Download Part II The Soil Community The soil community is made up of soil

Part II
The Soil Community
The soil community is made up of soil texture, and organic parts of the soil ecosystem.
Detritus, soil organisms, Humus, and Topsoil
The dead leaves, roots, and other detritus accumulated on and in the soil support a complex food
web, including numerous species of microorganisms.
Humus is the residue of partly decomposed organic matter which is not decomposed by the
digestive enzymes of decomposers. It is characterized by the black or dark brown spongy material.
Humus is formed as a result of composting. Composting is the process of fostering the decay of
organic wastes under more or less controlled conditions.
Soil Structure
Soil structure refers to the arrangement of soil particles. A loose soil structure is ideal for infiltration,
aeration, and workability. A humus rich soil is clumpy, loose and is best for supporting plant growth.
Decomposers and detritus feeders play an important role in maintaining the best soil structure for
the growth of the plants. For example: The earthworms ingest important mineral materials along
with the detritus. These glue together and are expelled from their body as castings. These
excrements are relatively stable clumps of inorganic particles plus humus.
The development of topsoil from the sub soil or parent soil takes hundreds of year , so it is very
important to preserve it.
There are some important interactions between plants and soil biota>
 a symbiotic relationship between the roots of some plants and fungi mycorrhizae. The
fungus penetrate the detritus, absorb the nutrients and transfers them to the plant.
 Symbiotic association of nitrogen fixing bacteria and the roots of legume plants
Soil Enrichment or Mineralization
The loss of humus and and the consequent collapse of top soil is referred to as the mineralization of
soil. As a result of this only the gritty mineral content-sand, silt or clay is left without the humus.
Mineralization of soil happens as the soil’s humus content declines and the clumpy aggregate
structure created by soil particles glued together with the humus breaks down. Water and nutrient
holding capacities, infiltration and aeration decline correspondingly.
Mineralized soils can be revitalized through generous additions of compost or other organic matter.
Soil Degradation
When key soil attributes required for plant growth or for other ecosystem services deteriorate over
time, the soil is considered degraded.
GLASOD- is the Global Assessment of Soil Degradation map prepared between 1987 and 1990.
World economic forum declared in 2002 that the GLASOD data are suspect and certainly out of date.
Burkina Faso
Erosion
The process of soil and humus particles being picked up and carried away by water or wind is known
as erosion. Erosion follows anytime soil is bared and exposed to the elements. The removal may be
slow or sudden.
Splash, Sheet and Gully Erosion
When falling raindrops breaks up the clumpy structure of the topsoil, the erosion is known as splash
erosion.
The dislodged particles by splash erosion wash into spaces between other aggregates, clogging the
pores and thereby decreasing infiltration and aeration. The decreased infiltration results in more run
off and carrying away the fine particles from the surface. This phenomenon is known as sheet
erosion.
As further runoff occurs, the water converges into streams, which have greater volume, velocity, and
energy and hence greater to pick up and remove soil. This results into gully erosion.
splash
erosion
sheet
erosion
gully
erosion
Wind and water erosion always involve the differential removal of soil particles. The lighter particles
are the first to be carried away, while the larger particles stay behind leaving the soil sandy, stony
and finally rocky. This leads to desert pavement.
Homework
Due in next class
1. What are the main things that plant roots must obtain from the soil? Name and
describe a process that can keep plants from obtaining the amounts of each of these
things they need for survival.
2. Describe, in terms of both content and pgysical structure, the soil environment that
will best fulfill the needs of plants.
3. State and define the relationships among humus, detritus, and soil organisms.
Describe the role each of these factors plays in creating a soil favorable to plants.
4. What is meant by mineralization? What causes it? What are its consequences for soil?
5. How does a vegetative cover protect and nurture the soil in a way that supports a
plant’s growth?
6. What is the impact of water and wind on bare soil? Define and describe the process of
erosion in detail.
Expect a quiz in next class on the above topic