of the complexities of practically managing N2O production from soil. In addition to pH other soil parameters such as; soil water content, temperature, aeration, organic content, mineral N availability and soil texture have an effect on N2O production. These parameters not only have an effect individually but also combine and interact in ways which are challenging to model. The best approach for effective mitigation of N2O is arguably to carry out case-by-case mitigation strategies as opposed to broad scale guidelines offered by bodies such as the IPCC. However, the challenge really lies in incentivising land owners to carry out such assessments which may seem to them to involve additional cost and little economic return.

How can I read the full report?

The full thesis is available to download here.

29.09.15 Focusing on soil structure to retain healthy grasslands

A recent Defra-funded study of 300 grassland fields found that just 40 per cent had good soil structure. That alarming figure serves to reinforce the importance of an ongoing initiative from AHDB’s beef, lamb and dairy sectors – Healthy Grassland Soils – which aims to help grassland farmers study soil properties and choose the best management practices.

At this time of year, farmers should be investigating the health status of grassland soils, as where action needs to be taken this can be done straight away. At the end of the summer, soils are less dry and it’s a good time to assess their structure. Using aerators or sward lifters in the autumn also means that the soil and the roots have the winter to recover before the high demands of spring when grass growth really gets going.

In cases of mild compaction, soils do have a capacity to recover on their own, especially if the cause, such as grazing livestock, is be removed. In these situations it may be worth monitoring the field over a few weeks to see whether it improves. Taking photos on a phone is a simple but useful way to track soil condition.

There is good evidence that using aerators or sward lifters in soils without poor structure has limited benefit and can cause damage, especially if the soil conditions are not appropriate.

If an aerator or sward lifter needs to be used, it is important to make sure soil moisture conditions are correct to avoid further damage. If a handful of soil obtained from the depth that needs to be worked gives a moist smooth surface when rolled then it is too wet to work. If the soil starts to crack then the soil conditions are appropriate.

Aerators and sward lifters need to be working 2.5cm below the problem area so dig holes to make sure the equipment is doing the correct job.

As part of the Healthy Grassland Soils project, soil structure assessment tools and a website — — have been developed with more technical information, especially in relation to soil biology. An assessment sheet and pocketbook is available from the AHDB Beef & Lamb Better Returns Programme.

Source:Farming Futures blog 

29.09.15 Mitigation of nitrous oxide emissions from livestock part 2

Following on from the blog at the end of last week looking at mitigation of nitrous oxide emissions from livestock systems, this second part of the report looks at some of the science behind management that has been advocated to reduce GHG emissions (in particular nitrous oxide), and how these can integrate into management changes on the farm.

The diagram below comes from the paper (link here) that these blogs are based on, and highlights some of the areas to consider when looking to reduce nitrous oxide emissions from your system. If you click on the picture it will enlarge.

Animal management and housing

Structures used to house livestock do not directly affect the processes resulting in nitrous oxide and methane emissions, however the type of structure used determines the manure management methods used to handle, store, process and use the manure.

Housing systems with solid floors that use straw accumulate manure with a lighter DM which when stored in piles created conditions for nitrification and denitrification and thus greater nitrous oxide emissions. Farmyard manure and deep litter manure handling systems tend to produce greater nitrous oxide emission than slurry based systems.

Dietary effects on manure emissions

Manipulating rations to reduce nutrient excretion of N and P are well studied, but relating it to mitigation of methane and nitrous oxide is fairly new. Data in the effect of dietary protein on manure Nitrous oxide emissions is not consistent. Tannins as a dietary supplement has been studied, but more studies are needed in terms of relating tannin application through the diet to manure and GHG emissions.

Grazing practices

Improving pasture quality in terms of forage digestibility is an efficient way of decreasing GHG emissions from the animal and the amount of manure produced. In pasture based systems, improving forage quality often means increasing Nitrogen fertiliser application rates which can have a negative impact on urinary N excretion and thus ammonia and nitrous oxide emissions.

Reduction of nitrous oxide emissions from intensive grazing systems can be achieved by several strategies:

Improving N use efficiency through reducing the amount of N excreted by grazing animal

Optimising soil management and Nitrogen inputs

Optimising pasture renovation

Manipulating soil N cycling processes through soil additives

Selecting for plants and animals that maximise N utilisation

Altering grazing and feeding management

Manure storage and treatment

Greenhouse gas emissions from stored manure  are primarily in the form of methane (due to anaerobic conditions) although nitrous oxide emissions can occur and ammonia volatilisation losses are often large.

A direct way to avoid cumulative GHG emissions is to reduce the amount of time manure is stored.

Storage covers

Semipermeable covers tend to increase Nitrous oxide emissions because they provide optimal aerobic conditions for nitrification at the cover surface and at the same time create a low oxygen environment just below the cover favourable for denitrification and the production of nitrous oxide.


Due to the nature of the composting process N losses can be high and are influenced by a number of factors including temperature C to N ratio, pH, moisture and material consistency. Compost can be a source of nitrous oxide emissions with both nitrification and denitrification processes occurring during composting.

Land application

Application method and emissions

An important difference between mineral fertiliser and manure is that manure contains organic Carbon which, depending on soil condition may affect Nitrous oxide emissions.

Manure carbon may increase microbial respiration rates in soil, thus depleting oxygen providing the anaerobic conditions required for denitrification. Compared with mineral Nitrogen sources, manure applications increases soil Nitrous oxide flux in soils with low Carbon content. Soil nitrous oxide emissions can vary greatly and emissions factors of up to 12% of N input (for nitrate based fertiliser) and 5% for manure have been reported.

Incorporating manures can greatly reduce ammonia emissions, leaving more N susceptible to emissions as nitrous oxide. However reduction in ammonia losses with incorporation means that smaller quantities of manure are required and potential for nitrous oxide production is reduced.

Urease and nitrification inhibitors

Microbial processes that result in nitrous oxide production can be manipulated through the use of chemical additives (see earlier blogs).

Cover crops

Cover cropping can reduce soil erosion, improve soil quality and fertility, improved water, weed, disease and pest management and enhance plant and wildlife diversity on the farm,

Reduction of Nitrogen fertiliser use by growing leguminous cover crops has a direct mitigation effect on soil nitrous oxide emissions by reducing soil nitrate availability and potential leaching. Cover crops can increase plant N update and decrease nitrate accumulation and thus reduce nitrous oxide production through denitrification but the results on overall GHG emissions have not been consistent.

What does this show?

There are a number of animal and manure management practices that are feasible and can effectively reduce methane and nitrous oxide from manure storage and for land application. Therefore due to numerous interactions at the animal, storage and land applications phases of the manure management process, GHG mitigation practices should not be evaluated individually in isolation but as a component of the livestock production system as a whole.

Source: Montes et al (2014) Mitigation of methane and nitrous oxide emissions from animal operations: II. A review of manure management mitigation options, J. Anim.Sci. 2013.91:5070-5094

25.09.15 Nitrous oxide emissions and manure management

So for the last couple of blogs looking at nitrous oxide before we move onto something else, a big subject which hasn’t really been tackled yet is manure management and the impact of manure storage and application on nitrous oxide.

Animal manure is a nutrient resource containing most of the essential elements required for plant growth and can be a significant source of N in both intensive and subsistence production systems.

Applying this manure to fields (as we all know) has numerous benefits including building soil organic matter levels, microbial biomass and mineralisation rates, and improves soil tilth, water holding capacity, oxygen content and fertility, as well as reducing soil erosion, reduces nutrient leaching and increases yields. There is also the added benefits that come from using these manures as a source of fertiliser and when this is synchronised with crop requirements and uptake is a very cost effective resource of nutrients.

If these materials are not managed correctly however they can present environmental risks, including emitting Nitrous oxide (alongside methane and ammonia), which we want to avoid, not only because of its deleterious effects in terms of our GHG credentials, but also (more importantly from the farmer’s perspective) because it’s a source of nitrogen that we could potentially use to improve yield but is being lost to the environment.

Nitrous oxide emissions from manure

Nitrous oxide emissions from soil application of manure are a major contributor to total GHG emissions from agriculture.

Direct emissions of nitrous oxide from manure storage are small when compared with methane emissions. For nitrous oxide emissions to occur, manure must first be handled aerobically (with oxygen present) when ammonium or organic Nitrogen is converted to nitrate and nitrite during nitrification and then handled anaerobically (without oxygen) when the nitrate and nitrite are reduced to nitrogen and nitric oxide through denitrification.

Most of the nitrous oxide resulting from manure is produced in the soils where manures have been applied. The bits of the nitrogen cycle that produce nitrous oxide (bad) are the microbes present in the soil working on the manure under aerobic conditions (part of the natural process that can’t really get away from) and partial denitrification under anaerobic conditions (what we want to try and minimise), as it is the anaerobic conditions which produces more nitrous oxide.

Manure contains most of what it needs to kick-start the processes in the soil of nitrification and denitrification. However these processes are pretty fickle beasts and the rate of them occurring will depend on the amount and type of nitrogen present, the available carbon sources, water content, temperature of the soil and what bugs are there to work on the manure.

As you may be appreciating it’s a fairly complex system which depends on lots of variables as to where the emissions occur and whether its nitrous oxide, ammonia or methane that is the main issue. As nitrous oxide is emitted as a result of different microbial processes the rate of emissions is highly variable. This causes a bit of a problem when looking for those nice ‘one size fits all’ answers which we all want which will tell us how to minimise the emissions of nitrous oxide when we are applying manures (with all the great agronomic and economic benefits that occur).

What does the research say?

Scientists have been puzzling with this for a while, and clever computer models alongside very sophisticated measuring and monitoring equipments, means that it is now possible to look at how effective different mitigation practices are at controlling nitrous oxide and look at the effect this may have on the livestock production system.

However there is a further complication (nothing is ever simple).

Due to the nature of the processes that result in methane and nitrous oxide being produced, some practices that result in the reduction of methane emissions (yay!), increase nitrous oxide emissions. For example, one practice advocated by some is the aeration of slurry and manure during storage which reduces methane emissions. However if the aeration rate is sufficient to create an aerobic environment, the rate of nitrous oxide emission will often be increased.

It’s an area where we are not completely there yet. There is still much to learn about the benefits (and potential drawbacks) of particular mitigation practices, the effect of combining mitigation practices, the response of environmental indicators and the effect on the environmental and financial performance of the farm as a whole.

What this report does highlight is some indications of where efforts should be addressed.

To save the blog being massive, I’ll delve into some of these next week.

Source: Montes et al (2014) Mitigation of methane and nitrous oxide emissions from animal operations: II. A review of manure management mitigation options, J. Anim.Sci. 2013.91:5070-5094

14.09.15 Personal experience with global warming drives mitigation behaviour

A number of studies have shown that the public misunderstand global warming. Taking a fresh approach, this study investigated the willingness of the public to take part in activities that mitigate climate change. An international survey of 24 countries revealed that this is strongly related to personal experiences with global warming. The authors say linking actions to benefits could encourage climate change mitigation behaviour.

While we know public perception of climate science is often inaccurate, understanding of what causes beneficial behaviour change is less complete. The factors that influence the decision to take part in actions to mitigate global warming include not only knowledge but also beliefs in personal experience of unusual weather, general beliefs and worldviews.

In this study, researchers conducted an international survey to determine the factors that are most influential. The US-based researchers administered an online survey to 25 samples of participants in 24 different countries, gaining a total of 11 614 responses. The survey was designed to measure six key factors: belief in global warming, environmental worldview, self-efficacy (an individual’s judgement of their ability to have a significant effect on outcome), personal experience with global warming, belief in the free market system, and knowledge about the causes of global warming.

The survey also asked the participants about their general intentions to mitigate climate change, and willingness to take part in specific activities. General intentions were measured by statements such as “I plan to take some actions to stop global warming”, while specific behaviours included “Concerns about global warming guide my voting behaviour” and “I intend to carpool and drive less”.

Most samples endorsed general action more than specific actions, although several Asian countries did not follow this trend. In all samples, the most endorsed specific action involved adjusting home temperature (e.g. using less heating in the winter), followed by changes to commuting and then voting.

The researchers next analysed which factors best predicted intention to act, both for general and specific actions. Most significantly, they found that personal experience (e.g. “Changes in global warming have impacted my life already”) is most important in predicting specific action, while self-efficacy is more important for general intention to act.

The authors say this is because intention to perform concrete actions is strongly linked to personal experiences that highlight the value of these actions, while thinking about general mitigation action is more associated with abstract or ‘big-picture’ thinking and therefore feelings of self-efficacy.

The three factors most important in predicting action were pro-environmental worldview, personal experience with global warming, and feelings of self-efficacy.The least important predictors were gender, age, belief in the free market system, political affiliation and knowledge of global warming.

The researchers also found that differences between individuals within samples were greater than differences between samples, suggesting that willingness to take part in mitigation actions (and its drivers) does not much differ between nations and cultures. Importantly, this indicates that climate change communication schemes could be used across the world with little variation.

The authors provide recommendations on how to use their findings to encourage climate change mitigation behaviour among citizens.

For example, the study found that while most respondents were generally willing to mitigate climate change, they were much less willing to perform specific actions. The authors say this common problem could be tackled by highlighting the personal effects of future climate changes, such as more frequent flooding or the later blossoming of plants in a local area.

While personal experiences foster one’s perceived value of mitigation action, the random variability of experiences does not generate consistent (sustained) action that is needed. The researchers suggest that communication and education strategies focus on additional (or alternative) sources to foster perceived value in mitigation action.

For instance, as different locations will experience varying effects of climate change, which may increase variability in public opinion. An alternative way to motivate mitigation behaviour could be to link actions to their effects on the wider environment. The authors say this would improve ‘causal mental models’ and help the public to visualise the effects of their actions.

Source: Science for Environmental Policy Briefing, 10th September 

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