furrows and using the subsoil of each furrow to make the ridges. Leguminous cover
crops cultivated on each ridge have a stabilizing effect, thus avoiding a collapse
during the wet season. This cover crop may also be cut/pruned and used as mulch in
the furrow to add organic matter and nitrogen for use by the alley crops, having
additional positive impacts on the system. Furthermore, drip irrigation, as an
additional practice, can be useful during the 4 months of the dry season (January
to April) in order to reduce water stress and increase the yield/quality of multiple
fruit production activities using the alley cropping systems. Farmers, however, can
achieve these benefits if, and only if, fruit crops are included and sound support is
given in terms of extension services while establishing this approach.
7.3 Timeframe for Soil Conservation Technologies to Become
Effective and to Improve or Sustain Crop Yields
In this section, soil conservation is interpreted in its broader sense to include both
the control of soil erosion and the maintenance of soil fertility.
2 This follows the
assumption that erosion lowers soil fertility through a removal of organic matter
and nutrients in eroded sediments, and the recognition that soil degradation by
either biological, chemical or physical processes other than erosion are grouped as a
decline in soil fertility (Young 1996). In this context, soil fertility is understood as
the capacity of the soil to support plant growth, and may encompass parameters
such as plant available nutrients, soil organic matter (SOM), or soil structure
(Lal 1998). Based on the soil conservation techniques reported in Sect. 7.2, soil
cover plays a crucial role in this concept, usually in the form of a barrier such as
grass strips, which are used to directly influence the strength and impact of run-off
and soil removal, or surface covers such as mulching and minimum/zero tillage
systems which are used to reduce the impact of raindrops and run-off. Important in
this aspect is the timeframe given for SCT to become, not only effective, but also
significantly improve or sustain crop yields. Such a feedback from the biophysical
environment can become a key driver in the successful adoption of SCT. In
addition, soil degradation can negatively influence the establishment of SCT, as
low initial stocks of plant available nutrients may hamper the development of a
protective soil coverage during erosive rainfall events (Bonell and Bruijnzeel 2005;
Lippe et al. 2011; Pansak et al. 2008).
To improve our understanding of the importance of initial soil fertility
conditions, interactions and feedback mechanisms, and the timeframe of selected
SCT, this section draws on the results of three case studies carried out in the
mountainous north-east of Thailand and north-west of Vietnam. The results of the
study in north-east Thailand were published by Pansak et al. (2007, 2008), whereas
the results of the case study in north-west Vietnam are preliminary and based
2 This section was written by Melvin Lippe, Thomas Hilger, Wanwisa Pansak, Tuan Vu Dinh.
240
T. Hilger et al.
crops cultivated on each ridge have a stabilizing effect, thus avoiding a collapse
during the wet season. This cover crop may also be cut/pruned and used as mulch in
the furrow to add organic matter and nitrogen for use by the alley crops, having
additional positive impacts on the system. Furthermore, drip irrigation, as an
additional practice, can be useful during the 4 months of the dry season (January
to April) in order to reduce water stress and increase the yield/quality of multiple
fruit production activities using the alley cropping systems. Farmers, however, can
achieve these benefits if, and only if, fruit crops are included and sound support is
given in terms of extension services while establishing this approach.
7.3 Timeframe for Soil Conservation Technologies to Become
Effective and to Improve or Sustain Crop Yields
In this section, soil conservation is interpreted in its broader sense to include both
the control of soil erosion and the maintenance of soil fertility.
2 This follows the
assumption that erosion lowers soil fertility through a removal of organic matter
and nutrients in eroded sediments, and the recognition that soil degradation by
either biological, chemical or physical processes other than erosion are grouped as a
decline in soil fertility (Young 1996). In this context, soil fertility is understood as
the capacity of the soil to support plant growth, and may encompass parameters
such as plant available nutrients, soil organic matter (SOM), or soil structure
(Lal 1998). Based on the soil conservation techniques reported in Sect. 7.2, soil
cover plays a crucial role in this concept, usually in the form of a barrier such as
grass strips, which are used to directly influence the strength and impact of run-off
and soil removal, or surface covers such as mulching and minimum/zero tillage
systems which are used to reduce the impact of raindrops and run-off. Important in
this aspect is the timeframe given for SCT to become, not only effective, but also
significantly improve or sustain crop yields. Such a feedback from the biophysical
environment can become a key driver in the successful adoption of SCT. In
addition, soil degradation can negatively influence the establishment of SCT, as
low initial stocks of plant available nutrients may hamper the development of a
protective soil coverage during erosive rainfall events (Bonell and Bruijnzeel 2005;
Lippe et al. 2011; Pansak et al. 2008).
To improve our understanding of the importance of initial soil fertility
conditions, interactions and feedback mechanisms, and the timeframe of selected
SCT, this section draws on the results of three case studies carried out in the
mountainous north-east of Thailand and north-west of Vietnam. The results of the
study in north-east Thailand were published by Pansak et al. (2007, 2008), whereas
the results of the case study in north-west Vietnam are preliminary and based
2 This section was written by Melvin Lippe, Thomas Hilger, Wanwisa Pansak, Tuan Vu Dinh.
240
T. Hilger et al.