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Recent patterns of crop yield growth and stagnation

Recent patterns of crop yield growth and stagnation ARTICLE Received 12 Jun 2012 | Accepted 15 Nov 2012 | Published 18 Dec 2012 DOI: 10.1038/ncomms2296 1 2 1 1 1 Deepak K. Ray , Navin Ramankutty , Nathaniel D. Mueller , Paul C. West & Jonathan A. Foley In the coming decades, continued population growth, rising meat and dairy consumption and expanding biofuel use will dramatically increase the pressure on global agriculture. Even as we face these future burdens, there have been scattered reports of yield stagnation in the world’s major cereal crops, including maize, rice and wheat. Here we study data from B2.5 million census observations across the globe extending over the period 1961–2008. We examined the trends in crop yields for four key global crops: maize, rice, wheat and soybeans. Although yields continue to increase in many areas, we find that across 24–39% of maize-, rice-, wheat- and soybean-growing areas, yields either never improve, stagnate or collapse. This result underscores the challenge of meeting increasing global agricultural demands. New investments in underperforming regions, as well as strategies to continue increasing yields in the high-performing areas, are required. 1 2 Institute on the Environment (IonE), University of Minnesota, St Paul, Minnesota 55108, USA. Department of Geography and Global Environmental and Climate Change Center, McGill University, Montreal, Quebec H3A 2K6, Canada. Correspondence and requests for materials should be addressed to D.K.R. (email: dray@umn.edu). NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 1 & 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 he global demand for agricultural crops is expected to collapsed to the 1960s level (Fig. 1c). Fourth, ‘yields still roughly double by 2050, driven by increases in population, increasing’—areas where yields are still increasing (Fig. 1d). Based 1–3 Tmeat and dairy consumption and biofuel use . However, on recent rates of yield improvement, we can further divide this between 1985 and 2005, the total global crop production category into the top 25% of yield-improving regions—‘yields increased by only 28% (through a B2.5% net expansion of increasing rapidly’; the bottom 25% of yield-improving regions— global cropland area, an B7% increase in the frequency of ‘yields increasing slowly’; and the intermediate 50% of yield- harvesting, and an average B20% increase in crop yields per improving regions—‘yields increasing moderately’. hectare) . Clearly, these recent gains in global crop production fall Overall, our analysis shows that most of the world has his- short of the expected demands, leaving us with an important torically experienced significant yield improvements (Fig. 2, question: Which crops and which geographic regions offer the Table 1). The percentage of the world that never experienced any best hope of meeting projected demands, and where are maize, rice, wheat or soybean yield improvement is small (B1% improvements most needed? of each harvested crop areas; Table 1). Adding to this concern, some authors have suggested that We find that the world’s maize, rice, wheat and soybean crops yields for many important crops may be stagnating in some are continuing to experience yield increases in over 70, 63, 61 and 5–10 regions around the world . In particular, there are concerns 76% of their harvested areas, respectively—corresponding to 103, that yields may be stagnating or declining for three key crops— 96, 130 and 63 million hectares (m. ha) (Fig. 2; Table 1). Globally, maize, rice and wheat—which together produce B57% of the however, rice (35%) and wheat (37%) have substantial areas that world’s agricultural calories . A slowing, or worse, stagnation or are now witnessing yield stagnation. Maize (26%) and soybean collapse in the yield gains in these crops would have profound (23%) have less area in yield stagnation. Furthermore, we find implications for the world food system. that 3% of maize, 1% rice and 1% of wheat areas have experienced Although some authors have already noted some specific local- yield collapse. or national-scale examples of where crop yields may have Areas where yields are still increasing currently contribute 5–7,10–12 stagnated , no spatially detailed assessment of global roughly 79%, 57%, 56% and 82% of the total global production in crop yield trends has been attempted to date. To consider the maize, rice, wheat and soybean, respectively. The remainder current state and trends in yields of the world’s four key crops comes primarily from regions witnessing yield stagnation. This (maize, rice, wheat and soybean) that currently provide B64% of then means that for wheat and rice, at least, yield stagnation may agricultural calorie production , we employed new long-term and have profound implications on the ability of agriculture to meet high-resolution geospatial databases of global agricultural the growing global demands for these commodities. systems , synthesized from B2.5 million census observations Below, we explore in more details the major regional patterns (Supplementary Note 1, Supplementary Methods, Supplementary for these four crops. For statistical modelling used, model fits and Table S1 and Supplementary Figs S1 and S2). Using these data, we classification used to determine yield trend category, please refer analysed detailed spatial and temporal patterns of yields, to the (Supplementary Note 1, Supplementary Methods and determining where these four key crops have experienced yield Supplementary Figs S3–S5). stagnation and where crop yields are still increasing. These new data give us a dramatically improved understanding of crop yield and area changes across regional and global scales, Regional summaries. Only B1% of global maize areas never saw which are otherwise often obscured using only national census yield increases, and the significant areas were in Morocco and statistics . For example, using only the United Nations Food and parts of India (0.4 m. ha) (Fig. 2a). Yields are stagnating in 26% of Agricultural Organization’s national crop statistics suggests that maize-harvested areas (Fig. 2a)—in the United States, generally American wheat yields increased everywhere at B0.01 tons on the fringes (for example, portions of the Great Plains) of the 1  2 ha year (0.3%/year) between 1999 and 2008. Using our vast US Corn Belt (yields peaked mostly from mid 1990s, new high-resolution geospatial data set, we were able to identify Supplementary Fig. S6), more widespread portions in eastern and that yields in B36% of the American wheat-harvested areas (B7 southern Mexico (yields peaked mostly early 1990s) and in million ha) are not improving; only in the remaining B64% of smaller areas of other major Latin American countries. In some wheat land (B13 million ha) are yields improving, and at parts of Western Europe, maize yield improvements have stag- different identifiable rates. nated, especially, in Spain, Italy and Greece. Africa has a large Here we analyse changes in yields over time at each of the extent of maize yield stagnation (yields here peaked mostly from political units where maize, rice, wheat and soybean were the late 1990s). In Asia, in India and China, maize yields have harvested. We find that across 24–39% of maize, rice, wheat stagnated across B31 and B52% of the maize-growing areas. and soybean-growing areas, yields have either never improved, Maize yields have collapsed in only 3% of global areas promi- stagnated or collapsed. This result highlights the increasingly nently in Dominican Republic, parts of northeast Brazil, Mol- difficult challenge of meeting increasing global agricultural dova, Africa (Chad, Rwanda, Angola, Zimbabwe and Lesotho) demands. and South Asia (0.07 and 0.2 m. ha in India and Nepal, respec- tively). Maize yields are still increasing in 70% of global areas: in the vast United States Corn Belt, western and central Mexico, and Results most of Brazil and Argentina. Many other European, African and Global yield trends. We found that global yield trends can be Asian maize areas are also witnessing steady maize yield broadly divided into four types (Fig. 1). First, ‘yields never improvement. The fastest maize yield improvements globally improved’—areas that have witnessed no significant yield were found in the Corn Belt of the United States (B37% of all improvements to date (Fig. 1a). Second, ‘yields stagnated’—areas maize-harvested areas) and in Latin America, especially Argen- where yields previously improved, but now are stagnating or tina (78% of all maize-harvested areas), and Brazil. There are also declining (Fig. 1b). This category includes a range of yield trends some isolated similar fast increasing areas in Portugal, France, post a year of yield maximum, including yields hovering near the Eastern Europe, Turkey, Nigeria, South Africa, Pakistan, India, yield maximum (that is, a yield plateau) and yield declines at China, Vietnam and Indonesia. In most of the United States and various rates. Third, ‘yields collapsed’—areas where yields Western Europe, maize yields are improving at either fast or decreased since the 1960s, or initially increased and then moderate rates. 2 NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications & 2012 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 ARTICLE Yields never improved Yields stagnating Maize − Harvey County, Kansas, USA Maize − Morocco Rice − Hokkaido, Japan Rice − North korea Wheat − Basse−Normandie, France Wheat − Glacier County, Montana, USA Soybean − Anoka county, Minnesota, USA Soybean − Lubbock County, Texas, USA 5 5 3 3 2 2 0 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 1965 1970 1975 1980 1985 1990 1995 2000 2005 Yields collapsed Yields still increasing Maize − Moldova Maize − Clay County, Minnesota, USA Rice − Enuga, Nigeria Rice − Faulkner County, Arkansas, USA 9 9 Wheat − Central west, New South Wales, Australia Wheat − Big Stone County, Minnesota, USA Soybean − Dem. Rep. of Congo Soybean − Baradero Municipio, Buenos Aires, Argentina 7 7 6 6 5 5 4 4 2 2 1 1 0 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 1965 1970 1975 1980 1985 1990 1995 2000 2005 Figure 1 | Illustrative examples for each of the four types of global crop yield trends. The solid filled circles in each panel are the observed crop yields from various global locations to serve as illustrative examples. Colour codes indicate the crop. The solid curves are the statistical model fits to the data and similarly colour coded according to the crop type. (a) Yields never improved. (b) Yields stagnating. (c) Yields collapsed. (d) Yields still increasing. Only B1% of the global rice-growing areas never saw yield (B5%), Peru (B11%), Nigeria (100%), Lesotho (100%), Mon- increases; these areas were found in parts of Brazil (northeast golia (B64%) and parts of Australia (B4%) (Fig. 2c). Wheat Brazil), Greece, Mexico and India, as well as in Gabon, Gambia, yields collapsed in an extremely small fraction of the world (B1% Democratic Republic of Congo and North Korea (Fig. 2b). Rice globally corresponding to 1.6 m. ha, out of which B1.5 m. ha was yields are stagnating across 35% of rice-harvested areas globally: in Australia). Yields are stagnating in 37% of global areas in the US state of California (yields peaked here in the late 1990s, including B27% of wheat areas in the United States (primarily in Supplementary Fig. S6), parts of Latin America (Fig. 2b), most of the Great Plain states where stagnation occurred after peaking Europe and parts of Africa (Fig. 2b). In Asia, the major rice- mostly in the early to mid 1990s, Supplementary Fig. S6). Fur- growing continent, yields are stagnating in China, India and thermore, wheat yields have been stagnating in parts of Argentina Indonesia across 79%, 36% and 81% of rice-growing areas, (B1.8 m. ha or B34% of areas since the late 1990s) and almost respectively. Rice yield have collapsed in 1% of the world’s rice- everywhere in the highly productive wheat-growing areas of harvested areas. The largest areas of rice-yield collapse were in Western Europe as well as Eastern Europe. They are also stag- Brazil (northeast Brazil), Sierra Leon and parts of Nigeria in nating in Turkey (in B5.4 m. ha or B64% of their wheat- Africa, Iraq and parts of India. Areas with ongoing rice-yield growing areas), China (56% of areas) and India (in B70% of increases are found in all continents in 63% of global areas areas). Wheat yields began stagnating in the Khyber Pakh- (except Australasia). However, large areas of rapidly increasing tunkhwa and Balochistan states of Pakistan (starting after rice yields are found only in some countries: USA, Colombia, B2000), and in Australia, wheat yields are stagnating inB44% of Peru, Argentina, Uruguay, Brazil, Spain, India, China, Vietnam, its areas. In all, 61% of global wheat areas are witnessing yield Afghanistan and Bangladesh. increases. Most of Canadian wheat areas, B64% of United States Wheat yields never improved in 1% of global areas: in large wheat areas, Russian wheat, most African wheat areas, some areas parts of the United States (B9% of its harvested areas), Argentina of Asian wheat and B40% of Australian wheat areas are still NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 3 & 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 Maize Rice Yields never improved Yields never improved Yields stagnated Yields stagnated Yields collapsed Yields collapsed Yields increasing rapidly Yields increasing rapidly Yields increasing moderately Yields increasing moderately Yields increasing slowly Yields increasing slowly Wheat Soybean Yields never improved Yields never improved Yields stagnated Yields stagnated Yields collapsed Yields collapsed Yields increasing rapidly Yields increasing rapidly Yields increasing moderately Yields increasing moderately Yields increasing slowly Yields increasing slowly Figure 2 | Global maps of current crop yield trends. At each political unit where (a) maize, (b) rice, (c) wheat and (d) soybean crop yields were tracked globally, we determined the status of their current yield trend. The trends were divided into the six categories and colour coded. We show in the maps only those areas in the political unit where the crop was harvested. witnessing yield improvement. Although there are many coun- crops are stagnating in more than a quarter of our croplands. Can tries with some fraction of their wheat areas witnessing rapid we reverse the yield stagnation in these areas? At the field to yield improvement, the countries with the top five spatial extent country scale, there are numerous studies showing that both are (in m. ha): China (B8), Iran (B4), United States (B4), biophysical and socio-economic causes, often not mutually Afghanistan (B2) and India (B2). exclusive, are the drivers of these yield changes. The lack of Soybean yields never improved in B0.8 m. ha (1% of all global readily available data regarding all possible drivers of global areas); these areas are concentrated in the United States (B0.4 m. agriculture at the level of our analysis precludes any effort to ha), Argentina, Brazil and Mexico (Fig. 2d). Soybean yields col- ascribe the causes behind the observed yield trends. However, lapsed in an insignificantly small area globally (0.2% of global below we discuss some of the reported field to country-scale areas). Brazil had a large area of soybean yield collapse (B0.1 m. causes of yield changes with an emphasis on Europe, Asia- ha), as did smaller areas in Uruguay and the Democratic Republic Australasia and Africa; these are the continents where yield of Congo. Globally, soybean yield stagnation covers B19 m. ha stagnation appears particularly widespread (Fig. 2). (B23% of harvested areas), and countries with more than a In the Americas, maize yield stagnation is especially wide- million ha in yield stagnation are (in decreasing order): China, spread only in Mexico. Here reduced fallow periods in areas of India, United States, Paraguay, Brazil and Argentina. Yield shifting cultivation without concomitant adoption of modern improvements are also fairly widespread but are more prevalent management practices , or non-introduction/adoption of non- (B76% of global areas); countries with the largest spatial extent local but high-yielding maize seeds by farmers , may be of yield improvements (again listed in decreasing order and more responsible. In the United States, greater adoption of no-till than a million ha each) are: United States, Brazil, Argentina, practice by farmers in the semi-arid areas of the Great Plains has China and India. coincided with intensified crop rotations (for example, wheat- maize rotations as opposed to a fallow following wheat). Farmer net incomes may have consequently increased, but intensified Discussion crop rotations may have also led to increased yield variability and 17 18 Today, a global food crisis is looming as the world population crop failures in an area of already limited water resources . increases, more people shift towards meat and dairy intensive Our analysis shows widespread yield stagnation in these regions, 1–4 diets and more cropland is diverted to grow biofuel crops . especially for wheat (Fig. 2a and c). How will we meet these growing demands, especially when recent In Europe, wheat yields may have declined because of climate crop-production trends were insufficient to do so, and many changes in some countries of Western Europe , though regions are showing significant stagnation and declines in yield elsewhere in more northern countries, the warmer climate may improvement? have led to fewer low yield years, and even expansion of wheat 14,19 Looking forward, we must first ensure that areas still increasing areas . Elsewhere in Europe, warmer temperatures may have yields do not falter, while at the same time improving manage- had no effect on boosting either maize and wheat yields . ment practices to reduce impacts on the environment . Next, we Confounding the climate-change effects in Europe are socio- have to identify why yield gains for our most important cereal economic and policy decisions to reduce farmer remuneration for 4 NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications & 2012 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 ARTICLE Table 1 | Yield status globally and for the top 10 producers. Maize Rice Wheat Soybean m. ha % m. ha % m. ha % m. ha % NI 43.7 29.9 NI 57.4 37.5 NI 82.8 38.8 NI 20.1 24.3 a 0.9 0.6 a 1.6 1.0 a 2.8 1.3 a 0.8 1.0 Global b 38.2 26.1 Global b 53.7 35.1 Global b 78.4 36.8 Global b 19.0 23.0 c 4.7 3.2 c 2.1 1.4 c 1.6 0.8 c 0.2 0.2 IM 102.7 70.1 IM 95.6 62.5 IM 130.4 61.2 IM 62.6 75.7 USA NI 2.4 7.6 China NI 22.7 78.7 China NI 12.8 55.5 USA NI 2.6 9.0 IM 28.8 92.4 IM 6.1 21.3 IM 10.3 44.5 IM 26.3 91.0 China NI 14.6 52.2 India NI 16.0 37.1 India NI 18.9 69.9 Brazil NI 2.1 14.1 IM 13.3 47.8 IM 27.1 62.9 IM 8.1 30.1 IM 12.5 85.9 Brazil NI 1.8 18.8 Indonesia NI 9.8 81.4 USA NI 7.4 35.9 Argentina NI 1.7 12.4 IM 7.8 81.2 IM 2.2 18.6 IM 13.2 64.1 IM 12.2 87.6 Mexico NI 2.2 31.0 Bangladesh* NI 0.0 0.0 Russian Federation* NI – – China NI 5.4 58.1 IM 4.8 69.0 IM 10.6 100 IM 24.0 100 IM 3.9 41.9 Argentina NI 0.1 5.2 Vietnam NI 0.2 2.1 France NI 4.2 79.2 India NI 3.8 51.4 IM 2.6 94.8 IM 7.2 97.9 IM 1.1 20.8 IM 3.6 48.6 France NI 0.2 10.5 Thailand NI 0.3 2.6 Canada NI 0.08 0.8 Paraguay NI 2.2 98.4 IM 1.5 89.5 IM 10.0 97.4 IM 9.3 99.2 IM 0.04 1.6 India NI 2.9 37.1 Myanmar* NI 0.0 0 Germany NI 1.5 80.4 Canada NI 0.0 0.0 IM 4.9 62.9 IM 7.6 100 IM 0.4 19.6 IM 0.9 100 Indonesia NI 0.07 1.9 Philippines NI 0.5 11.9 Pakistan NI 1.1 13.4 Bolivia NI 0.9 99.8 IM 3.5 98.1 IM 3.7 88.1 IM 7.3 86.6 IM 0.0 0.2 Italy NI 0.7 59.2 Brazil NI 0.5 21.2 Australia NI 7.7 60.2 Indonesia NI 0.3 59.2 IM 0.5 40.8 IM 1.8 78.8 IM 5.1 39.8 IM 0.2 40.8 South Africa NI 0.0 0.0 Japan NI 0.3 19.3 Turkey NI 5.4 63.6 Italy NI 0.1 99.9 IM 2.8 100 IM 1.4 80.7 IM 3.1 36.4 IM 0.0 0.1 Abbreviations: NI, yields not improving; IM, yields improving. Global breakup into the three NI yield trend types also provided ((a) Yields never improvedþ (b) Yields stagnatingþ (c) Yields collapsed). Percentages may not add up to 100% because of rounding. See Supplementary Data 1 for details of all countries analysed. *Only national analysis. Top ten producers based on average production for the decade ending 2008 as reported by FAO. Areas are based on the average harvested area for 2004–2008. intensive cultivation, or to reduce the environmental tolerant varieties for the growing conditions in East Asia . 6,7,10,21,22 burden , which may have reduced farmer inputs Similarly, rice cultivars that provide high yields in nutrient- 11 36 leading to yield stagnation but improved environmental deficient soils are needed to boost yields. Changing the length quality . However, there are clearly both regional/country and and type of crop rotation with better management could also crop specificities. There may now be fewer incentives to boost boost Asian rice and wheat yields . wheat yields in Western European countries (namely in France, In Africa, crop yields may have stagnated due to a complex Germany and United Kingdom), which correlates with our results combination of factors, many of which may ultimately be due to showing widespread areas where yield increases have ceased socio-economic limitation. Specific constraints to crop yield (B80% of the wheat areas in France and Germany, and B99% in increases include variability of dry spells and lack of field-water the United Kingdom). However, maize yields are increasing management strategies in the drier parts of the continent , 39,40 almost everywhere in France and Germany (B90% and 100% of absence of significant irrigation infrastructure , low nutrient maize-growing areas, respectively). Spain, Portugal and Italy on application and absence of fallows to restore soil fertility 41,42 the other hand have a larger fraction of their wheat areas showing levels , lack of availability of suitable high-yielding crop yield increases (82%, 89%, and 76%, respectively) compared with varieties that in turn could be related to institutional and political 42–44 maize (48%, 65%, and 41%, respectively). conditions , and the lack of farmer expertise in appropriate In Asia and Australia, yields of wheat and rice may have agronomic practices . However, when combinations of socio- stagnated as shown in our analysis (see Fig. 2b,c) due to a economic factors align to overcome the biophysical limitations, combination of factors that are location-specific, including significant yields gains are achieved . For example, landscape- 24,25 39 46 47 climate-change-related heat stress , increased night time scale modelling results , field trials and policy experiments , 26 12,27 temperatures , depletion of soil fertility and salinization , all demonstrate that fairly small increase in inputs is sufficient to 27 28 soil erosion , increasing competition for water resources , pest double maize yields in Africa. 27 29 and disease build-up and a lack of capital to buy more Although we have found widespread yield stagnation, an expensive inputs while the real crop prices declined . Wheat increase in the number of crops per cropping cycle or 31 48–50 yields may have stagnated in Bangladesh , and in parts of India intercropping with other crops can increase net food also because of current cultivars approaching their yield supply and farmer incomes .Indeed, global harvested areas potentials . The effect of water scarcity for irrigation, falling have increased at nearly three times the rate of global croplands 18,27,33 4 groundwater water tables and soil-quality depletion may be areas since 1985 . In some areas, farmers may have prioritized 34,35 even more pronounced for rice , leading to the widespread livestock over grain crops, and in other regions, yields may rice-yield stagnation (Fig. 2b). The need for new wheat cultivars is have stagnated, but the total factor productivity (the ratio of the 21,51 another major challenge; specifically, varieties are needed that are total output to the total input) increased .However,globally, heat- and water logging-tolerant for growing conditions in South there remain many regions where both the growth in yields and Asia where wheat follows rice in the crop rotation, and frost- total factor productivity of agriculture remain low, perhaps NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 5 & 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 because of a lack of established agricultural research and parameters themselves guided the classification of yield trends into the four basic categories. An intercept-only model indicated that ‘yields never improved’. If the investment . model chosen was linear with positive slope, it indicated that ‘yields were still At the global scale, yields are being affected by both improving’, whereas a linear model with negative slope showed that ‘yields 52,53 22,29,40 biophysical and socioeconomic factors. Differences in collapsed’. Similarly, the sign of the quadratic term when the model chosen is 4,5,32,39 crop performance create yield gaps that could be overcome quadratic, and the year of the inflection points when the model chosen is cubic, 54,55,39 determined the yield trend category for quadratic and cubic fits. Classification of by adoption of best management practices . Understanding these models is more complex with details included in Supplementary Note 1 and how changes to management practices (including fertilizer Supplementary Methods. The statistical fits are appropriate over the observed application, irrigation, pest management and others) could period, and thus have unknown predictive capacity for future years. Also see close yield gaps is critical to addressing stagnating yields on Supplementary Tables S2 and S3 for comparisons with other national scale studies and utility of conducting sub-national studies. our most important croplands. Failure to identify and alleviate Outliers in the data may have influenced model choice in some cases, but it was causes of yield stagnation, collapse and never improving yields not possible to remove these data from the analysis, given that it was generally will have an impact on the future of global food security. unclear which outliers were real (for example, because of weather fluctuations, pest Our global analysis shows that maize, rice, wheat and soybean infestation and so on) and which were erroneous. crops are continuing to experience yield increases in 61–76% of their global harvested areas. This implies that between 24–39% of References these cropland areas are no longer witnessing yield increases; the 1. Godfray, H. C. J. et al. Food security: the challenge of feeding 9 billion people. spatial extent of such rice and wheat areas is now particularly Science 327, 812–818 (2010). extensive (37% and 39% of global areas, respectively). In all, 43% 2. 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Contr. 19, 716–723 (1974). demand for crop production: the challenge of yield decline in crops grown in short rotations. Biol. Rev. 87, 52–71 (2012). Acknowledgements 38. Barron, J., Rockstro¨m, J., Gichuki, F. & Hatibu, N. Dry spell analysis and maize We thank the NASA and DOE of the United States, NSERC of Canada and the Gordon yields for two semi-arid locations in east Africa. Agricult. Forest Meterol. 117, and Betty Moore Foundation for their support. N.D.M. was supported with a NSF 23–27 (2003). Graduate Research Fellowship. We also thank George Allez, Laura Bryson and Amy 39. Mueller, N. D. et al. Closing yield gaps: nutrient and water management to Kimball for their help in collecting and digitizing a portion of the data. This work was boost crop production. Nature 490, 254–257 (2012). also benefitted from the comments of the Foley lab members, as well as editing by Emily 40. Portmann, F. T., Seibert, S. & Doll, P. MIRCA2000-Global monthly irrigated Dombeck. 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Field Crop Res. 34, 357–380 (1993). stagnation. Nat. Commun. 3:1293 doi: 10.1038/ncomms2296 (2012). NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 7 & 2012 Macmillan Publishers Limited. All rights reserved. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Nature Communications Springer Journals

Recent patterns of crop yield growth and stagnation

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Springer Journals
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Copyright © 2012 by Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
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Science, Humanities and Social Sciences, multidisciplinary; Science, Humanities and Social Sciences, multidisciplinary; Science, multidisciplinary
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10.1038/ncomms2296
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Abstract

ARTICLE Received 12 Jun 2012 | Accepted 15 Nov 2012 | Published 18 Dec 2012 DOI: 10.1038/ncomms2296 1 2 1 1 1 Deepak K. Ray , Navin Ramankutty , Nathaniel D. Mueller , Paul C. West & Jonathan A. Foley In the coming decades, continued population growth, rising meat and dairy consumption and expanding biofuel use will dramatically increase the pressure on global agriculture. Even as we face these future burdens, there have been scattered reports of yield stagnation in the world’s major cereal crops, including maize, rice and wheat. Here we study data from B2.5 million census observations across the globe extending over the period 1961–2008. We examined the trends in crop yields for four key global crops: maize, rice, wheat and soybeans. Although yields continue to increase in many areas, we find that across 24–39% of maize-, rice-, wheat- and soybean-growing areas, yields either never improve, stagnate or collapse. This result underscores the challenge of meeting increasing global agricultural demands. New investments in underperforming regions, as well as strategies to continue increasing yields in the high-performing areas, are required. 1 2 Institute on the Environment (IonE), University of Minnesota, St Paul, Minnesota 55108, USA. Department of Geography and Global Environmental and Climate Change Center, McGill University, Montreal, Quebec H3A 2K6, Canada. Correspondence and requests for materials should be addressed to D.K.R. (email: dray@umn.edu). NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 1 & 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 he global demand for agricultural crops is expected to collapsed to the 1960s level (Fig. 1c). Fourth, ‘yields still roughly double by 2050, driven by increases in population, increasing’—areas where yields are still increasing (Fig. 1d). Based 1–3 Tmeat and dairy consumption and biofuel use . However, on recent rates of yield improvement, we can further divide this between 1985 and 2005, the total global crop production category into the top 25% of yield-improving regions—‘yields increased by only 28% (through a B2.5% net expansion of increasing rapidly’; the bottom 25% of yield-improving regions— global cropland area, an B7% increase in the frequency of ‘yields increasing slowly’; and the intermediate 50% of yield- harvesting, and an average B20% increase in crop yields per improving regions—‘yields increasing moderately’. hectare) . Clearly, these recent gains in global crop production fall Overall, our analysis shows that most of the world has his- short of the expected demands, leaving us with an important torically experienced significant yield improvements (Fig. 2, question: Which crops and which geographic regions offer the Table 1). The percentage of the world that never experienced any best hope of meeting projected demands, and where are maize, rice, wheat or soybean yield improvement is small (B1% improvements most needed? of each harvested crop areas; Table 1). Adding to this concern, some authors have suggested that We find that the world’s maize, rice, wheat and soybean crops yields for many important crops may be stagnating in some are continuing to experience yield increases in over 70, 63, 61 and 5–10 regions around the world . In particular, there are concerns 76% of their harvested areas, respectively—corresponding to 103, that yields may be stagnating or declining for three key crops— 96, 130 and 63 million hectares (m. ha) (Fig. 2; Table 1). Globally, maize, rice and wheat—which together produce B57% of the however, rice (35%) and wheat (37%) have substantial areas that world’s agricultural calories . A slowing, or worse, stagnation or are now witnessing yield stagnation. Maize (26%) and soybean collapse in the yield gains in these crops would have profound (23%) have less area in yield stagnation. Furthermore, we find implications for the world food system. that 3% of maize, 1% rice and 1% of wheat areas have experienced Although some authors have already noted some specific local- yield collapse. or national-scale examples of where crop yields may have Areas where yields are still increasing currently contribute 5–7,10–12 stagnated , no spatially detailed assessment of global roughly 79%, 57%, 56% and 82% of the total global production in crop yield trends has been attempted to date. To consider the maize, rice, wheat and soybean, respectively. The remainder current state and trends in yields of the world’s four key crops comes primarily from regions witnessing yield stagnation. This (maize, rice, wheat and soybean) that currently provide B64% of then means that for wheat and rice, at least, yield stagnation may agricultural calorie production , we employed new long-term and have profound implications on the ability of agriculture to meet high-resolution geospatial databases of global agricultural the growing global demands for these commodities. systems , synthesized from B2.5 million census observations Below, we explore in more details the major regional patterns (Supplementary Note 1, Supplementary Methods, Supplementary for these four crops. For statistical modelling used, model fits and Table S1 and Supplementary Figs S1 and S2). Using these data, we classification used to determine yield trend category, please refer analysed detailed spatial and temporal patterns of yields, to the (Supplementary Note 1, Supplementary Methods and determining where these four key crops have experienced yield Supplementary Figs S3–S5). stagnation and where crop yields are still increasing. These new data give us a dramatically improved understanding of crop yield and area changes across regional and global scales, Regional summaries. Only B1% of global maize areas never saw which are otherwise often obscured using only national census yield increases, and the significant areas were in Morocco and statistics . For example, using only the United Nations Food and parts of India (0.4 m. ha) (Fig. 2a). Yields are stagnating in 26% of Agricultural Organization’s national crop statistics suggests that maize-harvested areas (Fig. 2a)—in the United States, generally American wheat yields increased everywhere at B0.01 tons on the fringes (for example, portions of the Great Plains) of the 1  2 ha year (0.3%/year) between 1999 and 2008. Using our vast US Corn Belt (yields peaked mostly from mid 1990s, new high-resolution geospatial data set, we were able to identify Supplementary Fig. S6), more widespread portions in eastern and that yields in B36% of the American wheat-harvested areas (B7 southern Mexico (yields peaked mostly early 1990s) and in million ha) are not improving; only in the remaining B64% of smaller areas of other major Latin American countries. In some wheat land (B13 million ha) are yields improving, and at parts of Western Europe, maize yield improvements have stag- different identifiable rates. nated, especially, in Spain, Italy and Greece. Africa has a large Here we analyse changes in yields over time at each of the extent of maize yield stagnation (yields here peaked mostly from political units where maize, rice, wheat and soybean were the late 1990s). In Asia, in India and China, maize yields have harvested. We find that across 24–39% of maize, rice, wheat stagnated across B31 and B52% of the maize-growing areas. and soybean-growing areas, yields have either never improved, Maize yields have collapsed in only 3% of global areas promi- stagnated or collapsed. This result highlights the increasingly nently in Dominican Republic, parts of northeast Brazil, Mol- difficult challenge of meeting increasing global agricultural dova, Africa (Chad, Rwanda, Angola, Zimbabwe and Lesotho) demands. and South Asia (0.07 and 0.2 m. ha in India and Nepal, respec- tively). Maize yields are still increasing in 70% of global areas: in the vast United States Corn Belt, western and central Mexico, and Results most of Brazil and Argentina. Many other European, African and Global yield trends. We found that global yield trends can be Asian maize areas are also witnessing steady maize yield broadly divided into four types (Fig. 1). First, ‘yields never improvement. The fastest maize yield improvements globally improved’—areas that have witnessed no significant yield were found in the Corn Belt of the United States (B37% of all improvements to date (Fig. 1a). Second, ‘yields stagnated’—areas maize-harvested areas) and in Latin America, especially Argen- where yields previously improved, but now are stagnating or tina (78% of all maize-harvested areas), and Brazil. There are also declining (Fig. 1b). This category includes a range of yield trends some isolated similar fast increasing areas in Portugal, France, post a year of yield maximum, including yields hovering near the Eastern Europe, Turkey, Nigeria, South Africa, Pakistan, India, yield maximum (that is, a yield plateau) and yield declines at China, Vietnam and Indonesia. In most of the United States and various rates. Third, ‘yields collapsed’—areas where yields Western Europe, maize yields are improving at either fast or decreased since the 1960s, or initially increased and then moderate rates. 2 NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications & 2012 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 ARTICLE Yields never improved Yields stagnating Maize − Harvey County, Kansas, USA Maize − Morocco Rice − Hokkaido, Japan Rice − North korea Wheat − Basse−Normandie, France Wheat − Glacier County, Montana, USA Soybean − Anoka county, Minnesota, USA Soybean − Lubbock County, Texas, USA 5 5 3 3 2 2 0 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 1965 1970 1975 1980 1985 1990 1995 2000 2005 Yields collapsed Yields still increasing Maize − Moldova Maize − Clay County, Minnesota, USA Rice − Enuga, Nigeria Rice − Faulkner County, Arkansas, USA 9 9 Wheat − Central west, New South Wales, Australia Wheat − Big Stone County, Minnesota, USA Soybean − Dem. Rep. of Congo Soybean − Baradero Municipio, Buenos Aires, Argentina 7 7 6 6 5 5 4 4 2 2 1 1 0 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 1965 1970 1975 1980 1985 1990 1995 2000 2005 Figure 1 | Illustrative examples for each of the four types of global crop yield trends. The solid filled circles in each panel are the observed crop yields from various global locations to serve as illustrative examples. Colour codes indicate the crop. The solid curves are the statistical model fits to the data and similarly colour coded according to the crop type. (a) Yields never improved. (b) Yields stagnating. (c) Yields collapsed. (d) Yields still increasing. Only B1% of the global rice-growing areas never saw yield (B5%), Peru (B11%), Nigeria (100%), Lesotho (100%), Mon- increases; these areas were found in parts of Brazil (northeast golia (B64%) and parts of Australia (B4%) (Fig. 2c). Wheat Brazil), Greece, Mexico and India, as well as in Gabon, Gambia, yields collapsed in an extremely small fraction of the world (B1% Democratic Republic of Congo and North Korea (Fig. 2b). Rice globally corresponding to 1.6 m. ha, out of which B1.5 m. ha was yields are stagnating across 35% of rice-harvested areas globally: in Australia). Yields are stagnating in 37% of global areas in the US state of California (yields peaked here in the late 1990s, including B27% of wheat areas in the United States (primarily in Supplementary Fig. S6), parts of Latin America (Fig. 2b), most of the Great Plain states where stagnation occurred after peaking Europe and parts of Africa (Fig. 2b). In Asia, the major rice- mostly in the early to mid 1990s, Supplementary Fig. S6). Fur- growing continent, yields are stagnating in China, India and thermore, wheat yields have been stagnating in parts of Argentina Indonesia across 79%, 36% and 81% of rice-growing areas, (B1.8 m. ha or B34% of areas since the late 1990s) and almost respectively. Rice yield have collapsed in 1% of the world’s rice- everywhere in the highly productive wheat-growing areas of harvested areas. The largest areas of rice-yield collapse were in Western Europe as well as Eastern Europe. They are also stag- Brazil (northeast Brazil), Sierra Leon and parts of Nigeria in nating in Turkey (in B5.4 m. ha or B64% of their wheat- Africa, Iraq and parts of India. Areas with ongoing rice-yield growing areas), China (56% of areas) and India (in B70% of increases are found in all continents in 63% of global areas areas). Wheat yields began stagnating in the Khyber Pakh- (except Australasia). However, large areas of rapidly increasing tunkhwa and Balochistan states of Pakistan (starting after rice yields are found only in some countries: USA, Colombia, B2000), and in Australia, wheat yields are stagnating inB44% of Peru, Argentina, Uruguay, Brazil, Spain, India, China, Vietnam, its areas. In all, 61% of global wheat areas are witnessing yield Afghanistan and Bangladesh. increases. Most of Canadian wheat areas, B64% of United States Wheat yields never improved in 1% of global areas: in large wheat areas, Russian wheat, most African wheat areas, some areas parts of the United States (B9% of its harvested areas), Argentina of Asian wheat and B40% of Australian wheat areas are still NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 3 & 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 Maize Rice Yields never improved Yields never improved Yields stagnated Yields stagnated Yields collapsed Yields collapsed Yields increasing rapidly Yields increasing rapidly Yields increasing moderately Yields increasing moderately Yields increasing slowly Yields increasing slowly Wheat Soybean Yields never improved Yields never improved Yields stagnated Yields stagnated Yields collapsed Yields collapsed Yields increasing rapidly Yields increasing rapidly Yields increasing moderately Yields increasing moderately Yields increasing slowly Yields increasing slowly Figure 2 | Global maps of current crop yield trends. At each political unit where (a) maize, (b) rice, (c) wheat and (d) soybean crop yields were tracked globally, we determined the status of their current yield trend. The trends were divided into the six categories and colour coded. We show in the maps only those areas in the political unit where the crop was harvested. witnessing yield improvement. Although there are many coun- crops are stagnating in more than a quarter of our croplands. Can tries with some fraction of their wheat areas witnessing rapid we reverse the yield stagnation in these areas? At the field to yield improvement, the countries with the top five spatial extent country scale, there are numerous studies showing that both are (in m. ha): China (B8), Iran (B4), United States (B4), biophysical and socio-economic causes, often not mutually Afghanistan (B2) and India (B2). exclusive, are the drivers of these yield changes. The lack of Soybean yields never improved in B0.8 m. ha (1% of all global readily available data regarding all possible drivers of global areas); these areas are concentrated in the United States (B0.4 m. agriculture at the level of our analysis precludes any effort to ha), Argentina, Brazil and Mexico (Fig. 2d). Soybean yields col- ascribe the causes behind the observed yield trends. However, lapsed in an insignificantly small area globally (0.2% of global below we discuss some of the reported field to country-scale areas). Brazil had a large area of soybean yield collapse (B0.1 m. causes of yield changes with an emphasis on Europe, Asia- ha), as did smaller areas in Uruguay and the Democratic Republic Australasia and Africa; these are the continents where yield of Congo. Globally, soybean yield stagnation covers B19 m. ha stagnation appears particularly widespread (Fig. 2). (B23% of harvested areas), and countries with more than a In the Americas, maize yield stagnation is especially wide- million ha in yield stagnation are (in decreasing order): China, spread only in Mexico. Here reduced fallow periods in areas of India, United States, Paraguay, Brazil and Argentina. Yield shifting cultivation without concomitant adoption of modern improvements are also fairly widespread but are more prevalent management practices , or non-introduction/adoption of non- (B76% of global areas); countries with the largest spatial extent local but high-yielding maize seeds by farmers , may be of yield improvements (again listed in decreasing order and more responsible. In the United States, greater adoption of no-till than a million ha each) are: United States, Brazil, Argentina, practice by farmers in the semi-arid areas of the Great Plains has China and India. coincided with intensified crop rotations (for example, wheat- maize rotations as opposed to a fallow following wheat). Farmer net incomes may have consequently increased, but intensified Discussion crop rotations may have also led to increased yield variability and 17 18 Today, a global food crisis is looming as the world population crop failures in an area of already limited water resources . increases, more people shift towards meat and dairy intensive Our analysis shows widespread yield stagnation in these regions, 1–4 diets and more cropland is diverted to grow biofuel crops . especially for wheat (Fig. 2a and c). How will we meet these growing demands, especially when recent In Europe, wheat yields may have declined because of climate crop-production trends were insufficient to do so, and many changes in some countries of Western Europe , though regions are showing significant stagnation and declines in yield elsewhere in more northern countries, the warmer climate may improvement? have led to fewer low yield years, and even expansion of wheat 14,19 Looking forward, we must first ensure that areas still increasing areas . Elsewhere in Europe, warmer temperatures may have yields do not falter, while at the same time improving manage- had no effect on boosting either maize and wheat yields . ment practices to reduce impacts on the environment . Next, we Confounding the climate-change effects in Europe are socio- have to identify why yield gains for our most important cereal economic and policy decisions to reduce farmer remuneration for 4 NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications & 2012 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 ARTICLE Table 1 | Yield status globally and for the top 10 producers. Maize Rice Wheat Soybean m. ha % m. ha % m. ha % m. ha % NI 43.7 29.9 NI 57.4 37.5 NI 82.8 38.8 NI 20.1 24.3 a 0.9 0.6 a 1.6 1.0 a 2.8 1.3 a 0.8 1.0 Global b 38.2 26.1 Global b 53.7 35.1 Global b 78.4 36.8 Global b 19.0 23.0 c 4.7 3.2 c 2.1 1.4 c 1.6 0.8 c 0.2 0.2 IM 102.7 70.1 IM 95.6 62.5 IM 130.4 61.2 IM 62.6 75.7 USA NI 2.4 7.6 China NI 22.7 78.7 China NI 12.8 55.5 USA NI 2.6 9.0 IM 28.8 92.4 IM 6.1 21.3 IM 10.3 44.5 IM 26.3 91.0 China NI 14.6 52.2 India NI 16.0 37.1 India NI 18.9 69.9 Brazil NI 2.1 14.1 IM 13.3 47.8 IM 27.1 62.9 IM 8.1 30.1 IM 12.5 85.9 Brazil NI 1.8 18.8 Indonesia NI 9.8 81.4 USA NI 7.4 35.9 Argentina NI 1.7 12.4 IM 7.8 81.2 IM 2.2 18.6 IM 13.2 64.1 IM 12.2 87.6 Mexico NI 2.2 31.0 Bangladesh* NI 0.0 0.0 Russian Federation* NI – – China NI 5.4 58.1 IM 4.8 69.0 IM 10.6 100 IM 24.0 100 IM 3.9 41.9 Argentina NI 0.1 5.2 Vietnam NI 0.2 2.1 France NI 4.2 79.2 India NI 3.8 51.4 IM 2.6 94.8 IM 7.2 97.9 IM 1.1 20.8 IM 3.6 48.6 France NI 0.2 10.5 Thailand NI 0.3 2.6 Canada NI 0.08 0.8 Paraguay NI 2.2 98.4 IM 1.5 89.5 IM 10.0 97.4 IM 9.3 99.2 IM 0.04 1.6 India NI 2.9 37.1 Myanmar* NI 0.0 0 Germany NI 1.5 80.4 Canada NI 0.0 0.0 IM 4.9 62.9 IM 7.6 100 IM 0.4 19.6 IM 0.9 100 Indonesia NI 0.07 1.9 Philippines NI 0.5 11.9 Pakistan NI 1.1 13.4 Bolivia NI 0.9 99.8 IM 3.5 98.1 IM 3.7 88.1 IM 7.3 86.6 IM 0.0 0.2 Italy NI 0.7 59.2 Brazil NI 0.5 21.2 Australia NI 7.7 60.2 Indonesia NI 0.3 59.2 IM 0.5 40.8 IM 1.8 78.8 IM 5.1 39.8 IM 0.2 40.8 South Africa NI 0.0 0.0 Japan NI 0.3 19.3 Turkey NI 5.4 63.6 Italy NI 0.1 99.9 IM 2.8 100 IM 1.4 80.7 IM 3.1 36.4 IM 0.0 0.1 Abbreviations: NI, yields not improving; IM, yields improving. Global breakup into the three NI yield trend types also provided ((a) Yields never improvedþ (b) Yields stagnatingþ (c) Yields collapsed). Percentages may not add up to 100% because of rounding. See Supplementary Data 1 for details of all countries analysed. *Only national analysis. Top ten producers based on average production for the decade ending 2008 as reported by FAO. Areas are based on the average harvested area for 2004–2008. intensive cultivation, or to reduce the environmental tolerant varieties for the growing conditions in East Asia . 6,7,10,21,22 burden , which may have reduced farmer inputs Similarly, rice cultivars that provide high yields in nutrient- 11 36 leading to yield stagnation but improved environmental deficient soils are needed to boost yields. Changing the length quality . However, there are clearly both regional/country and and type of crop rotation with better management could also crop specificities. There may now be fewer incentives to boost boost Asian rice and wheat yields . wheat yields in Western European countries (namely in France, In Africa, crop yields may have stagnated due to a complex Germany and United Kingdom), which correlates with our results combination of factors, many of which may ultimately be due to showing widespread areas where yield increases have ceased socio-economic limitation. Specific constraints to crop yield (B80% of the wheat areas in France and Germany, and B99% in increases include variability of dry spells and lack of field-water the United Kingdom). However, maize yields are increasing management strategies in the drier parts of the continent , 39,40 almost everywhere in France and Germany (B90% and 100% of absence of significant irrigation infrastructure , low nutrient maize-growing areas, respectively). Spain, Portugal and Italy on application and absence of fallows to restore soil fertility 41,42 the other hand have a larger fraction of their wheat areas showing levels , lack of availability of suitable high-yielding crop yield increases (82%, 89%, and 76%, respectively) compared with varieties that in turn could be related to institutional and political 42–44 maize (48%, 65%, and 41%, respectively). conditions , and the lack of farmer expertise in appropriate In Asia and Australia, yields of wheat and rice may have agronomic practices . However, when combinations of socio- stagnated as shown in our analysis (see Fig. 2b,c) due to a economic factors align to overcome the biophysical limitations, combination of factors that are location-specific, including significant yields gains are achieved . For example, landscape- 24,25 39 46 47 climate-change-related heat stress , increased night time scale modelling results , field trials and policy experiments , 26 12,27 temperatures , depletion of soil fertility and salinization , all demonstrate that fairly small increase in inputs is sufficient to 27 28 soil erosion , increasing competition for water resources , pest double maize yields in Africa. 27 29 and disease build-up and a lack of capital to buy more Although we have found widespread yield stagnation, an expensive inputs while the real crop prices declined . Wheat increase in the number of crops per cropping cycle or 31 48–50 yields may have stagnated in Bangladesh , and in parts of India intercropping with other crops can increase net food also because of current cultivars approaching their yield supply and farmer incomes .Indeed, global harvested areas potentials . The effect of water scarcity for irrigation, falling have increased at nearly three times the rate of global croplands 18,27,33 4 groundwater water tables and soil-quality depletion may be areas since 1985 . In some areas, farmers may have prioritized 34,35 even more pronounced for rice , leading to the widespread livestock over grain crops, and in other regions, yields may rice-yield stagnation (Fig. 2b). The need for new wheat cultivars is have stagnated, but the total factor productivity (the ratio of the 21,51 another major challenge; specifically, varieties are needed that are total output to the total input) increased .However,globally, heat- and water logging-tolerant for growing conditions in South there remain many regions where both the growth in yields and Asia where wheat follows rice in the crop rotation, and frost- total factor productivity of agriculture remain low, perhaps NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 5 & 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms2296 because of a lack of established agricultural research and parameters themselves guided the classification of yield trends into the four basic categories. An intercept-only model indicated that ‘yields never improved’. If the investment . model chosen was linear with positive slope, it indicated that ‘yields were still At the global scale, yields are being affected by both improving’, whereas a linear model with negative slope showed that ‘yields 52,53 22,29,40 biophysical and socioeconomic factors. Differences in collapsed’. Similarly, the sign of the quadratic term when the model chosen is 4,5,32,39 crop performance create yield gaps that could be overcome quadratic, and the year of the inflection points when the model chosen is cubic, 54,55,39 determined the yield trend category for quadratic and cubic fits. Classification of by adoption of best management practices . Understanding these models is more complex with details included in Supplementary Note 1 and how changes to management practices (including fertilizer Supplementary Methods. The statistical fits are appropriate over the observed application, irrigation, pest management and others) could period, and thus have unknown predictive capacity for future years. Also see close yield gaps is critical to addressing stagnating yields on Supplementary Tables S2 and S3 for comparisons with other national scale studies and utility of conducting sub-national studies. our most important croplands. Failure to identify and alleviate Outliers in the data may have influenced model choice in some cases, but it was causes of yield stagnation, collapse and never improving yields not possible to remove these data from the analysis, given that it was generally will have an impact on the future of global food security. unclear which outliers were real (for example, because of weather fluctuations, pest Our global analysis shows that maize, rice, wheat and soybean infestation and so on) and which were erroneous. crops are continuing to experience yield increases in 61–76% of their global harvested areas. This implies that between 24–39% of References these cropland areas are no longer witnessing yield increases; the 1. Godfray, H. C. J. et al. Food security: the challenge of feeding 9 billion people. spatial extent of such rice and wheat areas is now particularly Science 327, 812–818 (2010). extensive (37% and 39% of global areas, respectively). In all, 43% 2. 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Field Crop Res. 34, 357–380 (1993). stagnation. Nat. Commun. 3:1293 doi: 10.1038/ncomms2296 (2012). NATURE COMMUNICATIONS | 3:1293 | DOI: 10.1038/ncomms2296 | www.nature.com/naturecommunications 7 & 2012 Macmillan Publishers Limited. All rights reserved.

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