Gardening Etcetera: Life down under with inoculated soil – Arizona Daily Sun


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Gardening Etcetera: Life down under with inoculated soil

Root nodules on leguminous plants, like this locoweed, work with soil bacteria to make atmospheric nitrogen available to the plant. This is just one instance of many where life underneath the ground enriches and nourishes soil.

Cindy Murray

Striding through the forest one Sunday afternoon, my husband and I came upon a small grouping of flourishing pinyon pines. I stopped and handed Hugh a trowel, declaring, “Here’s a great spot. Let’s start digging!” He queried, “Jog my memory. What are we digging for?”I had recently read an article about the benefits of mycorrhizae, a group of fungi that forms symbiotic relationships with plant roots. For pinyon pines, this partnership serves the tree in a number of ways including enhancing its uptake of food and water. In turn, the pine supplies the fungus with nutritious carbohydrates. The author had advised that when planting pinyon pine seeds, gardeners should mix into the soil a small portion of native soil dug from under healthy pinyon pines.Well, I didn’t have pinyon pine seeds, but I did have two foot-long seedlings, which I believed would profit from this technique. A few days later I threw in a few handfuls of this “pinyon soil” as I planted my seedlings. My soil was now inoculated; only time would tell whether my pinyons would thrive.The symbiotic mycorrhizal-plant relationship is merely one of an assortment of fascinating cases where plants benefit from underground lifeforms. Myriads of bacteria and fungi play major roles in the Earth’s nitrogen cycle, a biogeochemical process where nitrogen, an essential plant nutrient, is chemically changed as it circulates among the Earth’s atmosphere, ground, and oceans. Without these microorganisms, very little nitrogen would be in the proper molecular forms plants and roots can absorb.One case in point is Symbiotic Nitrogen Fixation. Here bacteria of the genus Rhizobium form a mutualistic partnership with nodules on the roots of legumes (the bean or pea family), whereby they convert atmospheric nitrogen into compounds plants can utilize. Not only does this benefit the host plant, it also releases plant-usable nitrogen compounds into the soil when the plant or portion of the plant dies and decomposes. This is one reason why farmers and gardeners often grow leguminous cover crops like clover, vetches, and peas to till into the soil before planting the primary crop.Northern Arizona hosts a number of native legumes: an assortment of vetches (Astragalus spp.), the attractive, yet poisonous, locoweed (Oxytropis lambertii), the ground-hugging false mesquite (Calliandra humilis), a few daleas, some tick clovers, the large shrub false indigo (Amorpha fruticosa), New Mexico locust (Robinia neomexicana), and several lupines (Lupinus spp.).While many of us associate bacteria with germs, probiotics, or cheese and yogurt, in fact, many bacteria and fungi are decomposers (saprophytes) of excrement and dead plant and animal matter. During this process the microbes take in carbon and other nutrients, and in exchange, the soil gets a boost in a variety of plant nutrients including available nitrogen.We all know the earthworm is a gardener’s best friend. Here’s why: it works in tandem with other microorganisms to decompose organic material, considerably increasing the availability of nutrients. At the same time, it aerates the soil and enhances water infiltration.Gophers and prairie dogs may be the bane of many gardeners, yet they play an intricate role in nature. Their digging habit mixes nutrients into the soil, allows water to permeate the ground and loosens compacted dirt. Whenever our own vegetable plots get low on loose, friable soil, we add soil dug up from prairie dog and gopher mounds and craters.It has been 14 years since my husband and I dug up the “pinyon soil” to add to planting holes. Now our pinyon pines are robust and thriving. I like to think the inoculated soil did its job, but then again, it could be because we keep our pinyons well-watered (never soggy), or a combination of the two.Cindy Murray is a biologist, co-editor of Gardening Etc. and a Coconino Master Gardener with Arizona Cooperative Extension.If you have a gardening question, send a message to [email protected] and a Coconino Master Gardener will answer your question.The Online Master Gardener Course will be offered this fall. Contact Gayle Gratop for details: [email protected] or 928-773-6112.

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Root nodules on leguminous plants, like this locoweed, work with soil bacteria to make atmospheric nitrogen available to the plant. This is just one instance of many where life underneath the ground enriches and nourishes soil.

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