Agriculture Reference
In-Depth Information
especially with small trees like guavas that are pruned, travelling sprinkler
systems can be used successfully. Sprinkler irrigation does not require level
land, uses little labour and improves soil structure; water volumes can be
regulated; it wastes less water than surface irrigation, but it requires more
pump power, and it is more expensive to install than furrow or basin irrigation.
Sprinkler systems sometimes interfere with farm machinery operations.
Sub-irrigation
Sub-irrigation can be used in very permeable soils like the coralline soils of
Florida. Water is pumped into the drainage system and this makes the water
table rise, so that the root zone becomes saturated.
Irrigation control
An excess of water or drought af ects plant functions and thus tree yields.
Drought will reduce water availability and consequently nutrient uptake; the
stomata will close and less carbon dioxide is available for photosynthesis. With
fewer sugars produced by photosynthesis, translocation of carbohydrates
will be reduced, as well as hormonal transport from the roots to the canopy.
Excess water will create a shortage of oxygen in the soil, leading to anaerobic
conditions, which are toxic and reduce root activity and growth, often leading
to root death. Root death results in reduced water absorption and hormone
production by the roots and more pathogenic activity, which can cause root
rot and fi nally tree death.
Irrigation has to meet the plant's needs, which depend on the species, the
tree size and age, foliar density and the climatic conditions. Any irrigation
plan has to take into account the water retention of the soil, the rate of water
penetration, the distribution and depth of the root system and the amount
of water the crop uses. The amount of water to apply will depend on soil
structure and texture, and depth of the root system. Irrigation must take into
account the depth that water should reach in the soil profi le, and this is based
upon root distribution and where the majority of roots are active. During tree
growth, root distribution shifts from the roots being concentrated near the
surface to becoming deeper in distribution. If irrigation is too shallow, the root
system will also remain shallow, forcing more frequent irrigation. If irrigation
is too abundant, water will pass below the main root zone and take with it
many nutrients needed for plant growth.
After heavy rain or irrigation, the soil is saturated and begins to drain
under gravity, and it reaches a point called fi eld capacity (FC) about 24 h
later; that water is held by the soil against gravity. The potential (force) that
this water is held at is about 7 kPa (7 cbars, ~0.07 atmospheres) and it is
readily available for the plants. At FC, there is more water in a heavy than in
a light soil. If no further water is received by the soil, it will start to dry out,
