Yield gaps revisited

By Joern Fischer

Yet again, there’s a new paper on yield gaps, and yet again, I can’t help myself but comment on it. Mueller et al.  have published another global analysis in Nature looking at yield gaps arising from nutrient and water management around the world.

Unless I misunderstand their findings, the bottom line with respect to Eastern Europe is:

– there are major yield gaps for wheat especially (and a bit for maize)

– those could be closed through increasing nutrient inputs, e.g. in Central Romania, increasing them by about 75 kg of nitrogen per ha (per year, presumably — the the figure above).

What does that mean? Frankly, I’m not sure and that’s why I’m writing this blog entry. I’d be really happy for people to comment! Would 75 kg of N per ha be detrimental to biodiversity or not?

A few additional questions I would pose for Central Romania in particular:

Who would benefit from intensification? All locals or just a few (those able to afford inputs)? What would intensification mean for social justice?

And how will the food get from Central Romania to the hungry, given we don’t manage to get food to the hungry right now?

Yet again, we have a nice global map, which shows that “it can be done” but which ignores all socio-economic and regional complexities. Is it okay to ignore those? Or is it in fact vitally important NOT to ignore local complexities … ?


9 thoughts on “Yield gaps revisited

  1. Transylvania is home to different plant communities, of which some rare and endangered species can be found in low nutrient grassland (Akeroyd 2007, Jones 2008). The plant species richness in these biotopes can be dramatically decreased by increasing fertilizer use (Kleijn et al. 2008), and nitrogen as well as phosphorous (which are part of chemical fertilizers) cause this species loss (Ceulemans et al. 2012). As nitrogen deposition is already happening via the atmosphere, every additional kilogram of nutrients affect these highly adapted communities. And as plants often are the basis for existence of other species, e.g. arthropods, butterflies and bees, their disappearance would open a Pandora´s box for the biodiversity.
    One could ask if the distinctiveness of the plant richness justifies low agricultural productivity- but I think by homogenization of the environment by enriching the soil Romania would in the long term not satisfy the hunger of the poor but inhibit to live and benefit from a healthy and reslient environment.

    Ceulemann et al. 2012: Global Ecol. Biogeogr.
    Kleijn et al. 2008: Proceedings B
    Akeroyd, J.R. (2007) The floral riches of southern Transylvania. The Plantsman, NS, 6: 152–156.
    Jones, A. (2008) The challenge of High Nature Value grasslands conservation in Transylvania. Transylvanian Review of Systematical and Ecological Research, 4: 73–81.

    • Thanks for these details — and how does 75 kg / ha relate to this — is it relatively high (compared to what these communities are adapted to), or perhaps “not a big deal”? Would this cause problems for grasslands, too? Would it be safe to fertilise arable land, as long as the grassland remains untouched? … just wondering …

      • Already an increased deposition of 10 kg Nitrogen per hectare and year cause decreases of plants pecies richess up to 17 % (Clark & Timan 2008 in Nature). Atmospherical Nitrogen deposition in Central Europe has been estimated to be 17 kg per hectare and year, and many studies show that adding between 5-35 kg Nitrogen on top of these correlate negatively with species richness. So for me, it seems that adding 75 kg of Nitrogen would be indeed a “big deal”! Furthermore, the nutrients will not just stay in the arable land, but will for example spread into streams and rivers and get dispersed. I´d like to mention that during my studies this year, we found rare plant and butterfly species related to low nutrient grasslands close to arable land and in side strips of arable land- these could be seriously affected by application of fertilizers.

  2. The last two blogs contrast nicely different approaches to sustainability/conservation science. The large carnivore paper takes a holistic approach, and demonstrates the importance of social-ecological interactions, while the yield gaps paper uses a blinkered approach, with limited appreciation of the broader situation and social-ecological interactions. It is interesting that papers that claim to focus on food issues, but instead focus solely on increasing food production, continue to be published, particularly in journals like Nature. The logic that producing more food will somehow solve current/future food issues, when these problems are associated with food distribution and equality, seems a little naive. How well does the traditional, reductionist approach to science serve sustainability and biological conservation sciences?

    The suggestions of Muller et al are of limited practical value. There are already major problems associated with irrigation (eg. salinization and river health decline in Australia) and eutrophication (eg. Dead zone, Gulf of Mexico) from excessive NPK usage worldwide. Applying the recommendations of Muller et al. throughout the areas with predicted major yield gaps, would create increasingly unsustainable agriculture at a huge environmental cost. As alluded to, there would also be significant social implications in some regions that are ignored, like increased income disparity. It would be sad to see countries like Romania repeat the mistakes that have been made in countries such as Australia and the USA. Additionally, closing yield gaps brings increased reliance on fossil fuels and in an era of increasing fossil fuel costs and predicted scarcity, this is likely to create future problems.

    • But what if, one might say, those fertilisers were primarily organic, and after all, nutrient use will be REDUCED in the green parts of the map? … i.e. Mueller et al are not quite as naive as you suggest 🙂
      Still I appreciate the thoughts

      • I didn’t mean to suggest that Muller et al were naive, but that some of the debate itself was a little narrow. But realistically, I think there is a large gap between academic discussion on best practice sustainable intensification versus what will actually happen: are the majority of increased inputs likely to be organic? (It would be a nice surprise)

  3. I definitely agree with Ben on the narrowness of the debate, and the significant differences between the likely actual realization of sustainable intensification/closing yield gaps in the current system, and a theoretical realization assuming/hoping for best practices.

  4. Pingback: Johan Rockström on sustainable intensification | Ideas for Sustainability

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