Page 136 - Soil Degradation, Conservation and Remediation

Chapter 5
Chemical Soil Degradation

Estimates in 1991 suggest that about 240 M ha land is chemically degraded. Nutrient
depletion has affected 136 M ha, salinization damaged 77 M ha, and acidification
degraded 6 M ha. Another 11 M ha is affected by soil pollution. Agricultural
mismanagement (58 %) and deforestation (28 %) are the main causes of chemical
degradation of soil. Nutrient depletion is the most prevalent in Africa (65 M ha) and
South America (68 M ha), while salinization is the major chemical degradation in
Asia (53 M ha). Nutrient depletion has caused serious nutrient imbalances in soils
under low-input agriculture in marginal lands. In a study, all the African agricultural
soils exhibited negative NPK balances. Nutrient depletion is caused by leaching,
residue harvest and burning, erosion, and crop removal. Salinization occurs naturally
by pedogenic processes in different climatic conditions, but human-induced
salinization has compelled to abandon many soils, which were productive earlier.
The principal cause of human-induced salinization is inappropriate irrigation system
in arid and semiarid regions. Leaching of salts by extra irrigation and growing
salt-tolerant crops are the strategies for salty soil management. Soils are acidified
by acid rains, base leaching, and by the use of acidifying fertilizers. Liming is an
ancient method of reclaiming acidic soils. Growing crops suitable for the current
soil pH may be profitable in low to medium acidic soils.

5.1 Chemical Degradation of Soil and Its Extent

Chemical degradation of soil refers to the undesirable changes in soil chemical
behavior so that the quality of soil declines due to human interventions. Almost
240 M ha of land is affected by chemical degradation including 229 M ha in loss of
nutrients (136 M ha), salinization (77 M ha), and acidification (6 M ha). Another
11 M ha is affected by soil pollution which is described in Chap. 6. Chemical soil
pollution accounts for about 12 % of the total area affected by human-induced soil
degradation (Oldeman 1994). In Africa, Asia, Central America, and Europe, about
12 % of the degraded soils are chemically affected. In South America, about 30 %

K.T. Osman, Soil Degradation, Conservation and Remediation, 125
DOI 10.1007/978-94-007-7590-9_5, © Springer Science+Business Media Dordrecht 2014