Field Guide of Discovery-based Exercises for - Aseanipm ...

Exercise No. 3.13
UNDERSTANDING ACTIVITIES OF SOIL ORGANISMS
BENEFICIAL TO ORGANIC VEGETABLE PRODUCTIVITY
BaCKGroUND aND raTIoNalE
In their influence on crop production, soil fauna and flora are
indispensable. Of their many beneficial effects on organic
vegetable productivity, only a few most important can be
emphasized here, as follows 80 :
104
Field Guide of Discovery-based Exercises for Organic Vegetable Production
when is this exercise most
appropriate?
ɶ In FFS, TOT, and VST
sessions, as component
of the topic on
‘Ecosystem’
ɶ When farmers want to
understand activities of
soil flora and fauna that
are beneficial to organic
vegetable productivity
• Organic matter decomposition. Perhaps one most
significant contribution of soil fauna and flora to organic
vegetable productivity is that of organic matter decomposition. By this process, plant residues
are broken down, thereby preventing an unwanted accumulation. Furthermore, nutrients held
in organic combinations within these residues are released for use by plants. Nitrogen is a
prime example. At the same time, stability of soil aggregates is enhanced not only by slimy
intermediate products of decay, but by more resistant portion, humus.
• Inorganic mineral transformation. The appearance in soil of ammonium compounds and
nitrates is a result of long series of biochemical transfer beginning with proteins and related
compounds. These successive changes are of vital importance to organically-grown vegetables
since plants absorb most of their nitrogen in ammonium and nitrate forms. Similarly,
production of sulfates is roughly analogous to biological simplification of nitrogen. Here again,
a complicated chain of enzymatic activities culminates in a simple soluble product, in this case
sulfate, the only important form used by organically-grown vegetables.
Other biologically instigated inorganic changes that may be helpful to organically-grown
vegetables are those relating to mineral elements such as iron and manganese. In well-drained
soils, these elements are oxidized by autotrophic organisms to their higher valent states, in
which forms their solubilities are very low at intermediate pH values. This keeps greater
portion of iron and manganese, even under fairly acid conditions, in insoluble and non-toxic
forms. If such oxidation did not occur, plant growth would be jeopardized because of toxic
quantities of these elements in solution.
80 Brady, N.C. 1985. The nature and properties of soils. 9 th Edition. Macmillan Publishing Company, 866 3 rd Avenue, New York, New York, USA. Pp250-
251.