Is Precision Agriculture the Way to Peak Cropland?
The Unsung Hero of Agricultural Innovation
As threats to wildlife and habitats go, the global expansion of farmland – including land used for crops and livestock – is unrivaled. Forests, grasslands, and wetlands representing more than two-fifths of the earth’s ice-free surface have given way to farming.1 Over the past half century alone, farmland has grown by more than 400 million hectares2 – an area nearly half the size of the United States. More than half of recent agricultural expansion in the tropics has come at the expense of old-growth forests.3 Conversion of natural habitats to farmland has been a leading cause of precipitous declines in terrestrial wildlife populations, which on average fell by more than half between 1970 and 2012.4
If farmland continues to grow over the next several decades, the consequences for habitats and wildlife would be dire. As such, slowing, halting, and eventually reversing the growth in agricultural area must be a top priority – perhaps the top priority – for global conservation.
“Peak farmland” itself does not guarantee an end to habitat loss, since other land uses, especially cities, are expanding.5 And since farming is shifting from temperate to tropical regions, deforestation in the latter could continue, even if farmland stopped expanding on a net global basis.3 Regardless, peak farmland would take a whole lot of pressure off forests and other natural habitats, and enable greater opportunities for conservation efforts like protected areas.
The challenge is daunting. By midcentury, the global population will be approaching ten billion,6 and demand for crops in 2050 could be twice as high as in 2005.7 Crop yields – the amount of crops harvested per unit of land – will have to rise by at least as much as crop demand to avoid further encroachment of cropland into natural habitats.
Dramatic increases in crop yields would not be unprecedented. In the twentieth century, a powerful package of technologies, including better seeds, synthetic fertilizers and pesticides, irrigation, and machinery, boosted yields by a factor of two or three, first in the United States and Europe, and later in much of the rest of the world, in what became known as the Green Revolution.8–11
But today, with the exception of Sub-Saharan Africa, this crude but effective recipe has mostly run its course. Applying more fertilizers will increase pollution, not yields. Irrigation has only a modest potential to expand, as many rivers and aquifers are already tapped and subject to many competing demands.12 The groundbreaking new rice and wheat varieties that underpinned early yield gains in places like India and the Philippines were a one-off boost that cannot easily be repeated. Furthermore, several major crop-producing regions have seen yields stagnate in recent years,13 and “yield gaps” – the difference between current and potential yield at a given location – are getting smaller for many crops.14,15
This poses two questions: what sorts of innovations can drive yield improvements once the basic set of modern farming technologies have been adopted – that is, post-Green Revolution – and can these new methods drive rapid enough gains for the world to meet rising food demand without further growth in cropland?
Much of the debate on this issue has focused on biotech, and particularly genetically modified organisms (GMOs). But the emphasis on GMOs – and the heated debates it has given rise to – risks obscuring the bigger picture. In the past few decades, innovators, agronomists, and farmers have developed a powerful suite of technologies and practices under the banner of precision agriculture, which has played a large and underappreciated role in driving up yields and reducing pollution. Looking forward, precision agriculture presents some of the best opportunities to meeting growing global food demand while minimizing environmental impacts. As such, it needs to become a central component of the conversation about agricultural innovation and sustainability.
Precision Farming: The Unsung Hero of Agricultural Innovation
The Green Revolution averted a looming food security crisis and spared vast land areas from being converted to cropland, greatly attenuating the loss of wildlife and natural habitats.10,16,17 It also had manifold negative impacts, including pollution from nutrient overload and pesticides, freshwater depletion, and social disruption.10,18 Many of these negative impacts, however, have been mitigated over time, as production increases are stemming less from increasing inputs like water and fertilizers, and more from smarter farming decisions, including more efficient use of these inputs. By one estimate, chemical inputs, land, irrigation, and area expansion accounted for 93% of increased global agricultural production at the height of the Green Revolution in the 1970s, but only 27% in the 2000s. The rest – now representing about three-quarters of production growth – comes from what is called total factor productivity, or more simply, efficiency.19
After a period of blunt and wasteful applications of fertilizers, pesticides, water, and other inputs, agriculture, especially in developed countries, has been cleaning up its act. Farming in many parts of the world has entered an era of “sustainable intensification,” where production continues to increase but with less and less inputs and pollution for each ton of output. Perhaps because of the incremental nature of this shift, it has often escaped notice.
The share of fertilizers that is not taken up by crops and thus escapes into water and air has been declining for decades in developed countries.20–22 In the United States, pesticides have declined both in terms of the absolute amount used and in terms of toxicity.23 Soil erosion is on the decline in developed countries, as is the amount of water used per ton of crops in irrigated farming.20,24 And, by one estimate, global farming generates about 40% fewer greenhouse gas emissions per unit of production than it did 50 years ago.25
Alongside these improvements in input efficiency, yields have also continued to improve, as a result of ongoing seed improvements and what is known as precision agriculture: using the right inputs, in the right amounts, at the right time, for each field and crop.
A new wave of innovators and venture capitalists has brought precision farming to the forefront in the last few years. A long list of promising, if not widely adopted, advanced technologies ranging from satellite imagery to big data to drones is in various stages of development and deployment.26 But while these technologies grab headlines, a set of more prosaic technologies has made precision farming the unsung hero of agricultural advancement, yield gains, and lower environmental impacts for decades.
A big reason precision farming has raised yields in past decades is, perhaps, also the least sexy: plant density. With corn, for example, farmers have gone from 30,000 plants per hectare in the 1930’s to over 80,000 today.27 The implications for how much corn can be produced on a given piece of land are obvious. These gains have been driven by a range of technologies including GPS-driven tractors that can drive straight, tight rows, and planters that can put individual seeds at specified distances.26,28
A GPS-enabled tractor receives detailed location data from satellites to plough crop fields in perfectly straight lines.
In addition to higher density, higher precision in the application of fertilizers, pesticides, and water helps ensure that fewer plants suffer deficiencies at any time, while also greatly reducing excess applications.14 No plant left behind, one might say. Today it is increasingly recognized that applying smaller amounts of fertilizer at multiple times over the growing season, rather than dumping all of it around the time of planting, can avoid both leaching of fertilizer into the water supplies and late-season nutrient scarcity that can hamper growth.29 New equipment can apply liquid fertilizer right at the base of the plant,30 such that each plant gets its fair share, and vary the application rates across the field in response to small-scale variations in soil conditions.31
Behind these improved machines are farmers equipped with improved data and decision support tools, which help to make better decisions throughout the growing season. Analytics help farmers decide what and when to plant, how densely to plant the seeds, and when water and fertilizer is needed. Increasingly these decisions are optimized for each field based on location, local weather, and soil type.32
While new tools and machinery are important to precision farming with increased yields and efficiencies, few of these practices would have been possible without concomitant developments in breeding and genetics, which are inseparable and co-evolving.27,33 Higher plant density, for instance, can only work with seeds that are bred to cope better in crowded conditions.27,34
Not every yield-boosting farming practice falls under the banner of precision agriculture. Earlier planting, which gives crops more time to grow before harvest, has made an important contribution to raising yields in many places, including the United States.33,35 Crop breeding that confers greater resistance to drought, pests, waterlogging, and cold also contributes to yield improvements.27
Is Peak Cropland in Sight?
With developing countries still squeezing the last drops out of the Green Revolution, and developed countries seeing gains from precision agriculture, global yields have, on average, increased steadily over the entire period from 1960 to today.36 But this does not necessarily mean that we are on track to meet future food demand without further expansion of cropland.
Forecasts for how much more crops the world will need in 2050 vary. The Food and Agriculture Organization (FAO) projected an increase in crop demand by 56% between 2006 and 2050.37 Tim Searchinger and colleagues adjusted this forecast to account for revised population growth estimates and the need to ensure adequate nutrition in all world regions, arriving at 69% higher crop demand in 2050 compared to 2006.12 David Tilman and colleagues, using a different methodology, estimated that crop demand would grow by a daunting 100% between 2005 and 2050.7 These estimates do not assume significant growth in biofuels, perhaps the biggest wild card in the equation. They also, quite realistically, do not assume radical reductions in meat consumption or food waste.
While population forecasts and predicted dietary changes explain some of the discrepancies in the food demand scenarios, they cannot explain all of it. Different assumptions about beef production are another important factor. Cattle finished in feedlots are fed grains, in contrast to those raised entirely on pasture. The highest figure for future crop demand7 is based on the assumption that more livestock will be finished in feedlots, thus requiring more grains, whereas the lower two forecasts12,37 assume little change in the overall global proportions of pasture- and feedlot-finished cattle. However, increased use of feedlots reduces the area of pasture faster than it increases the area of cropland, leading to a net reduction in total farmland.38
If demand for crops grows faster than yields, the area required to meet that demand increases. To get a sense of whether we are on track towards peak farmland or not, we need to compare these two trajectories. To do so, the first thing to note is that yields, the amount of crops produced in each harvest, tend to grow linearly, not exponentially, which means that a roughly constant amount is added to the average harvest every year.13 For cereals, this has been a bit over 40 kg per hectare per year, but with increasing yields, the percentage change has dropped from about 3% per year in the early 1960s to about 1% today.12
Projecting historical yield trends for cereals gets us about 45% higher yields in 2050 compared to 2010.12 Deepak Ray and colleagues forecast yields to grow by 67% for corn, 42% for rice, 38% for wheat, and 55% for soybean between 2008 and 2050.39
Most of these forecasts have yields growing slower than projected demand up to 2050, implying that more land would need to be converted to cropland to meet demand. The upshot is that to avoid further expansion of cropland, yields would have to grow faster in the next few decades than they have in previous decades.
Without this acceleration, cropland may need to expand by hundreds of millions of hectares in order to meet demand, potentially exceeding the combined expansion of cropland and pasture between 1960 and 2010.40,41
In addition to increasing the amount of crops in each harvest, farmers can also, under certain circumstances, raise total production by doing more harvests per year. This has contributed to increased production over the past few decades, and could continue to do so in some places,42 although the potential for this is disputed.12
In sum, cropland expansion is not inevitable – but to avoid it, the world probably needs the optimistic scenarios for both crop demand and yields to come true.
A net expansion of cropland between now and 2050 would not necessarily imply that peak cropland is not in sight – only that it will occur at a level higher than today. As more and more people around the world reach the limit of how much food, especially meat, they want to consume, and as population growth continues to abate, global crop demand inevitably slows down. This might allow yield growth rates to overtake demand growth rates and thus start shrinking global cropland area. Peak cropland might be on the horizon – the question is just how much damage will have been done to natural habitats by the time it occurs.
Yields: How Much Higher Can They Go?
All of these projections of crop demand and yields are, of course, speculative. How much crops humanity will need by 2050 is sensitive to population growth rates, income growth, dietary preferences, and whether cattle are fed with forage or grains. Wildcards such as the possible diffusion of lab-grown meat are, understandably, totally missing.
Future yield gains are perhaps even more uncertain. There is no guarantee that crop yields will continue rising the way they have over the past half century, a period when the Green Revolution offered an unprecedented, largely one-off boost to yields through relatively simple means like irrigation and fertilizers.
One major challenge to rising global yields is that, in the next few decades, agriculture will have to increasingly grapple with the effects of climate change. While some of these effects, like higher CO2, can boost photosynthesis and yields, increases in droughts, floods, and extreme heat could have major negative impacts.43
But even in a stable climate, yields might not be able to go up forever. There are already worrying signs that yields in certain regions are growing more slowly than in the past, or not growing at all.13,44 In less developed regions, this can be explained by inadequate access to inputs, lack of education, poorly functioning markets, and the like.13,44 Here, yields could begin or resume their upward trajectory if these barriers were removed. More concerning, however, is the evidence that yields in highly productive parts of the world, where markets, technology and so on present less of an obstacle, are starting to stagnate.
Patricio Grassini and colleagues found that areas representing more than one-fifth of global rice, wheat, and corn production have reached what they call “upper yield plateaus” in the last one or two decades.13 This includes one-third of rice production, 27% of wheat production, and 5% of corn production. Upper yield plateaus are now present for rice in California, China, and Korea; wheat in India and northwest Europe; and corn in France and Italy.
While the cause of these trends is hard to establish definitively, we cannot rule out that it is due to crops in these places approaching their potential yields – the yields that could be achieved with the best cultivars and under optimal management, with adequate water and nutrients and without any stress from pests or diseases. These potential yields, which are typically assessed at local or regional levels, are in theory only limited by sunlight and temperature.45 (Under rainfed farming, temporary scarcities of water, which hamper plant growth, have to be taken into account in making a realistic estimate of potential yields across multiple years in any given place.)
With any given set of cultivars, the room for further growth through better agricultural practices is referred to as the “yield gap” – the difference between current and potential yield at a given location.
Potential yields are not fixed, and can be raised, most importantly by creating seeds that have greater photosynthetic capacity and that allocate more of their biomass to the part of the plant that is harvested for human consumption. Breeding that improves resistance to pests, droughts, cold, and other stressors are critical to raising yields on farms, but they don’t count towards potential yields in the strict sense, which assumes that such stressors are absent.45
There are many ways of estimating potential yields, each with its own limitations.45 Rigorous estimates are relatively few and far between, but those that do exist give us a decent picture of the prospects for further yield gains in the most important crops. One should not, however, assume that the potential yield will ever be realized in practice. Farmers do not optimize for yield, but for profit.45 The smaller the yield gap, the harder and more expensive it gets to raise yields, and, at some point, diminishing returns make it uneconomic to try to push yields any further.
For rice, there is little evidence of improvements in potential yields since the first semi-dwarf varieties were introduced several decades ago, and the yield gap appears to be closing in key rice-producing countries like China, Japan, Korea, and India.13,14,46,47 However, there are reasons to think that recent advances in breeding could lift the potential yields significantly. Hybrid rice cultivars can deliver a 15% boost compared to the more commonly used inbred varieties, and new cultivars like the Chinese “super rice” can go even higher.46–49 Meanwhile, large yield gaps persist in many parts of the world – Nigeria, for instance, could nearly triple its rice yields.50
Similarly, corn appears to have seen little if any improvements in potential yields in recent decades, although when resistance to stresses like plant crowding is taken into account, the yields that have been possible with the best practical management have indeed risen significantly.33,51,52 US corn yields, especially on irrigated land, might be approaching a ceiling, although in most regions, several more tons can probably be squeezed out of each hectare.45,53 Elsewhere in the world, corn yields could be dramatically increased. Places like Ethiopia, India, and Kenya are at less than 14% of their potential – allowing for yields to increase by a factor of four or five.50
Wheat stands out as a major cereal crop where significant and consistent progress on potential yields has taken place over the past few decades.46,47 Field experiments in the United Kingdom show that potential yields have actually grown faster than average farm yields, at least until the last decade.33 This would suggest the yield gap has been widening rather than shrinking, giving hope that yields could continue to rise for the foreseeable future. As with rice and corn, many parts of the developing world, such as India and Bangladesh, have yields at less than half their potential for irrigated wheat.50
The number we would all like to see is the global yield gap – how much more crops the world could produce on existing farmland, with existing technologies. Most attempts so far have measured yields within broad climate zones, and defined the yield gap as the difference between the average yields and those in the most productive part of the climate zone.54 A variety of such estimates have tended to cluster around 50%.55–57
Like predictions of future food demand, these estimates are fraught with uncertainty, and are probably not particularly reliable.54 On the one hand, they may not accurately take into account limits on key inputs such as water, both in the form of rain and irrigation potential. On the other hand, by defining potential yields as the highest yields in a region, they do not account for the fact that even those top achievers might be performing well below their potential, especially in places like Sub-Saharan Africa.
How do these factors add up? So far, it is impossible to tell, and we will probably have to wait for projects like the Global Yield Gap Atlas to give us more robust estimates at larger scales.54
Even though the size of the yield gaps, especially at the global level, are unclear, what seems almost certain is that potential yields are not growing at a rate consistent with meeting a 40-70% increase in food demand by 2050.33,46 This means that, even if average farm yields can keep pace with growing demand, the yield gap is likely to shrink, making incremental gains more and more difficult to achieve. This is not a time to sit back and expect peak cropland to spontaneously occur.
Agricultural Innovation In the Post-Green Revolution Era
The Green Revolution has not yet reached every corner of the world. Sub-Saharan Africa stands out as the region where farming has modernized the least. For lack of locally adapted seeds and inputs like fertilizers and irrigation – as well as poor infrastructure, markets, and institutions –yields in this region have grown only marginally.8,10,58 The Green Revolution recipe, crude but effective, could still work wonders for this region.59,60 But as more and more of the world has adopted the Green Revolution’s technologies and practices, and as yields gaps likely narrow, it is going to be increasingly difficult to squeeze more crops out of each hectare. This portends an increased role for innovation, as fine-tuning modern agricultural systems requires ever more advanced technology.
Debates around agricultural innovation today often center on the use of biotech and, in particular, GMOs. Widespread resistance to these technologies has been a real obstacle to progress, likely having slowed both innovation and adoption.61,62 If this resistance remains, there is a real risk that important and useful opportunities in crop breeding will be lost. This includes transgenics, where a gene is transferred from one organism to another to confer a particular trait, but also other emerging techniques like gene editing.
Yet despite its outsized attention, genetic engineering is only one of many components of agricultural innovation. First of all, not all biotech is about genetic modification per se. Marker-assisted selection and many other techniques are making a difference to crop breeding without much public opposition.46
Secondly, not all progress in crop germplasm is about biotech. The vast majority of genetic improvements to date have come from conventional breeding,46 where parent seeds are crossed and the best performing progeny are selected for further rounds – a practice that dates back many hundreds of years. Old-school empirical breeding is still the chief way to improve potential yields of crops, since the genetic basis for photosynthesis is far more complex than can be fixed by changing one or a handful of individual genes though genetic engineering.46
GMOs, or more specifically transgenics, have made a noticeable difference to yields of corn, soy, and cotton, by improving resistance to certain pests and enabling conservation tillage, which, in turn, allows for earlier planting and thus more time for the plants to grow.33,63–66
There is every reason to believe that genetic modification, through transgenics and other techniques like gene editing, can continue improving plants’ resistance to stresses like droughts, flooding, cold, and heat, thereby raising yields.67 Even here, though, traditional breeding has so far made faster progress than GM techniques in many cases.68,69 As such, traditional breeding will likely remain a mainstay of genetic improvement for the foreseeable future.46
Thirdly, and most importantly, far from all progress in yields and environmental sustainability is about genetics. Advances in agronomy have to date been at least as important in pushing up yields as has genetics, and there is good reason to think that this will remain the case.
The potential of precision technologies, in particular, is far from fully tapped. Most of today’s precision tools help create uniformity. Closer, straighter rows or single-seed planting are not about adjusting to small-scale variations across fields as much as being consistently accurate and precise over large areas. Tailoring the application of water, nutrients, and other inputs to very fine scales – down to the square meter or even individual plants – is increasingly possible, but its potential to boost yields is, at this point, less well established.14
Many of the tools already exist, including tractor implements that can vary the application of inputs across a field.70 Sensors are becoming better and cheaper, and will increasingly allow farmers to monitor a host of variables, including humidity, soil nutrient content, and even the amount of crops harvested at ever smaller spatial scales.70 Furthermore, per-plant management is already a regular practice in very high-value crops, such as wine grapes, with an expectation that these techniques can be adapted over time to crops with lower per-plant value.26
The weakest link in precision technology today is often the knowledge of how best to use it.14 Just because it is mechanically possible to put different amounts of fertilizer or water in each part of a field does not mean that we know the best amount to put there. Companies, from the biggest corporations to well-funded startups, are investing heavily in the data collection, analytics and decision-support systems that will allow farmers to optimally use precision capabilities.71,72 However, this new wave of agronomic decision support is in its very early stages, and its promise yet to be fulfilled.
In some ways, precision agriculture takes us back to the future. In some developing countries, very small farms tend to have marginally higher yields than somewhat larger farms.73 This can in part be explained by the relatively higher labor input on small farms, which can rely largely on unremunerated family labor.73 Under these circumstances, it is possible to check on every corner of the field on a daily basis, pull out weeds individually, and apply grains of fertilizer in little cups next to each plant – also known as microdosing.
The way that records in the US yield contests are achieved draw from the hands-on farming of the past and today’s practices in developing countries. One of the lessons of these records – as well as the very high yields in field experiments – is simply very intensive, fine-grained management in both space and time, which takes very small-scale variations into account and target management decisions at fine scales.74,75 This is done by farmers and agronomists visiting their plots more frequently, observing the plants and the soils, and fine-tuning their operational plan.74
For all but the poorest countries, these labor-intensive practices are often impractical and uneconomic. Families are smaller, food is cheap and more widely available, and labor is more valuable in other sectors of the economy. In modern, intensive farming, equipment may only go through the field a handful of times per year and the ratio of land to people is such that a very small fraction of the land is visited on foot in any given year.
But today, robots, drones, sensors, and AI software are beginning to make it possible to employ the sort of intensive, fine-grained management practiced by poor farmers and yield contest winners at scales that have been previously unimaginable.26 Soil properties that affect crop performance on the scale of weeks or even days may one day be measured or remotely sensed in ten-square-meter units as compared to every 10 or 100 hectares. Application of fertilizers may be adapted to each little corner of a field, as opposed to a uniform rate across an entire farm.
In short, global agriculture might follow the evolution of global manufacturing from hand crafting to mass production to mass customization, giving each plant the benefit of hand crafting, but with the efficiency of mass production.
The 30 odd years from now until 2050 is a long time in the fast-paced world of innovation. There is no reason to believe that our vision of 2050 agricultural practice will be any more accurate than a 1980’s corn farmer walking into a corn farming operation today. Our GPS-driven tractors, harvesters that create detailed yield maps, and seeds that resist common diseases and pests and can thrive at unheard-of plant densities would all seem other-worldly to a 1980s time traveler. And remember that our 1980s corn farmer had never heard of the Internet.
As a result, there is no reason to believe that we can even enumerate all of the technologies that will be making a difference in crop yield or demand in 2050. Maybe some important ideas will come out of indoor farming and be successfully adapted at mass scale. Maybe our increasing insight into the role of the microbiome in the health of all macro-organisms will yield a wonder, pro-biotic seed coating. Or maybe, like the Internet or GPS, an innovation will be so fantastic that, sitting here 30 years prior, we can’t even see it coming.
In the end, none of these technologies, evolutionary or revolutionary, will be adopted overnight, and their diffusion will depend not just on their cost but also on broader socioeconomic factors.76 Neither success nor failure is inevitable – a lot depends on the choices that are made today by farmers, corporations, nation-states, and international organizations. Progress in breeding and agronomy have been, and will likely continue to be, closely correlated with the resources invested in technological innovation through research in both the public and private sectors, and in agricultural extension to ensure rapid technology transfer.17,77–80
Much work remains to be done to reach peak farmland while minimizing agriculture’s harmful impacts on the environment. Yet the technologies and practices that are being developed and adopted today give us plenty of hope that this can ultimately be achieved.
1. Ramankutty, N., Evan, A. T., Monfreda, C. & Foley, J. a. Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000. Global Biogeochem. Cycles 22, 1–19 (2008).
2. FAO. Inputs - Land. FAOSTAT (2015). Available at: http://faostat3.fao.org/browse/R/RL/E. (Accessed: 22nd May 2015)
3. Gibbs, H. K. et al. Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s. Proc. Natl. Acad. Sci. U. S. A. 107, 16732–7 (2010).
4. WWF. Living Planet Report 2016. (2016).
5. Angel, S., Parent, J., Civco, D. L., Blei, A. & Potere, D. The dimensions of global urban expansion: Estimates and projections for all countries, 2000–2050. Prog. Plann. 75, 53–107 (2011).
6. Gerland, P. et al. World population stabilization unlikely this century. Science (80-. ). 234, (2014).
7. Tilman, D., Balzer, C., Hill, J. & Befort, B. L. Global food demand and the sustainable intensification of agriculture. Proc. Natl. Acad. Sci. 108, 1–5 (2011).
8. Evenson, R. E. & Gollin, D. Assessing the impact of the green revolution, 1960 to 2000. Science 300, 758–762 (2003).
9. Press, A. Spectacular Increases in Crop Yields in the United States in the Twentieth Century Author ( s ): G . F . Warren Published by : Weed Science Society of America and Allen Press Stable URL : http://www.jstor.org/stable/3989099 Education / Teaching / Extensio. 12, 752–760 (2016).
10. Pingali, P. Green Revolution: Impacts, Limits, and the path ahead. Proc. Natl. Acad. Sci. 109, 12302–12308 (2012).
11. Egli, D. B. Comparison of corn and soybean yields in the United States: Historical trends and future prospects. Agron. J. 100, 79–88 (2008).
12. Report, W. R. & Findings, I. Creating a Sustainable Food Future. (2013).
13. Grassini, P., Eskridge, K. M. & Cassman, K. G. Distinguishing between yield advances and yield plateaus in historical crop production trends. Nat. Commun. 4, 1–11 (2013).
14. Cassman, K. G. Ecological intensification of cereal production systems: yield potential, soil quality, and precision agriculture. Proc. Natl. Acad. Sci. U. S. A. 96, 5952–9 (1999).
15. Fischer, T., Byerlee, D. & Edmeades, G. Crop yields and global food security. Aust. Cent. Int. Agric. Res. 660 (2014).
16. Hertel, T. W., Ramankutty, N. & Baldos, U. L. C. Global market integration increases likelihood that a future African Green Revolution could increase crop land use and CO2 emissions. Proc. Natl. Acad. Sci. U. S. A. 111, 1–6 (2014).
17. Stevenson, J. R., Villoria, N., Byerlee, D., Kelley, T. & Maredia, M. Green Revolution research saved an estimated 18 to 27 million hectares from being brought into agricultural production. Proc. Natl. Acad. Sci. U. S. A. (2013). doi:10.1073/pnas.1208065110
18. Griffin, K. The Political Economy of Agrarian Change: An Essay on the Green Revolution. (Springer, 1979).
19. Fuglie, K. in Productivity Growth in Agriculture: An International Perspective (eds. Fuglie, K., Wang, S. L. & Ball, V. E.) (CAB International, 2012).
20. OECD. OECD Compendium of Agri-environmental Indicators. (OECD Publishing, 2013). doi:10.1787/9789264186217-en
21. Lassaletta, L., Billen, G., Grizzetti, B., Anglade, J. & Garnier, J. 50 Year Trends in Nitrogen Use Efficiency of World Cropping Systems: the Relationship Between Yield and Nitrogen Input To Cropland. Environ. Res. Lett. 9, 105011 (2014).
22. Zhang, X. et al. Managing nitrogen for sustainable development. Nature 528, 51–59 (2015).
23. Fernandez-Cornejo, J. & Nehring, R. Pesticide Use in US Agriculture: 21 Selected Crops, 1960-2008. 1960–2008 (2014).
24. Field to Market. Environmental and Socioeconomic Indicators for Measuring Outcomes of On-Farm Agricultural Production in the United States. Second Report, (Version 2 (2012).
25. Bennetzen, E. H., Smith, P. & Porter, J. R. Decoupling of Greenhouse Gas Emissions from Global Agricultural Production: 1970 - 2050. Glob. Chang. Biol. n/a-n/a (2015). doi:10.1111/gcb.13120
26. Lowenberg-deboer, J. & Lowenberg-deboer, J. The Precision Agriculture Revolution. 105–112 (2015).
27. Duvick, D. N. The Contribution of Breeding to Yield Advances in maize (Zea mays L.). Adv. Agron. 86, 83–145 (2005).
28. Precision Planting. vSet. (2016). Available at: http://www.precisionplanting.com/#products/vset/. (Accessed: 1st January 2016)
29. Corn and Soybean Digest. Sidedressing. Corn and Soybean Digest (2015). Available at: http://cornandsoybeandigest.com/sidedressing. (Accessed: 1st January 2016)
30. Ag Alternatives. Y-Drop. (2014). Available at: http://agalternatives.com/y-drop.html. (Accessed: 1st January 2016)
31. Gebbers, R. & Adamchuk, V. I. Precision agriculture and food security. Science 327, 828–31 (2010).
32. IBM Research. Precision agriculture. (2016). Available at: http://www.research.ibm.com/articles/precision_agriculture.shtml. (Accessed: 12th January 2016)
33. Fischer, R. A. & Edmeades, G. O. Breeding and cereal yield progress. Crop Sci. 50, S-85-S-98 (2010).
34. Mansfield, B. D. & Mumm, R. H. Survey of plant density tolerance in U.S. maize germplasm. Crop Sci. 54, 157–173 (2014).
35. Kucharik, C. J. Contribution of planting date trends to increased maize yields in the central United States. Agron. J. 100, 328–336 (2008).
36. FAO. Production - Crops. FAOSTAT (2016). Available at: http://faostat3.fao.org/download/Q/*/E. (Accessed: 27th November 2016)
37. Alexandratos, N. & Bruinsma, J. World Agriculture Towards 2030/2050: The 2012 Revision. (2012).
38. Capper, J. L. Is the grass always greener? Comparing the environmental impact of conventional, natural and grass-fed beef production systems. Animals 2, 127–143 (2012).
39. Ray, D. K., Mueller, N. D., West, P. C. & Foley, J. a. Yield Trends Are Insufficient to Double Global Crop Production by 2050. PLoS One 8, e66428 (2013).
40. Smith, P. et al. Competition for land. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 365, 2941–57 (2010).
41. Schmitz, C. et al. Land-use change trajectories up to 2050: insights from a global agro-economic model comparison. Agric. Econ. 45, n/a-n/a (2013).
42. Ray, D. K. & Foley, J. a. Increasing global crop harvest frequency: recent trends and future directions. Environ. Res. Lett. 8, 44041 (2013).
43. Jaggard, K. W., Qi, A. & Ober, E. S. Possible changes to arable crop yields by 2050. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 365, 2835–51 (2010).
44. Ray, D. K., Ramankutty, N., Mueller, N. D., West, P. C. & Foley, J. a. Recent patterns of crop yield growth and stagnation. Nat. Commun. 3, 1293 (2012).
45. Lobell, D. & Cassman, K. Crop yield gaps: their importance, magnitudes, and causes. Annu. Rev. (2009). doi:10.1146/annurevfienviron.041008.093740
46. Hall, A. J. & Richards, R. A. Prognosis for genetic improvement of yield potential and water-limited yield of major grain crops. F. Crop. Res. 143, 18–33 (2013).
47. Cassman, K. G., Dobermann, A., Walters, D. T. & Yang, H. Meeting Cereal Demand While Protecting Natural Resources and Improving Environmental Quality. Annu. Rev. Environ. Resour. 28, 315–358 (2003).
48. Peng, S., Cassman, K. G., Virmani, S. S., Sheehy, J. & Khush, G. S. Yield Potential Trends of Tropical Rice since the Release of IR8 and the Challenge of Increasing Rice Yield Potential. Crop Sci. 39, 1552 (1999).
49. Peng, S., Khush, G. S., Virk, P., Tang, Q. & Zou, Y. Progress in ideotype breeding to increase rice yield potential. F. Crop. Res. 108, 32–38 (2008).
50. GYGA. Global Yield Gap and Water Productivity Atlas. (2016). Available at: http://www.yieldgap.org/. (Accessed: 1st January 2016)
51. Tollenaar, M. & Wu, J. Yield improvement in temperate maize is attributable to greater stress tolerance. Crop Sci. 39, 1597–1604 (1999).
52. Duvick, D. N. & Cassman, K. G. Post–Green Revolution Trends in Yield Potential of Temperate Maize in the North-Central United States Breeding Methods and Investment. (1999).
53. Grassini, P., Thorburn, J., Burr, C. & Cassman, K. G. High-yield irrigated maize in the Western U.S. Corn Belt: I. On-farm yield, yield potential, and impact of agronomic practices. F. Crop. Res. 120, 142–150 (2011).
54. Van Ittersum, M. K. et al. Yield gap analysis with local to global relevance-A review. F. Crop. Res. 143, 4–17 (2013).
55. Licker, R. et al. Mind the gap: how do climate and agricultural management explain the ‘yield gap’ of croplands around the world? Glob. Ecol. Biogeogr. 19, 769–782 (2010).
56. Foley, J. A. et al. Solutions for a cultivated planet. Nature 478, 337–42 (2011).
57. Mueller, N. N. D. et al. Closing yield gaps through nutrient and water management. Nature 1–28 (2012). doi:10.1038/nature11420
58. Fischer, R. A., Byerlee, D. & Edmeades, G. O. Can Technology Deliver on the Yield Challenge to 2050? in Expert Meeting on How to Feed the World in 2050 2050, (2009).
59. Sánchez, P. a. Tripling crop yields in tropical Africa. Nat. Geosci. 3, 299–300 (2010).
60. Cassman, K. G. & Grassini, P. Can there be a green revolution in Sub-Saharan Africa without large expansion of irrigated crop production? Glob. Food Sec. 2, 203–209 (2013).
61. Lucht, J. M. Public acceptance of plant biotechnology and GM crops. Viruses 7, 4254–4281 (2015).
62. Paarlberg, R. Starved for Science: How Biotechnology Is Being Kept Out of Africa. (Harvard University Press, 2009).
63. Carpenter, J. E. Peer-reviewed surveys indicate positive impact of commercialized GM crops. Nat. Biotechnol. 28, 319–321 (2010).
64. Klümper, W. & Qaim, M. A Meta-Analysis of the Impacts of Genetically Modified Crops. PLoS One 9, (2014).
65. Barrows, G., Sexton, S. & Zilberman, D. The impact of agricultural biotechnology on supply and land-use. Environ. Dev. Econ. 1–28 (2014). doi:10.1017/S1355770X14000400
66. National Academies of Sciences, Engineering, and M. Genetically Engineered Crops: Experiences and Prospects. (2016). doi:10.17226/23395
67. Searchinger, T. I. M., Hanson, C. & Lacape, J. Crop Breeding : Renewing the Global Commitment. World Resour. Inst. 1–20 (2014).
68. Gilbert, N. Cross-bred crops get fit faster. Nature (2014). Available at: http://www.nature.com/news/cross-bred-crops-get-fit-faster-1.15940. (Accessed: 1st January 2016)
69. Gilbert, N. The race to create super-crops. Nature (2016). Available at: http://www.nature.com/news/the-race-to-create-super-crops-1.19943. (Accessed: 1st January 2016)
70. Pierce, F. J. & Nowak, P. Aspects of precision agriculture. Adv. Agron. 67, (1999).
71. Burwood-Taylor, L. Agriculture Technology Investment Storms to $4.6bn in 2015 as Global Investors Take Note. AgFunder News (2016). Available at: https://agfundernews.com/agriculture-technology-investment-storms-to-4-6bn-in-2015-as-global-investors-take-note5380.html. (Accessed: 1st January 2016)
72. Upbin, B. Monsanto Buys Climate Corp For $930 Million. Forbes (2013). Available at: http://www.forbes.com/sites/bruceupbin/2013/10/02/monsanto-buys-climate-corp-for-930-million/#37b1e9975ae1. (Accessed: 1st January 2016)
73. Larson, D. F., Otsuka, K., Matsumoto, T. & Kilic, T. Should African rural development strategies depend on smallholder farms? An exploration of the inverse-productivity hypothesis. Agric. Econ. 45, n/a-n/a (2013).
74. NCGA. Economize Without Compromise. National Corn Yield Contest (2015). Available at: http://dtnpf-digital.com/publication/?i=288631. (Accessed: 1st January 2016)
75. Van Roekel, R. & Purcell, L. Student Researches Recipe for Record-Setting Soybean Yields. University of Arkansas Division of Agriculture Research and Extension (2012). Available at: http://www.arkansas-crops.com/2012/02/10/student-researches-recipe-for-record-setting-soybean-yields/. (Accessed: 1st January 2016)
76. Robert, P. C. Precision agriculture: A challenge for crop nutrition management. Plant Soil 247, 143–149 (2002).
77. Perez, N. D. . & Rosegrant, M. W. . The impact of investment in agricultural research and development and agricultural productivity. 40 pages (2015).
78. Alston, J. M. J. M., Beddow, J. M. J. M. & Pardey, P. G. P. G. Mendel Versus Malthus: Research, Productivity and Food Prices in the Long Run. Agric. Econ. 325, 1209–1210 (2009).
79. Alston, J. M. et al. A Meta-Analysis of Rates of Return to Agricultural R&D. World (2000).
80. Jin, Y. & Huffman, W. E. Measuring public agricultural research and extension and estimating their impacts on agricultural productivity: new insights from U.S. evidence. Agric. Econ. n/a-n/a (2015). doi:10.1111/agec.12206