Soil erosion control (soil conservation) and water conservation are closely linked. In the past we have treated them under one heading. The impact of the effects of climate change on farm water supplies and the adequacy of sufficient soil moisture for plant growth is becoming critical. Rainfall events are tending to be fewer but more extreme, resulting in increased flooding and rainfall loss to the farm and longer periods between rainfall events when soil moisture is not replenished. Related to this is the diminishing volume of ground water that effects many aspects of farm water requirements from irrigation to watering of livestock.
Redistribution of rainfall runoff – Vetiver hedgerows as used for erosion control will slow down run off spreading it behind the hedge, thus recombining the concentrated flows resulting from soil rills. Concentrated flows reduce the rainfall runoff distribution over a crop field resulting in lower and patchy soil moisture content and increased crop stress. The combined flows, that occur at the upslope face of the hedgerow, seep evenly through the hedge barrier and move with better distribution over the down slope land area until such time increased velocity and water concentration occurs – the trick is to establish a hedge at that point to slow down and respread the water runoff. As a rule of thumb the placement of another hedge is generally at a 2m Vertical Interval below the hedge above it. Soil moisture is often improved to the extent that the wilting point of a plant under drought stress can be extended by 10 days or more – often the difference between a good crop or a total failure! Soil moisture is an essential component of improving the performance of soil macro and micro fauna/flora the enhancement of soil fertility. Vetiver hedgerows will often reduce rainfall runoff by as much as 70% – especially important where rainfall events are few and far between.
Use of Vetiver Grass for Soil and Water Conservation in Nigeria NIG_soil con.pdf (vetiver.org)
Ground water – Vetiver hedgerows have been proven to increase ground water recharge by as much as 20%. This is because vetiver’s deep penetrating roots open up infiltration pathways for the water passing through the hedge as well as creating better distribution of slowed down rainwater. This is a very low cost and effective way to recharge water tables. There are many examples from the field of this. In Ethiopia, vetiver protected farmland result in the rehabilitation of dried-up wetlands, renewal of annual spring flows, recharge of pond water, and permanent domestic well water.
Vetiver Potential for Increasing Groundwater Recharge – Thailand Microsoft Word – DAS01 Boonma Deesaen#153875.doc (vetiver.org)