Agriculture Reference
In-Depth Information
Yield (tons/ha)
3
Field average
2
1
0
8h
9h
10h
0.5h
1h
2h
3h
4h
5h
6h
7h
Distance from windbreak
(h = height of trees)
FIGURE 7.8 Influence of windbreak protection on soybean yield at varying distances from the windbreak. Source: Data from
Baldwin and Johnston 1984.
pears, and grapes show yield increases from 10 to 37%,
subtropical fruits such as kiwi, oranges, and lemons show
yield increases up to 30% (as well as important gains in
fruit quality), and tropical fruits such as bananas show
yield gains of at least 15%, primarily due to a reduction
in lodging of the mature stems.
the primary crop, this technique offers considerable
flexibility to the farmer. Minimal time is lost and mini-
mal space is occupied by the barrier.
Sunflowers are frequently used as annual wind barri-
ers to improve crop conditions for tomatoes, broccoli,
lettuce, and other annual crops in windy areas of the
Salinas Valley of California, and corn is often used to
protect strawberry crops from abrasion of the leaves, fruit
damage, and reduction of the dispersal of pest mites in
coastal areas of central California. Yields of annual crops
such as snap beans and fresh market tomatoes have been
shown to be improved by as much as 30% with the use
of such barriers (Bilbro and Fryrear, 1988).
Crop plants themselves can also be planted to make
them more resistant to lodging and other forms of wind
damage. For crops that are able to produce adventitious
roots on the lower stem, deeper planting can help anchor
the plant more firmly in the ground. Cruciferous crops
such as Brussels sprouts, cabbage, and broccoli benefit
greatly when transplanted seedlings are buried deeply
enough to cover most of the stem below the cotyledons,
allowing the plant to form more roots as it develops.
Otherwise, the small seedling with a few leaves can be
whipped around like a kite on a string if it is too windy,
eventually breaking off at ground level. In windy areas of
Mexico, corn seed is often planted deeply in the base of
a furrow, so that as the plant develops, soil can be built
up around the base of the stem as a part of cultivation for
weed control. By the time the crop is almost fully devel-
oped, the corn plants appear to be planted on the top of
the rows, and as a result of their stronger anchoring in the
soil are much more resistant to the lodging that can occur
when convective thunderstorms create high-velocity
winds (Figure 7.9).
Planting Techniques
An alternative to permanent windbreaks made up of
trees or shrubs is the planting of annuals within the field
that work to protect the main crop from wind. Corn
( Zea mays ), sunflowers ( Helianthus annus ), and a range
of grain crops such as sorghum ( Sorghum bicolor ) and
pearl millet ( Pennisetum americanum ) are examples of
annual plants used for this purpose. Such annual barriers
have certain advantages over perennial woody shelter-
belts in that they are easier, faster, and cheaper to establish,
and may allow more flexibility in the farming opera-
tions. Like windbreaks, annual barrier plants reduce
wind speed, thus improving moisture and temperature
conditions for adjacent plants. They are usually planted
at the same time as the main crop, often as individual
rows interspersed among the main crop. Another tech-
nique is to plant the barrier plants (often rye) as a fall
cover crop and then to reduce this crop to alternating
strips in the spring by tilling when the main crop is
planted. Research has shown that barrier porosity of 40
to 50% has the best impact on crop yields, and that
plants need to be resistant to lodging, spaced according
to the needs of the associated crop and the local wind
conditions, and established early enough to give the
necessary protection. Because the planting of annual
windbreaks is incorporated into the process of planting
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