Here in mid Wales we’ve been working on a method which we hope could increase the efficiency of use of biologically fixed nitrogen to fertilise crops. After reading Table’s excellent Nitrogen Explainer i thought i’d ask here for feedback on our project.
We sum up our view of the nitrogen problem in this table:
We’ve recently made a short film (7 minutes) about Perennial Green Manures and how we think they could help. I’d love it if Table folk could watch it and tell us what you think. https://www.youtube.com/watch?v=CkgFmRnQpXY
Beautiful simple and correct summary. I would add that there can be a loss of production from green manures although this depends on purpose. Legumes also release a little nitrous oxide when replaced but I think we could consider this as a detail. To avoid going down a rabbit hole, keep in the back of your mind that GHG from Haber Bosch is not an essential requirement and wasn’t the case historically. It IS an energy-intensive process but the hydrogen was historically split from water and the process operated using hydroelectric power. HEP is sometimes still used for processing but the hydrogen comes from natural gas (leaving CO2 as a bi-product - UK fertiliser plants were subsidised to open not for the fertiliser but for the CO2!) because the energy input is lower. (A point for the hydrogen energy fans out there.)
Thanks Simon. That’s interesting! What was the CO2 being used for? Can’t imagine we needed that many fizzy drinks… Refrigeration? Fire extinguishers??
Yes, as i understand it, nitrogen could be fixed using the “surplus” energy from renewables which is generated when power demand is low e.g. wind power at night. so N fertiliser production could be near carbon neutral? Though perhaps if food production by precision fermentation becomes widespread that will also be a demand on those energy sources (to produce H ions for H oxidising bacteria). So i guess it depends on whether it really is “surplus” or whether using renewable energy for it would cause fossil fuel energy to be used for something else, somewhere else.
Beautiful simple and correct summary. I would add that there can be a loss of production from green manures although this depends on purpose. Legumes also release a little nitrous oxide when replaced but I think we could consider this as a detail. In addition, to avoid going down a rabbit hole it is always just having in the back of your mind that GHG from Haber Bosch is not an essential requirement and wasn’t the case historically. It IS an energy-intensive process but the hydrogen was historically split from water and the process operated using hydroelectric power. HEP is sometimes still used but the hydrogen comes from natural gas (leaving CO2 as a bi-product - UK fertiliser plants were subsidised to open not for the fertiliser but for the CO2!) because the energy input is lower. (A point for the hydrogen energy fans out there.)
There are lots of fizzy drinks and some beer! Also to manufacture dry ice for preservation and to stun animals. I am not sure why nitrogen is not used for some of these purposes given how plentiful it is. Some of the CO2 supply is now from anaerobic digestion gas to grid plants.
Until zero carbon energy is plentiful I suspect hydrogen will largely be obtained when the wind blows and the sun shines as a means of storing a premium energy when electricity is in surplus. It could also be obtained from biogas potentially with a lower energy input to split hydrogen from carbon as it is in natural gas.
I’m a veganic home-grower (no imported fertilisers or pesticides), so familiar with the technique. I’m in QLD Australia. My garden is surrounded by local-native shrubs and trees. Birds manage pests and drop small amounts of manure. Leaves for nutrients. I’m also intercropping with peanuts. And sugar cane mulch might complicate (very hot here). What has never been clear, though, including from this explainer, is whether moving nutrients from shrubs and trees, hence from the underlying soil, is over time draining that soil until it would become impoverished. I suppose there we look to coppicing for information. Other questions arise about the more intensive labour in a a system where shops and customers demand low prices (and an inequitable system of poverty for some). And whether collecting, drying, thrashing, milling, and distributing is fossil-fuel driven in some countries, and whether that should be accounted for right now, or left to policy change/transitional. The plastic bags also begs questions in a system. If you wanted feedback on the explainer as a communication tool, I enjoyed it and informative. In any remake, you might consider where you introduce the Trees Feeding Soil part, because at 0:42 it moves on without explaining to the need in crops and the problems of industrial nitrogen. My personal expectation was that I’d hear about trees immediately. So a quick intro of what will be covered and then sections, of hold back of mentioning trees as a solution until after explaining the problem. Also, I’m might have missed it but did you consider the trees being croppable? Fruit? Whether leaf collection could be timed, affect crops, of whether collecting fruit and leaves would overwhelm the trees or soil? I hope something here helps! Such and important project, this. Well done.
Thank you! Such important questions - which we don’t have the answers to yet. I think that over time the bioservice areas which provide the tree leaves are likely to become depleted in nutrients other than nitrogen such as potassium and phosphorus, but i imagine this would take a very long time, as trees can be coppiced for many years without it becoming an issue. I wonder if this could be overcome by occasionally adding waste products such as sewage sludge to the bioservice areas which would make it a more cyclical system. Also, if the bioservice areas are well situated they also have a function of intercepting occasional leachate from agricultural land which will add some nutrients e.g. phosphorus back in.
The energy cost of processing the PGMs is definitely an issue and needs researching. On a small scale it can be done without an energy input e.g. by drying in the sun to separate leaves from branches. We haven’t yet worked out the energy cost of pelleting and i think there are various different machines with different energy uses. However, if this was possible using “spare” renewable energy (as discussed above in relation to the Haber Bosch process) then it could be a sustainable option. The advantage of pellets is that they are more user friendly for many farmers who otherwise would not add much organic matter to their soil.
So, there’s lots of issues to solve, but our feeling is that the overall system of “growing nitrogen on trees” really could have multiple benefits, so we want to spread the word and get others thinking about how to develop this into a method.
Thanks for your feedback on the film. It’s been through many edits and another re-make isn’t possible at the moment, but we’ll keep your comments in mind for the future.
And here is a diagram showing one way we think the bioservice areas could fit into the landscape to provide multiple benefits e.g. to uptake leachate if situated lower down on slopes to the cropland
Thank you, Clo for your further thoughts.
I think the sewage use could be good but good to consider the distribution of microplastics contains therein. They will likely enter the trees and ultimately back to people in the vegetables. Although they have not been shown to harm people yet, they have been found in various human tissues. Some chemicals in plastics are known to have obesogenic properties. I understand you’re doing a great job and sometimes we have to run with imperfections in a messy system. Whether there is a way to filter them in a bioretention basin in the flow you describe, I don’t know. Another consideration is if a new ecology encourages wildlife that then means you cannot crop the trees, or have to consider their lifecycle. It’s complex, isn’t it? As I find here in my garden! If I were to remove a lime leaves right now, citrus swallowtail caterpillars would be removed and harmed, for example.
You’re right Paul in that cutting the vegetation without harming wildlife is an issue that needs consideration. We’ve discussed this and a few of the other complications a little in some webinars etc that you can find on the website. I think there are various ways it could work without compromising the wildlife value and i’ll do my best to summarise these in the final report.
The microplastics is a much more all-pervasive issue, which needs some big overarching changes to tackle - well beyond the scope of our tiny project! I think all we can do there is try to keep up with the latest research and mitigation strategies.
