technologies to be used for soil erosion control and soil conservation. It then
analyzes their drawbacks and investigates adoption constraints in Southeast Asian
highland farming systems, based largely on case studies carried out in the upland
areas of northern Thailand and northern Vietnam.
7.2 Effective Soil and Water Conservation Technologies
for Sustainable Highland Agriculture in Southeast Asia
7.2.1 Drivers, Orders of Magnitude and Consequences of Soil
Erosion in Asia
In Asia, farming systems have undergone significant changes in the recent past.
1
Increased population pressure, improved infrastructure, migration and ‘market
forces’ have contributed to this development, resulting in widespread and
accelerated land degradation (Pingali and Shah 2001; Valentin et al. 2008), including tillage erosion, inter-rill and rill erosion, gully erosion and landslides
(Turkelboom et al. 2008).
Soil erosion in Southeast Asia is strongly related to agricultural land use, in
particular on the sloping lands of headwater catchments (Phan Ha et al. 2012). The
impact of erosion and the amount of sediment yielded are both influenced by land
use type, its location in the landscape, topography and the hydrology of the
watershed (Gao et al. 2007; Vezina et al. 2006; Chaplot et al. 2005). Erosion affects
more than 300,000 km
2 or 65 % of the cultivated land area in Thailand (Kunaporn
et al. 1999), and 130,000 km
2 or 40 % of the total land surface in Vietnam (Vezina
et al. 2006). Soil losses in northern Thailand reach up to 297 Mg ha
À1 yr
À1 under
rainfall amounts ranging from 1,132 to 1,723 mm yr
À1 (Vlassak et al. 1992; cf.
Panomtaranichagul et al. 2004). In a study of north-east Thailand, Pansak et al.
(2008) reported soil losses of up to 25 Mg ha
À1 yr
À1 in maize-based systems, even
on only moderate slopes of 21–28 %, and in the absence of soil conservation
measures. Similar amounts of soil erosion were found by Dung et al. (2008) in
shifting cultivation systems with cassava and upland rice in northern Vietnam, but it
is not uncommon for soil losses to reach values of up to 150 Mg ha
À1 yr
À1 in maize
systems under local farmers’ practices, as was reported by Vu Dinh et al. (2010) for
north-west Vietnam, where losses strongly depended on crop species, slope
gradient and length, and field size.
Soil losses and run-off have a strong impact on crop yields, but the impact varies
greatly between crops, continents and soil types. In Africa, Asia, Australia and
Latin America, den Biggelaar et al. (2001) estimated a relative erosion-associated
crop yield decrease per centimeter of soil loss two to six times higher than that for
1 This section was written by Mattiga Panomtaranichagul and Thomas Hilger.
7 Soil Conservation on Sloping Land: Technical Options and Adoption Constraints
231
analyzes their drawbacks and investigates adoption constraints in Southeast Asian
highland farming systems, based largely on case studies carried out in the upland
areas of northern Thailand and northern Vietnam.
7.2 Effective Soil and Water Conservation Technologies
for Sustainable Highland Agriculture in Southeast Asia
7.2.1 Drivers, Orders of Magnitude and Consequences of Soil
Erosion in Asia
In Asia, farming systems have undergone significant changes in the recent past.
1
Increased population pressure, improved infrastructure, migration and ‘market
forces’ have contributed to this development, resulting in widespread and
accelerated land degradation (Pingali and Shah 2001; Valentin et al. 2008), including tillage erosion, inter-rill and rill erosion, gully erosion and landslides
(Turkelboom et al. 2008).
Soil erosion in Southeast Asia is strongly related to agricultural land use, in
particular on the sloping lands of headwater catchments (Phan Ha et al. 2012). The
impact of erosion and the amount of sediment yielded are both influenced by land
use type, its location in the landscape, topography and the hydrology of the
watershed (Gao et al. 2007; Vezina et al. 2006; Chaplot et al. 2005). Erosion affects
more than 300,000 km
2 or 65 % of the cultivated land area in Thailand (Kunaporn
et al. 1999), and 130,000 km
2 or 40 % of the total land surface in Vietnam (Vezina
et al. 2006). Soil losses in northern Thailand reach up to 297 Mg ha
À1 yr
À1 under
rainfall amounts ranging from 1,132 to 1,723 mm yr
À1 (Vlassak et al. 1992; cf.
Panomtaranichagul et al. 2004). In a study of north-east Thailand, Pansak et al.
(2008) reported soil losses of up to 25 Mg ha
À1 yr
À1 in maize-based systems, even
on only moderate slopes of 21–28 %, and in the absence of soil conservation
measures. Similar amounts of soil erosion were found by Dung et al. (2008) in
shifting cultivation systems with cassava and upland rice in northern Vietnam, but it
is not uncommon for soil losses to reach values of up to 150 Mg ha
À1 yr
À1 in maize
systems under local farmers’ practices, as was reported by Vu Dinh et al. (2010) for
north-west Vietnam, where losses strongly depended on crop species, slope
gradient and length, and field size.
Soil losses and run-off have a strong impact on crop yields, but the impact varies
greatly between crops, continents and soil types. In Africa, Asia, Australia and
Latin America, den Biggelaar et al. (2001) estimated a relative erosion-associated
crop yield decrease per centimeter of soil loss two to six times higher than that for
1 This section was written by Mattiga Panomtaranichagul and Thomas Hilger.
7 Soil Conservation on Sloping Land: Technical Options and Adoption Constraints
231