World’s Soil Resources

10.3.4 | Soil acidification
There is large area of acid soils distributed across the tropical and subtropical regions of Asia, mainly in
Southeast Asia, parts of East Asia and parts of South Asia. Acid sulphate soils are widely distributed in the
coastal plains of Southeast Asia and southern China. The total area of acid sulphate soils in Southeast Asia is
7.5 million ha and there are about 112 thousand ha of these soils in China (Shamshuddin et al., 2014). The soils in
these regions are also sensitive to external acid such as acid deposition (Hicks et al., 2008).
In Vietnam, ferralitic, basaltic, and grey degraded soils, which cover about one third of the country, have
strong potential for acidification and degradation because of their nature (NISF, 2012). A leading contributor
to soil acidification in Vietnam is the unbalanced and unsuitable application of chemical fertilizers. Data
from the International Fertilizers Association (IFA) show that from 1961 to 2012, total NPK chemical fertilizer
use in Vietnam increased 31 times (IFA, 2012). The increase in fertilizer application and unbalanced use lead
to inadequate presentations of acidic factors in soil solutions. Some types of fertilizers (including organic
fertilizers) can make the soil more acidic (Nguyen, 2014). Another reason for the acidification process in
Vietnam is the presence of sulphate soil. The area of sulphate soil in the Red River delta has increased by 7 000
ha and the content of S in this soil has also strongly increased. In the Mekong river delta, the area has reduced
by 261 000 ha and the content of total exchangeable cations and total dissolved salts has also reduced.
Increase in temperature, change of precipitation, and sea level rise due to climate change may also be having
negative effects on this process in Vietnam.
The total area of Indonesian acid upland soils (pH