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Summary WIND PROTECTION
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- University Of The Freestate (UFS)
wind protection using windbreaks
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THEME 11: WIND PROTECTION11.1 INTRODUCTION
We all know that the environment is not optimal and must be changed
under certain circumstances, for example, a windy area needs to have
some type of windbreak to protect crops.
A windbreak is any structure that decreases the wind speed.
A shelterbelt is a row of trees planted for shelter.
Both can change the environment and this benefits crop growth.
Farmers have always used them.
The main purpose of using windbreaks is to conserve soil water
ET wind speed
Decrease wind => decrease ET and
increase in wind => increase ET.
ETpot α ↑wind speed
So if wind speed is low, then soil water is conserved.
It is difficult to predict effect of wind speed.
The advantage is that for low wind speed, seed germination is good,
because soil surface stays moist longer,
but plants grow quicker, roots & foliage is larger and this then
⇒ use of soil water more quickly.
This in turn can lead to water stress behind windbreak.
WUE ↑ behind windbreak and T: Es ↑
⇒↑ biomass, ↑ yield /unit water.
254
, Experimental results for Canadian wheat yields (t ha-1). Height of windbreak
is h.
Heavy snow Med. Snow
Distance (of sheltered zone) 0-15 h 15h-25 h 0-15 h 15h-25 h
Yield +1.82 +1.35 +1.61 +1.48
According to the above table, the highest yields for wheat were attained in
heavy snow in the zone 0 to 15 x height of the windbreak. For example, if
the windbreak was 2 m high, then the zone would measure 0 to 30 m.
Wheat yields were thus highest (+1.82) in the zone nearer to the
windbreak, although yields were still high (+1.35) in the 30 to 50 m zone
WUE of beans, rye, oats, potatoes, also ↑ with use of windbreaks in
studies in Poland.
Even under irrigation, windbreaks still influence plant water relations,
therefore it is the windbreak’s influence on soil and plant water relations
that is the critical factor.
Very complex relationships-
influenced by geometry, spacing, age, height, density of wind break.
11.2 WIND SPEED & TURBULENCE IN SHELTERBELT
Aim: to reduce force of wind.
Design is very difficult if to function properly.
Flow patterns very complex around barriers.
Effectiveness – depends on height, porosity, length.
↑ Height (h) => ↑ distance of effect up & downwind.
A thick barrier => shelter distance of 10-15 * h.
But an ↑ Porosity ≅ => influence 20-25 * h.
255
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