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54 WINES&VINES July 2018 BOOK EXCERPT facilitate getting a suite of essential micronutri- ents into plants — things like copper and zinc that we don't tend to think of as nutrients but that healthy plants and people alike need in small quantities. Soil-dwelling microbes work like little chemists to convert nutrients to plant- available forms. But in a soil sparsely populated with life, crucial nutrients remain parked out- side of a plant's root zone, like goods on a ship stranded at sea far from port. Biological bazaar From bacteria to beetles, soil life forms an underground community that breaks down organic matter, yielding organic by-products and metabolites rich in nitrogen and mineral- derived elements. Soil life also influences the ability of plants to defend themselves — when insects or herbivores graze on foliage, some plants exude compounds that rhizosphere- dwelling microbes metabolize. Plants then use the microbial metabolites to drive away the herbivores. In other words, plants outsource the production of pest repellent to microbes that get paid with root exudates. When the rhizosphere is full of beneficial microbes, pests and pathogens have a harder time finding a seat at the crowded table. The slow pace of rock weathering and lim- ited availability of biologically-critical elements on Earth's surface means that recycling these elements is essential to growing and sustaining abundant life. Over geologic time, microbially- mediated processes refined and built up the stock of ingredients circulating through ter- restrial ecosystems. Soil life not only turns the wheel of life, it procures and stores nutrients essential for new life and keeps them from leaching out of the soil. Heavy fertilizer applications can alter soil microbial communities, make the soil acidic and harm beneficial microbial life. Although Inspecting earthworms, which are one sign of healthy, fertile soil.