Issue link: http://read.dmtmag.com/i/662797
www.goodfruit.com GOOD FRUIT GROWER APRIL 15, 2016 41 Tips to improve your soil A lthough the study of soil microbiology is barely out of the starting gate, U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) research microbiologist Michael Lehman said growers can already take steps to reduce and even reverse soil degradation: —Disturb the soil as minimally as possible. One of the main consequences of disturbance is the destruction of the soil structure, which disrupts soil habitats for valuable microbes and removes organic carbon from the soil faster than it is naturally replenished. —Keep something growing on the soil all year round. "This is kind of a big deal, because plants will take about 25 percent of what they fi x as carbon from their photosynthesis and inject it into the soil," Lehman said. "By doing that, they're providing an organic source for the organisms that live near the plant and therefore maintain the biomass of microbes, their activities and also their diversity." —Maintain diversity where possible. For fruit growers, this could mean growing a diversity of plants as cover crop between tree rows or in adjacent plots. Research has linked the diversity of plants to increased nitrogen and carbon retention provided by soil microbes. A mix of perennials could be a good option, because they have deep roots that stabilize soil, access nutrients and water from deeper in the profi le, and stimulate microbes through a greater cross-section of soil, he said. —Avoid heavy inorganic-fertilizer use. "There's plenty of literature out there and more research still coming out, that suggests that if you add high levels of inorganic phosphorus and nitrogen, you can suppress certain populations of microbes that would otherwise be benefi cial to the plants," Lehman said. He acknowledged that fi rm guidelines are not yet available for fertilizer use, and may not be forthcoming anytime soon. "Today's fertility recommendations were made under a standard set of conditions that did not optimize soil biology," he said, adding that the recommendations are for "average" conditions so they may not apply well to every orchard or vineyard. "To translate the new understanding of soil biology into recommendations is going to take a long time." —Use compost and manure. Organic compost and manure trump inorganic fertilizers, he said. "They increase the health of soil by adding carbon in the organic form that stimulates biological activity in a way that inorganic doesn't. With inor- ganics, you're putting out a pool for plants to uptake. With organic forms, you're stimulating the biological cycle so it can provide the nutrients to the plant." —L. Mertz phosphorus, potassium and various trace nutrients more available to plants, and if those microbes are encouraged, the need for fertilizer could potentially be reduced. "So we're learning that there are all kinds of ways that the microbes support plants," he said. Two U.S. efforts are under way to chip away at the vast mystery of soil biol- ogy. One is the National Corn Growers Association's Soil Health Partnership (soilhealthpartnership.org), which is studying soil-management practices at 60 demonstration farms, 20 of which will be added in 2016. The other is a national soil-health assessment to be spearheaded by the newly launched Soil Health Institute (soilhealthinstitute.org) based in Research Triangle Park, North Carolina. Similar studies of soil health are underway in the European Union, Brazil, Argentina and Australia. Said Lehman, "Soil biology has become a global interest, and I think studies like these will yield important advancements about how farm practices can positively infl uence soil health." Lehman and his co-authors wrote their paper to stimulate interest and awareness of soil biology to everyone from scientists and crop producers to policy makers and nonprofi t organizations, he said. "We wanted to reach a lot of different audiences to illustrate how little we know about soil health, how far we need to go, and what we need to do to get to that endpoint," he said. "We also wanted to try to spur additional efforts, whether they are government or nonprofit initiatives that are coordinated across regions, or individual investigator-led projects." The main point, he added, is that soil biology is too important to ignore. "If it weren't for the microbes in the soil, life wouldn't exist. Period." • ONLINE Lehman, R. M., et al. 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