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Posted by
Maendeleo Vijijini
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Despite the benefits of greenhouse technology, most farmers face numerous challenges. They include:
TEMPERATURE AND HUMIDITY
Many
farmers fail to get good profits from greenhouse crops because they
cannot manage the two important factors that determine plant growth and
productivity. Greenhouse temperatures below 13 degrees Celsius and above
30 degrees Celsius in the case of dry air or higher than 30 to 35
degrees Celsius in cases of high air humidity affect growth and
productivity of most crops. The optimal temperatures for production of
greenhouse tomatoes, pepper and eggplant should be 15 to 30 degrees
Celsius and not beyond 35 degrees Celsius.
The
temperatures should be maintained at around 16 to 30 degrees Celsius
during the day and 13 to 18 degrees Celsius during the night.
Some
tomato farmers close the greenhouses the whole day without ventilation
resulting in excessively high temperatures beyond 40 degrees Celsius
that lead to reduced performance of the crops. Generally, small-scale
greenhouses are prone to overheating when the sun is too hot.
Farmers
should, therefore, open the doors and sides of the greenhouse from 8am
to 5pm for ventilation and close them at night to reduce heat loss.
Greenhouses with only insect nets on the walls are unsuitable for areas
with low temperatures like the highlands of Kericho, Mau Narok, Molo and
Mt Kenya regions but may have positive effects in hot and warm areas
such as Mombasa, Kitui, Kisumu, Machakos and Garissa. Ideally, farmers
should have a thermometer for measuring temperature inside the
greenhouse for effective management.
High relative
humidity resulting from crop transpiration, water evaporation from the
humid soil or other growing media and condensation of water vapour on
the different greenhouse surfaces is another challenge.
Relative
humidity above 80 per cent coupled with high temperatures increases
incidences of bacterial and fungal diseases like bacterial wilt and
botrytis (gray mold) while greenhouse conditions with relative humidity
below 60 per cent and high temperatures create favourable micro-climate
for rapid multiplication and development of mites and insect pests.
Humidity
in the greenhouse should, therefore, be regulated by ensuring adequate
ventilation, maintaining high temperatures at night, using plastic
mulching on planting beds and avoid wetting of the greenhouse floor.
LOSS OF SOIL FERTILITY
This
is a common problem as most farmers plant one crop continuously without
rotation. This can be overcome by rotating crops, for example growing
onions or melons, pepper or eggplant after tomatoes and the use of both
organic and inorganic fertilisers to replenish soil fertility.
Farmers
can also replace greenhouse soil by bringing quality soil from outside.
Adopt the technology of growing crops in pots or soilless cultures. The
soils when used continuously with same crop will have a buildup of
diseases, especially bacterial wilt, bacterial canker, fusarium and
verticilium wilts.
Greenhouse farmers are, therefore,
encouraged to treat the soil by sterilisation, solarisation or
fumigation using fumigants such as Dazomet, Metam Sodium and Chloroptin.
Greenhouses get contaminated by people visiting the
structures or by use of infected planting material, water and farm
tools. Have a foodbath at the entry.
LACK OF QUALITY WATER SOURCES
Many
parts of the country are deficient of good water sources and rivers or
boreholes may also be absent. In addition, available water could be
saline, chlorinated or contaminated with diseases like bacterial wilt,
hence it is of poor quality.
Contaminated water is
common in areas where farmers in sources of water plant crops like
potatoes, tomatoes and water flowing downstream is collected by farmers
for greenhouse farming. This introduces bacterial wilt in greenhouse
tomato.
PESTS AND DISEASE
Management
of insect pests and diseases is the biggest challenge in greenhouse
farming. This depends on the type of the crops that are planted.
However, generally, pathogens and insects can be established in a
greenhouse very fast. They are very difficult if not impossible to get
rid of effectively. For greenhouses that are covered with plastic, the
use of ultraviolet-absorbing plastics can reduce insect problems.
Dr Samuel Nyalala and Carol Mutua, Department of Crops, Horticulture and Soils, Egerton University.
SOURCE - NMG
SOURCE - NMG
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