DEAR NEW FARM:
Here in the UK, organic yields are widely thought to be
about two thirds those of conventional yields, due mostly
to traditionally perfect environments for chemical farming.
That environment is now less reliable, so your trials become
very interesting. As a horticulture student now working on
the soil science module of my course, I have been reading
books on soil science and have found that these books are
not about organics, nor are not overly concerned about the
practical application of their contents. What's striking is
how, without knowing it, they support organic growing methods.
For example, humus is shown to have the highest cation exchange
capacity of all the soil colloids—most of the nitrogen
in the soil is in the organic matter and soil microbes are
shown to be responsible for nutrient cycling. One chapter
explained buffering capacity, how available nutrients are
replaced from the pool of unavailable nutrients as the available
nutrients are removed by plants. Could the improvement in
the yield of your organic plots be due to an increase in its
buffering capacity, due to the build up of humus and organic
matter? I would think of it in terms of capital and interest.
To start with, you had a small amount of capital and only
being able to reinvest some of the interest your capital grew
slowly, but over time the rate of growth increased so that
now you can harvest large crops and still have lots of fertility
left in the soil for the next crop.
As you are finding out by reading your soil science book,
organic farming principals are not new, and they are based
on sound agronomic principals. Soil management practices that
conserve and increase the soil organic matter level are beneficial
to any farmer, conventional or organic. These soil management
practices will improve soil health, soil structure, tilth
and productivity. The improvements in the yields of our organic
plots are based on the increase of soil organic matter over
time. Numerous factors are improved by a small increase in
soil organic matter. The buffering capacity as you mention
is improved. Organic matter provides both cation-exchange
and anion-exchange capacities. Organic matter stores and supplies
nutrients such as nitrogen, phosphorous and sulfur, which
are needed for the growth of plants and soil microorganisms.
One of the most critical plant nutrients is water. Soil organic
matter increases the rate of water infiltration, reduces runoff
and facilitates the penetration of plant roots. So in a dry
year more of the rainfall is infiltrated into the soil and
is also held by the soil organic matter for plant uptake.
Nitrogen in the organic form is conserved, is slowly made
available by microbial decomposition and cycling, and is not
leached as easily as soluble synthetic nitrogen sources. Utilizing
cover crops in our rotation is a key to conserving and building
soil organic matter. Another practice is composting—when
we apply compost to our soils the nutrients are available
for several years, and all the crops in the rotation benefit.
us with comments, suggestions and questions.