ZIMSEC O Level Geography Notes:Agriculture:Factors influencing farming: Physical or Environmental factors
- These are critical for plant growth because each plant or crop type requires a minimum growing temperature.
- In temperate latitudes this is 6°C. Below this members of the grass family, including cereals, cannot grow.
- Growing Season is the number of days between the last frost of spring and first frost of autumn.
- Growing season varies by crop; Cotton needs 200, Spring Wheat needs 90.
- The mean annual rainfall for an area determines whether farming is likely to be based upon tree crops, grass, cereals or irrigation.
- Few crops can grow when there is less than 250mm a year.
- Seasonal distribution is more significant than annual total rainfall.
- Long steady periods of rain allow the water to soak into the soil.
- Short heavy downpours lead to surface runoff and soil erosion.
- Growth is controlled by decrease in temperature at height.
- In Britain few grasses (including hay) can produce commercial yields above 300m.
- In warmer latitudes wheat can ripen at 3000m.
- Wind increases evapotranspiration rate.
- This allows the soil to dry out and to become vulnerable to erosion.
- Some winds are beneficial to agriculture, for example Chinook.
- Chinook winds are a warm dry wind which blows down the east side of the Rocky Mountains in Canada at the end of winter.
- This melts snow on the prairies, lengthening the growing season.
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