Carbon balance as affected by biosolid application in reforestations

Soils of Mediterranean drylands are characterized by a low fertility and organic matter content because of past land use and disturbances regime. The restoration of these degraded lands faces at the same time problems related to water scarcity and the unpredictability of precipitations with problems with soil physical, chemical, and microbiological properties. Organic amendments may help to improve soil properties and, consequently, enhance planted seedling establishment and performance. In this study, we assessed the C balance of 3 Mediterranean areas planted with Pinus halepensis Mill. seedlings with different treatments of biosolid application. The assessment was conducted at different times after the establishment of treatments and the C dynamics are discussed. We considered 3 biosolid types (air‐dried, fresh sludge, and composted sludge) in application doses ranging from 10 to 320 Mg (d.w.) ha−1. We quantified basal area, pine biomass, biomass of spontaneous vegetation, litter, root density, and soil organic matter. All 3 experimental restoration studies improved restoration success in terms of basal area (ranging from 15% to 300%), especially in composted biosolid at 30 Mg (d.w.) ha−1, whereas litter and, especially, root biomass increased with all biosolid treatments and times since application. Soil organic C was higher in application doses above 30 Mg (dry weight) ha−1 due to the organic matter applied with the sludges. The increment in C sequestration rates associated to these restoration treatments ranged between 0.046 and 0.293 kg C m2 yr−1. These results confirm the suitability of organic amendments as restoration technique in Mediterranean degraded drylands.

This research was conducted within the framework of research projects funded by the Spanish Ministries of Environment (BIOMET‐608/2006/1‐4.4), the European Commission FP7 (CASCADE/GA283068), and the Government of the Valencia Region (DESESTRES‐PROMETEUII/2014/038).