Plant-Soil Interactions and Desertification: A Case Study in the Northern Negev, Israel

The impact of grazing, tilling, soil movement, among others on ecosystem health is often examined in well-defined separate experimental plots and protocols. The purpose of this project was identification of the mechanisms of soil degradation and rehabilitation in drylands. We analyzed the gradual changes in biotic and soil characteristics at the interface between strongly degraded and conserved arid shrubland restored by 20 years of conservation grazing. We defined a soil transect of 60 m crossing the border between conserved and long term degraded shrubland. Soil moisture content, water infiltration, soil organic matter (SOM), soil nitrate content, and biological activity (germination frequency, biomass productivity, patch frequency, and insect activity) were determined in equally spaced plots along the degradation gradient. Productivity expressed by the amount of herbaceous above ground biomass at the end of the growing season was one third in the degraded area compared to the conserved area. This is caused by reduced germination rates and poorer seedling growth due to lower nitrate and soil moisture content in the degraded soil. Biological productivity was enhanced in the conserved area by exponentially increasing density of perennials and shrub patches. Our results indicate that severe depletion of SOM is a leading cause for long-term soil degradation in drylands with the sparse annual vegetation incapable of restoring the SOM pool.