Agriculture Reference
In-Depth Information
is excessive rain, it's safe to assume much of what was added (other than
Phosphorus) will be leached out and will need to be added again.This may call for
frequent soil tests and amending if an optimum yield with maximum nutrient
content is desired.
Note that even though a large amount of base cations may need to be added to
achieve the minimum amounts of Ca, Mg, and K, as long as the concentration of
anions (P, S, NO
3
, Cl) is also at optimum, the soil's
H+ : OH-
balance will settle out
at around pH 6.5
Increasing the Exchange Capacity
The longer-term answer is to increase the exchange capacity of the soil. This can
be done by adding or increasing.
Soil Organic Matter (SOM), as stable humus
Humate ores
Charcoal or Biochar (e.g. terra preta soils)
Low-fired pottery sherds (also found in terra preta soils)
Expanded Vermiculite
High-CEC clay such as Calcium bentonite/montmorillonite clay
Zeolites
Adding or Increasing Organic Matter
Stable humus has a CEC of up to 200meq and significant anion exchange
capacity as well. Organic matter in the process of breaking down doesn't have
much exchange capacity; it only achieves that when it is broken down to stable
humus that can no longer readily serve as food for plants and soil organisms.
Organic matter decomposing into stable humus will only happen efficiently in a
biologically active, mineral balanced soil with optimal levels of N, C, S, and Ca.
Even if the
Carbon:Nitrogen ratio
of the decomposing organic matter is
an ideal
25 or 30:1
, without sufficient S to form Sulfur-containing amino acids like cysteine
and methionine, Nitrogen released during decomposition can be lost to the
atmosphere as ammonia NH
3
gas, or form water-soluble nitrate NO
3
and be
leached away. Likewise without sufficient Ca
2+
to bind with the CO
3
2-
carbonate
ions produced during decomposition (forming stable Calcium carbonate CaCO
3)
,
the Carbon released may be lost to the atmosphere as CO
2
.
Only with the proper mineral balance in the soil (or compost pile) will the
maximum amount of stable humus with optimum exchange capacity be
formed and conserved.
The strategy of building humus to increase exchange capacity
only works well
in
cooler temperate climates
where the annual precipitation is equal to or greater
than the average annual amount of precipitation that evaporates from the
soil or transpires from the plants
(called
the evapo-transpiration ratio or
rate
). In warmer tropical and sub-tropical climates the biological activity is high
