Assessment of effects of two runoff control engineering practices on soil water and plant growth for afforestation in a semi-arid area after 10 years

Water is the primary constraint for vegetation development in the semi-arid area in the loess plateau of China. Afforestation aimed at runoff control in association with engineering practices have been considered an effective approach to improving the utilization of limited rainfall in the ecological restoration of wild lands and abandoned farmland in semi-arid areas in China. This research investigated the long-term effects of two adopted engineering measures on soil water content, total water consumption, and plant growth after having been applied in afforestation areas for 10 years. These engineering measures included: slope-separate flat terraces (SSFT) and cone-shape focused fluid pit (CFFP). The results indicated that the mean annual soil water deficit with SSFT on the forested site that originated from wild land was 6.7 mm with evapotranspiration of 419.66 mm while the mean annual soil water deficit from abandoned farmland with CFFP was 9.26 mm with evapotranspiration of 422.26 mm. The mean annual soil water deficit in the abandoned farmland site with SSFT was 15.60 mm with evapotranspiration of 428.60 mm. This research strongly suggested that the engineering runoff control practices in the study effectively reduced soil erosion, increased water storage, and eased the water demand of forest-grass vegetation at the beginning of afforestation, but over-consumption of soil water that may not have been replenished by the limited rainfall, could potentially cause the soil to dry-out. Consideration of soil water storage capability and plant water demand, with possibly a lower initial tree density, should be considered when designing engineering practices for regulating runoff water in afforestation.