These trials were undertaken in Karnataka State in India -- a semi arid zone where moisture stress is considerable. Tree planting in contour "V" ditches optimizes the soil moisture regime for individual trees. "V" ditches are 100+ cm wide and 50 cm deep.
Vetiver hedgerows planted on the contour will behave in the same way by holding back rainfall runoff and spreading the available water evenly along the hedgerow. Trees should be planted 30 to 50 cm from the hedgerow on the upside. They will then get full advantage of the water spreading impact of the hedgerows as well as the benefit of trapped nutrients.
In the histograms below the survival and growth rates of different species are compared using three different planting systems: pits (cross section 50x30 cm), contour trenches (cross section 50x 50 cm), and contour "V" ditches (100 cm wide and 50 cm deep). All three are costly to construct compared to using vetiver hedgerows. Once silted up rainfall runoff will not be trapped and will no longer benefit the trees. With vetiver hedgerows the longterm benefits in moisture conservation for tree growth will be significant.
DS= Dalbergia sissoo, AI= Azadirachta indica, AA= Acacia auriculiforum, SJ= Syzgium jambolana, LL= Leuceana leucocephala, CS= Casia siamea, AM= Aegle marmeios, TI= Tamarindus indica, PE= Phylanthus embilica
