Albaladejo, Juan (CEBAS-CSIC,
Campus
Restoration of Desertified Lands by Organic Amendment: Medium-Term Effect on Carbon Sequestration
J. Albaladejo*, M. Martinez-Mena, R. Ortiz, J. Lopez, V.Castillo
Soil erosion and degradation in desertification-prone areas lead to a drastic decrease in the soil potential for carbon sequestration. Restoration of degraded lands could be a way to reverse this environmental degradation process in semiarid areas and mitigation of greenhouse gases. The strategy of restoration used in this experiment starts from the hypothesis that the improvement of soil characteristics favours the growth of a spontaneous vegetal cover, stimulating de carbon cycle. The aim was to evaluate the effectiveness at medium-long term of a unique addition of organic refuse on the soil potential for carbon sequestration. An addition of 25 kg m-2 of solid urban refuse was applied, in 1988, into the top 10 cm of a 85 m-2 plot, with other plot without treatment as control. The plots are sited in an open scrubland, (2-4% cover) of desertic appearance, with 5% slope. The climate is semiarid to arid with 300mm of average total annual precipitation and 17º C annual mean temperature. The soil is a Xeric Torriorthent with high physical and biological degradation. Sixteen years later a monitoring was carried out to state the lasting of the organic addition effect on the SOC pools and soil physical characteristics improvement. The TOC contents were 9.5 g kg-1 and 16.4 g kg-1 in the control and restored plots respectively. This mean 1.42 kg m-2and 2.46 kg m-1 of OC in the control and restored plot, respectively, in the top 10cm of the soil. Thus, the land restoration led to 10.3 Mg ha-1 of C sequestration. An important pool of the sequestered C remains in the soil as recalcitrant pool. This assumption may be supported by two facts: 1) The texture is coarser in the restored plot than in the control, probably due to the increase in microaggregates clay-humus, strongly stabilized and very difficult to breakdown for chemical dispersion, and 2) The higher difference between TOC and humic substances C in the restored plot, showing that an important proportion of SOC after restoration, was incorporated into the soil as long-term stable humin. Likewise, statistically significant higher values in bulk density, saturated hydraulic conductivity and aggregate stability were displayed in the restored plot at 0-10 cm depth. Soil porosity and water retention capacity showed, as well, higher mean values in the restored plot, but without significant differences. In addition, soil erosion was strongly reduced. The ratio annual sediment in restored plot/annual sediment in control plot, range from 18.8.10-3 to 1.7.10-3 along the years. The results obtained in this experiment point out the effectiveness of restoration of eroded and degraded soils, by means of an unique addition of organic amendment, to increase the recalcitrant pool of SOC.