How to Interpret Soil Foodweb Assays

Ratios

Total Fungal Biomass to Total Bacterial Biomass
Different plants require different processes in the root system, different pH, different structural conditions, different rates of nutrient availability, and different forms of nutrients. By controlling the biology around their root systems, the plant can modify the soil environment, and their leaf surface environment to some extent. In this way, the organisms around the plant can be modified to select for different plant species.

Is the ratio of fungi to bacteria correct for the plant you desire? If the ratio is greater than one, the fungi are predominant, but if the ratio is less than one, the bacteria are winning.

In general, very early successional species such as most weedy species, brassicas, mustards, wetland annuals, require a strongly bacterial food web. Early successional grasses require slightly less bacterial dominance, only about 2 times more bacteria than fungi, for example, to make the soil most selective for Bermuda, Zoysia, most Bromus species. Vegetables, most cut flowers, and other annual plants need about 1 quarter to a third more bacteria than fungi, but most row crop plants need an equal ratio of bacteria and fungi.

Perennial plants typically do much better in fungal-dominated soils. Clover, some soybean, and strawberry plants do best in slightly fungal soils, while shrubs, bushes and early successional deciduous trees like alder, popular and small understory trees also can outcompete annual plants when the soil is 5 to 10 times more fungal than bacterial. Deciduous trees, like beech, maple, oak and elm need 10 to 100 time smore fungi than bacteria to be healthy. Conifers usually do better when the fungal biomass is in the 100 to 1000 times more fungal than bacterial.
Again, these are based on representative plants growing without disease or need for fertilizer additions. Not-healthy plants will eke out an existence in soils that aren’t right for them, in stressed condition, with poor growth and poor yield. Balance the soil to help the plant, and these plants grow better.

Ratios of active to total bacteria, or active to total fungi -

How active is the bacterial or fungal populations? The more the population is growing, the more rapid the recovery of a community. Addition of foods for bacteria or fungi will increase activity, but of course, the organisms have to be present to use that food and increase their populations. If you plan on bagging or bottling a material, activity has to be less than 10% of both populations, or the sealed container will implode or more often, explode through accumulation of respiratory gases.

Ratio active fungi to active bacteria -

Will the soil, compost or compost tea become more fungal, or more bacterial? This ratio lets you know. If the ratio is greater than one, fungi will be gaining ground over the bacteria, but if the ratio is less than one, the bacteria are winning.

Plant available N, in micrograms actual nitrogen, made available in the next three months per acre of soil – This is calculated from the number of protozoa and nematodes present and active. Research shows that these organisms consume and mineralize N from bacteria and fungal biomass. Given certain rates of consumption of their prey per day per unit biomass means a certain amount of nitrogen will be released.

Root-feeding nematodes – Are there any "bad guy" nematodes present? At economic damage levels? If there are, you can treat the soil to exit these problem nematodes. By improving mycorrhizal fungi, the root-feeders can be masked from finding the root. Beneficial nematodes also interfere with the root-feeders from being able to find the roots. And of course, nematode-trapping fungi, or nematode parasitic fungi can be effective bio-control agents. Root-feeding nematodes can be removed by getting these beneficial organisms back into the soil in a short period of time, if they are added in high enough number.

Amount of compost typically needed

In the fall, compost should be applied between 5 ton per acre (just a minimal inoculum) to 30 ton per acre to add organic matter as well as the inoculum of the organisms.

Again, in the spring, compost should be applied at rates required to bring the organism numbers back to desired ranges. If just an inoculum is needed, i.e., activity is adequate, but total biomass is low, then the lower rate is chosen. If long-term organic matter is needed to deal with high salt, pesticide residues or high nitrate, pH, or heavy metals, then addition of high rates of compost is indicated.

In turf, fairways can be treated as above, but the compost should be screened to prevent large chunks interfering with play. On greens, the lower rate is always chosen, and the compost should be finely screened, followed by tea use.

Given a source of good compost, minimal compost applications are possible to bring the foodweb back to health. BUT monitoring is necessary, to make sure the conversion to healthy actually is proceeding apace.

Amounts of compost tea typically needed

Compost applications can be replaced with fall and spring applications of 15 to 20 gal of tea per acre. Enough water is used, as a carrier, to allow easy application of the tea to the area desired.

Then, tea should be applied based on disease, weed and nutrient limitations in soil. Weekly applications of tea, made to offset the problems present (fungi maximized if lacking fungi, high concentration of humic acids if salt problems exist, calcium additions if composite weeds are a problem, or iron if moss is significant) should be made until disease problems are alleviated. Weed problems should be dealt with by altering the nutrient limitations that allow the weeds to out-compete the desired plants. Once the diseases are dealt with, and weed problems are minimized, reduction in tea applications should be possible. Typically, back off to twice a month applications, then to once a month applications, or less, depending on the plant response. If disease begins to rear it’s ugly head again, increase tea applications.

If the Extension Service announces a disease alert for your plant, you should increase applications to protect the plants ASAP. Even if you don’t see disease at this time, increased disease load needs to be off-set immediately.

Amendments

Kelp – can be set the stage to remedy plant health, and improve the plant’s ability to resist attack by Fusarium, Xanthomonas, black spot, and other bacterial diseases.

Molasses – contains some humic acid, so improves fungal biomass more than many other simple sugars. There are many types of sugar in molasses, so helps improve diversity of species that will grow in the tea.

Lime – calcium addition

Rock Dust – mineral nutrient addition. Make sure your plant needs to have these mineral elements increased before applying.

Please e-mail any questions to info@soilfoodweb.com and let us know if you have any problems interpreting the Food web, or need help with observation that you don’t understand.

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