> [!summary] Progressive Summary > This was an engagingly written book about soil. I learned a lot of things that I didn't know before. It synthesized a lot of research and hard-earned practical knowledge, taking a broad look at the importance of soil for human flourishing. It tries to put the biology back into the way we look at soil, emphasizing the miracle of the interactions between microbes, fungi, plants, minerals, sunlight, water, and air. It's tone was both urgent and hopeful. # Structured Notes ## Definitions Arbuscular mycorrhizal fungi - fungi that live off plant roots biochar - wood burned in a low-oxygen environment until it is porous, mostly carbon, and stable glomalin - a glycoprotein that protects hyphae, stores carbon, and gives soil its structure glycoprotein - a sugar-protein compound hydrogenotrophs - microbes that can convert carbon dioxide and hydrogen into protein methanotrophs - methane-eating microbes microbe - anything that can't be seen without a microscope microaggregates - orbs of minerals bunched together by bacteria in the soil rhizosphere - the area around a plant's roots that consists of a complex relationship between the roots and the surrounding bacteria, fungi and other microbes ## Chapter Summaries ### Chapter 1 - What You Eat is Made out of Thin Air #### Jan Baptista van Helmont Jan Baptista van Helmont was a Flemish physician who was born around 1579. He discovered that trees gained mass from water, not the soil. In one of his experiments, he planted a 2.2 kilogram willow in 90 kilograms of soil and kept it indoors for five years, adding water as needed. After five years, he weighed the tree again, and found that the tree had grown to 77 kilograms, but the soil had lost only 57 grams of weight. Van Helmont coined the term "gas" to refer to unidentified components of air. It is derived from the Greek word for gas -*khaos*. Gas became a standard term after the 18th-century French chemist Antoine-Laurent Lavoisier began using it. In one of his experiments, Van Helmont burned 28 kilograms of charcoal and found only half a kilogram of ash remaining. He concluded that the remaining mass must have escaped into the air as "gas". British chemist James R. Partington said of van Helmont: “He represents the transition from alchemy to chemistry, and is a worthy predecessor of Boyle.” #### Carbon Carbon is the basis for all life. Not only is life made out of it, but the fuel that life requires is sugar, which is made from carbon. And plants are the only life form that can make its own sugar. It does this through photosynthesis. Plants convert sunlight into chemical energy, which is used to strip carbon from carbon dioxide. The carbon is then added to the water molecule, to create carbohydrates, or sugar: $\ce{6CO2 + 6H2O -> 6O2 + C6H12O6}$ Plants provide *energy in digestible form*. #### Macronutrients and micronutrients Humans need both *macronutrients* and *micronutrients*. Our macronutrients consist of 3 main groups: carbohydrates, proteins and fats. Plants give us all 3. They take carbon from the air and combine it with water to make carbohydrates. They take nitrogen from the air to make proteins. Fats, like carbohydrates, are made from carbon, hydrogen and oxygen. The health of a soil determines the micronutrients we get from plants. Micronutrients are vitamins and minerals, phytochemicals and anti-oxidants. The 57 grams of soil that the plant took in van Helmnt's experiment - that contained all the micronutrients. --- Plants' macronutrients are nitrogen, phosphorus, potassium, magnesium, sulphur and calcium, along with carbon, oxygen and hydrogen. #### Diversity There are about 30,000 edible species of plants. Australian aboriginals had access to about 5,000 species of edible plants and animals. There can be many cultivars (varieties) of a single species. For example, at one point, there were 400,000 varieties of rice, just from one species. We are down to just five main land species - cows, chickens, pigs, goats and sheep. In the West, 90 percent of calories comes from just 30 plant species. In the UK, about 120 plant species were grown around the 1500s. This dropped to the lower point in the 1970s, and has rebounded slightly. --- ### Chapter 2 - Soil, the Earth's Miracle Skin #### Snowball Earth 3.6 billion years ago, the Earth's atmosphere became more oxygenated, as a result of cyanobacteria, one of the earliest forms of life. Oxygen enabled rocks to be broken down through the process of oxidation. The Great Oxidation Event doubled the amount of minerals in soil. "It rapidly escalated the possible diet of new life." About 700 million years ago, ice covered the entire globe. This was during the Cryogenian period. When the ice thawed, huge glaciers ground entire mountains into sand, silt and clay, releasing more nutrients such as iron, zinc, phosphates and potassium. #### Stages of erosion Continuous freezing and thawing cracks rocks. Rain and wind loosen rock crystals, which accumulate at the bottom of hills and valleys. Soil is more abundant where glaciers carved the Earth during the last ice age, about 12,000 years ago. #### Soil composition 5% of soil mass is organic matter, which gives soil its structure. The rest is sand, silt and clay, which are broken down rock. 25% of the volume of living soil is air. Ideal ratio of mineral contents of soil is 40% sand, 40% silt and 20% clay. Loam refers to soil that has equal portions of sand, silt and clay. There are more species in a shovelful of healthy soil than above ground in the entire Amazon rainforest. In one handful of soil, there are: - 100,000 protozoa (from up to 500 species) - 10,000 nematodes (from up to 100 species) - 500 metres of plant roots (from up to 50 species) - 100 billion bacteria (from up to 10,000 species) - 100 km of fungal filaments (from up to 1000 species) #### Loss of topsoil Depth of topsoil is about 15 cm. Depth of the Earth's crust, which contains all the minerals that make soil, is about 30-45 km. If Mother Earth were a person, the soil would be no thicker than a single cell on the outside of her body. Topsoil covers about a quarter of the Earth's surface, but only about 7.5% of the Earth's surface is available for agricultural land. The rest is ice, water, stone, too dry, too wet, too hot, or covered with cities. 40% of world's agricultural land has been abandoned because it was no longer fertile. We only have 60 years of topsoil left under industrialised agriculture. About 40-50 percent of current agricultural land is degraded, affecting up to 3.2 billion people. We lose a soccer pitch of soil every 5 seconds through desertification. ### Chapter 3 - The Earth's Kidneys #### Pollution In 2014, the Chinese government estimated that about 16% of soil and 19% of farmland was contaminated. China has less than 10% of the world's arable land, to feed 20% of the world's population. 1 out of 5 hectares is poisoned by cadmium, nickel and arsenic. Every year, China produces 12 million tonnes of grain contaminated with heavy metals. In early 2000s, 10% of rice in China was contaminated with cadmium. Cadmium causes bone and joint diseases. The contamination was caused by phosphates in fertiliser. #### Our water filter Land filters our water. But it's quickly becoming contaminated. 2/3rds of New Zealand's rivers are unswimmable, thanks to nitrogen run-off from dairy farms. In the US, at least one pesticide was found in 94% of water samples and 90% of fish samples. ### Chapter 4 - Plants Don't Eat Dirt #### Glomalin / We haven't been looking very closely at soil Glomalin stores one-third of the world's soil carbon, and it was only discovered in 1996 by scientist Sara Wright. It is the glue that holds soil together and creates what farmers call "tilth". It is a glycoprotein that holds [[Sand, silt and clay]] together. Glomalin is the protective sheath which protects hyphae, the threads which fungi use to transport water and nutrients around. Hyphae last for only a few weeks, but glomalin can remain in soil for up to 50 years, long after the hyphae, which 12,000 years ago - agriculture was discovered 5,500 years ago - the plough was invented 300 years ago - we learned about the bacteria that live in soil 100 years ago - we begin burning fossil fuels to fix nitrogen for artificial fertiliser 50 years ago - we put a Man on the moon 25 years ago - glomalin was discovered Other sources: https://mygreenmontgomery.org/2022/glomalin/ https://agresearchmag.ars.usda.gov/2002/sep/soil #### Fungi In most gardens, fungi consist of 10% of soil microbes. In a healthy forest, this is about 90%. For healthy gardens, we should be trying to achieve fungal density of 50%. Fungi are miners. They secrete acid to break down rocks, drill holes into them, and insert hyphae to extract minerals. They can lasso nematodes with their hyphae, constricting them by increasing the size of the hyphae cells, and then releasing enzymes to digest them. #### Exudates Plants can make at least 100,000 different chemicals which they release through their roots. They can be pushed out at a force of 100 psi through the root tips. > Plants are influencing, directing, managing things. They actually farm microbes in, on and underneath themselves. > > Plants can onyl do it, though, in healthy soil, with the enormity of underground life. Soil is the medium, life is the result. ### Chapter 12 - You'll Never Plough a Field by Turning it Over in Your Mind > Every time we grow food, something else wants to outcompete it or eat it. That's the whole reality of life. We can interrupt biological functions to get the food we want, by ploughing, adding artificial fertiliser, using pesticides. But all of these have a cost. Those interruptions affect the air in the waterways, and while the broader environment also suffers, most of the cost is actually borne by soil. Insect communities can rebuild, if left alone enough. Plants can re-colonise areas. But soil damage can be long term, because it's structural, biological *and* chemical. It's a three-dimensional ecosystem. ### Chapter 21 - What's the Beef with Methane? Archae are the only microbes that produce methane. They live in the stomachs of rumintants, feeding on cellulose, and releasing methane in the process. There are also microbes in the soil called methanotrophs that digest methane as an energy source. # Quotes # References