64
Despite several benefits, the use of terraces has decreased in recent years for
several reasons: costly to construct and maintain, and more difficult to farm, par-
ticularly with large equipment. The construction of terraces may result in soil fertil-
ity problems because topsoil is buried or moved downslope. Terraces are also
subject to failure during large, intensive rainfall events, resulting in considerable
damage that is costly to repair.
Conservation bench terraces (CBTs) or Zingg terraces are a type of rainfall mul-
tiplier. They use part of the land surface as a catchment to provide runoff onto level
terraces on which crops are grown. The method is particularly appropriate for large-
scale mechanized farming such as the wheat/sorghum farmlands in the southwest of
the United States of America, where this method was pioneered by Zingg in 1955
(Rockström 2000 ; WOCAT 2007 ; Al Ali et al. 2008 ).
4.2.7 Runoff Strips and Contour Furrows
This technique is applied on gentle slopes and is used to support field crops in drier
environments (such as barley in the badia) where production is usually risky or has
low yields. The farm is divided into strips following contour lines where one strip is
used as a catchment and the strip downstream is cropped. The cropped strip should
not be too wide (1–3 m), and the catchment width should be determined with a view
to providing the required runoff water to the cropped area. The same cropped strips
are cultivated every year (Fig. 9 a, b). Clearing and compaction may be implemented
to improve runoff (Oweis et al. 2001 ). Contour furrows are variations on the theme
of surface manipulation that require less soil movement than conservation bench
terraces and are more likely to be used by small farmers, or in lower rainfall areas.
Cropping is usually intermittent on strips or in rows with the catchment area left
fallow. The principle is the same as conservation bench terraces, that is, to collect
runoff from the catchment to improve soil moisture in the cropped area.
Fig. 9 Contour runoff strips (a) and contour furrows (b) (Source: http://www.icarda.org))
A. Yazar and A. Ali