Effects of rainwater harvesting on plant growth, soil water dynamics and herbaceous biomass during rehabilitation of degraded hills in Rajasthan, India

Degraded hills can be restored by afforestation and conserving soil and water through rainwater harvesting. Three slope categories viz. <10%, 10-20% and >20% of a degraded hill were treated with rainwater harvesting (RWH) structures: Contour trench (CT), Gradonie (GD), Box trench (BT) and V-ditch (VD) including a control with a view to rehabilitate it by conserving and minimizing gradient in soil water and nutrients. Soil water content (SWC), height and collar diameter of Acacia catechu, Azadirachta indicia, Emblica officinalis, Holoptelia integrifolia and Zyziphus mauritiana planted in August 2005, herbaceous biomass and photosynthetically active radiation (PAR) interceptions by tree, vegetation and tree-vegetation combine (PARintT/V/C) were monitored for suitability of RWH devices and tree species in rehabilitation. SWC decreased from December to June and it was linearly related to rainfall and vegetation height. PARint by tree, vegetation, and tree-vegetation combine were 30.0%, 54.6% and 84.6%, respectively and helped conserve soil water. SWC, plant and vegetation growth and PARintT were lowest (P < 0.05), whereas herbaceous biomass and PARintV were highest in 10-20% slope. Vegetation height and SWC were linearly related to biomass indicating improvement in micro-climate and herbaceous growth. Highest SWC in <10% slope promoted plant growth and mean annual increment (MAI) in height and collar diameter, which enhanced PARintT and PARintC. These variables were highest in CT/BT treatments and lowest in control plots. Characteristic root distribution of Acacia catechu and A. indica promoted growth in V-ditch, whereas E. officinalis, Z. mauritiana and H. integrefolia performed best in CT treatment. RWH enhanced herbaceous biomass between 22.4% and 60.7% over control. Conclusively, VD/GD structures found best for growth of herbaceous vegetation as well as A. catechu and A. indica plants, whereas CT/BT structures favoured growth of other tree species. Rainfall influenced SWC, but RWH helped conserve soil and water, promoted plantation and herbaceous growth and facilitated restoration process, and may be promoted to restore degrading lands.