Biomass Production and Development of Native Vegetation Following Biowaste Amendment of a Degraded, Semi-Arid Soil

Water erosion is a worrying environmental problem affecting many Mediterranean soils, which are subject to progressive degradation due mainly to the loss of organic matter. To promote the restoration of an abandoned, degraded soil with a semi-arid climate, sewage sludge (SS) and municipal solid waste (MSW) were surface-applied once only to field plots with an 8-12% slope at four different rates: 0, 40, 80, 120 Mg ha(-1). The growth of native plants was enhanced by the addition of these organic wastes. Total plant biomass and canopy cover increased significantly and remained higher in all the biowaste treatments over the 5-year study period. An estimated maximum biomass of 550 gm(-2) was obtained when 80 Mg ha(-1) of SS were applied; for MSW, a maximum estimated value of 361 g m(-2) was obtained with the 40 Mg ha(-1) rate. Native plant species richness decreased with an increasing biowaste application rate. Differences in the composition of native plant communities were observed among treatments, but with a reduction in perennial and an increase in annual plants seen in all biowaste treated plots. This was more remarkable in the plots in which SS was applied, and was seen throughout 5 years of the study. Increasing biowaste rates resulted in somewhat increased nutrient concentrations, mainly nitrogen; this effect was less evident in the last years. All plant heavy metal concentrations determined were below those considered hazardous.