Soil restoration increases soil health across global drylands: a meta-analysis.
Abstract
Soil degradation is one of the greatest environmental issues our planet faces today, with over 33% of Earth's soils currently degraded. Drylands are especially vulnerable to soil degradation given their history of intensive land use and desertification. Active soil restoration has been identified as a leading strategy to combat soil degradation and promote ecosystem recovery. However, soil-based dryland restoration techniques have shown varying success, potentially due to a lack of understanding of the ecological contexts in which soil-based treatments are most beneficial. To improve our understanding of how to best use active soil restoration to restore degraded drylands, we conducted a global meta-analysis of soil treatment effectiveness at improving soil health across varying environmental gradients. The soil health metrics we analysed were aggregate stability, bulk density, soil moisture, soil organic carbon (SOC), soil nitrogen, mycorrhizal colonization and basal respiration. For this meta-analysis we collected 155 publications, yielding 1403 unique studies spanning six continents. We found that overall, soil restoration had a beneficial effect on all measures of soil health ranging from a +11% increase in bulk density (inverse) to a +6967% increase in mycorrhizal colonization. Aridity and soil texture greatly influenced restoration effectiveness for certain soil health metrics. Specifically, for soil carbon and nitrogen, restoration was found to be most effective in arid, fine-textured soils and mesic, coarse-textured soils. Additionally, we found that organic amendments were most effective at increasing SOC, while fungi inoculation was most effective at increasing mycorrhizal colonization. Synthesis and applications: Our findings indicate that active soil restoration is an effective tool for increasing soil health and provide information on optimal treatments and site conditions for improving certain aspects of soil health. This could greatly help inform decision-making, and thus improve outcomes, in dryland restoration worldwide.