318R. Lal / Pedologist (2012) 315-325Fig. 2. Biophysical <strong>and</strong> anthropogenic processes, factors <strong>and</strong> causes of l<strong>and</strong> degradation.Fig. 3. Types of l<strong>and</strong> degradation <strong>and</strong> pedological processes.(SOM: soil organic matter)
R. Lal: Soil degradation processes319degradation of pedospheric processes by sal<strong>in</strong>ization.With regard to the threat of climate change, soil can bea source or s<strong>in</strong>k of atmospheric CO 2 <strong>and</strong> other radiativelyactive gases (e.g., CH 4 , N 2 O). Changes <strong>in</strong> the SOM poolhave strong implications on the atmospheric abundanceof CO 2 . Depletion of the SOM pool <strong>in</strong>creases the flux ofCO 2 from the soil <strong>in</strong>to the atmosphere, <strong>and</strong> accretion ofSOM can cause drawdown of CO 2 from the atmosphere. Achange <strong>in</strong> soil fauna <strong>and</strong> flora (below ground biodiversity),<strong>in</strong> conjunction with anaerobiosis <strong>and</strong> the degree of saturation(wetness), also impact methanogenesis (production<strong>and</strong> emission of CH 4 ) <strong>and</strong> nitrification/denitrification processes(production <strong>and</strong> emission of N 2 O). Other biologicalprocesses affect<strong>in</strong>g the quality of the pedosphere <strong>and</strong>its fractions <strong>and</strong> ecosystem services are the quality <strong>and</strong>quantity of the labile C pool, microbial biomass C (MBC),depth:distribution ratio (stratification) of the soil C pool,<strong>and</strong> the relative abundance of soil pathogens vs. predators(Fig. 3).Ecosystem characteristics also impact pedosphericprocesses <strong>and</strong> their ecological functions <strong>and</strong> services.Pr<strong>in</strong>cipal ecosystem services adversely impacted by thedegradation of the pedosphere <strong>in</strong>clude the quantity <strong>and</strong>quality of renewable water resources, ecosystem C pool,terra<strong>in</strong> characteristics <strong>and</strong> l<strong>and</strong> forms, <strong>and</strong> below <strong>and</strong>above ground biodiversity (Fig. 3). The downward spirallead<strong>in</strong>g to degradation of pedospheric processes is oftenset-<strong>in</strong>-motion by extractive farm<strong>in</strong>g (Fig. 4). Depletion ofthe SOM pool <strong>and</strong> decl<strong>in</strong>e <strong>in</strong> soil structure exacerbate thedegradation processes which control physical, chemical,biological, <strong>and</strong> ecological degradation.5. Methods of Assessment of Pedospheric <strong>L<strong>and</strong></strong><strong>Degradation</strong>A large number of reports provide statistics on theextent <strong>and</strong> severity of l<strong>and</strong> degradation, soil degradation,<strong>and</strong> desertification (e.g., Oldeman <strong>and</strong> Van Lynden, 1998;Dregne, 1998; Bai et al., 2008). However, the statisticsare often confus<strong>in</strong>g, contradictory, <strong>and</strong> not comparablebecause the data are based on different term<strong>in</strong>ology <strong>and</strong>on a wide range of non-st<strong>and</strong>ardized methods. The <strong>in</strong>formationis further confounded by the lack of ground truth<strong>in</strong>g<strong>and</strong> does not relate the severity of degradation to netprimary productivity (NPP), agronomic production, or useefficiency of <strong>in</strong>put.Table 1 outl<strong>in</strong>es some methods used <strong>in</strong> assess<strong>in</strong>g differenttypes of pedospheric l<strong>and</strong> degradation such as wa-Fig. 4. The downward spiral set-<strong>in</strong>-motion by l<strong>and</strong> misuse <strong>and</strong> soil mismanagement, <strong>and</strong> extractive farm<strong>in</strong>g whichcreate a negative C <strong>and</strong> nutrient budgets.
Change language