Nitrates/nitrites and nutrient ions in fertility cycles...
Nitrates, while toxic or wasteful in high concentrations, are a fundamental part
of a natural (or unnatural) fertility cycle. It is in the form of nitrate or
ammonium, dissolved in soil moisture in ionic (electrically-charged) form, that
plants roots absorb nitrogenous fertilizers. The nitrate ion is one of the
preferred forms of nitrogen released during the fertility cycle which plants are
able to take into their cellular tissues. All of the organic fertility materials
we add to our soil (mulches, composts, manures, etc) end at the same point in
the fertility cycle, by being consumed by soil micro-organisms, more
specifically bacteria. Materials consumed by macro- and larger micro-organisms
(earthworms, fungi, etc) are still on their way to the final step, consumption
by soil bacteria. It is at the point when these soil bacteria die, and their
cell walls disintegrate, that a plants roots are able to absorb the minerals
which were dissolved in the cells of the bacteria (not just nitrate ions but
ammonium ions, potassium ions, phosphorous ions, etc).
As the cell walls of soil bacteria die and their nutrients are released, the
nitrate ions basically do one of four things:
1) they are reabsorbed by other soil bacteria, fungi, etc. (healthy part of the
cycle);
2) they are dissolved in soil moisture and taken into plants roots (bingo);
3) they are released to the air as gasses after chemical conversion to ammonium,
a gas (not a great idea), or;
4) they are dissolved in soil moisture and leached or washed away, lost for
agricultural purposes to ground or surface waters (bad idea).
A couple facts combine in this process which are of interest to the soil
fertility cycle as it concerns nitrogen:
1) plants roots need to be PRESENT AT THE PLACE AND TIME WHEN BACTERIA DIE if
they are to absorb the nitrogen before it is transferred to other uses or
locations, and;
2) much nitrogen is lost to gassing leaching, or washing away if it is not
quickly absorbed by other micro-organisms or plants.
What the preceding paragraph means is that the greatest efficiency of nutrient
use/uptake per pound of nitrogen applied or fixed by legumes is obtained when
the breakdown of the fertility materials or nitrogen-fixing nodules by bacteria,
and the deaths of the consuming bacteria, occur IN THE ACTUAL ROOT ZONE OF THE
GROWING PLANTS. For this reason, much greater use of the nitrogen content of
fertility materials is made if they are applied as mulches as opposed to
composts. When composts are made, much nitrogen is lost to gassing and leaching
far from the actual roots of the plants being grown (Mollison mentions these
losses in Chapter 8 of the Big Book, p. 199. The entire chapter is excellent and
bears re-reading).
Further advantages of mulches over composts include:
1) soil cooling in hot environments (15 degrees F cooler at 6 depth than
unmulched soil as measured by myself in May in Texas);
2) narrowing of daily soil temperature swings, eg, cooler in daytime and warmer
at night;
3) importantly, earthworms are much happier under a mulch than under just
compost, for many of these reasons listed here, and also because they eat
soil-surface detritus and so will be found most numerous under a finely-chopped,
rich mulch. Ive found a great earthworm population difference over a short
distance, for instance, between mown grass clippings (many earthworms) and
un-chopped straw (far fewer earthworms). Calcium is also important to worms. In
a healthy, constantly-mulched garden, earthworms do a huge amount of work and
digging is not necessary, in fact is destructive to soil crumb structure
(Mollison speaks to this also in Ch. 8);
4) improved soil moisture retention through lowered evaporation (as well as
lower plant evapotranspiration due to lowered temperatures;
5) less soil compaction from impacting rain, less splashing by rains (dont you
just hate washing savoyed greens covered with dirt?), and;
6) ultimately, less work is performed if fertility materials are just mulched or
sheet-composted and left to do their own work.
The ionized state of soil fertilizers when dissolved and available to plants is
also a key to understanding another important soil fertility process, cation
exchange capacity (CAC, or soils ability to hold and release ions, including
paramagnetism). In strict terms, not only rock powders but also clays and humus
are paramagnetic in being able to attract and hold ionized nutrients
(electrically-charged dissolved particles) against leaching, even though they
are not strictly magnetic. Cation exchange capacity is an important adjunct to
soil biota; both serve to hold nutrients, serving as a valuable soil nutrient
bank instead of leaving the ions floating unattached in soil moisture to be
leached away with the first good rain.
CAC is a valuable property of both clays and humus (as well as of paramagnetic
rock powders); sand has little or no ability to hold dissolved ions against
leaching. It is important to CAC health to give the soil adequate calcium when
sodium ions are present (often the case), since calcium ions share CAC with
other nutrients, whereas sodium ions replace other ions, removing them from the
soils CAC and allowing them to be leached. Calcium will, because of this,
greatly increase the apparent fertility of soils (especially clays) where
calcium is low and sodium high (much of the southern and midwestern US, for
instance).
Sodium also causes clay soils to collapse and become dense, slippery and
impervious (salt, up to 4 pounds per square foot of pond surface area, is used
to seal leaky ponds in clayey areas because of this ability to collapse, or
deflocculate, clay soils). A side effect of the addition of calcium to
counteract the loss of a soils available CAC to excess sodium ions is the
apparently-magical fluffing of the previously-sodium-laden clay soil -- with
greatly increased tilth resulting. This effect can be dramatic, turning sticky
clay into dirt overnight. Quite gratifying.
Moral of the story: use rock powders (but go lightly), check calcium (total, not
available -- which means watch pH also), and place fertility materials right on
the ground, in the garden, to decompose. Brush your teeth, wear clean underwear,
question reality.
Jack Rowe
Seeds of Texas Seed Exchange
PO Box 9882
College Station, TX 77842
Cross Timbers Permaculture Institute
http://csf.colorado.edu/perma/