Influence of the Application Rate of an Organic Amendment (Municipal Solid Waste [MSW] Compost) on Gypsum Quarry Rehabilitation in Semiarid Environments

Rehabilitation of open-cast gypsum mines is made difficult by the permanent loss of the original soil resource. Soil development can be accelerated by using organic amendments (e.g., MSW compost), which provide both physical (structural) enhancement and chemical (nutrient) reinforcement. Excess of salts as a result of the effect of refuse application can lead to overfertilizing for some species and the species Atriplex halimus L. (Chenopodiaceae) can be considered an effective indicator of the optimum organic amendment rate. Four treatments of composted urban municipal solid waste (MSW compost) were applied to the top flat area of a gypsum spoil [soil-forming material (SFM)], being then the surface covered with natural topsoil layer coming from the head of the quarry. Soil and vegetation sampling was made over a four-year period. As a result of the physical and chemical effects of the organic amendment on soil properties, a close relationship existed between application rate and Atriplex halimus presence. Based on the results of this study, gypsum quarry rehabilitation in semiarid environments may be facilitated by the use of medium organic amendment rates. High rates caused halophyte species such as Atriplex halimus to grow in such a way that development of native gypsiferous species was hindered by the competitive processes. On the other hand, low rates seemed to have no beneficial effect on soil.