Windbreaks/Shelter Belts
Windbreaks have long been used to lessen windspeed and consequently, evaporative
demand, and to reduce damage by wind and wind-driven particles like sand etc. Neem has
been found to be very effective in drier areas, particularly on sandy soil where sand blastings
and desiccation can effect crop establishment. Vegetative windbreaks have a good potential.
Shelter belts/afforestation with suitable tree species including A. indica can be very effective
in controlling deep and narrow gullies against soil erosion. Recently, three rows of neem
tree, 250-300 km long have been planted in West Africa to check the advance of Sahara
desert. Studies conducted at the "CARE28 Neem (Azadirchta indica) Windbreak Project" in
the Majia valley, Niger, showed a 20% increase in Pearlmillet grain yield in crops grown
between young (ca.5 years) windbreaks spaced 100m apart.
Studies carried out on the sheltering
efficiency of 2 shelterbelts of different
species, composition was compared as a
basis for determining the extent of effective
erosion control. The efficiency of both belts
decreased with increasing distance from the
belt. Efficiency very close to the belt was
higher in A. indica than eucalyptus. An
optimum spacing between shelterbelts of
200 m for eucalyptus and 140 m for A. indica
is recommended where these species form
the main crop in shelterbelt establishment.
Under arid conditions Muthana et al.3l
studied the effect of shelter belt plantations
involving important tree species including A.
indica.
These shelterbelts showed that the yield increased as distance from the shelterbelts
increased. Data on the consumptive water use was recorded and water use efficiency was
also calculated. Growth and survival counts have also been reported.
Properly designed windbreaks are reported to improve the environment for agriculture in
most afforestation programmes in Nigeria. Oboho and Nwoboshi3O have investigated the
effects on microclimate of windbreaks made up of 6 rows of trees - two rows of A. nilotica on
the windward side, three rows of A. indica in the middle, and one row of A. nilotica on the
leeward side. A properly designed windbreak can protect a field at least 10 times as long as
the height of the tallest trees. Thus, if the trees are 10 meters tall, crops up to 100 meters
away can be protected.