Land Degradation and Pedological Processes in a Changing Climate

322R. Lal / Pedologist (2012) 315-325quality of degraded/desertified soils. The loss in productionis not only of immediate concern, but also has cumulativeeffects over time (Fig. 5).7. Climate Change and Pedospheric ProcessesSoils are affected by climate change. Thus, the importanceof including a soil evolution module in modelsfor predicting future climate change is widely recognized(Montagne and Cornu, 2010). Soils affect climate changethrough emission of radiatively active gases (i.e., CO 2 ,CH 4 , N 2 O). Depletion of SOM, through biological degradation,exacerbates gaseous emissions into the atmosphere.Increases in temperature due to global warming may accentuatethe rate of mineralization of SOM, reduce aggregationand aggregate stability, and accelerate soil erosionrisks. An increase in frequency of extreme events, largeand intense rains and high winds, can increase climaticerosivity. Therefore, climate change may accentuateclimate erosivity while increasing soil erodibility. An increasein evaporation can decrease available water capacity,reduce vegetation cover, and decrease the amount ofbiomass-C returned to the soil. Thawing of permafrost(cryosols) and drainage of peat soils can create positivefeedback, accentuating the rate of mineralization of SOMand further exacerbating climate change.Yet, restoration of degraded/desertified soils can increasethe ecosystem C pool and off-set some anthropogenicemissions. The potential of C sequestration is estimatedat 0.2–0.7 Pg C/yr through desertification control,and 0.3–0.7 Pg C/yr through restoration of salt affectedsoils. In addition, adoption of RMPs can sequester 0.4–1.2Pg C/yr in cropland soils, 0.3–0.5 Pg C/yr in grassland/grazing land soils, and 1.4–1.9 Pg C/yr through afforestation/deforestationand the establishment of forest plantations.Thus, the total technical potential of C sequestrationin the terrestrial biosphere is 2.55–4.96 Pg C/yr (Lal,2010).Thus, the threat of human-induced climate changecreates challenges and opportunities. The challenge liesin the increased risks of pedospheric land degradation becauseof higher rates of depletion of SOM, acceleration insoil erosion, and high risks of salinization. Yet, there areopportunities to improve soil quality, and restore degradedsoils by sequestration of C in the terrestrial biosphere.The win-win option is important for restoring degradedsoils, mitigating climate change, improving water qualityand the environment, and advancing food security.8. Technological Options of Restoring DegradedSoil and Desertified LandsThe key strategy of reversing the degradation spiral isrestoration of soil quality (Fig. 6). The goal is to conservewater and nutrients, increase vegetation cover, and improvethe SOM pool. Soil quality is indeed an appropriateindicator of sustainable land management (Herrick, 2000),and the quantity and quality of the SOM pool are importantdeterminants of soil quality. There is a threshold levelof SOM concentration in the root zone (1.9–3.4%), whichdepends on climate, soil type, landscape position, drainage,and profile/solum depth. Rather than concentratedonly in the surface soil, deep SOM storage is also a keyfactor, but the processes governing deep SOM (sub-soilbelow 50 cm depth) placement and dynamics are poorlyunderstood (Lorenz and Lal, 2005; Rumpel and Kogel-Knabner, 2011).There are strong synergies between mitigation of and adaptationto climate change, especially in the context of agriculture(Smith and Oleson, 2010). Biotic sequestration ofatmospheric CO 2 has strong cost-effectiveness. Becauseof the strong interaction between C and water (Evett andTolk, 2009), and between C and N (Lal, 2010), the strategyis to adopt land use and management practices whichaccentuate the use of efficient energy-based input (fertilizers,irrigation, tillage), and create a positive C budget(Lal, 2010). Management of soil fertility, in conjunctionwith that of C and water, is an important factor, especiallyfor restoring degraded soils managed by resource-poorfarmers through extractive farming practices in developingcountries. Land application of organic by-products orco-products (misnomered as waste) is relevant to restoringsoil ecosystem (Odlare et al., 2010). This strategy canbe adopted in conjunction with production of biofuels. Degraded/depletedsoils are prone to drought stress, havelow soil fertility, and are constrained by elemental imbalances(Al +3 toxicity). Such challenges of low soil fertility