conclusion

To summarise the posts over the last few weeks, I have looked at where and why domestication first happened and the debates surrounding the timing of its origins.  The timing of domestication's first effects on the climate has been an important point and is an on going debate.  The blog then proceeded to discussing how agriculture and its expansion has affected the environment and how cultivation contributes to climate change.  I then discussed some of the possible strategies to combat further increases in greenhouse gas emissions and the feasibility of their adoption. 

Through researching these posts I have discovered how interlinked climate and domestication really are.  Climate played a key part in why domestication developed and also agriculture is playing a main role in altering climate though emissions.  Climate is always affecting agriculture and the changes associated with anthropogenic climate change will be vital in determining food security in the future.   Agriculture will always be a key issue as people will always need food and as the population continues to grow so its will demand.  It has also come to light that looking at past practices in agriculture could help us in the future, returning perhaps to more sustainable methods used in the past will aid environmental problems that are arising such as soil degradation and erosion.  

Thank you for taking an interest and reading these posts, I hope they have bettered your knowledge of the relationship between domestication and climate. 

summary of mitigation

In the last few posts I have discussed various mitigation strategies that have been put forward aiming to reduce greenhouse gas emissions from agricultural sources.  

A key theme I noticed throughout looking at these articles was economic factors.  In many places around the world, especially in developing nations, it will be very difficult to implement a number of these strategies due to the economic cost.  Consequently, it would be beneficial to attempt as many as possible in countries that can afford to have the schemes, as this would reduce a proportion of emissions.  However, populations in the developing world are growing quickly and are projected to hold the majority of future growth.  This will mean a greater demand for food.  Many developing countries provide cultivated products that other places in the world rely on, such as rice.  Therefore it will be necessary to reduce emissions from these countries, but it will likely require subsiding and the provision of economic incentives for them to be adopted.  

Personally, the strategies I would consider best to implement would be those incorporating more organic methods.  These not only help with the reduction of fossil fuel burning and greenhouse gas emissions but they also improve food security around the world by improving soil quality to its former states.  To name a few of these practices would be,  no-till, crop rotations and cover crops.  I believe that draining rice paddy fields in the non growing is also a feasible and beneficial strategy, as it does nothing to the yield and lowers methane emissions.  Also better use of fertilisers is very important as this will reduce nitrous oxide emissions, reduce fossil fuel burning and avoid soil degradation.  Planting trees, or returning to native habitat on marginal croplands is also very beneficial, as it reduces emissions with very little impact.  All these strategies are less economically intense than some making them easier to implement.  

It is important when considering mitigation strategies that the yield is not changed.  This will make strategies more unpopular as they will be an economic cost to farmers and it will be uncertain if enough food can be produced for the population at the current price.  it is also important that the quality of produce is not affected by strategies as it will put people off buying it.  

Using mitigation strategies is necessary to reduce greenhouse emissions from agriculture as they do contribute to a large proportion of anthropogenic atmospheric inputs.  However it will be a lengthy process requiring management, ample research and high financial investment.  

is organic the way forward?

In recent years organic farming has become increasingly popular.  Not only is it perceived as being healthier, it is also believed that it can mitigate climate change.  Organic farming, as its name suggests is natural farming, where food is produced using techniques such as crop rotation, green manure, compost and biological pest control.  This is different to conventional farming which uses manufactured or synthetic fertilisers and pesticides, plant growth regulators livestock antibiotics, food additives and genetically modified organisms.  It is common belief that organic farming could mitigate climate change as it seems more natural.  This post is going to discuss ways organic farming can reduce greenhouse gas emissions and whether it is a feasible mitigation strategy.  

This article by the ITC (2007) suggests reasons why organic farming is a possible mitigation strategy, here is a summary of some of the main arguments put forward:  

The article stipulates how important synthetic nitrogen fertilisers are in conventional agriculture as high nitrogen concentrations are required to meet the required yield.  It states that in 2005 global nitrogen fertiliser consumption was 90.86 million tones, and it takes approximately 90 million tonnes of fossil fuel to produce this nitrogen fertiliser, this is about 1% of global fossil energy consumption.  By changing to organic farming it would not be necessary to produce this fertiliser, reducing carbon dioxide emissions.  

Organic agriculture is self sufficient in nitrogen, mixed organic farms recycle manures form livestock and crop residues into compost, these are then used as fertiliser.  Leguminous crops also provide additional nitrogen in sufficient quantities.  Emissions of nitrous oxide are directly related to the concentration of available nitrogen in the soil, therefore as I mentioned in a previous post if adequate nitrogen is in the soil for the crop then less is lost.  As mineral fertilisers are not used and there are reduced livestock units per hectare there is less nitrogen in the soil resulting in a smaller amount of loss as nitrous oxide.  

A reduction in nitrous oxide emissions can also be achieved though using diverse crop rotations, this improves soil structure and quality, reducing erosion which leads to loss of nutrients.  Soils managed organically are much more aerated and have significantly lower mobile nitrogen concentrations. 

Similarly, as soil quality is better where it is organically farmed, less carbon is lost.  Conventional farming encourages carbon loss due to soil erosion.  Carbon is stored in organic soils due to the use of green and animal manures, crop rotations with inter cropping, cover cropping and composting techniques.  Organic farms generally use conservation tillage or no-till, I explained how this benefits the soil in a previous post.  

this picture shows organic soil (on the left) to have better drainage and water holding capacity, it is less waterlogged than conventional (on the right) this reduces soil erosion

When looking at an opposing angle, put forward by Cassman et al (2003) surrounding nitrogen levels it is possible to see a different perspective on organic farming.  This article states that although it is believed that organic farming offers environmental benefits, it is just as difficult to prevent nitrogen loss from the soil from organic fertilisers as it is synthetic.  There have been many studies on leaching from organic soils, with varied results, some show it to be higher than synthetic and others lower.  Yield reductions are also associated with organic farming, and organic farming produces more expensive products whilst requiring more government subsidies to remain economically viable.  

Consequently this has created the idea of including some practices from organic farming in conventional systems.  This is suggested by Pimentel et al (2005).  There are many benefits of organic farming such as improved soil quality which could make conventional agriculture more sustainable.  Lal (2004) suggests that using practices from organic farming, such as no-till farming, cover crops, nutrient management, argo forestry, can improve carbon content of soils.  This in the long run can improve food security, which is becoming a more pressing issue as more soils are degraded. 

It would be effective to include some areas of organic farming in conventional farming, to make it more sustainable.  It does not seem logical to use organic farming as a mitigation strategy as it is not possible to determine whether producing food this way would yield enough for the global population.  Producing food organically also requires higher economic investment and produces more expensive products.  As Cassman et al state, organic farming could be feasible in industrialised countries but it would not be able to secure the food supply in the developing world where it is necessary to maintain low food prices.  

Eutrophication

As discussed in the previous post, the inefficient use of fertilisers in agriculture has lead to an excess of nutrients such as Nitrogen and Phosphorous in the soil, which is then leached or released as a gas to the atmosphere.  I have discussed the impacts of nitrous oxide, this post will analyse the impact of those nutrients leached.  

Eutrophication occurs where nutrients, namely phosphorous and nitrogen, found in agricultural fertilisers are washed (leached) by rainfall into a freshwater or coastal systems.  Here I am going to focus on freshwater systems.  Leaching causes increased productivity  lakes, causing large algal blooms to grow.  These dominate the lake preventing other plants from getting the nutrients and light they need, reducing the biodiversity of the lake and the water quality.  When these large algal blooms die they sink to the bottom where they decompose, causing deoxygenation of the water, affecting fish and other organism.  It becomes difficult for these organisms to live due to the deoxygenation of the lake and they eventually die.  Consequently lakes end up a green colour and are species limited, dominated by algae, these lakes referred to as being in a turbid state (see picture below).  These lakes are very common in agricultural areas.  

Below is a simple but effective animation of the process of eutrophication. 

There have been several strategies to prevent the situation getting worse, and to restore these freshwater systems.  As I mentioned in my previous post, better, more efficient use of fertilisers in agriculture is key as this reduces losses.  It is important to attempt to stop the problem at its source.  Over recent years buffer areas have been introduced.  Haycock and Burt (1993) showed this to be a successful measure at reducing the level of nutrients reaching freshwater systems.  They undertook a study on sections of the River Leach, making a grid of bore holes on the buffer area, from which they could take water samples to measure nutrient concentrations.  They found that there were sharp losses in nitrates with increasing distance into the buffer. This strategy has been successfully adopted.  Re-meandering rivers and streams is also a possible approach, as this means the water flows more slowly allowing more time for deposition before it reaches lakes.  These ideas intend to reduce the level of nutrients entering the lakes. 

However. restoring turbid lakes is much more difficult.  Even when the excess of nutrients being added to the lake has been stopped the lake still remains eutrophic due to nutrients embedded internally in the lake.  Therefore it is possible to dredge lakes of all there sediment, however this is a very expensive strategy and causes loss of the lake habitat.  Another possible restorative measure is biomanipulation.  This is where the lake ecosystem is manipulated, for example by removing fish, to see if the original ecosystem can be restored.  Sondergaard et al (2007) evaluated data from more than 70 restoration projects conducted in shallow, eutrophic lakes in Denmark and the Netherlands.  They found the most common biomanipulation measure to be removal of zooplanktivorous fish.  They showed some success, over half the lakes had decreased levels of phosphorous, nitrogen and chlorophyll a.  This shows potential for biomanipulation to work, however it is a very complex process.  The article states on the long term only a few lakes recovered, most returned to a turbid state after ten years or so.  Consequently, biomanipulation could work but it needs to be maintained and repeated over long time frames otherwise the fish recolonise and the turbid state returns. 

For more information on eutriphication, this article by Smith et al (1999) explains it well, explaining both coastal and freshwater eutriphication giving examples of restoration success stories.  

Reference: 
Haycock, N.E. & Burt, T.P. (1993) The sensitivity of rivers to nitrate leaching: The effectiveness of near-stream land as a nutrient reduction zone. In: D.S.G. Thomas & R.J. Allison. Landscape Sensitivity. John Wiley & Sons, 261-272.

improving the use of nitrogen in agriculture

Over recent years the use of fertilisers containing nitrogen has increased with demand for food.  Using these fertilisers adds nitrogen to the soil allowing a greater yield of crop to be grown.  They are used in both arable and livestock farming, spread or sprayed not fields for cattle to graze on.  In a previous post I discussed the problems relating to increased use of these fertilisers, namely nitrous oxide emissions, an important greenhouse gas.  These nitrous oxide emissions are resultant of both mineral fertilisers containing nitrogen and organic fertilisers such as animal manure.  A major issue arisen recently is that these fertilisers are not efficiently used.  In this post, articles suggesting various mitigation strategies to improve the efficiency of fertiliser use and consequently reduce nitrous oxide emissions will be discussed.  

Articles by Monteny et al (2005) and Pautisan et al (2004) discuss various strategies for reducing emissions describing and explaining how they work, as summarised bellow:

• Type of fertiliser - This is important as there are many different types of fertiliser and some such as nitrogen based fertilisers result in greater emissions than others, for example ammonium.  
• The use of slow release fertilisers - These have been formulated to attempt to coincide nitrogen release with plant growth.  Here the fertiliser has been coated meaning the release of nitrates is much slower and much more controlled.  This reduces nitrous oxide emissions as only one application of fertiliser is necessary and there is a much smaller pool of nitrogen in the soil, restricting loses.  
• Addition of nitrification inhibitor - this can be added to fertiliser, examples being Nitrapyrin and Dicyandiamide.  These inhibitors aim to delay the transformation of Nitrogen into nitrous oxide helping to match the timing of the supply with crop demand.  
• Land drainage - It is commonly thought that there is a relationship between nitrous oxide emissions and water filled pore space.  When water filled pore space is above 70%, it results in significant nitrous oxide emissions.  Therefore improving the soil’s physical conditions, for example reducing soil wetness through draining, will reduce emissions.  Wet, compact soil conditions lead to anaerobic conditions, enhancing denitrification.  
• Conducting soil Nitrogen tests - This is where soil is tested to discover how much fertiliser is actually required to achieve the desired crop yield.  It is a common problem that soil is over fertilised and too much nitrogen is added to the soil, meaning that the plants only use their required amount and the excess is lost, either as nitrous oxide or through leaching.  Therefore by measuring how much is in the soil and knowing how much is needed for the crop it is possible to add sufficient fertiliser to grow the crop rather than adding an excess amount.  Mcswiney and Robertson (2005) undertook a study in South West Michigan USA over three years to show that nitrous oxide emissions increase mainly in response to additions of nitrogen to crops that exceeded their needs.  They added different amounts of various fertilisers to nine fields and measure nitrous oxide fluxes, available nitrogen in the soil and grain yields.  They found that nitrous oxide fluxes could be reduced by using less fertiliser, whilst having no effect on crop yield.   
• Improving the timing of fertiliser addition - Often fertiliser is not added when the plants are at their full capacity to absorb it, consequently leading to losses through leaching and as nitrous oxide.  Chambers et al (2000) state that in order to reduce losses fertiliser should not be applied between autumn and early winter.  
• Cover crops - these can also reduce nitrous oxide emissions from soil as they can catch any residual nitrogen left in the soil instead of it being left bare, where it would otherwise be emitted as nitrous oxide or leached.  

An article by Zhu and Chen (2002) looks at the success that some of these strategies have had in China.  Through undertaking filed micro plot experiments with nitrogen based fertiliser they were able to demonstrate that nitrogen recovery in rice plants when fertiliser is added to the crop in its early growing stage, is in the range of 22-52%.  Whereas this can be increased to 55-69% when added at the vigorous growth stage, reducing nitrogen loss.  Another possible strategy discussed in this article is deep placement.  This is where fertiliser is placed deep into the soil, rather than just sprayed on the surface.  This again was successful in reducing nitrogen loses, in Fengqiu, Henan Province, nitrogen loss through ammonia volorisation was between 20-48% when urea was surface broadcast.  This was reduced to 11-18% when placed deep into the soil.  

There seem to be many positives regarding these strategies to reduce nitrous oxide emissions, many are easy to implement, are cost effective and are shown to be successful.  Most are related to improving the efficiency in using fertilisers, improving timing and reducing wastage though excess application.  Using control released fertilisers or nitrification inhibitors have the slight disadvantage in being more expensive, but in the long run less fertiliser is used and consequently the cost of labour to implement them is reduced which is attractive to farmers.  However a disadvantage is apparent that nitrous oxide fluxes are reliant on environment, experimentation is required on the local scale to develop an optimal nitrogen management scheme, which requires longterm investment and research.   

livestock cause climate change?

Farm animals account for a large amount of greenhouse gases emitted into the atmosphere from agriculture.  On average a cow releases between 70 and 120kg of methane per year!  Greenhouse gases are released from various areas of livestock breeding.  Carbon dioxide is released from the burning of fossil fuels for energy, such as electricity.  Monteny et al (2006) state an important source of methane is related to the way cows and other similar animals digest their food, whereas in chickens, pigs and other animals that digest their food differently, manure is the most important source of methane. The main sources of Nitrous oxide are in fertilisers, land applied animal manures and in the urine of grazing animals.  

Many mitigation strategies aim to reduce methane emissions from livestock as this is where the greatest proportions of emissions lie.  This is probably also because methane is one of the easier issues to mitigate as it is thought to be related to breed and diet of the animal.  This post will discuss the various ways in which methane can be mitigated through diet.  

Beauchemin et al (2007) undertook a study on cows, aiming to reduce methane emissions by altering their diet through adding lipids.  They found that cattle fed sunflower seeds produced less methane per day than cattle fed other lipid sources as the feed was less digestible.  Lipids reduce methane emissions by decreasing the amount of organic matter fermented in the rumen (part of the cow’s digestive system), as the lipids replaced barley grain.  Overall all lipid sources were equally effective in suppressing methane emissions (about 15%) when differences in intake and fibre digestion were accounted for.  However, adding lipids may increase the cost of feeding livestock, and therefore be less appealing to commercial farmers.  Beauchemin et al suggest sunflower oil as the best out of the three they used, as it increased rate of gain of the cattle as well as lowering methane emissions, hence being more attractive to farmers.  

Machmuller et al (2000) undertook a similar study to Beauchemin et al, but using sheep.  Sheep digest in a similar way to cows, so here they measured the change release of methane after adding different ingredients to their diets, against a control.  They found reductions in methane emissions from all, coconut oil 26%, rapeseed 19%, sunflower seed 27% and linseed 10%.  Again they found sunflower seed to reduce digestibility.  A possible problem with adding lipids and other supplements to animals diets is the reaction of buyers, people may be put off buying meat from animals that had these additives in their diet.  

Another possible way to alter livestock diet to reduce methane output is to change forage to concentrate ratios.  This is shown by a study by Lovett et al (2003), who investigated animal performance and methane emissions using 36 cows over an 11 week period.  They had various forage to concentrate ratios, some supplemented with coconut oils.  Reducing the forage to concentrate ratios resulted in significantly increased rates of weight gain, whereas the coconut oil had no impact on  weight gain of the cow.  Both the change to lower forage to concentrate ratios and the addition of coconut oil reduced daily methane emissions.  

These papers present reasonable strategies to mitigate methane emissions, an article by O’Mara et al (2008) in Livestock and Global Climate Change also suggests that both the addition of lipids and changing forage/concentrate ratio of livestock diets can reduce daily methane emissions.  However they say that more data and information need to be collected on diet alteration strategies .  It is necessary to ensure that these strategies are functional in different environments, can be easily adopted, and only have a small economic cost otherwise they will not appear appealing to farmers.   

Tillage??

This post is going to look at another crop management strategy, aiming to increase soil carbon content, tillage.  Tillage is the preparation of soil before crops are planted, it can be done by hand or machine and involves processes such as digging and overturning.  Altering tillage methods can now be used as a mitigation strategy for climate change across the world due to advances in farm machinery and farming methods.  

Tillage causes disturbance of the soil which stimulates losses of carbon through enhanced decomposition and erosion.  Therefore it has been put forward that changing conventional tillage methods to reduced/conservational tillage or no-till can result in carbon gain in the soil and a reduction in carbon dioxide emissions as a result of a lessened use of farm equipment.  The picture below describes the variation between the different types of tillage.  

A study done by West and Marland (2002) in the USA suggest that reduced tillage practices could contribute to making US agriculture ‘carbon neutral’ over the next forty years.  In this study, they compared conventional tillage methods with no-till.  They estimated the energy use and carbon emissions from all aspects of crop growing, such as including fuels, fertilisers and farm machinery.  They estimated no-till emitted less carbon dioxide from agricultural operations than conventional tillage and that no-till increased carbon sequestration due to less soil disturbance.  The enhanced carbon sequestration is limited over time as once it reaches a peak the soil will be unable to absorb anymore carbon, however they argue that if no-till practices are continued then the soil carbon content will be maintained, and the reduction in carbon dioxide emitted to the atmosphere as a result of lessened fossil fuel use will continue indefinitely.  Cerri et al (2004) undertook a similar study in Brazil and found that converting to no-till methods is increase carbon sequestration in the soil, currently accumulating 9 Mt C per year.  

Changing to reduced tillage or no-till seems a successful way of lowering carbon emissions, but there is some uncertainty whether converting to these methods is beneficial in all locations.  Hermle et al (2007) studied tillage in North East Switzerland.  They analysed different tillage methods in the region, from no-till to ploughing and found there was little difference in the amount of carbon sequestrated.  The reason given for this is the climatic conditions, being moist cold-temperate solid.  

Another problem that has arisen as a result of suggested tillage mitigation strategies is the impact on nitrous oxide emissions.  This is discussed by Li et al (2005), it is thought that switching from conventional to no-till can increase nitrous oxide emissions by 2.5±0.5 kg N ha^-1 yr.^-1 for humid environments and 0.8±1.0 kg N ha^-1 yr.^-1 for dry environments which offsets some of the carbon sequestration gains as nitrous oxide is also important greenhouse gas.  Some have found these nitrous oxide emissions to subside after a few years after the conversion but these results are variable.  Li et al do state that despite the nitrous oxide emissions, no-till cropping is beneficial as it reduces fossil fuel use, it reduces soil erosion, enhances soil fertility and also water holding capacity.  

Using reduced tillage or no-till does seem on the whole to be a successful mitigation strategy to improve carbon sequestration.  In many studies across the world it has shown to be effective in increase soil carbon content.  Using reduced tillage or no-till is also beneficial as it reduces carbon dioxide emissions from the practice of farming, such as machinery use.  These methods also improve the quality and fertility of the soil as less erosion occurs and less nutrients are lost, therefore despite uncertainty about nitrous oxide emissions, if the soil holds its nutrients better then perhaps fewer fertilisers can be used on the soil reducing nitrous oxide emissions in the long run.