| 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. |