Is Rainfall Becoming Less Effective?
HOEDSPRUIT (Kruger Times)- Two-thirds of South Africa receives less than 500mm of rain a year, and farmers say that the annual rainfall is declining.
The veld is also thought to be becoming less productive each year, possibly due to climatic factors. Another explanation is that rainfall is becoming less effective.
Effective rainfall is the amount of rainwater available to plants for growth, and produces greener grass and new growth. Rain is usually only effective when it has rained over a period of time and in successive rainfalls.
Grass, with shallow fine roots in the topsoil, is a good indicator of effective rainfall. Grasses compete with trees and shrubs for rainwater and must obtain water before it is absorbed into the soil or runs off. Water is absorbed through both leaves and roots, but most absorption occurs in the top 10cm of soil where the grass roots grow. Minerals are taken up with the water and are used for new growth and green leaves.
The first rainfall in September is seldom effective and can actually cause moisture stress. First rainfalls often evaporate, soak into the soil too fast or are absorbed by soil clumps.
A good early rainfall may produce enough moisture for grass to absorb, but is often followed by a few weeks of hot, dry weather. The grass is ‘switched on’ to growth after the first rainfall, and uses the first boost of growth to replenish root reserves depleted over winter.
At this point the plant is very sensitive to overgrazing by herbivores, which are keen to switch from dry, hard grass stalks to new growth. If the plants are grazed and lose part of their photosynthetic engine at this stage, they draw again on the root reserves. This drains the plant if successive rains do not then follow the first rainfall, and the grass is weakened before the grazing season begins.
This means that rainfall is only really effective when growth can be sustained. Effective rainfall is not only linked to how much rain falls and for how long, but also to how much rain soaks into the soil and becomes available to the plants.
Capped soils have a reduced ability to make rain effective, as most water evaporates or runs off. A healthy soil with a good structure retains more moisture and is favourable for plant growth. Plant root action, temperature and a good air to moisture balance will help grass plants survive the first grazing after the rain, making the rainfall more effective.
Pasture management for a healthy soil will increase the productivity of the veld and make the rain that falls more effective.
by Colleen Todd; edited by Melissa Wray, Kruger Times
The veld is also thought to be becoming less productive each year, possibly due to climatic factors. Another explanation is that rainfall is becoming less effective.
Effective rainfall is the amount of rainwater available to plants for growth, and produces greener grass and new growth. Rain is usually only effective when it has rained over a period of time and in successive rainfalls.
Grass, with shallow fine roots in the topsoil, is a good indicator of effective rainfall. Grasses compete with trees and shrubs for rainwater and must obtain water before it is absorbed into the soil or runs off. Water is absorbed through both leaves and roots, but most absorption occurs in the top 10cm of soil where the grass roots grow. Minerals are taken up with the water and are used for new growth and green leaves.
The first rainfall in September is seldom effective and can actually cause moisture stress. First rainfalls often evaporate, soak into the soil too fast or are absorbed by soil clumps.
A good early rainfall may produce enough moisture for grass to absorb, but is often followed by a few weeks of hot, dry weather. The grass is ‘switched on’ to growth after the first rainfall, and uses the first boost of growth to replenish root reserves depleted over winter.
At this point the plant is very sensitive to overgrazing by herbivores, which are keen to switch from dry, hard grass stalks to new growth. If the plants are grazed and lose part of their photosynthetic engine at this stage, they draw again on the root reserves. This drains the plant if successive rains do not then follow the first rainfall, and the grass is weakened before the grazing season begins.
This means that rainfall is only really effective when growth can be sustained. Effective rainfall is not only linked to how much rain falls and for how long, but also to how much rain soaks into the soil and becomes available to the plants.
Capped soils have a reduced ability to make rain effective, as most water evaporates or runs off. A healthy soil with a good structure retains more moisture and is favourable for plant growth. Plant root action, temperature and a good air to moisture balance will help grass plants survive the first grazing after the rain, making the rainfall more effective.
Pasture management for a healthy soil will increase the productivity of the veld and make the rain that falls more effective.
by Colleen Todd; edited by Melissa Wray, Kruger Times
Labels: climate
posted by Kruger2Canyons.com at
Sunday, October 24, 2004
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