Managing the Soil Food Web

Briefly, the plan is this:
 
  1. Determine the organisms present in the soil.
     
  2. Add back the organisms that are missing, or out-of-balance.
     
  3. Add food to make certain the added organisms can survive and grow.
     
  4. Check to make sure the foodweb is moving back into the correct balance for the desired plant.
     
  5. Repeat steps 2 - 4 until the correct foodweb is obtained.
     
  6. Monitor yearly to make certain soil remains healthy.
     

The benefits of doing this?
 
  1. Less disease - fewer and possibly no pesticide applications
  2. Reduced fertilizer requirements - fewer maintenance trips across the turf
  3. Better soil structure - less water required, better root growth, less compaction due to activities on the turf
  4. When pesticide has to be used, it will be degraded rapidly in the soil
  5. Run-off and groundwater contamination from the landscape will be reduced, if not eliminated.

How rapidly can these benefits be realized?
 
It depends on how rapidly the health of the soil can be brought back. We have two goals to reach in moving to a healthy soil. The goals reflect two very different levels of control, the first goal quite general, and the second quite specific.

Goal 1:
Balance the biomass of each organism group so the soil builds health of it's own accord. This must be done with regard to the plants desired in the system. This requires getting the right biomass of bacteria, fungi, protozoa, nematodes and microarthropods back into the soil. "Right" is related to the plants you are growing. We work with you to find out what the optimal "right" biomass of each group is for your particular microclimate, soil, and past-management practices. We look at ratios of fungi to bacteria, root-feeders to beneficials, protozoa to bacteria. It can take a few weeks to get these balances all right, or it may take years, depending on how badly the soil is out-of-balance, and what might be in the soil now that will prevent getting that balance back.

Certainly there's more to learn than we know right now. It's silly to think there aren't major gaps in our knowledge that need to be investigated. But we know one important goal to reach for, getting the general balance of soil organisms right for the plant species desired.

Goal 2:
Get the specific set of beneficial species back in the soil. This includes bacteria, fungi, protozoa, nematodes and microarthropods. Make certain that all the beneficial organisms are present in the soil, and certainly, make sure these species are those most beneficial for the specific plant being grown. Select against those organisms that might cause or encourage disease. This can be done for root-feeding nematodes in a general sense, but not the plant-specific sense. Fine-tuning is needed. Reduction in "false starts" toward getting long-term control would be good.

For bacteria, fungi and protozoa, we don't have good ways to assess whether certain beneficial species are present or not. We don't even know which ones are most beneficial for different plant species, much less be able to pick them out of the crowd. The classic way of assessing bacterial species is to spread a soil dilution on a specific kind of medium. This means only a limited number of foods are present, and perhaps only 10% of the species in the soil can even grow. Then the plate is incubated at a certain temperature, which further limits the set of species that can grow. Incubation occurs at a certain humidity, which further limits the species that can grow. So what is the relationship between the species found on a plate and the species present in the soil? Less than, say, 0.1 to 1% reflection. We realistically know nothing about soil bacterial species based on plate counts. And which of those species are beneficial? There are a number of programs around the world trying to understand which bacterial species are most beneficial for which plants. None of those labs get the funding they deserve.

Molecular approaches are the only way to understand the full set of bacterial, and fungal for that matter, species in soil. Estimates of bacterial species diversity in soil suggest that in a typical gram of agricultural soil that there are 10,000 to 15,000 species of bacteria present (Tiedje and Klug, Center for Microbial Ecology, Michigan State University). Forest soils have even more species, maybe upwards of 40,000 species per teaspoon. Which ones are beneficial? Which ones are beneficial for plant species A, but detrimental for plant species B? We have barely an inkling of information about this diversity.

Right now, at the cost of several thousand dollars per soil sample, we can begin to assess the whole bacterial community present. It takes months to perform this assessment as well. Clearly, we need to push the USDA to encourage development of this ability, but it is not practically available yet. So, we'll leave that to the future. Let's get going on Goal 1, and by the time the molecular methods are available at a decent price, Goal 1 will be achieved, and we'll be ready to work on Goal 2.

 

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