Construction of tied ridges has been found to result in striking yield increases for cotton, maize, cowpeas, millet and sorghum in the semi-arid tropical areas of Africa. This two year study compared tied ridges to simple contour ridges, quantifying their effects on the soil water regime, crop water use, and growth patterns of cowpeas (Vigna unguiculata) in Burkina Faso's Sudan Savanna. Ridges are tied by constructing smaller perpendicular cross ridges every few meters. In order to ensure that heavy rains do not wash out the main ridges, the cross ridges are never constructed as high as primary ridges. Crops are planted along the main ridges. Annual rainfall was 573 and 792 mm in 1985 and 1986 respectively.
Experiments conducted in sandy loam topsoil with a sandy clay subsoil suggest that tied ridges may present an alternative for semi-arid region farmers faced with unpredictable rains. In ridges manually tied with daba hand hoes, soil water content increased by an average of 30.5 and 24.6 mm per week in 1985 and '86 respectively over simple ridges. Root growth was increased by tied ridging. The tied ridges showed a higher level of vegetative growth which was positively linked to increased water availability during rainless growing season periods. Grain yields were 51% higher for tied ridges in 1985, a relatively dry year, but not significantly different in 1986, a high rainfall year.
However, the study also showed that waterlogging-induced plant
stress is more likely to occur in cowpeas planted with tied ridging
in years of above average rainfall. Cowpeas planted in both ridging
systems during 1986 showed signs of waterlogging stress but, because
the rains did not take place during the sensitive flowering and
pod formation phases, grain yields were unaffected. It should
be noted that cowpeas are particularly sensitive to waterlogging.