Bact-eria to the Future

Hey all. Your fabulous hip, non-hipster gardener is back with more sweet, fascinating, geeked out garden talk. You ready for another ride? Let us dig in…literally.

This past fall, Wellfield undertook a new step in its ongoing soil management plan: soil testing. Not traditional soil testing, which all smart gardeners should be doing regularly, but a test for soil microbiology. If you have read this blog with any frequency, you know I geek out when the topics of soils and soil ecology come up. I just love what goes on under our feet. I mean, I just spent the last two hours pouring over my college textbooks and reading scientific study abstracts because this stuff is so cool.

Why all the huff from this puff? Because as more understanding is gained of the key role soil microbes play directly and indirectly with plant health, performance and yield, the more obvious it should become that growers need to learn to “manage” their microherds. What is a microherd, you may ask? It represents the multitude of bacteria and other diverse microorganisms that create and sustain fertile living soil, thought of as a gardener’s “livestock”, if you will.

With regard to microherds, the old maxim “what you do not quantify, you cannot manage”, is so true. We emphasize in gardening books, college courses and adult continuing education classes the importance of traditional NPK (nitrogen, phosphorus, potassium) soil tests and take time to explain/understand the numbers, so why not attempt to run the numbers on soil microbes? Well, for one, there are few labs across the country offering such services and there is little demand either. There is also much less research concerning target numbers than for say pH or certain micronutrient needs.

Back to Wellfield and what we discovered with our testing. All existing gardens were tested for overall population (biomass) of bacteria, beneficial fungi, protozoa and nematodes. The results confirm Wellfield’s soil is young. What does that mean? Soils in nature take a long time to develop. If left alone, undisturbed by man or natural events, soils develop robust, resilient complex relationships and layers suitable for stable plant growth. Young soils lack a lot of nutrients available to most species of plants and are low in microbial biomass. They are characterized by high bacterial and low fungal populations, not to mention few single and multicellular organisms like protozoa or nematodes. So? Yawn. Get to the point right?

The answer is simple. Soil microbes are a key part of the complex methods by which plant roots absorb nutrients. Soils devoid of many soil microbes, especially bacterias and fungi, do not grow many plants. See corn growing on a recent lava flow? Seen large canopy trees growing in the shadow of a glacier? Nope. The soil is too new, too recently turned, disturbed as scientists like to call it.

Plant roots support large populations of bacteria because they release copious quantities of high energy foods bacteria love. Bacteria populations can be up to 50% higher in the rhizosphere  than in surrounding soil. Groovy, eh? This means plants are attracting a virtual melting pot of little guys, including free-moving nitrogen fixing bacteria, which is the main way plants obtain nitrogen. Oh wait, I am not finished! Gardening texts often bemoan the difficulty of getting phosphorus (important for many things such as beautiful flowers and a little thing called photosynthesis) because it is present in the soil in forms plants can not access easily. The availability of this super essential element could be affected by the activity of root and soil microbes capable of converting phosphorus into a usable form.

So enough about the bacteria outback. What about all those fun-guys in the soil? Fungi play an even more important role in plant health and nutrition. The most well documented is a group of fungi known collectively as mycorrhiza. There is much written on this topic, so for now I will highlight the following facts:

  • Over 80% of plant species on earth have formed these symbiotic relationships, including almost all economically important species.
  • Studies have shown pine and other tree species infected with mycorrhizae were able to produce 30 to 150% more mass than non-infected controls.
  • This fungi-enhanced growth appears due to great uptake of nutrients, especially good old phosphorous. Mycorrhizae added to the root system act as root extensions, drastically increasing the total surface area for nutrient uptake.

The all important number from the lab test is the fungi to bacteria ratio, or F:B for short. At this point, it looks like fungi collectively are more responsible for greater nutrient uptake assistance than bacteria. The more beneficial fungi are present in the soil, the more mature the soil and more supportive of a greater number of plant species typically. The more you turn the soil, say with a rototiller, the more you disrupt those all important fungal-root relationships. Needless to say, the higher the F:B ratio, the more supportive that soil will be to your precious garden plants.

To view and study (now that you are experts) Wellfield’s Microbe test results, click here: Wellfield Microbe test results.

Hopefully, I have convinced you of the need to test and manage the soil microbe numbers as closely as you manage your garden soil’s pH or iron content. Though small, your microherd needs to be heard.

Josh Steffen
Horticulture Manager

One comment

  1. We have not found anything yet that did not benefit from adding mycorrhizae. The soil here tends to be somewhat deficient. It is probably not so in much of the Santa Cruz Mountains.

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