Monday, February 5, 2018

Scaling Sustainable Agriculture

As part of getting trained in science communications via the Science Impact Project, I had to prepare and deliver a "TED-style" talk. It was terrifying and hard work, especially to slow down and take a more personal storytelling approach to my work (talking about my family's farm), but I'm pretty happy with the end result.

This blog includes the video of my talk at the top, and the text is more or less a transcript of what I say (with a few additions):

Scaling Sustainable Agriculture (blog at Cool Green Science)

Here is a pic of the farm (we couldn't find many):

and a pic of (from right to left) my great-grandfather Robert and great-grandmother Marjorie (the original farmers), my grandfather Hickman and grandmother Jurie, and two people I'm not sure about!

Thursday, February 1, 2018

February 2018 Science Journal Article Summary

Sad winter kale

The struggle to find good produce in the depth of winter (see my sad kale above) has me thinking about nutrients, so this month I've focused on papers about nutrients in the sense of fertilizer on croplands (focused on N & P, plus one about crop nutrition).

Interested in short blogs or talks? I have a new blog connecting the story of my family's farm with my work on scaling sustainable agriculture. The blog is at and was adopted from my "TED-style" talk: Here's another with the "so what" that was missing from my recent book chapter on global agriculture land use trends.

Finally: unrelated to science, I was impressed how much the Engaging Across Differences has jump-started the way I think about and engage around diversity. They're looking for people to sign up for the next workshops, and I'd encourage all TNC staff to give it serious thought. Let me know if you'd like to discuss further; it's led me to co-host an ongoing workshop at our headquarters about how we can all step up and be better allies to each other.

AGRICULTURE (NITROGEN)The first three papers all come from Xin Zhang at China Agricultural University in Beijing.
Zhang et al 2015 (in Nature) looks at global historic patterns of nitrogen fertilizer use and efficiency, identifying opportunities for improvement. Optimizing nitrogen use efficiency (NUE) means avoiding N loss to the air and water, but also ensuring crops have enough N. Start with Table 1 - which highlights the severe (and worsening) excess in India and China, driven partly by low subsidized fertilizer prices. Fig 4 is also really interesting - it compares efficency in the US and China, partly due to efficiency, and partly due to what we grow (e.g. in the US we grow a lot of soy that doesn't need N).

The other Zhang et al 2015 article (in JEQ) looks at how the economics of promoting technology and best management practices to improve nitrogen use efficiency (NUE) on farms. They model different kinds of improvements, whether they maintain yields at a lower input rate, improve yields at a similar input rate, or improve yields but require more fertilizer as well (e.g. by improving crop genetics). It's a cool (albeit wonky) paper, and Figures 4-7 explore the conditions under which implementing these practices can boost both profit and environmental outcomes. Table 4 shows that for Midwestern corn, at relatively high fertilizer prices improved genetics can be the best strategy, while at lower prices other approaches perform better (with changing the crop running the risk of environmental harm from excess nitrogen). They conclude with policy recommendations around how shifting from subsidies for fertilizer to subsidies for improved practices can help improve NUE. Table 6 has guidelines on how to find the optimal price ranges for both fertilizer and BMPs. A final twist: practices that don't boost yield are less likely to be adopted (even if they save cost), while yield-boosting practices are more appealing but also run more risk of excess N being lost.

Zhang et al. 2017 has some good news in the form of a case study in Huantai county in northern China. While China's overall NUE has gotten worse over the past several decades, it has improved in Huantai. Primary drivers appear to be incorporation of crop straw into soil, and subsidized mechanization of farmland in the area. Overuse of groundwater for irrigation, however, remains a major challenge. Nonetheless, this provides a road map for how the rest of China may be able to follow suit.

Wagner-Riddle et al. 2017 looks specifically at the importance of soil freezing and thawing in correctly estimating N2O emissions. Essentially, when frozen soil thaws, it emits a lot more N2o (a potent greenhouse gas). They estimate that global N2O emissions from cropland may be 17-28% too low due to neglecting to account for soil freezing and thawing.

Sweeney 2017 is another paper finding that long term no-till redistributes soil carbon to the surface but doesn't boost total soil carbon (this case was a claypan soil). More oddly, they found tillage and N fertilization didn't impact soil bulk density or resistance.

AGRICULTURE (phosphorous): The next two articles are cited in this blog about phosphorous (P) in Lake Erie (thanks to Joe F for passing it on, and to Carrie V-S for following up):
Christianson et al. 2016 is a review of phosphorous being lost via farm drainage, both subsurface (tile) drains and surface drains like ditches. There is a lot of interesting data packed in here, but three things jumped out at me. First is that overall P loads were higher in surface drainage than subsurface drainage (Fig 2). The other was that no-till fields lost about triple the P compared to conventional or even conservation tillage. So no-till may reduce sediment losses but increase P losses, presenting an interesting trade-off. Third is that P losses tend to be relatively small (<5% applied) compared to N losses (~15-20%), which reduces the economic incentive for farmers to address P loss.

Jarvie et al. 2017 looked at soluble reactive phosphorous (SRP) in the Western Lake Erie Basin, and looked for correlations with changing agricultural practices. They had data for changes in tillage, and used changing "flashiness" of river flow as a proxy for increased drainage. They note that many factors could have caused the increasing river SRP loads, but attribute 1/3 to increased drainage water flow and 2/3 to an increase in SRP delivery. They concluded that no-till and drainage were both likely responsible for the increasing SRP delivery, but I'm not convinced. Figure 3 and Table 4 show that across the three studied rivers there was not a clear relationship between tillage and drainage and SRP.

I had a few people mention stories about Myers et al 2014 recently about how climate change will impact crop nutrition. This study found that CO2 levels of ~550ppm (which we will likely hit in ~50 years) zinc and iron levels will be lower in wheat, rice, peas, and soy (and wheat and rice having lower protein as well). The decreases are modest; the biggest decline was in wheat, with 9% lower zinc and 5% less iron. This is a legitimate concern (albeit a minor one), but what I find most interesting is how people I spoke to thought the results were much worse. One person told me that even now (not 50 years away) even healthy foods like kale were basically junk food, another thought we were already seeing nutrient deficiencies because of this. So, let's watch out for how climate is changing nutrient density, but in the meantime, keep loading up on those collard greens! If you're worried about zinc and iron there are some great options like pumpkin seeds and sesame seeds. You can read a story about this at and the full article at

Christianson, L. E., Harmel, R. D., Smith, D., Williams, M. R., & King, K. (2016). Assessment and Synthesis of 50 Years of Published Drainage Phosphorus Losses. Journal of Environment Quality, 45(5), 1467.

Jarvie, H. P., Johnson, L. T., Sharpley, A. N., Smith, D. R., Baker, D. B., Bruulsema, T. W., & Confesor, R. (2017). Increased Soluble Phosphorus Loads to Lake Erie: Unintended Consequences of Conservation Practices? Journal of Environment Quality, 46(1), 123.

Myers, S. S., Zanobetti, A., Kloog, I., Huybers, P., Leakey, A. D. B., Bloom, A. J., … Usui, Y. (2014). Increasing CO2 threatens human nutrition. Nature, 510, 139. Retrieved from

Sweeney, D. W. (2017). Does 20 Years of Tillage and N Fertilization Influence Properties of a Claypan Soil in the Eastern Great Plains? Agricultural & Environmental Letters, 2(1), 0.

Wagner-Riddle, C., Congreves, K. A., Abalos, D., Berg, A. A., Brown, S. E., Ambadan, J. T., … Tenuta, M. (2017). Globally important nitrous oxide emissions from croplands induced by freeze–thaw cycles. Nature Geoscience, 10(March).

Zhang, X., Davidson, E. A., Mauzerall, D. L., Searchinger, T. D., Dumas, P., & Shen, Y. (2015). Managing nitrogen for sustainable development. Nature, 528(7580), doi:10.1038/nature15743.

Zhang, X., Mauzerall, D. L., Davidson, E. a, Kanter, D. R., & Cai, R. (2015). The economic and environmental consequences of implementing nitrogen-efficient technologies and management practices in agriculture. Journal of Environmental Quality, 44(2), 312–24.

Zhang, X., Bol, R., Rahn, C., Xiao, G., Meng, F., & Wu, W. (2017). Agricultural sustainable intensification improved nitrogen use efficiency and maintained high crop yield during 1980–2014 in Northern China. Science of The Total Environment, 596–597, 61–68.

Wednesday, January 3, 2018

Take 2: what I wish I'd put in my recent book chapter

I asked my wife Sarah to take a look at my recent chapter in the book "Effective Conservation Science: Data Not Dogma" and she made an excellent point: what should the take-away be? Here are the things I was hoping to convey but wasn't sufficiently clear about.

The key fact I wanted to convey is that the global agriculture situation is complex: the global land used for agriculture hit its peak in 1998 (so it's not true agricultural land is rapidly expanding around the world), BUT in some places there is a lot of agricultural expansion and/or reliance on unsustainable levels of water and nutrients. So there is good news and bad news.

Some other important facts I didn't go into in much detail:
  • In the last two decades we have been able to meet increasing demand for food through intensification (producing more food on existing lands). But going forward projected demand rises faster than what we're likely to be able to produce through intensification. So between 2030-2050 we can expect conversion to agriculture to speed up and lead to a net expansion of land used for agriculture.
  • Agriculture in many regions currently relies on unsustainable irrigation. As groundwater is depleted and crops get thirsty we can expect yields to eventually fall substantially on agricultural lands in water-scarce areas. The California drought gives us a taste of what that could look like. Note that changes in irrigation technology are likely insufficient to solve this on their own (see the summary of Richter 2017).
  • Other agricultural inputs may start to run out or at least limit improved crop yields. That could include rock phosphate for fertilizer or even nitrogen fertilizer if actions to limit climate change make it more expensive.
The key message of the piece for other scientists is: don't assume that things that seem obvious (like ag land rapidly expanding) are true, and don't assume that global data sets are reliable enough to inform policy or other action. Dig deeper! Ask questions, and look for more local data to corroborate your suspicions.

Let me know if you have other questions or suggestions!

Monday, January 1, 2018

January 2018 science journal article summary

Happy new year! Here are a handful of articles focused on global agriculture analyses, plus one with bad news on climate change, and a 2018 #MyScienceResolution. 

Cauliflower, romesco, and broccoli at the farmer's market

 I also want to pass on a cool resource Eddie Game alerted me know. It's a tool to help you figure out which journal to submit a paper to:  You enter the title and abstract of your paper and it gives you a list of appropriate journals. You may also want these tips on how to write an abstract to get found easily in Google and Google Scholar:

On to the articles!

Somehow I'd missed West et al 2014, which is a great (and very short) summary of opportunities to improve agriculture around the world. Just looking at the two figures is highly educational: Fig 1 shows the potential to increase yields on poorly performing croplands to even 50% of their potential yields (which would provide enough food for 850 million more people, while still leaving plenty of room to improve), and Fig 2 shows how much we can reduce environmental impacts of ag in key regions without reducing yields. The spatial patterns aren't surprising, but the specific numbers are highly motivating. For example, China alone produces 28% of global N2O emissions (a potent greenhouse gas). Reducing excessive nutrients and improving water efficiency of crops around the world would have a big impact, as would reducing the amount of animal products we eat and the amount of food that is wasted. Be sure to check out the supplement for more great maps.

Phalan et al 2016 tackles a tricky problem at the heart of TNC's work with ag: how can we ensure that intensification reduces conversion rather than incentivizing it through higher profits? It's under two pages, so I'd recommend just reading it. But the mechanisms they propose to boost yield and promote nature are: 1) land use zoning (specify land for ag and land for conservation, as Costa Rica did), 2) use payments, subsidies, or land taxes (e.g. a program in India where herders set aside habitat in exchange for insurance and technical assistance), 3) "spatially strategic" deployment of tech / infrastructure / ag knowledge (e.g. focusing on staple crops which have more stable demand), and 4) standards (including voluntary ones) and certification. I found this to be good food for thought about how TNC could tighten our theory of change.

Hanspach et al 2017 looks at trade-offs between food security and biodiversity for ag in the "global south" (developing countries). They surveyed 110 self-reported experts and looked for patterns. Surprisingly, while in many landscapes there were clear trade-offs between food security and biodiversity, several respondents reported other cases where the two goals were linked (either in "win-win" or "lose-lose" cases). Figure 2a shows where each landscape fell. Infrastructure, market access, and financial resources were all associated with poor biodiversity but good food security, meaning investment in intensification on its own will likely not lead to conservation outcomes. Social equity and land access were found to be necessary but not sufficient for both food and biodiversity goals. Relying on expert assessments isn't a replacement for good empirical data, but this still has useful elements for TNC to incorporate in our ag work.

Gerber et al 2016 is a global analysis of N2O emissions from croplands. The key point is that areas with very low N use and production can use much more fertilizer with relatively small increases in N2O emissions, while areas with high N excess can use a little less to get big reductions in N2O. For example, cutting N application by 5% in Shandong province (China) would reduce N2O by 9%. Be sure to check out Table 2 (N application totals and rates by country) and Fig 3 (N2O emissions per unit of N applied at a sub-national level), and fig 4 if you're interested in specific crops. Note that they used a new approach which in general predicts significantly lower emissions than other models (they go over several caveats in detail).

Zomer et al 2017 estimates that globally cropland soils could sequester 0.90-1.85 Pg C / yr (1 Pg = 1 billion metric tons) for at least 20 years. This estimate derives from how much soil C has been lost relative to historic levels, along with estimates from an earlier paper of how much sequestration can be achieved through a range of conservation practices (e.g. cover cropping, conservation tillage, rotational grazing, etc.). Table 2 and Figure 2 show where the authors see the most room for improvement (the Midwest US, India, and Europe in particular). TNC's Deborah Bossio is second author so she should be able to answer any questions you may have.

A new paper from NatureNet fellow Kyle Davis (2017) investigates the impact of changing and moving crops on existing croplands around the world to improve yield and reduce water consumption. The hypothetical optimal crop patterns consumed 14% less rainwater and 12% less "blue" water (irrigation from surface and ground), while also producing 10% more calories, 19% more protein, and other benefits. A big caveat is that this involves not only shifting what is grown where (already a big task) but also shifting how much we produce of each crop. For example, they cut production of wheat, rice, corn, and sugar in favor of more soy and tubers (like potato and sweet potato). The interesting part to me is thinking about how this approach could be used in a national land use planning exercise with more realistic constraints.

Brown & Caldeira 2017 has some bad news about climate change. They looked at several climate models and scenarios and evaluated how well they predicted the recent past (looking at 9 variables, not just temperature). They predict warming ~15% higher than currently predicted and have a narrower confident interval for predictions. For climate wonks, they note that emissions in line with the RCP 4.5 scenario are likely to produce warming previously associated with RCP 6.0. There are several important caveats in the discussion, but this nonetheless raises the urgency to take aggressive action on climate to minimize the projected impacts. Take a look at Figuyre 2 which shows the new narrower predictions in red for different emissions scenarios. You can read an overview of the paper here or a longer blog from the authors here:


I haven’t read the Pelger 2017 study it’s based on, but this blog post gave me an idea for a 2018 science resolution! Essentially students writing for a non-scientific audience found that it helped their science writing as well. So if you work as a scientist, commit to writing a blog, or talking to your friends and family about your work without making their eyes glaze over! I'm going to shoot for my next peer-reviewed article to be readable by an ordinary human being. If you need more motivation, check out this inspirational talk by Dan Rather with a vision for a revolution in science communications as a foundation for changing how we think about truth and “fake news” in society: (thanks to Laurel Saito for the link).

Brown, P. T., & Caldeira, K. (2017). Greater future global warming inferred from Earth’s recent energy budget. Nature, 552(7683), 45–50.

Davis, K. F., Rulli, M. C., Seveso, A., & D’Odorico, P. (2017). Increased food production and reduced water use through optimized crop distribution. Nature Geoscience, 10(12), 919–924.

Gerber, J. S., Carlson, K. M., Makowski, D., Mueller, N. D., Garcia de Cortazar-Atauri, I., HavlĂ­k, P., … West, P. C. (2016). Spatially explicit estimates of N2O emissions from croplands suggest climate mitigation opportunities from improved fertilizer management. Global Change Biology, 22(10), 3383–3394.

Hanspach, J., Abson, D. J., French Collier, N., Dorresteijn, I., Schultner, J., & Fischer, J. (2017). From trade-offs to synergies in food security and biodiversity conservation. Frontiers in Ecology and the Environment, 15(9), 489–494.

Phalan, B., Green, R. E., Dicks, L. V., Dotta, G., Feniuk, C., Lamb, A., … Balmford, A. (2016). How can higher-yield farming help to spare nature? Science, 351(6272), 450–451.

West, P. C., Gerber, J. S., Engstrom, P. M., Mueller, N. D., Brauman, K. A., Carlson, K. M., … Siebert, S. (2014). Leverage points for improving global food security and the environment. Science, 345(6194), 325–328.

Zomer, R. J., Bossio, D. A., Sommer, R., & Verchot, L. V. (2017). Global Sequestration Potential of Increased Organic Carbon in Cropland Soils. Scientific Reports, 7(1), 15554.