Establishing Acacia salicina under dry Mediterranean conditions: The effects of nursery fertilization and tree shelters on a mid-term experiment with saline irrigation

Abstract

The restoration of dry lands in the Mediterranean is a challenging task because harsh abiotic conditions hamper the counteraction of feed-back degradation processes. Active restoration through planting must be performed to deter this process. In this study, we tested the influence of mineral nutrition in the nursery (two formulations of controlled release fertilizer at two rates each) and tree protection after planting (by using tube shelters) on the nine-year performance of Acacia salicina irrigated with low-quality (saline) water. The overall survival at the end of the study period was 58.2%, with the electrical conductivity of the soil saturation extract reaching 5.4 dS·m-1 after nine years. The survival and growth (in height) were greater for seedlings fertilized with more than 1.5 g·L-1 of 9-13-18, although the survival differences became significant only after the seventh year. The basal stem diameter (BSD) of seedlings that were fertilized at higher rates was significantly greater than those that were fertilized at lower rates during the first two years of planting; the differences were no longer present thereafter. The seedlings in shelters had marginally superior survival, faster growth during the first four years, and smaller BSD values after the third year compared to those of the unprotected seedlings. In comparison with a parallel study that was conducted under drought conditions, irrigation reduced some differences among treatments, but it increased others. These results emphasize the importance of the size and mineral nutrient status of nursery stock in irrigated plantations under dry Mediterranean conditions, with highly fertilized seedlings showing superior performance. Long-term planting studies are crucial for gaining a greater understanding of seedling performance and for providing a better rationale for treatment recommendations.