Role of organic amendment application on soil quality, functionality and greenhouse emission in a limestone quarry from semiarid ecosystems

Abstract

One strategy for restoring degraded soils by opencast mining in semiarid regions is the application of organic amendments. However, selecting an appropriate organic amendment that improves soil quality and functionality for recovery in the short-term without a high contribution to increased CO₂ emissions is important for improving restoration strategies. Therefore, the objective of this work was to study the short and medium-term changes in physico-chemical and biological properties in restored soils with organic amendments from a limestone quarry (SE, Spain). Several restoration treatments were applied consisting stabilized sewage sludge, vegetable compost garden waste, vegetable compost from greenhouse crop residues and two mixtures thereof, then native plants were planted. After six months several soil properties were evaluated (electrical conductivity (EC), pH, total organic carbon (TOC), total nitrogen (TN), assimilable phosphorus (AP), soil water retention, carbohydrates and polyphenols content, enzymatic activities, bacteria and fungi fatty acids and soil respiration). Some physico-chemical soil properties and the survival rates and biovolume of the introduced native plants, as well as the percentage of land cover occupied by wild plants, were also analyzed 2 years after the application of the amendments. Organic amendments improved significantly all soil properties compared with unamended soils. Labile organic matter forms (carbohydrates and polyphenols) showed significant positive correlations with parameters related to microbial activity. Restored soils with sewage sludge had the highest significant labile C values, following by its mixtures. All organic amendments increased in situ CO₂ release, a positive priming effect and organic matter mineralization, being these properties higher in sludge-treated soils than in the rest restored and non-amendment soils. The content of TOC and TN and water retention remained similar two after the application of the amendments, but the EC decreased in restored soils. Nevertheless, despite PCA analysis clearly demonstrated that all restoration treatments had an important effect on the functionality and soil quality, vegetable compost from garden waste or from horticultural greenhouse crop waste amendments were the best restoration treatments for short and medium-term restoration of degraded quarry soils in harsh environmental and climate conditions because they also presented lower CO2 emission rates to the atmosphere and the highest survival and growth rates of the introduced plants and wild cover in the experimental plots.