Until the plant needs these nutrients the microbes
remain sleeping (dormant) and stuck tightly to the
soil so they don’t wash away as HICs do. The plant
farms the microbial population to release its con-
tents to the plant when the plant needs them -- this
is on demand feeding. The plant grows the micro-
bial population by releasing sugars and other nutri-
ents that grow the bacterial population. This in turn
feeds a growing protozoal population which feed
the larger soil animals and this cycle releases the ni-
trogen and other nutrients that are stored in the soil.
HICs kill microbes by increasing the salt level.
We routinely see well below 100ug/g microbial car-
bon in such soils. Since it is the microbes that are
supposed to provide the plant with N, P, K etc. we
now have to provide these nutrients in chemical
form. But this creates problems: the microbes pro-
vide nutrients on an as needed basis, HICs must be
added to bare or nearly bare soil and in order for
there to be sufficient left in the soil for when the
plant needs them, far too much must be used – the
excess washes into streams and rivers.
Healthy soil farming increases the fertility of the
soil because it increases the soil’s organic matter.
Ninety percent of soil organic matter is microbial re-
mains but the original source of the carbon was the
plant material that microbes digested. SOM is carbon
rich; in fact there is 3-4 times more carbon in the
soil than in the atmosphere. Estimates are that mod-
ern farming methods have decreased soil carbon by
almost half. We have been discussing that microbes
supply the plant with N, P, K and other minerals so
what is the importance of the carbon rich SOM to
the system? Microbes need a carbon source to grow
and their carbon source is the SOM, the exudates of
plants or carbon supplying fertilizers.
Today there is a lot of discussion about the
need for soil microbial diversity. The term diversity
is used differently by academics and practitioners.
Practitioners tend to mean that diversity means, bac-
teria, fungi, protozoa etc. whereas academics tend to
use the term to indicate riches of species, e.g. how
many different kinds of bacteria. No matter how you
use the term, we know that diversity is good and
that research has shown is that a microbe rich sys-
tem is rich in diversity. Research has shown that the
microbial populations of soil are predominately dic-
tated by climate and soil composition factors. Plants
may control the microbial population composition of
the rhizosphere, but beyond the rhizosphere climate
and soil composition rule.
Further, we know that the microbial popula-
tion together with the soil plants form an extremely
complex and interdependent society, so complex
and interdependent that at this stage of knowledge
it is almost impossible to remediate soil with various
species. A cubic centimeter of good soil contains >
26
400 ug/MBC, that means that the top 1 cc x 10 cm
of soil contains over 4000 ugMBC; a cubic meter
contains 1.6x 10 -7ugMBC; An acre 6.4 x 10 -11
.ug MBC. The best amendments and compost teas
provide only 400ug MBC/10ml and if sprayed at 100
gals/acre provide only 1.6 x 10-5. This translates to
the tea/amendment providing 1 microbe to every 4
million endogenous soil microbes making it hardly
likely that the added microbe would have any ef-
fect, especially if it is not native to that soil– one of
the characteristics of microbial populations is that
they fiercely defend their area from intruders, this is
why they are so good at protecting their areas from
pests. So why is compost tea such a potent organic
fertilizer: because it contains soluble organic mat-
ter and the quality of that SOM is predicted by the
fact that it supports a healthy microbial population.
Compost tea fertilizes mainly because of the SOM it
contains: the microbes that it contains probably die
or are eaten by the soil microbes. Foliar tea sprays
on the other hand can contain microbes that appear
to be effective.
The above discussion of microbial additions to
soil does not apply to seed and root amendments.
Fortunately, we are beginning to know enough
about many of the microbes that live attached to or
within the plant or in the rhizosphere to be able to
supplement seeds and roots with beneficial organ-
isms.
Via exudates including chemical messengers, the
plant tightly controls the size and even the compo-
sition of the microbial population in the root area
(rhizosphere which extends only 1 mm around the
root) and this