Trading in soil carbon stocks

Soil carbon has become a hot topic, with carbon sequestration in soil a possible method for reducing atmospheric CO2. But this isn’t an easy task, and there’s a lot more to soil carbon than just sequestration. Here, we provide an overview of soil carbon flows and what they mean in the context of the global food system.

The term soil carbon refers to carbon stocks, in various forms, present in the world’s soil. Soil carbon can be organic (e.g. living or decomposing organisms, humus) or inorganic (e.g. carbon-containing minerals such as calcite).

The amount of carbon in the world’s soils is estimated in the region of 2500 gigatons, more than three times that present in the atmosphere and more than four times that in all living organisms. Organic matter in the soil, including soil carbon, is vital to good soil health, improving water and nutrient retention, maintaining soil structure and as nutrient sources for plant and microbial life.

Soil carbon content can be understood as the balance between carbon inputs and carbon losses. A major contributor to soil carbon inputs is photosynthesis. Plants capture atmospheric CO2, which is transferred below the soil surface via the roots. As well as contributing to the structure of the plant, some carbon is passed to rhizobial microorganisms, the microbial populations that live in close association with plant roots. As root structures and microbial populations in the soil grow, so too does the bound soil carbon.

Carbon can also be added to the soil through decomposing plant and animal material. The process of decomposition involves microbial respiration, which releases CO2 into the atmosphere, but some of the carbon in the decomposing material remains in the soil. The net balance between carbon inputs and losses to the atmosphere determine whether the soil carbon concentration increases or decreases.

However, further complexity is added to the system by other, abiotic factors. Soil composition, temperature, water content and erosion all influence soil carbon cycling. Naturally, this means that soil carbon stocks vary enormously between different parts of the world, from less than 1 tonne of carbon per hectare in desert environments to several hundred tonnes in tropical forests. Even within local regions, soil type can result in significant differences in soil carbon concentrations. This variation makes quantifying soil carbon challenging.

Agriculture directly influences soil carbon stocks. Clearing of land for agriculture, and tillage and cropping are generally considered to reduce soil carbon concentrations. However, this is not always the case: in certain systems, conversion of forest to grassland results in increased soil carbon concentrations, but it is uncertain how permanent this change is.

A number of activities exist that can increase carbon sequestration in the soil, or decrease the rate of carbon loss incurred by agriculture. Reducing tillage and soil erosion minimises carbon loss to the atmosphere or to waterways, while organic fertiliser application can add to the carbon input on agricultural land. The use of cover crops, which prevent leaving the soil bare between cropping cycles, can also help to maintain or even increase soil organic carbon.

The benefits of such practices are both local and global. Increased soil carbon benefits soil health, increasing crop yields in some systems. The benefits to soil structure of high soil carbon also allow for better retention of micronutrients, such as iron and zinc. This can result in higher concentrations of these mineral in crops, and thus in our own nutrition.

However, there are challenges in increasing agricultural soil carbon stocks in many areas. It is far easier to add to soil carbon in areas where the current concentration is low than in areas with relatively high existing stocks, which may be close to saturation with carbon. Moreover, it is easier for agricultural interventions to increase carbon concentrations in the upper layers of soil than the deeper layers.

Perhaps the greatest driver of recent interest in soil carbon is for its potential in sequestering atmospheric carbon emissions from human activity. Atmospheric carbon, in the form of CO2, is well known as a greenhouse gas. Thus, the possibility of using soil as a carbon sink is gaining momentum.

The potential of this possibility has recently been demonstrated in Australia. Australia has an existing Carbon Farming Initiative that provides the legislation for obtaining carbon credits by demonstrating increases in soil carbon on owned land. Recently, an Australian cattle farm sold carbon credits to Microsoft to the value of $500,000, obtained entirely from soil carbon sequestration from the management of the farm’s grazing land.

Schemes like the Carbon Farming Initiative have the potential to spread. However, in order to quantify changes in soil carbon stocks, it is essential to measure changes in soil carbon over time. This can be done by taking soil samples from a number of representative sites and quantifying the carbon present. These measurements can then be repeated to establish changes in soil carbon concentration over time. However, the wide variation in soil carbon even within a small area makes generalisation of carbon concentrations difficult. Currently, work is underway to benchmark New Zealand soil carbon concentrations, with a view to tracking changes in the future. This work will have to contend with the difficulties of varied concentrations, but may ultimately lead to some form of soil carbon credit system in New Zealand.

Study of soil carbon is benefiting from the interest sparked by the need to reduce atmospheric carbon concentrations. However, its importance to the global food system reaches beyond carbon sequestration. Healthy soils play a role in reducing the environmental impacts of agriculture by retaining nutrients and structure, and enabling optimum crop yield and nutrient content. In the future, the drive for carbon sequestration may also influence land management and provide another source of income for food producers.

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Food Systems Summit wants to hear from you

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The United Nations Food Systems Summit, an international event to make plans for the transformation of the global food system to align with the Sustainable Development Goals, is set to take place in September this year. If you have an interest in the food system, the Summit wants to hear from you.

It is widely accepted that the current global food system is not sustainable in the long term from a nutritional, environmental or economic standpoint. Its complexity and interconnectedness are also clear. The Food Systems Summit hopes to increase awareness of food system dynamics and spark international action towards more sustainable practices.

To inform the discussion, the Summit is encouraging a number of Summit Dialogues. These are smaller events, organised either by the UN, member states, or independently. Anyone can convene their own Summit Dialogue, following guidance available on the Summit website. You can also read through the findings of previous dialogues and learn about upcoming events you can be a part of.

The purpose of these dialogues is to bring the voices of all stakeholders to the discussion table. The combined views of food producers and consumers, scientists and economists, nutritionists, environmentalists and governments will be necessary to direct future policy on the global food system.

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Social perspectives on the future of livestock

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A recent article in Animal Frontiers identifies the social perspectives on the sustainability of animal-sourced food production, with a view to what this production might look like in the future.

The increasing global population and per capita income is predicted to drive food demand up by around 50%. But it is challenging to predict what role livestock will have in satisfying this demand.

As well as requiring increases in productivity with a reduced environmental footprint, animal-sourced food producers must maintain their “social license to operate” – the acceptance of their practices by consumers. General interest in how animal-sourced foods are produced is rising, and the author contextualises this discussion with some statistics for the US livestock industry.

From an environmental perspective, improvements are being made in reducing the amount of feed, land, water and greenhouse gas emissions of animal-sourced foods due to improved genetics, crop yields and management practices. US beef production reduced its land use footprint per kilo of beef by 33% between 1977 and 2007 and greenhouse gases by 16%. US pork production reduced its feed use per kilo of pork by 67% between 1959 and 2009, and water use by 22%. US milk production has reduced land use, fuel use and greenhouse gas emissions by around 20% each in just the ten years up to 2017.

There is also evidence that further improvements can be made, with wide differences in the footprints of animal-sourced food production even within the same country. Bringing the average closer to best practice should be as much a goal as pushing the boundaries of how small these footprints can become. These improvements must also be communicated to consumers.

The article identifies three key issues that should be prioritised by the animal-sourced food industry when considering its future: accounting for greenhouse gases equitably, with consideration of their differing lifespans; wider use of non-human-edible by-products as animal feed; and greater consideration of animal health and welfare. Each of these priorities will have benefits for the production, environmental sustainability and consumer perceptions of animal-sourced foods.

The author’s final thought is around demonstration and communication of the facts around animal-sourced food production, to ensure than consumer choices are evidence-based.

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Dietary Guidelines for Americans 2020 – 2025 published

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The USDA has released their latest dietary guidelines document, with a new emphasis on the importance of considering different life stages when designing guidelines.

A new set of dietary guidelines are designed for the US population every five years, based on the recommendations of a scientific advisory committee who review the latest nutrition and health research, ensuring up-to-date advice.

In this document, specific dietary recommendations for infants and toddlers appear, where before this advice was absent. These recommendations cover breastfeeding and infant formula use, as well as complementary foods. Strong emphasis is placed on food variety for toddlers, as well as on the importance of iron and zinc intake.

The guidelines recommend that Americans should eat more whole fruits, vegetables, and whole grains, while limiting added sugars and saturated fat to less than 10% of daily calories each. While this largely chimes with the advisory committee’s scientific report, they had suggested that only 6% of daily calories be from added sugar, due to the negative health outcomes of high dietary sugar intake. The committee were also cautious on the contentious subject of saturated fat, not recommending any change to the current guidelines and mentioning that replacement of these fats with carbohydrates is not advised.

Nutrient density and dietary patterns were pulled out as important terms in the report. Nutrient dense foods are recommended throughout, and listed as vegetables, fruits, whole grains, seafood, eggs, beans, peas, lentils, unsalted nuts and seeds, fat-free and low-fat dairy products, and lean meats and poultry. However, the recommendations put emphasis on dietary patterns rather than on individual foods or food groups to enable adaptations that fit cultural, personal and individual needs and preferences. The three food patterns of the guidelines are the Healthy U.S-Style Pattern, the Healthy Vegetarian Pattern and the Healthy Mediterranean-Style Pattern. All three patterns provide most of their energy from plant-based sources, provide protein and fat from nutrient rich sources and limit intakes of added sugars, solid fats and sodium.

This is consistent with the results of the DELTA Model which illustrates that most of our energy should come from nutrient rich foods to ensure all nutrient requirements are met. Nutrient poor foods such as sugar should be minimised, and it is essential to consider the different needs of different demographic groups.

Interestingly, the guidelines make no mention of the environmental sustainability of different foods or diets. Several countries already make this inclusion, with this number likely to increase, but it will be at least 2025 before any such recommendations appear in the US dietary guidelines.

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WWF encourage planet-based diet

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The WWF report Bending the Curve: The Restorative Power of Planet-Based Diets joins other efforts to demonstrate the negative health and environmental consequences of our current way of producing and consuming food, while proposing ways to turn this around.

The report opens with the assertion that our food system must provide healthy, safe, affordable and nutritious diets for all, with reference to the UN Food Systems Summit later this year and the Sustainable Development Goals. This is completely in line with the principles of SNI: nutrition must come first when considering the global food system. The report then goes on to define planet-based diets as win-wins: healthy and with low environmental impacts and explores how these can be achieved.

A major recommendation of the report is that national dietary guidelines need to be more ambitious. This echoes a results of a previous WWF model. Currently, these guidelines largely reflect a healthier version of current consumption patterns and do not consider environmental impacts. The report argues that guidelines could be simultaneously healthier and more sustainable.

The main health recommendation of the report is to increase the plant-based proportion of the diet and decrease overconsumption. This is supported by the Global Burden of Disease study findings, indicating that low wholegrain and fruit intake, as well as high sodium intake, were the greatest dietary risk factors.

Beyond these overarching directions, recommendations for dietary and production change vary on a regional level. This is due to the difference in dietary, health and environmental factors seen in different parts of the world.

Countering biodiversity loss also requires a nuanced approach. For example, the report finds that most of the biodiversity loss associated with the Danish diet is due to imports of coffee, tea, cocoa and spices. Contrastingly, red meat holds this place for Latin American countries.

Similarly, the report states that we must feed our population on existing agricultural land and not further expand, but again the implications vary by region. Countries suffering from widespread undernutrition may need to expand their agricultural land to ensure healthy diets for their population, while more developed countries may need to contract.

The same regional variability is true for the planting of trees for carbon sequestration, conversion of grazing land to arable or optimising water use. The results of the report emphasise careful consideration of actions at a national level, as healthier diets can lead to increased environmental damage of one kind or another in vulnerable regions. A one-size-fits-all approach will not lead to a sustainable food system.

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FAO Statistical Yearbook 2020 shows big changes

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The latest global statistics from FAO show large increases in both crop and animal-sourced food production, but also reductions in cropland and agricultural employment.

Since 2000, there has been a drop of just over 1 billion people from the agriculture workforce, going from 40% of global employment to just 27% in recent years.

Countering this, use of agricultural pesticides increased sharply between 2000 and 2012, before levelling off. Increases were also seen for fertiliser, contributing to the 50% increase in crop production since 2000. Sugar cane, maize, wheat and rice dominate crop production, and the production of each is dominated by two or three countries.

The total agricultural land these crops are grown on showed reduction since 2000, decreasing by 75 million hectares, with a similar decrease of 89 million hectares of forest land.

In terms of animal-sourced foods, chicken showed the greatest increase of the meats, growing by 47% and reaching similar production quantities to pork, the highest producing meat sector. Milk production increased by 45%, while egg production increased by 50%.

Fisheries production showed a similar increase of 42% and is still dominated by marine fish. However, the expansion of aquaculture led to a 131% increase in freshwater fish since 2000. Aquaculture now represents 46% of total fisheries production, compared to 26% in 2000, with China largely responsible for the increase.

The increased food production coupled with decreased agricultural land and employment emphasise the increased efficiency, intensity and automation in food production. However, it should be noted that this is a global picture and that insights at a regional level are also necessary to fully understand the global food system.

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GMO crops in the global food system

Genetically modified organisms (GMO) are already major contributors to the global food system since their commercial introduction in the 1990s. For example, over 90% of US corn and soy acreage is planted with GMO seeds. Despite this, the use of GMO is still controversial, with many individuals against their use and many authorities strictly regulating their production and consumption. Here, the arguments for and against GMO use in crop production are presented. 

GMO are defined as organisms, and products thereof, that are produced through techniques in which the genetic material has been altered in a way that does not occur naturally by mating and/or natural recombination. 

The process in which GMO are created differs depending on the degree of modification required but generally, a desirable trait is identified in one organism that could be of benefit in another. The trait is studied and, if possible, the gene(s) responsible for the trait are isolated. These genes are then introduced to the target organism, either via bacterial or viral infection, where the microorganism carries the target gene into the organism for uptake, or by bombarding the organism with particles coated in the target gene. 

The outcome of the process is a GMO that expresses the desired trait isolated from the original organism. 

Advantages of GMO  

The ability to transfer desirable traits between distantly related crops that cannot be interbred has obvious benefits. Examples of GMO use include the ability to increase photosynthetic rate, develop crops that are drought-tolerant with increased yields, and produce crops with disease resistance, such as blight-resistant potatoes

Moreover, crops can be developed that have greater nutritional value than conventional varieties. There exists a long list of such biofortified crops, including cassava with increased zinc, iron, protein and vitamin A content, high lysine maize, high provitamin A rice, and corn with increased provitamin A and folate. These crops are of particular value in global regions where nutrient deficiencies are a high priority public health issue. 

One widely used GMO is Bt-maize. This crop takes its name from Bacillus thuringiensis, the bacterium that donated to the maize plant the trait of producing an insecticidal toxin. Thus, Bt-maize is more resistant to pest insects than conventional maize, leading to higher yields and reduced pesticide use. As a result, 82% of the crop grown in the US in 2020 was the Bt variety. 

Disadvantages of GMO  

The arguments against GMO are largely based on health and environmental risks. The approval process for GMO is nationally administered, so differs between countries. Largely, these processes are more rigorous than for conventional foods and assess both the health and environmental risks of the GMO. 

The World Health Organisation states that no negative health consequences of approved GMO have been shown to date. However, concerns and risks do exist. One health concern raised is the possibility of allergenicity being unintentionally transferred between organisms. An example of this was when early GMO researchers, hoping to increase methionine content, found that the main allergen from Brazil nuts retained its allergenicity after transfer into a GMO soybean. As a result, the GMO soybean was never released commercially and allergenicity is now an important consideration when selecting donor crops. 

From an environmental perspective, there is the possibility that the GMO crop itself, or the introduced gene via cross-breeding or gene transfer, could escape the farmed environment and become a pest. The implications of this would depend entirely on the nature of the GMO crop; for example, transfer of a herbicide resistance gene to a non-target organism could lead to difficulties in controlling its growth. Alternatively, GMO crops could outcompete other plants due to the introduced trait, resulting in decreased biodiversity with unknown downstream implications. While the risk of these unintended consequences is low, they should be considered in the design and management of GMO. 

Finally, some express the opinion that GMO are morally wrong, as they involve too great an interference with living organisms. Such a decision can only be weighed by the individual but will likely mean that a proportion of the population will continue to avoid foods containing GMO products. 

This avoidance is challenging given the ubiquity of GMO products in many foods and by the difficulty for a consumer in identifying GMO foods. Different authorities take different stances on GMO labelling. For example, GMO are not specifically labelled in the US, rather foods that contain ‘bioengineered’ ingredients must be labelled as such. However, specific food labelling for certain types of GMO is on the horizon. The EU has stricter rules, with a requirement for GMO ingredients to be listed on food packaging. However, major food retailers have previously been forced to change their GMO policies due to the increasing “risk of finding GM material in non-GM food”. 

Conclusion 

GMO are widespread in the global food system, but not equally distributed.  

Moreover, regulation of GMO production varies and is not always clear and explicit. There are countries, like the US, where GMO crop production is widespread. Contrastingly, 19 member countries of the European Union have previously voted to either partially or fully ban the use of GMO. In New Zealand, no GMO crops are commercially grown. These variations in use and acceptance will certainly limit investment and development of future GMO. However, there is the opportunity for countries that have a GMO-free stance to use this status to market their products at a premium. 

GMO crops generally result in decreased pesticide use, coupled with increased yields and profitability. Moreover, there are those that believe that GMO will be necessary to adequately nourish a growing population and to adapt production to changing climates. The risks of GMO largely relate to unintended and uncertain consequences that must certainly be properly managed if GMO use and development is to increase. 

This Thought for Food was written by Cody Garton, a summer intern from Pūhoro STEM academy

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Trends in undernourishment show promise

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A study of undernourishment in 76 countries found positive results, but not all global regions are progressing at the same rate.

Although overnutrition continues to grow globally, undernutrition rates are decreasing. Undernutrition currently affects more than 800 million people, either as protein-energy malnutrition or micronutrient deficiencies. 

The researchers used data from 1991-2013 from the FAO and the World Bank to analyse both undernutrition and related factors. The countries studied were mostly developing countries located in sub-Saharan Africa, Asia or Latin America. 

Undernourishment and child mortality showed decreasing trends overall. Urban populations, GDP, food production and agricultural land had all increased over the study period. However, when grouped into regions, the Eastern Mediterranean countries (Iran, Iraq, Jordan, Tunisia and Yemen) showed a late upwards trend in undernourishment, possibly due to political unrest in this region in the latter years of the study period. 

A problem noted by the authors is in equal distribution of food, both between countries and within national populations. This is a conclusion also reached by the DELTA Model, which shows that apart from a few micronutrients, the global food system in 2018 would have supplied sufficient nutrition for the world’s population, had it been equally distributed. The problems of unequal distribution are bound up in many other social, economic, political and environmental factors. 

While it is reassuring to see the decreases in undernourishment and infant mortality shown by this study, it also highlights areas that remain to be improved.

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Peas please

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Food Foundation in the UK are gaining traction with their ‘Peas Please: Making a pledge for more veg’ initiative, the results of which were recently described in Nutrition Bulletin. 

Despite a historically growing UK market for fruit, which has increased by around 50% since 1970, vegetable purchasing was seen to slowly decline over the same period. The common perceptions of vegetables as boring or not that tasty was likely not helped by minimal publicity, with only 1.2% of the UK food advertising spend used to market vegetables. On top of this, there are questions around the environmental impacts of the average UK shopping basket, and ample evidence that field-grown vegetables have small environmental footprints. 

Most of the UK public do not meet dietary guidelines for vegetables, particularly those with lower incomes. On top of low purchase rates, 40% of purchased vegetables in the UK are wasted at home. This matches the global trends of food waste shown by the DELTA Model, where most of the nutrient waste is from plant-sourced foods. Altogether, the nutritional and health implications of low vegetable intake due to consumer choice and waste needs to be tackled. 

The ‘Peas Please’ initiative aims to make eating vegetables more healthy, affordable, sustainable and pleasurable. Organisations, such as supermarkets and restaurants, pledge to follow these directives, in the hope of changing the way the country treats vegetables. Their website features ways in which individuals, communities and businesses can engage with the initiative and forge better relationships with vegetables. 

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Comparing apples with potatoes: the Vego-guide

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Researchers in Sweden have designed a tool for comparing the environmental impacts of different plant foods. The tool is designed for interested consumers who want to know more about the environmental implications of these foods in their diets. 

Using life-cycle analysis data for 90 plant foods, the Vego-guide considers the climate, biodiversity, water use and pesticide use impacts of each food. This information is used to generate a traffic light rating for each food, from orange (greatest negative impacts) to green star (least negative impacts). 

The tool is currently in further development for application to the Swedish market, but we can expect to see similar tools becoming available worldwide as consumer desire to make food choices based on their environmental impacts increases. 

Currently, the only nutritional consideration in the model is to group plant foods together based on their main role, e.g. carbohydrate source, protein source and so on. This is important, as the carbohydrate sources (such as pasta and potatoes) receive better Vego-guide ratings than fruits. Care must be taken to ensure that these higher ratings do not influence consumers to choose energy dense foods over nutrient dense foods, a choice that would be detrimental from nutrition and health perspectives. 

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