Wind - Agroecology: The Ecology of Sustainable Food Systems - page 95

Impermeable Windbreak

Wake zone

Quiet zone

Permeable Windbreak

Wake zone

Quiet zone

FIGURE 7.7 Wind profiles of a barrier windbreak and filter windbreak. A filter (permeable) windbreak reduces windspeed more
effectively than a barrier (impermeable) windbreak and does so over a greater distance. Adapted from McNaughton 1988 and Guyot 1989.

In an extensive review of research on the benefits of
windbreaks to field and forage crops around the world,
Kort (1988) found that most of these crops show better
yields when grown in fields with windbreaks, but that some
benefit more than others. A broad-leafed forage crop such
as alfalfa, with a high rate of transpirational water loss
in the wind, appears to benefit most from a windbreak, and
short-cycle grains such as spring wheat and oats benefit
the least. Kort's findings are presented in Table 7.1
In a review of the influence of windbreaks on vege-
table and specialty crops, Baldwin (1988) reports that
there is overwhelming evidence to support and illustrate
the positive benefits of wind shelter. Yield increases range
from 5 to 50% for a variety of crops including beans, sugar

beets, tomatoes, potatoes, melons, tobacco, berries, cacao,
coffee, cotton, rubber, and okra. Most benefits occur
within ten heights on the leeward side, with maximum
benefits seen between three and six heights. Benefits are
also seen within zero to three heights to windward. An
example of how the improved yield caused by a windbreak
varies with distance from the windbreak is shown for
soybeans in Figure 7.8. With this crop, peak benefit
was seen at four heights to the leeward; interestingly,
however, yields were reduced within a distance of one
height, presumably from either shading, root competition,
or allelopathy.
With vegetable and specialty crops, crop quality
improvement may be as important a benefit as increased
yield. Crop quality can be improved in a variety of ways,
including an increase in sugar content in crops such as
sugar beets and strawberries, reduced abrasion by wind-
blown sand on crops such as melons, and earlier ripening
for most crops. Since vegetable and specialty crops are
usually highly susceptible to wind damage and wind abra-
sion, improvements in crop quality are easily converted
into better economic return, which adds to the gains from
yield increases.
Windbreaks have also been shown to provide substan-
tial benefits in the production of orchard and vineyard
crops (Norton, 1988). Year-round protection is critical to
the survival and proper development of trees and vines.
Orchard microclimate modification in the form of a wind-
break can improve pollination and fruit set, in turn leading
to greater yields. Mechanical damage is also reduced,
improving fruit quality and economic gain. Proper wind-
break design and management can also reduce evapora-
tion, increase the flexibility of the application of pest
management materials, and even assist in frost manage-
ment. Wind-protected temperate fruits such as plums,

TABLE 7.1
Relative Impacts of Windbreaks on Yields of
Various Grains and Forage Crops

Yield Increase, in Percentage, Relative
to Fields without Barriers Crop

Alfalfa 99

Millet 44

Clover 25

Barley 25

Rice 24

Winter wheat 23

Rye 19

Mustard 13

Corn 12

Flax 11

Spring wheat 8

Oats 3

Source : Kort J. 1988. Agriculture, Ecosystems and Environment
22/23: 165-190.