Cover Image
close this bookConsultancy report on first extension staff training in horticulture. (1998)
close this folderBasic understanding of horticulture
close this folderReview of effects of physical factors of the environment on horticultural crops
View the document(introduction...)
View the documentTemperature
View the documentLight
View the documentRainfall
View the documentWind
View the documentSoils
View the documentBiotic factors

(introduction...)

The factors that were lectures and discussed included:

Abiotic factors.

Weather and climate. Each horticultural crop has certain climatic requirements. Unfavourable weather and climatic conditions produce a stress. Components of weather and climate include:

Temperature

Temperature influences all physiological activities by controlling

- Phytosynthesis
- Respiration
- Enzymic activity
- Organic matter decomposition
- Microbial growth and development
- Flowering
- Pollen viability
- Fruit set
- Hormonal balance
- Rate of maturation
- Rate of senescence
- Quality
- Yield
- Shelf life
- Harvest duration
- Vernalization of biennials
- Seed germination
- Root development
- Water and nutrient absorption
- Pests and disease occurrence

Extremes of temperatures

- Frost damage at 0 °C
- Chilling injury 0 - 2 °C or lower but above freezing point.

Light

Photosynthesis uses light. Light intensity and duration are important for crop growth and development. Low light causes plants to be spindly, small leaves, bud blades, poor pollination and poor fruit quality.

Plants differ in light requirements. An example was given for horticultural crops.

- Light affects pollen viability and fruit set.
- Certain seed require light to break dormancy e.g. lettuce.
- Some horticultural crops are sensitive to protoperiod.
Examples were given.
- Short day plants flower rapidly when the days get shorter.
- Long day plants flower when days are longer.
- Short days hasten tuber formation in potatoes, root enlargement in sweet potatoes.
- Long days and high temperatures keep plants in staminate (phase) in Cucurbits.

Light intensity and duration are important for crop growth and development:

- Photosynthesis uses light

- Low light causes plants to be long and this (spindly), small leaves, bud blades, poor pollination and poor fruit quality.

- Photosynthesis is stopped at high light intensity depending on species.

- Plants differ in light requirements.

- Certain seeds require light and break dormancy.

- Some plants are sensitive to photoperiod or day length.

- Short day plants flower rapidly when the days get shorter.

- Long day plants flower when days are longer.

- Short days hasten tuber formation in potato, root enlargement in sweet potatoes.

- Long days and high temps keep plants in staminate (phase) in cucurbits.

Rainfall

- Water comprises more than 80% of the living plants, providing structural integrity for the plant.
- Rainfall natural source of water.
- Water is a major determinant of crop productivity and quality.
- Required in large quantities for plant growth than any other of the growth factor.
- Solvent for nutrients, minerals, etc..
- Water improves the germination of seeds.
- Essential to establish transplanted seedlings.
- Essential for faster establishment of the crop.
- Essential to facilitate application and distribution of fertilizers and pesticides.
- Provides protection in cold temp (frost).
- Facilitates harvesting of underground crops in dry soils.
- Cooling of the leaves during respiration.
- All crops have moisture range at which crop response is optimum. Examples were given.
- Crop differ in their tolerance of continuous wet conditions.
- Hydrophytes - aquatic.
- Mesophytes - most common of terrestrial plants.
- Xerophytes - can endure long period.
- Root systems affect the amount of water uptake..

Negative aspects of rainfall

- Waterlogging
- Drought
- Storms

Wind

- A slight wind is necessary to replenish Carbondioxide near plant surface.

- Wind carries oxygen away from the plant.

- Less wind, less evaporation, less water requirement.

- Wind can be a limiting factor in vegetables production where strong winds (a ver. Wind speed of 7.2 km/hr) occur e.g. Typhoons (wind speed of 60 km/hr)

- Use of windbreaks (shelter belts) minimize damage, a relatively slow wind.

- Dusting plants - affects rate of photosynthesis of coating the photosynthesizing leaves and green stem.

- May blow away pests and diseases thus carry pests to or away from crop.

- May interfere with farm operations e.g. spraying, etc..

- May aid in pollination.

Soils

Horticultural crops are adapted to a wide range of soil types at times with specific requirements. Soils particle types include clay 0.002 mm or less, silt 0.05 to 0.002 mm and sand 0.05 mm or above. Aspects of soil fertility and soil pH were discussed. Organic and inorganic fertilizers as source of nutrients were also discussed.

Biotic factors

- Insect pests
- Bacteria
- Fungi
- Nematodes
- Viruses
- Weeds
- Domestic and wild animals