1.74 | Fall 2020 | Graduate

Land, Water, Food, and Climate

SECTION 3 | Reconciling Demand and Supply: Context

Overview

How can we achieve a sustainable balance between food supply and demand in a diverse and changing world?
What do we need to consider in our search for practical ways to reconcile food supply and demand?

The readings and supplementary information provided in Section 2 make some points that we need to consider when looking for ways to reconcile food demand and supply:

  • Demand reductions alone will probably not be sufficient to meet the nutritional needs of the 21st century global population. Food production will also need to increase. The amount of increase required will depend on uncertain changes in per capita demand and population.
  • At the same time, agricultural technology and management practices will need to be more sustainable than they have been, so that increases in production can be maintained over the long term.
  • The agricultural system will need to be more resilient so it is able to respond to climate change, disease, and uncertain trade policies.
  • Food will need to be more accessible to populations that are vulnerable to malnutrition.

In this section we examine several topics that provide context for our subsequent discussions of strategies for meeting projected demand for food.

Class 5 considers the critical role of crop yield. The strategy of sustainable intensification, which we have already encountered, relies on finding environmentally acceptable ways to increase yield. This can be done i) by increasing potential yield, which is the yield that can be obtained for a particular crop under ideal conditions, or by ii) reducing sources of stress that cause actual yield to be below potential yield. The readings for this class provide good introductory discussions of the factors that both limit yield and contribute to high yield variability. Class 5 provides background for our later discussion, in Class 11, of yield increases in the Green Revolution and beyond.

Class 6 considers the effects of agriculture on the environment, with an emphasis on important ecosystem and nutrient cycle changes that could impact future production. The readings deal with depletion of water supplies, impacts of nutrient and pesticide application, soil degradation, and ecosystem changes. We consider these topics so we can properly evaluate the environmental impacts of increasing crop inputs such as irrigation water, fertilizer, and pesticides.

Class 7 takes a closer look at smallholder farmers, who produce and consume large fractions of the global food supply. This discussion is useful for assessing the challenge of improving food security for everyone, including the rural poor in developing regions. Class 8 considers climate changes of particular relevance to agriculture, with an emphasis on impacts that could affect crop yield, smallholder farmers, and pest control.

Class 9 discusses two new technologies, genetically engineered crops and precision agriculture, that could have significant impacts on crop production. Class 10 examines the roles of trade and optimization as strategies for making better use of limited and unevenly distributed resources. Trade has the effect of transferring land and water over time and space, reducing regional or seasonal imbalances between supply and demand.

Our readings on these topics, together with the Supporting Information, provide important background needed to evaluate the management options considered in Section 4.

Section 3 Class Topics

Class 5: Crop Yield
Class 6: Environmental Impacts of Agriculture: Protecting Natural Resources
Class 7: Smallholder Farming: Focus on Africa
Class 8: Climate Change and Agriculture
Class 9: New Technologies and Practices: Genetic Engineering, Precision Agriculture
Class 10: Trade and Optimal Resource Allocation

Section 3 Supporting information (SI)

S9. Soil Properties, Soil Suitability Measures, and Changes in Soil Quality
S10. Global and Regional Farm Characteristics
S11. World Greenhouse Gas Emissions: 2016
S12. Adoption of Genetically Engineered Crops in the USA

FAOSTAT indicates that in 2017 global crop production was sufficient to feed approximately 7.4 billion people a diet of over 2900 kcal per person per day. This is well above the FAO recommended minimum of 2400 kcal per person per day, enough to eliminate undernourishment if the food could be distributed equitably. However, the current high rate of undernourishment (10%) indicates that the extra food produced in areas of surplus is not reaching people in areas of shortage. Trade and food aid make it possible to redistribute crops and the resources needed to grow them. In this class we examine the role of international food trade as well as local reallocation of natural resources to better reconcile regional differences in food supply and demand.

We begin with the paper by D’Odorico et al. (2014), which explores how trade improves food security. It uses FAOSTAT national production, trade, and crop calorie data for 2009 to determine that about one fourth of the 2009 global population was fed on imported food in that year. The exact figures depend on the way that total crop production is distinguished from the quantity actually consumed. However, it is clear from the analysis that trade plays a major role in meeting global food demand. The paper provides maps that show how calories flow from the small number of major exporters to the much large number of importing nations.

Additional insight is provided by MacDonald et al. (2015), who evaluate the quantity of virtual (or embodied) natural resources transferred geographically through trade. The paper looks at agricultural trade in terms of calorie content, cropland and pasture area, and irrigation volume transferred from exporting to importing countries. The attached figure from the optional reading by Dalin et al. (2012) shows how virtual water transfers between continents increased from 1986 to 2007. Similar calculations could be made, but are not included in the paper, for nutrients, pesticides, labor, and other inputs. It is notable that trade alleviates imbalances in food supply and demand at the expense of exporting virtual resources, including water, that may be in short supply in the exporting region.

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An alternative to reallocating (virtual) resources through food trade is to reallocate actual land and water resources by changing the crops and irrigation diversions assigned to individual parcels of cropland. The idea here is to optimize the allocation of land and water to crops with respect to an appropriate measure of benefit, such as net revenue or number of people fed, or to minimize a cost measure, such as water used or imports required. An example is discussed in the paper by Davis et al. (2017), who use a sequential replacement algorithm to discover crop patterns that reduce irrigation (“blue”) water use without reducing calorie or protein production, farm revenue, or crop diversity. The authors estimate that the crop allocation changes outlined in their paper will feed over 825 million more people while saving water. However, this requires dietary changes (e.g. eating more legumes and fewer cereal crops). Reallocation of crops and water to land helps because it improves on the existing cropping strategy, which does not necessarily optimize resource use. Although the particular dietary and cropping changes suggested in this paper may be difficult to implement, the analysis does indicate what could be achieved if land and water resources were used more efficiently.

Required Readings

Trade and Food Security

Trade and Virtual Resource Transfers

Optimal Allocation of Natural Resources

Optional Reading

Trade and Virtual Resource Transfers

Discussion Points

  • Considering the D’Odorico et al. and Sen (Class 1) papers, why hasn’t trade eliminated malnutrition? What are the barriers that are preventing more food from getting from regions of surplus to regions of shortage?
  • What incentives do you think could prompt growers to make the changes needed to “optimize” crop distributions, as outlined in the Davis et al. paper?  How reasonable is it to use models and optimization procedures to guide resource use? Do we have better alternatives?

If crop production is to be increased through intensification, without significantly expanding harvested area ), then crop yield (which is the ratio of production to area) must increase. This raises the following important questions:

  • How much can crop yields be increased above present levels?
  • What will be required to achieve increased yields?
  • What are the possible environmental consequences of significant yield increases?

Class 5 provides a preliminary assessment of these questions with two papers that address the “yield gap”: the difference between potential yields achieved with ideal management practices and average farmer yields achieved in the field. It is especially important to recognize practical and theoretical limits on both potential and actual yields since yield improvement is a possible option for achieving sustainable increases in global food production.

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Both of our Class 5 readings focus on cereal yields because of the important role of cereals in supplying food energy. The paper by Lobell et al. (2009) defines different types of yield gaps that rely on different methods for estimating yield potentials. The accompanying figure summarizes these definitions. The ideal site-specific yield potential is an upper limit on yield that is achieved when the crop is not subject to stress from controllable factors, such as nutrient limitations. Uncontrollable site-specific factors that affect yield potential include solar radiation, temperature, and water availability (for rainfed systems). The potential value can be inferred from crop growth models, field experiments, or observed maximum farmer yields. The authors suggest that, although it may be possible to increase yield potential, that will require fundamental changes in plant function that go beyond improvements in management practices. Examples include the high yield cereals bred during the twentieth century “Green Revolution” discussed in Class 11.

The Lobell et al. survey of observed yield gaps indicates that average farmer yields range from only 20% of irrigated yield potential for rainfed maize in Africa to nearly 80% or higher for wheat and rice in irrigated areas with adequate nutrient application and good pest control. The authors’ list of factors responsible for yield gaps include stresses related to imperfect nutrient and water applications, planting practices, and seed quality, as well as pests, storm damage, and soil deficiencies. It is difficult to identify which factors predominate in a given location and season. The data presented in the paper show the large variability in yield observed even in relatively homogeneous regions such as the US corn belt. This variability does not seem to be explained primarily by farmer decisions but, rather, reflects the ever-changing aggregate effect of all the management and environmental factors listed above.

The short paper by Mueller et al. (2012) summarizes a particular data and model-based study of yield gap variability. The paper’s global map of the fraction of; yield potential achieved , which is a convenient normalized measure of yield gap, is included in S8, together with a summary of the procedure used to obtain it. Mueller et al. also consider the effects of nutrient and irrigation practices on yield in different regions. Although the analysis is relatively simplified and the data needed for a comprehensive global study are limited the paper makes a reasonable case that crop production in some regions (e.g. sub-Saharan Africa) could be significantly increased above current levels through expanded use of fertilizers and irrigation.

The optional readings by Licker et al. (2010) and Ray et al. (2012) provide further discussion of yield gaps and yield saturation. Ray et al. suggest that it may not be either; feasible or desirable to close yield gaps. There is no guarantee that further increases in inputs can actually raise yields significantly for all crops. Even if they can, the environmental impacts may not be acceptable.

A major question that remains after reviewing these readings is whether it should be possible to increase yield potential through breeding and genetic engineering efforts that could duplicate some of the successes of the Green Revolution. This question is considered but not really resolved in Cassman et al. (1999), a required reading in Class 11. It seems likely that crop production increases will be achieved primarily by bringing actual yields closer to current yield potentials. New breeding and genetic engineering developments could play an important role in this process by helping to reduce plant stress. But we cannot reasonably expect another Green Revolution to solve our food security problems by increasing the yield potentials of all the major staple crops. We will return to this topic in subsequent classes.

Required Readings

Crop Yield Overview

Optional Readings

Variations in Crop Yield and Yield Gaps

Crop Yield Saturation

Discussion Points

  • Do you think it should be possible to increase potential yields without increasing water or nutrient requirements? What would you need to know in order to give an informed answer to this question?
  • How would you structure a detailed investigation of yield variability within a given region, such as East Africa? Try to identify, as specifically as you can, the data and methods you would need to use.

Class 6 begins with a survey paper by Tilman et al. (2002) that presents the case for sustainable intensification, which we first encountered in Godfray et al. (2010) in Class 1. This approach to improving food security seeks to sustainably increase crop yield so that more food can be grown without expanding cropland. The tricky part is sustainability, which implies that yield increases must not cause environmental problems that jeopardize future agricultural production. The optional reading by Matson (1997) deals with this topic from a more ecological perspective. Both papers provide concise summaries of environmental issues that we need to consider when evaluating options for increasing food production. These include:

  • Changes in nutrient cycles (especially nitrogen, phosphorus, and carbon)
  • Soil degradation
  • Depletion of groundwater reserves and reductions in river flows (see Class 3)
  • Ecosystem changes that can adversely affect the complex communities that sustain crops

The papers by Gruber and Galloway (2008) and Cordell (2009) provide more detail on the nitrogen and phosphorus cycles, respectively. The attached figure from Gruber and Galloway identifies important global nitrogen fluxes, with rough estimates of their magnitudes. One of the environmental concerns discussed in both papers is the accumulation of unprecedented amounts of biologically available nutrients in soil and water reservoirs. This accumulation could have adverse consequences for important ecological communities (e.g. the soil biota that support crop growth). Other forms of nitrogen emitted to the atmosphere can have adverse effects on both crops and humans. The optional readings by Smil (1997, 1999), Galloway and Cowling (2002) and Childers (2011) provide additional information on nitrogen and phosphorus and their environmental impacts.

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Soil degradation stems from a variety of natural and human causes that include agricultural operations, both crop and livestock production. Fertile soil is the source of the water, nutrients, and trace minerals required for successful crops. The impacts of soil quality on crop yield and resilience are poorly understood but well appreciated by farmers who observe the results of soil degradation first-hand. Tilman et al. (2002) briefly review some of the ways that agriculture can adversely affect soil quality, including loss of nutrients and organic matter and damage to microbial communities. These occur through processes such as erosion, leaching, and non-target pesticide toxicity, which can be aggravated by poor management practices. The adverse impacts of agriculture on soil quality can reduced and even reversed through practices such as crop rotation, cover crops, fallow periods, reduced tillage, soil amendments and careful livestock management, sometimes collectively referred to as Conservation Agriculture. Supporting information in S9 provides more discussion of the problems with trying to characterize soil quality on a global scale. The optional reading by McCauley et al. (2005) provides some basic background on soil properties.

Section 4 of the Yudelman (1994) paper follows up on our Class 2 reading from the same paper by considering the environmental impacts of pesticides. The conflict between better environmental quality and increased crop production is apparent in the discussion. This conflict has prompted interest in more environmentally benign methods for managing pests. Some options are discussed in Sections 5 and 6 of the Yudelman (1994) paper (not required reading). A more recent perspective is provided by Peterson et al. (2018), who advocate an ecological interpretation of Integrated Pest Management (IPM), which they define as “a comprehensive approach to managing host stress that is economically and ecologically sustainable.” If sustainable intensification is to work on a global scale it will probably need to follow some of the pest management concepts outlined in this article, including greater emphasis on the needs of the host plants and less on elimination of pests.

Overall, the readings for this class outline broad goals for a more environmentally sustainable and productive global agricultural system. Since most of the specific methods for achieving these goals are described anecdotally, for particular study sites, it is difficult to assess how well they will work at large scales and to determine whether they can really achieve the yields required to meet projected food demand. There is a real need for additional research on the effectiveness and scalability of practices such as Conservation Agriculture and Integrated Pest Management. These practices are appealing at first glance but are not always tested under the diverse conditions needed to show that they can provide significant production increases while also satisfying sustainability criteria. We will return to this topic in Section 4.

Required Readings

Sustainable Agriculture

Nitrogen

Phosphorus

Pest Management

  • Montague Yudelman, Annu Ratta, and David Nygaard. 1998. Pest Management and Food Production: Looking to the Future (Section 4). International Food Policy Research Institute. Washington, DC 20006–1002.
  • R. K. Peterson, L. G. Higley, and L. P. Pedigo, 2018. “Whatever happened to IPM?” American Entomologist. 64, no. 3: 146–150.

Optional Readings

Sustainable Agriculture

Human Impacts on Ecosystems

Nitrogen

Phosphorus

Soil Properties

  • Ann McCauley, Clain Jones, and Jeff Jacobsen. 2005. “Basic Soil Properties (PDF).” Soil and Water Management Module. 1, no. 1: 1–12. Montana State University Extension Service.

Discussion Points

  • Considering the papers we have read so far, do you think cropland expansion (extensification) should be ruled out as a major option for increasing food production? Why is expansion continuing so rapidly in tropical regions (see S7) if it is such a bad idea?
  • What is your overall conclusion about sustainable intensification? Is it feasible?
  • Do you think agriculture’s large impact on the nitrogen and phosphorus cycles is a serious problem or an acceptable side effect needed to achieve dramatic increases in food production? Elaborate on the basis for your opinion.
  • After reading the pest management papers for this class as well as Yudelman’s discussion (Class 2) on crop losses to pests, what is your opinion about the best way to manage pests to increase food production?

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It is important when reviewing options for improving food security to consider the full range of production systems that feed the global population. The background data presented in S10 show that farms vary greatly in size, income, and productivity. In particular, the larger more profitable farms that are typical in the US, Canada, Australia, and parts of South America represent one end of a continuum. Elsewhere, much smaller low-income farms are more common. Very small farms of only a few hectares dominate agriculture in China, India, and Africa and provide food and limited cash income for about 2 billion smallholders, roughly one quarter of the global population.

In this class and in S10 we examine the smallholder agriculture system that still feeds much of the developing world. We shall see that the survival of the smallholder farmer is very much in question. If smallholder agriculture declines there will need to be substantial changes in the food production and distribution systems that serve much of the world’s population. That is why both smallholder and larger commercial farming need to be part of any discussion of global or regional food security.

We focus our discussion on sub-Saharan Africa because this is a region where smallholders are especially vulnerable to the pressures imposed by rapid population growth, difficult agroclimatic conditions, and changing economic incentives. The twentieth century Green Revolution that transformed smallholder agriculture in Asia and parts of Latin America largely bypassed sub-Saharan farmers (this topic is discussed further in Section 4). These farmers are still struggling with low crop yields, inadequate infrastructure, poor access to inputs and markets, and insufficient resources to invest for the future.

Smallholders in Africa and elsewhere are frequently very poor, with minimal cash income coming primarily from contract labor or off-farm employment. Many of them need to grow a sizable fraction of the food they consume. When conditions such as a drought or pest outbreak make this difficult and they have limited reserves these farmers may not have enough to eat. Smallholders make up about half of the world’s malnourished population, despite the fact that they normally produce much of the food grown in their own countries. These farmers contribute significantly to food production but they are also especially vulnerable to food insecurity.

The challenges faced by smallholders in sub-Saharan Africa are discussed in the readings by Jayne et al. (2010) and Carr (2001). The economic challenges mentioned by Jayne et al. include shrinking farm sizes, decreasing productivity, marketing problems, limited off-farm employment opportunities, and changing international trade and development policies. Carr provides useful historical context and emphasizes agronomic challenges, including the need for better access to fertilizer, higher yield cultivars suitable for local conditions, and expanded irrigation to reduce water stress on rainfed crops. Similar challenges arise in varying degrees throughout the world but they are particularly problematic in sub-Saharan Africa, where farm incomes and assets are unusually low, soil fertility is often poor, climate extremes can be severe, and state support of agricultural development can be erratic and underfunded. The plots in the optional reading by Rapsomanikis (2015) provide convenient summaries of smallholder economic life in several developing countries, including some in Africa. Relevant statistics are also provided in S13.

The issues identified by Jayne et al. and Carr raise the question of whether smallholder agriculture can be expected to meet the food needs of Africa’s growing population. This question is addressed in the next two papers. Larson et al. (2016) argue that the high-input smallholder model that has been so successful in Asia is the best option for Africa. By contrast, Collier & Dercon (2014) favor more reliance on larger commercial operations, which they feel benefit from economies of scale. The two papers agree that there is a need for a mix of small, medium, and large farms, although they differ on the relative importance of each category. Their debate is central to African development discussions.

One aspect of the smallholder vs. commercial farm debate is the feasibility of increasing crop yields, which tend to be low in sub-Saharan Africa for farms of all sizes. The role of yield is addressed in the paper by van Ittersum et al. (2016), which considers whether food needs in selected African countries could be met by closing yield gaps. (see S6). Their analysis indicates that some of the larger countries (e.g. Nigeria and Kenya) will have difficulty meeting their needs with domestic production, even with nearly complete elimination of yield gaps, while others (e.g. Ethiopia) have a better chance. Although closing yield gaps may not be sufficient to feed some sub-Saharan countries with domestic production, food demands could still be met with imports, particularly if per capita incomes grow enough. In these countries food security is closely tied to economic development outside as well as inside the agricultural sector.

The choice for governments and donors between encouraging smallholder vs. larger commercial farming is difficult since there are compelling arguments on both sides. However, the future of global food security could depend significantly on the priority given to each alternative.

Required Readings

Challenges of Smallholder Agriculture in Sub-Saharan Africa

Smallholder vs. Commercial Agriculture for Sub-Saharan Africa

Closing Yield Gaps in Africa

Optional Reading

Smallholder Economic Profiles

Farm Size and Distribution

Discussion Points

  • What is your conclusion about the merits of directing government and donor resources to smallholder vs. larger commercial farming? How convincing do you find the arguments in the two readings on this issue?
  • Based on what you have read for this class, what would you say are the most significant factors that distinguish agricultural development in Africa from other regions? What are the prospects for African agriculture and food security?
  • The reading by Collier & Dercon includes an extended discussion of labor productivity and migration, implying that migration is the best way to increase the low labor productivity of smallholders and, consequently, to reduce their poverty. Do you think there is a chance that improved technology could also increase labor productivity. For example, how about more extensive use of fertilizers and herbicides?

This class provides a quick survey of the effects of climate change on agriculture as well as the effects of agriculture on climate change. Climate changes of particular importance to crop production include:

  • Increases in mean and extreme temperatures
  • Shifting and extended growing seasons
  • Changes in the distribution and intensity of precipitation
  • More frequent severe weather events.
  • Increases in atmospheric carbon dioxide (can enhance photosynthesis, up to a point)
  • Ecosystem changes driven by temperature and precipitation.

The nature of these changes remains highly uncertain.

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The key question for agriculture and food security is how climate change will impact crop yields. It is possible that some crops, some farmers, and some regions will benefit from climate change while others will suffer adverse consequences. The problem of assessing the impacts of climate change on agriculture requires not only an ability to predict climate but also a better understanding of environmental influences on crop yield. To a first approximation, the net effect of climate change on yield at a given location for a given crop reflects the combination of negative impacts due to increases in temperature (and possibly decreases in rainfall) and positive impacts due to increases in carbon dioxide and a longer growing season (and possibly increases in rainfall).

In the other direction, the most direct impacts of agriculture on climate occur through greenhouse gases emitted by agricultural operations. However, there are also indirect contributions such as the emissions created as by-products during nitrogen fertilizer synthesis or during the clearing of forests for cropland (see S11).

Our readings start with the most recent (2014) “Synthesis Report” from the Intergovernmental Program on Climate Change (IPCC), a United Nations group that regularly compiles information on observations and predictions of climate change. The required portion (SPM1 and SPM2) is a concise summary of findings intended for policy makers but useful to anyone interested in the topic. The additional recommended portion (Topics 1 and 2) provides more detail, including discussions of some of the alternative scenarios considered in the discussion of future climate. This report is useful not just as background but to introduce the vocabulary and perspective of the ‘climate change establishment’. The optional IPCC reading by Stocker et al. (2013) provides more detail on the physical science basis for the findings presented in the Synthesis Report.

The Synthesis Report’s division into sections on past and future climate is representative of research on this topic. Prediction is needed to determine how the climate might change in response to different policies and practices, often formalized in terms of specific scenarios. Analysis of past climate is needed to confirm the accuracy of the models used to make predictions, to obtain better understanding of uncertain physical processes, and to establish context for scenario predictions. Since different models can give significantly different predictions, for example predicting an increase vs. a decrease in average rainfall, it can be difficult to interpret model-based forecasts of climate change. The IPCC reports try to convey the diversity of results obtained from different models and to distinguish predictions that are reasonably certain from those that are more uncertain.

The book chapter by Ruane and Rosenzweig (2019) provides a focused discussion of the connections between climate and agriculture. The prediction section of the paper relies on 29 different climate models and a smaller number of global crop models. The results presented suggest that yields for major grains will generally be adversely impacted by climate change in lower latitude and semi-arid regions and more favorably impacted in colder regions, so long as local soils support increased production.

Morton’s (2007) paper discusses climate change impacts on smallholder and subsistence farmers who are especially vulnerable to reduced yields and increased occurrence of extreme events such as droughts and floods. Most smallholders live in tropical regions where climate-related crop yield reductions and livestock losses are more likely. Climate change adds to a long list of “non-climate stressors” that are already making life difficult for these smallholders. Overall, the Morton paper is useful for emphasizing that climate change will likely have especially devastating impacts on rural low-income populations in developing countries, reflecting the effects of both geography and poverty.

Deutsch et al. (2018) provide a review of possible impacts of climate change on insect pests. This example illustrates one way that climate change could modify ecosystems that are important to agriculture. The analysis depends on a particular model of the effects of temperature changes on the growth and metabolic rates of insects that threaten food crops. The conclusion is that insect-related crop losses could increase substantially (by 10%–25% per degree C of warming) in the temperate areas where most grain is produced. Since the study is based on a relatively simple model and uncertainties are substantial it serves primarily to pose a hypothesis that deserves further investigation.

The readings in this class provide a just glimpse of the many connections between climate and agriculture. However, they clearly convey the view that climate change will be a key consideration in developing a strategy for achieving food security in the 21st century.

Required Readings

Climate Change Summary

  • IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. [Required reading: Summary for Policy Makers, Sections SPM1 and SPM2, pp. 1–16; Recommended reading: Topics 1 and 2, pp. 39–74]

Climate and Agriculture

  • A. C. Ruane and C. Rosenzweig. 2019: “Chapter 5: Climate Change Impacts on Agriculture.” In Agriculture & Food Systems to 2050. P. Pingali and R. Serraj, Eds., World Scientific Series in Grand Public Policy Challenges of the 21st Century, vol. 2. World Scientific, pp. 161–191.

Climate and Smallholders

Climate and Pests

Optional Reading

Climate Change Physical Science Basis

  • T. F. Stocker, D. Qin, et al. 2013. “Technical Summary.” In Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Discussion Points

  • Do you think there is a convincing case that the net effect of climate change on global food production is negative? Is the possible threat to food production as serious a problem as some of the other adverse effects of climate change (e.g. effects on human habitability or on severe weather events)? Please justify your answer.
  • Now consider an expanded version of the first question, which addresses not just food production but food security, by including food accessibility and utilization as well as stability/reliability of supply. Does this change your answer?
  • After reading Morton (2007) what do you think is the best way for smallholders to protect themselves from the adverse effects of climate change? What role do you see for international agencies/governments? 
  • How would you convince a neutral to skeptical ‘policy maker’ to support potentially controversial adaptation and/or mitigation measures to deal with the possible effects of climate change on food security? What measures would you put at the top of your list?

Our analysis so far suggests that our water and land resources may not be sufficient to grow the additional food required to provide global food security throughout this century, at least with current technology and management practices. It seems quite possible that climate change may make things even more difficult. Also, there is no guarantee that it will be possible to meet food demands with sustainable intensification that raises yield on existing cropland through increased nutrient and pesticide inputs and expanded irrigation infrastructure. So it is natural to ask whether new technologies and the improved management practices they enable could be the answer.

This class looks at two promising and much discussed new technologies—agricultural biotechnology and precision agriculture. One of the primary goals of biotechnology in the agricultural sector is to improve plant capabilities for dealing with environmental stresses that limit yield. Of particular interest are stresses from pests and disease, and from extreme events such as heat waves, droughts, and floods. Other important goals include increasing potential (unstressed) crop yields, reducing pesticide use, and improving crop nutritional quality. It is worth mentioning that biotechnology also has a role in improving the quantity and quality of livestock products. This aspect is important but not discussed here.

The paper by Ronald (2011) provides a useful introduction to agricultural biotechnology. It focuses on examples of insect resistant, herbicide resistant, and viral resistant crops that are all being used in the field and it provides shorter discussions of possible future applications that go beyond pest control.  The examples are illustrated and updated in Ronald’s TED video. The video by Jill Farrant provides an interesting example of ongoing research on drought resistance, which has yet to be put into practice. The optional paper by Ricroch & Hénard-Damave (2016) gives a sense of the range of genetically engineered agricultural products in development at the publication time. Hefferon and Herring (2017) discuss some new approaches in genomic technology.

The stated goals of agricultural genetic engineering are generally admirable but the means used to achieve these goals are controversial. Although some have raised concerns about human health impacts the most credible concerns are related to ecological aspects. Some examples are:

  • New varieties of pests that are resistant to genetic innovation can evolve through natural selection. This is a problem that is also associated with the use of traditional chemical pesticides.
  • Genetically engineered crops could be invasive, with related loss of biodiversity
  • Genetically engineered crops could have adverse effects on non-target organisms and ecosystems, including soil microbiological communities
  • New viruses with unknown properties could develop in transgenic viral-resistant plants.

The paper by Wolfenberger and Phifer (2000) reviews some of these concerns. Gilbert (2013) provides a journalistic look at resistance as well as some other ecological and social issues that have been raised by opponents of genetic engineering.

Concerns about genetic engineering were largely hypothetical and speculative when the Wolfenberger and Phifer (2000) paper was published. The situation has not changed much since then. The community that voices these concerns still has strong but thinly documented reservations about possible adverse environmental impacts but rarely mentions the possibility that modern biotechnology could provide additional food for millions. On the other hand, the community advocating genetic engineering barely mentions environmental concerns. There are still surprisingly few data-driven papers that address both sides of the issue. The controversy has become quite polarized, partly because of strict European limits on the development and use of genetic engineering in agriculture. The optional reading by Paarlberg (2010) provides an interesting policy perspective, considering differences between European and African food security needs. The reading by the US National Academy of Sciences (2016) summarizes an effort to build a consensus position.

Overall, biotechnology is a promising development for food security that has already had an impact on agricultural production (see S12). Much of the practical success to date has been in genetically engineered pest control techniques that improve on traditional pesticides but share the need to continually deal with acquired pest resistance. There is still much uncertainty about the longer-term effectiveness and environmental impacts of current genetic engineering technology.

Our second technology, precision agriculture, seems to have little downside, other than affordability. Precision agriculture technologies are designed to make crop production more efficient, with respect to the use of water, nutrients, pesticides, labor, capital, and other inputs. They do this by combining new high-resolution sensors, information technology, and cultivation equipment in an integrated package. Widespread adoption of precision agriculture methods could have positive environmental impacts if they reduce water use and undesirable off-farm losses of fertilizer and pesticides. The article by Gebbers and Adamchuk (2010) provides a concise overview of relevant technology while the paper by Bogue (2017) surveys some precision agriculture sensors and equipment in current use or in development. The Millennial Farmer video shows an example of a popular precision agriculture product on a large US farm.

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There are few comprehensive studies of the effects of precision agriculture on crop yield and farm revenue. Some of the equipment required is expensive so its advantages must be weighed in light of the capital investment required, especially for applications to small farms in developing countries. However, it seems likely that demand for precision agriculture technology will increase and prices will fall if this technology can be shown to significantly reduce crop inputs while also improving yield. To date, precision agriculture innovations have tended to be driven by corporate research and development but academic research can be expected to have an increasingly important role in sensor development and in applications of robotic, “big data,” and artificial intelligence technologies to the agricultural sector. The challenge will be to ensure that these developments will find their way to smallholders and poorer farmers.

Required Readings

Genetic Engineering and Food Security

Ecological Risks of Genetically Engineered Crops

Summary Statement on Genetic Engineering

Precision Agriculture

Optional Readings

Genetic Engineering

Videos

The Case for Genetically Engineered Food

Genetic Engineering for Drought Resistance

Precision Agriculture Demonstration

Discussion Points

  • How would you compare the desirability and feasibility of meeting projected food demand by 1) reducing meat consumption and closing developing country yield gaps by expanding fertilizer use and irrigation vs. 2) replacing traditional crops with more robust higher yield genetically engineered crops?
  • Do we really need genetically engineered crops?
  • What kinds of precision agriculture products do you think would attract a market among small farmers in the developing world?

Farm Category, Area, and Production Distributions

Recent refereed publications have started to provide a more accurate picture of the global farm system. The information cited here is peer reviewed and should be reproducible from cited data sources. This is in contrast to statistics found in many reports and articles issued by international agencies, who sometimes do not identify their sources.

A good place to start in our survey of global farm characteristics is Figure S10.1, which shows two gridded maps that identify a) the percentage of pixel area devoted to crop production and b) a categorical estimate of crop field size. Both are derived from the same global land use data. Categorical field size estimates can be inferred from satellite data and have been shown to correlate with farm size. Details of the mapping procedure are described in Fritz et al. (2015)

The darker shaded 1 km pixels on the cropland percentage map indicate more densely cultivated regions. The four colors on the field size map show the characteristic crop field size (from “very small” to “large”) identified with a given pixel. The dark green areas in a) are the major food producing regions. The dark blue (large field size) areas in b) generally coincide with the major food exporting areas (North America, Australia, and parts of South America). The red (very small field size) areas in b) indicate regions where smallholder farms dominate (China, India, and sub-Saharan Africa).

Figure S10.1: Gridded 1km pixel maps of   a) percentage of land in each pixel devoted to crop production
b) characteristic field size category for each pixel. (Fritz et al., 2015).

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Figure S10.2 shows information from global land census surveys conducted in 1990 and 2000 in 111 countries and compiled by Lowder et al. (2015).  Panel a) shows the fraction of farms in each of several size categories, based on data from 460 million farms in 111 countries. Since the survey is reasonably inclusive the paper assumes that the fractions in the chart apply to the global total, which is estimated to be at least 570 million farms. The chart indicates that 94% of global farms are smaller than 5 ha. Based on this and a conservative assumption of up to 4 people per farm household, we can estimate that there are up to 2 billion people on farms smaller than 5 ha (perhaps more). This is roughly consistent with uncited estimates given in UN documents.

Panel a) is a snapshot of the global farm size distribution from around 1990-2000. Farm size distributions and averages change over time. The trend plot in Panel b) shows that average farm sizes in high income countries (left scale) continually increased between 1960 and 2000 while farm sizes in other countries generally decreased. African countries are indicated by the dotted line (right scale).  More recent data suggest that the trends in each region still have the same direction.

Figure S10.2 Global farm size category and area distributions and trends. (Lowder et al., 2015).

Courtesy Elsevier, Inc., http://www.sciencedirect.com. Used with permission.

Although farms over 5 ha only account for 6% of all global farms the land area they each contribute is large. To address this, the Lowder et al. paper also estimates the total cropland area in each size category. Cropland area provides a basis for comparing, for example, the relative contribution to production from smallholders, medium size farms, and large farms. The global cropland area distribution in Panel c) clearly indicates that small farms are more numerous (dark gray) but that larger farms contribute more total area (light gray). Farms smaller than 2 ha and 5 ha account, respectively, for 12% and 18% of global cropland area while farms larger than these thresholds account, respectively, for 88% and 82% of the global total area. We can expect global crop production contributions of small vs. large farms to roughly correlate with these global cropland area figures (see next section).

Figure S10.3 shows a similar plot with results for sub-Saharan Africa. Here larger farms contribute a smaller fraction of the regional total area (also, note the change in the horizontal scale). Farms smaller than 2 ha and 5 ha account, respectively, for 38% and 66% of sub-Saharan Africa cropland area while farms larger than these thresholds (but smaller than 50 ha) account, respectively, for the remaining 42% and 34% of area. This suggests that smallholder production is a major fraction of total domestic food production in sub-Saharan Africa.

Figure S11.3 Sub-Saharan farm size category and area distributions compared (Lowder et al., 2015).

Courtesy Elsevier, Inc., http://www.sciencedirect.com. Used with permission.

A recent study by Ricciardi et al. (2018) provides smallholder cropland area estimates that are somewhat higher than Lowder et al. and are based on a somewhat smaller number of country surveys. The Ricciardi et al. (2018) paper estimates that smallholder farms less than 2 ha occupy 24% of global cropland area (rather than 18%). It also indicates that these farms generate 28-31% of global crop production and 30-34% of global calorie production. These results confirm Lowder’s conclusion that smallholder farms contribute significantly to the global food supply. The Ricciardi et al. (2018) paper does not provide results for particular regions, such as sub-Saharan Africa but it does provide size category distributions for particular crops.

References:

Steffen Fritz, Linda See, et al. 2015. “Mapping Global Cropland and Field Size.” Global Change Biology, 21, no. 5: 1980–1992.

IFAD International Fund for Agricultural Development. 2010. “Rural Poverty Report 2011 - New Realities, New Challenges: New Opportunities for Tomorrow’s Generation.” Annexes 1 and 2. IFAD, Rome

Sarah K. Lowder, Jakob Skoet, and Terri Raney. 2016. “The Number, Size, and Distribution of Farms, Smallholder Farms, and Family Farms Worldwide.” World Development, 87, 16–29.

Vincent Ricciardi, Navin Ramankutty, et al. 2018. “How Much of the World’s Food Do Smallholders Produce?” Global Food Security, 17, 64–72.

Figure S11.1, from the World Resources Institute (WRI) compares greenhouse gas emissions from agriculture to other major sources in 2016. The primary gases considered are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The units are the number of gigatons (GtCO2e) of carbon dioxide that give the same radiative forcing as the indicated gas. Most of the direct agricultural emissions are methane and nitrous oxide from manure, soil denitrification, and rice cultivation. A relatively small fraction takes the form of carbon dioxide emissions from agricultural fossil fuel use (included under “Other Fuel Combustion”).

Overall, direct agricultural operations contribute about 13.5% of total global radiative forcing. It should be noted, however, that another 8–10% of agriculturally-related radiative forcing is contributed by the ‘burning’ and ‘cropland’ categories listed under ‘land use change and forestry’ and by industrial operations that support agriculture, most notably fertilizer production. Additional radiative forcing not explicitly noted on the chart is associated with transportation and processing of food after harvest. Although agriculture is an important contributor to radiative forcing, totaling over 20% when all direct and indirect sources are included, it is difficult to see how its emissions could be decreased significantly, especially if meat and rice remain important parts of the global diet.

All calculations in the chart are based on CO2 equivalents, using 100-year global warming potentials from the IPCC (1996), based on total global emissions of 49.4 GtCO2 equivalent.

Figure S11.1 Global greenhouse emission contributions in 2016, by economic sector (World Resources Institute, Accessed August, 2020).

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Adoption of genetically engineered crops varies greatly across countries due to different regulatory conditions, public attitudes, and agronomic factors. The USA has, by far, the largest genetically engineered acreage, with Brazil, Argentina, India, and Canada making up the remaining countries in the top five. Figure S12.1 shows how genetically engineered soybean, maize and cotton acreage in the US grew between 1996 and 2018. The label HT refers to crops engineered to be herbicide resistant and primarily used with glyphosate (Roundup) herbicide. The label BT refers to insect resistant crops containing a gene from Bacillus thuringiensis. Some crops combine both traits.

This plot shows a dramatic increase in the use of two important genetic engineering technologies. In 2018 the genetically engineered US maize, soybean, and cotton crop areas were all well over 90% of the total planted area.

Figure S12.1: Trends in crop acreage devoted to genetically engineered cotton, maize, and soybeans.
Sources: USDA Economic Research Service (2002)

Courtesy of USDA Economic Research Service.

References:

National Agricultural Statistics Service. Annual Reports for June. 2000–2018.

US Department of Agriculture, Economic Research Service Report AER–810. 2002.

University of Michigan Extension website, “Why Many Growers Are Quick to Adopt Genetic Modification Technology.” Accessed 14 July 2020.

Soil is comprised of inorganic minerals, organic matter, water, and air. It typically forms in layers (or soil horizons) when it develops from the weathering and transport of mineral or organic parent material (Figure S9.1).

Figure S9.1: a) Primary components of soil, fractions are representative but change over time. 
b) Soil horizons found in a typical agricultural soil profile. From Brady and Weil (2002).

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The chemical and biological composition of the soil components as well as their physical arrangement affect the movement and retention of air, water, and nutrients in the subsurface. Bulk soil has a number of properties that collectively determine its fertility or quality for agricultural applications. A concise discussion of these properties as well as the soil column that includes the crop root zone is provided in the optional Class 6 reading by McCauley et al. (2005).

The short list of agriculturally relevant soil properties given below can be used to concisely characterize a particular soil, This list is constructed from suggestions by NCERA-59, an inter-state group in the US (Doran and Parkin, 1994) and by the Soil Health Institute (Wander, 2019): 

Physical properties:
 Soil texture
 Rooting depth
 Bulk density
 Infiltration rate
 Water holding capacity
 Wet aggregate stability
 Penetration resistance erosion rating

Chemical properties:
 pH
 Total nitrogen (N)
 Total organic carbon (TOC)
 Electrical conductivity (EC)
 Phosphorus (P)
 Potassium (K)
 Base saturation
 Cation exchange capacity (CEC)

Biological properties
 Carbon mineralization
 Nitrogen mineralization

It is common to use quantitative or categorical indices derived from soil property values to assess the suitability of a given soil for a given crop. Recent FAO-funded data acquisition efforts have produced global soil property data sets that have been harmonized to reconcile different national measurement and reporting methods (FAO, 2012). The functions given in Figure 2 of Zabel et al. (2014) from Class 4 provide simple examples of how soil properties can be mapped to soil suitability indices. Fischer et al. (2012) describe a more complex soil suitability classification approach based on some of the soil properties listed above.

Unfortunately, data limitations make it difficult to use such methods to analyze temporal trends in soil quality or to identify where agricultural practices are either degrading or improving soil. Current approaches for looking at soil quality trends are imperfect and controversial.  Gibbs and Salmon (2015) is one of the few papers that compares different approaches for mapping global soil degradation trends (expert opinion, satellite-derived net primary productivity, biophysical models, and abandoned cropland). This paper shows large variations across different estimates of regional and total soil degradation (see Figure S9.2), suggesting that we still do not really know how much agriculture has changed the soil resources needed to grow food. This uncertainty complicates global assessments of the impacts of different agricultural practices on soil health.

However, there is still ample local evidence that soil quality has declined in particular agricultural areas that have experienced intense cultivation or grazing pressure. These include parts of North and South America, India, China, and sub-Saharan Africa. In these areas it is likely that yield has suffered or, in some cases, that the land is no longer suitable for agriculture.

Figure S9.2: Four different estimates of global soil degradation with a common color scale (percent of land
degraded) and 20km resolution, ca. 1990 (GLASOD) and 2010 (others), from Gibbs and Salmon (2015).

Courtesy Elsevier, Inc., http://www.sciencedirect.com. Used with permission.

References

 Nyle C. Brady and Ray R. Weil. 2002. The Nature and Properties of Soils, 13th Edition. Prentice Hall. Upper Saddle River, New Jersey. 960 p. ISBN: 9780130167637.

John W. Doran and Timothy B. Parkin. 1994. “Defining and Assessing Soil Quality.” Defining Soil Quality for a Sustainable Environment, 35: 1–21.

FAO/IIASA/ISRIC/ISSCAS/JRC. (2012). “Harmonized World Soil Database v 1.2.” FAO, Rome, Italy and IIASA, Laxenburg, Austria.

Günther Fischer, F. Nachtergaele, et al. 2012. “Global Agro-Ecological Zones (GAEZ v3. 0) - Model Documentation.”

H. K. Gibbs and J. M. Salmon. 2015. “Mapping the World’s Degraded Lands.” Applied Geography, 57, 12–21.

McCauley, A., Jones, C., and Jacobsen, J. (2005). “Basic Soil Properties (PDF).” Soil and Water Management Module. 1, no. 1: 1–12. Montana State University Extension Service.

Michelle M. Wander, Larry J. Cihacek, et al. 2019. “Developments in Agricultural Soil Quality and Health: Reflections by the Research Committee on Soil Organic Matter Management.” Frontiers in Environmental Science, 7, 10.3389/fenvs.2019.00109.

Florian Zabel, Birgitta Putzenlechner, and Wolfram Mauser. 2014. “Global Agricultural Land Resources—A High Resolution Suitability Evaluation and Its Perspectives until 2100 under Climate Change Conditions.” PLoS One, 9, no. 9.

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