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Automatic TRANSCRIPT

Got into soil as an undergraduate student at the University of Osmar. This is Asmara at Bir. Hey she's a professor of soil bio geochemistry at the University of California and mirsaid where we went to visit her but her lifelong love affair with soil began in Eritrea. So when I started I was an eighteen year old student at the university. It didn't know really anything about soil. And I took an introduction to soil science course I was blown away at how that opened my world in my eyes. I was hooked still learning Asmara at fell in love with something that seems just like this every day brown thing we might occasionally get stuck to our shoes but really what is it. What is soil? It's a product of breakdown of rocks and also incorporated incorporates residues of dead plants and animals that used to live in the land before but the mixture of this breakdown products of rocks and residue of organic matter that lived creates these incredibly rich resource that we then every living thing on. The face of the earth depends on for our life for our livelihood for our food. Fiber needs in everything else. You can imagine there's only about six foot of this magical rock and residue mix covering the earth surface on average and so it's not very deep when you think about it in reality it's that thin veil that represents the difference between life and likeness in the system all this is beautiful and obviously incredibly fundamental life on earth and there's plenty we could and probably will say in the future about soil and food but this episode we're focusing specifically on the carbon and soil in carbon is continuously being exchanged between the soil and the atmosphere because when plants photosynthesis they take up carbon dioxide from the atmosphere and then they use it to build their bodies and upon death the bodies in the bodies of every living things that consume the plants into the soil and get stored there are soil carbon basically carbon gets into the soil through two main butts. There's the plant matter itself when it dies but also while the plan is live its roots. Push out carbon-based sugars into the soil to feed microbes. Those microbes are also of course made of carbon. So that's more carbon the soil but like Asmara's said this is a cycle plants take up soil. Carbon use it for food and some of the carbon escapes back into the atmosphere some carbon just cycles through soil really quickly. It doesn't stay in the soil but some of it does. There are particular microbes that can help soil carbon get stuck together into clumps so it can't be consumed or escape to the atmosphere and there are particular soil minerals that react with soil carbon and form chemical bonds that also keep it from being consumed in released scientists call these clumps aggregates basically they're like little vaults some carbon might leak out of those vaults but most of it stays there for decades some of it stays for centuries so in a way you can think about the soil serving as the bank for Carbon Carbon comes in carbon comes out Just like we deposit money in our bank and then was drove over time. But if you deposit more than you withdraw than your bank account grows and the soil carbon over time basically grew because the system as a whole we were depositing more into the soil carbon bank than we were withdrawing but right now we're doing the opposite in the past our soil. Carbon Bank account was in good shape. We're talking geological time here but over billions of years more carbon got deposited than was released. That's what made places like the midwestern prairies. The world's great agricultural soils so fertile. But here's the thing in the past two Hundred Years. We've released a lot of carbon from soil. Scientists disagree about the exact amount but everyone agrees it's a lot billions and billions of tons. So how exactly did we lose all that carbon for soil bank account? What have we been doing since the war? The farmer has nearly doubled his production until today. He is beating himself and seventeen others. What made this greater increase possible. Power power made available through the farm tractor which meant greater efficiency modern agriculture and especially tractors. Anytime you break up soil and expose it those clumps. We talked about release. Their carbon in the past farming was more small scale and not mechanized so it causes less disturbance in the soil and so it released less carbon. But that's not how things work today. Tractors Rolling over fields and breaking them up so they can be easily planted that releases a lot of carbon quickly over a much larger area plus all these machines mean. We can farm a lot more land more quickly which means we release. Its carbon to the amount of land used for farming around. The world has grown exponentially especially since World War Two. Of course there are other things that expose and break up. Soil deforestation draining wetlands but agriculture is huge. A profound drop in Solar Ganic matter has happened virtually everywhere we've farmed no one contests this somewhere. Between thirty and seventy percent of the Solar Ganic matter is gone from agricultural fields after several decades once. You Start Farming Tim. Cruz is the director of research at the Land Institute in Salina Kansas and he says soil that has lost that much. Carbon is considered degraded so there was a recent report released by the UN that stated that close to about half of the world soil so now considered degraded half which is obviously not good. So why don't we stop with all the tractors in the plowing to understand why we need tractors our current system? Why we tear up the soil for all our crops. The critical thing to understand is that nearly all of our crops are annual plants. Annuals have to be planted each year and at the end of the season they die. Most plants in the world are not annual plants there. What's called perennials? They just grow and then one day after decade or hundreds of years in the case of trees they die. It's interesting note that there's almost no natural. Ecosystems that are dominated by annual plants in the world it just does not exist prairies forests savannahs deserts. Tundra and rainforests all of these ecosystems are overwhelmingly dominated by perennial species. And it's the roots of those species that developed the soils have the world most plants are perennials are of course some manuals in nature as well but if most plants are perennials. Why are nearly all the plans we use for food annuals to answer that we have to go back thousands of years to before the start of agriculture so when you start looking for grains to eat annual wild plants tend to have relatively large seed and relatively large amounts of them? Wild Bernal's tend to have lower C- deal so if you're looking for something to eat usually going to be attracted to that while Daniel Plant laid to haunt is a plant breeder who works with Tim at the Land Institute and he says our ancestors would have found these large seeded annual grasses bringing up in disturbed areas maybe like an animal wallow because that's the ecosystem that annuals are adapted to. They thrive on freshly churned up land but annuals turned out to have an even bigger benefit for our ancestors than just their grain size now of course thousands of years ago. They didn't know anything about genetics or breeding but they would have planted seeds of those annuals and then each year. They chose their favorites to eat and replant. Annuals were perfect. For this process you can get robbed cycles. Obstruction happening unintentionally. Because every year. It's going to have to come from a if you had perennials growing out. There very hard to just accidentally improve them improve their seats is because you just keep going back to the same old plants and harvesting them and they would never change so there was some sense to choosing annuals for our food crops but that choice locked us into tearing up the soil each year to make the kind of environment are food. Plants prefer so with agriculture. What we have to do is mimic disturbance so when I give a presentation to show a picture of volcano. 'cause that's kind of what we do every year. Now you're cultures we level everything we'd wipe out all above ground plant life and re seed our annual grain crop so you're starting from kind of biological ecological ground zero every year we do it. Some perennials mostly fruits and nuts that grow on trees. There are some wild grains like wild rice that's a perennial but eighty percent of all. Our crops are annuals and we locked into that way of growing food at the beginning. And we've lived this legacy when farmers plow their fields before sowing the seeds each spring that triggers a big withdrawal from the soil carbon bank because it busts open those aggregates that were guarding carbon safely in the soil. And when you break it open with with tillage plow disc microbes have access to that stored carbon and they have a heyday. They just start shout out and they eat up that Solar Ganic matter and they breathe out carbon dioxide in the process micro string and honestly a drink might not be a bad idea at this point because the impact of tilling the soil like this is pretty bad first of all like we said disturbing the soil releases a bunch of carbon into the atmosphere and then of course that carbon isn't available in the soil for the plans to use his food soil carbon is also critical for water storage because those clumps help soil hold onto water when the klumps break up the structure of the soil changes. It doesn't hold water as well. Water runs off the fields. Instead of thinking in and the soil runs off to erosion becomes a bigger problem so carbon storage and soya's good for many many reasons beyond climate change mitigation but also so carbon is really important in terms of climate. Change Mitigation. Because there's so much carbon and soil compared to the atmosphere the small change in the amount of carbon stores and soil can dramatically change the concentration of greenhouse gases in the earth's atmosphere and hence the atmosphere temperature and because so much of the earth is farmland a third of the entire planets ice-free surfaces farmland. That means changing the amount of carbon and agricultural soils would have an outsized impact. Carbon in soil is great for plants and great for the environment and so people have been working on ways to get more carbon into soil for a while but this focus on climate change is a new one because it's becoming clearer and clearer each year that we have to do something anything about our carbon emissions. So what do we do? How do we build our soil carbon backup? I mean the only way to get it back totally is to reverse the process totally and go back to how that organic matter was accumulated in the first place which involved perennial species and not disturbing the