Geoscience Reference
In-Depth Information
mean to stay here in this humus. It was of interest to me that the principle linguistic
root of humus was kept in his exclamation: a signifi cant proportion of the mass of
the stove was formed by organic matter. On the other hand, had it been soil humus,
I would not have had to tolerate its stench that fi lled every room in the bungalow.
That soil humus does not stink is one of its many positive features. The experi-
enced farmer recognizes the quality of his soil after he wets and stirs the soil between
his fi ngers and merely sniffs its aroma. Soil humus improves soils rather than
belonging to materials that depreciate them. With the degree of soil improvement
depending on the characteristics of humus, farmers and soil scientists maintain their
sniffi ng ability to diagnose aromas into an array of humus qualities ranging from
mediocre to top notch. Soils rich in high-quality humus are very fertile and have
many properties useful for plants and for many factors of the environment that
include hydrology, landscape stability, and air quality. No matter where a person
lives within a local environment of any continent - on a farm, in a small village, or
in a huge metropolitan region far from a farm - the aroma from a moist fertile soil
never fails to stimulate the pleasant feelings and thoughts of life.
5.3.2
Humifi cation
As we mentioned already above, the transformation of all organic matter into humus
is called humifi cation. Sources for this process are the remnants of plants originally
formed by photosynthesis like leaves, needles, plant stems, branches, and trunks of
trees, everything that grew above the surface and fell on the surface after dying off.
Added to them are organic wastes and sewage from human activities. From the
broad beginning of agriculture about 8,000-5,000 years ago, manuring soils with
dung or composted waste was a very important practice for improving and sustain-
ing soil fertility. Ancient Greek and Roman authors described the importance of
composts. For example, the essay
De Agri Cultura
(About Agriculture) was a farm-
er's manual for good day-to-day management and purifi cation of a farm written by
M. Porcius Cato (160 BC). But it was more than hundred years later when Marcus
Terentius Varro discussed much greater details including the procedure on how to
reach a good-quality compost in his
Rerum Rusticarum Libri Tres
(Agriculture
Topics in Three Topics).
The great majority of all plant remnants lying dead on the soil surface were
drawn into the soil during humifi cation with virtually none of them left on the sur-
face. In addition to these “top” materials, organic bits and pieces consisting of
decayed plant and tree roots, dead fungi growing originally on the roots, dead
microorganisms, and dead soil fauna were all involved in the humifi cation process
occurring below the soil surface. Groups of living micro- and macroorganisms
attacked all of those organic substances with each group specialized to decompose
certain types of waste characterized by their composition of peculiar organic com-
pounds. For example, fungi are the main group decomposing wood that is always
rich in lignin, while the remains of cultivated plants with lots of cellulose are
