An
inflorescence of Pitcairnia imbricata growing epiphytically
near the crater of Volcan Mombacho, Nicaragua. |
The physical
condition of a soil can be defined as soil tilth; that is the bulk density,
porosity, structure, and aggregate characteristics as they relate to water
movement, nutrient retention, and stimulation of microbial and microfauna
populations. Soil tilth is important because it affects all processes
occurring in the soil matrix. A healthy rhizosphere (the root zone) is
the key to a healthy plant.
Soil tilth
is often inversely related to soil strength. On a construction site structural
fill is often brought in and compacted to withstand the load of the structures
to be built on top of the fill. The result of this action is that 90%
to 95% of all the voids in the soil have been removed and dense, compacted
zones have formed within the soil profile. That leaves very little space
for water and oxygen (and roots) to move through the soil resulting in
a soil medium with poor tilth and aggregate characteristics; a very poor
habitat for most plants. Structural soil also contains a minimum of organic
matter. These conditions are common for many landscape installations on
new construction sites. Also, areas that have vehicles constantly driving
over or even foot traffic can end up becoming compacted to a point where
plants will not grow well because of the resulting surface crust and possible
underlying compaction.
Caralluma
acutangula (syn. C. retrospicens) may be the largest of the stapeliads.
This plant was photographed in Orman Botanic Garden, Giza, Egypt.
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Two of the
most traditional practices in farming and horticulture are composting
and the use of mulch as a topdressing. Mulch can either be freshly chipped
plant or tree material or what is known as “green mulch” which
is growing short lived plants for the nutrients that they accumulate and
release into the soil when the plants are either cut down or die naturally.
For millennia, green mulching has been utilized to return nutrients to
the soil thereby improving the microflora and fauna of the rhizosphere.
The practice of mulching imparts many advantages to soil tilth. Organic
residue decreases water loss from the soil and acts as a thermal barrier
to heat exchange thereby keeping the soil cooler, increases water infiltration,
reduces erosion, provides a more stable soil microclimate for biological
activity, a supply of nutrients for microbial populations, and impedes
soil compaction. Weeds are inhibited from growing by simply being excluded
from the sunlight that is blocked out by the mulch. Under certain circumstances
freshly chipped tree mulch can be used for cold protection since the active
bacteria generate enough heat to warm the ground and underlying roots.
Composting is the simple practice of utilizing natural fungal and bacterial
processes to create soil out of organic matter or residue. This process
is actually what occurs to mulch as it breaks down. Another major benefit
of incorporating the use of mulch and/or compost in horticultural operations
is the potential removal of atmospheric CO2 by carbon sequestration in
vegetation and storage in biomass and soil.
The articles
in this section will give you a glimpse into these natural processes and
how they should be a major component of any horticultural Integrated Pest
Management or Plant Health Care program.
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Different
color forms of Caladium bicolor found on Volcan Mombacho, Nicaragua. |
Tithonia
diversifolia, Tree Marigold has been shown to be a high quality
nutrient resource of phosphorous when used as a green mulch
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Natural
nutrient recycling on the forest floor in Taman Negara, Malaysia
(click for larger view)
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Lignum-vitae,
Guaiacum sanctum from Grand Bahama Island.
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Aechmea
gamosepala, a small epiphytic bromeliad from Brazil. |
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