After 3 h measuring, infiltration rates (K in mm h
À1 ) were only high on the top of
and in the basal slope area of catena 1, as well as at site 4 (Fig. 2.19b). Moderate
values were found in the lower parts of catena 1 and across catena 2. At catena 2 this
was despite the higher proportion of coarse pores in the sandy textured soils (9–19
Vol-%) when compared to all the other sites investigated (4–16 Vol-%). Infiltration
rates decreased during the measuring time in most soils – quite drastically, and the
reduction in K max (at the beginning of the experiment) and K min (after 3 h)
amounted to between 30 % and 61 %. With a reduction of 11 % and 28 %,
infiltration rates were more stable during the experiment in the soils of catena 1
(top slope) and site 4 (mid-slope). Both soils had a relatively high soil organic
matter content in the top layer (12.6 and 15.9 g kg
À1 ), proving the positive effects of
soil organic matter on the stabilization of soil aggregates. The C and N content did
not differ significantly between the soils (6–16 g C kg
À1 , 0.3–1.2 g N kg
À1 ), but less
eroded soils revealed the highest amounts in the top soil (11.6–15.9 g C kg
À1 ,
1.0–1.2 g N kg
À1 ). OM and N stocks were lower in the soils of catena 2 (around 5 kg
C m
À2 , < 0.4 kg N m
À2 ) than in the soils of catena 1 and at site 4 (up to 13 kg
C m
À2 , 0.9 kg N m
À2 ), but did not differ much within the catenas (Fig. 2.19d, e).
The serious impact of erosion on arable land could be studied at site 4, deforested
only 7 years before, by comparing the two profiles at the mid-slope level, but with
different inclinations and erosive lope lengths (Table 2.15). Assuming that at site
3 the OM stocks were equal at both profiles prior to deforestation, stocks of OM had
reduced by erosion by 58 % at a rate of 3 mS-2 in the topsoil and by 26 % in the ERS
during the previous 7 years – the greater susceptibility to erosion occurring due to
the higher inclination and longer slope length. The S-values differed markedly
between soils of different origins and degrees of erosion. In siltstone soils less
affected by erosion (catena 1 T, uS and site 4) S-values were assessed as high and in
soils derived from sandy parent materials and/or more affected by erosion (catena 2,
catena 1 mS, lS) or sedimentation (bS position of catena 1 and 2), the S-values were
moderate or low (Fig. 2.19c). The texture of the soils in the basal slope positions of
both catenas was coarser and the C-content lower than on the upper slopes,
indicating that during erosion events the clay fraction of the soils and organic
substances, important for soil fertility, were transported further away in the catchment. A study of sediment effects on the fertility of paddy fields in Chieng Khoi
(Schmitter et al. 2010) confirmed this deduction; the authors showed that only fine
sediments originating from the irrigation system increased soil fertility, while
sediment deposition originating from the erosion of surrounding cultivated slopes
decreased it. Long-term fallow was expected to have a positive effect on soil
fertility in general (Kubiniok 1999), and when comparing the two profiles in catena
2 (2 uS-1, 2 mS-2) – both left fallow for the last 57 years and showing similar
characteristics in terms of depth of the ERS, AWC and erosion disposition – the
importance of exchangeable cations for soil fertility was revealed. Soil profile
2 mS-2 exhibited considerably higher S-Values, because they were influenced by
calcareous conglomerates, but also had higher amounts of OM and Nt than profile
2 uS-1, as derived from sandstone. These findings indicate that a sufficient cation
supply is a prerequisite for increasing soil organic matter during fallow periods.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
101
À1 ) were only high on the top of
and in the basal slope area of catena 1, as well as at site 4 (Fig. 2.19b). Moderate
values were found in the lower parts of catena 1 and across catena 2. At catena 2 this
was despite the higher proportion of coarse pores in the sandy textured soils (9–19
Vol-%) when compared to all the other sites investigated (4–16 Vol-%). Infiltration
rates decreased during the measuring time in most soils – quite drastically, and the
reduction in K max (at the beginning of the experiment) and K min (after 3 h)
amounted to between 30 % and 61 %. With a reduction of 11 % and 28 %,
infiltration rates were more stable during the experiment in the soils of catena 1
(top slope) and site 4 (mid-slope). Both soils had a relatively high soil organic
matter content in the top layer (12.6 and 15.9 g kg
À1 ), proving the positive effects of
soil organic matter on the stabilization of soil aggregates. The C and N content did
not differ significantly between the soils (6–16 g C kg
À1 , 0.3–1.2 g N kg
À1 ), but less
eroded soils revealed the highest amounts in the top soil (11.6–15.9 g C kg
À1 ,
1.0–1.2 g N kg
À1 ). OM and N stocks were lower in the soils of catena 2 (around 5 kg
C m
À2 , < 0.4 kg N m
À2 ) than in the soils of catena 1 and at site 4 (up to 13 kg
C m
À2 , 0.9 kg N m
À2 ), but did not differ much within the catenas (Fig. 2.19d, e).
The serious impact of erosion on arable land could be studied at site 4, deforested
only 7 years before, by comparing the two profiles at the mid-slope level, but with
different inclinations and erosive lope lengths (Table 2.15). Assuming that at site
3 the OM stocks were equal at both profiles prior to deforestation, stocks of OM had
reduced by erosion by 58 % at a rate of 3 mS-2 in the topsoil and by 26 % in the ERS
during the previous 7 years – the greater susceptibility to erosion occurring due to
the higher inclination and longer slope length. The S-values differed markedly
between soils of different origins and degrees of erosion. In siltstone soils less
affected by erosion (catena 1 T, uS and site 4) S-values were assessed as high and in
soils derived from sandy parent materials and/or more affected by erosion (catena 2,
catena 1 mS, lS) or sedimentation (bS position of catena 1 and 2), the S-values were
moderate or low (Fig. 2.19c). The texture of the soils in the basal slope positions of
both catenas was coarser and the C-content lower than on the upper slopes,
indicating that during erosion events the clay fraction of the soils and organic
substances, important for soil fertility, were transported further away in the catchment. A study of sediment effects on the fertility of paddy fields in Chieng Khoi
(Schmitter et al. 2010) confirmed this deduction; the authors showed that only fine
sediments originating from the irrigation system increased soil fertility, while
sediment deposition originating from the erosion of surrounding cultivated slopes
decreased it. Long-term fallow was expected to have a positive effect on soil
fertility in general (Kubiniok 1999), and when comparing the two profiles in catena
2 (2 uS-1, 2 mS-2) – both left fallow for the last 57 years and showing similar
characteristics in terms of depth of the ERS, AWC and erosion disposition – the
importance of exchangeable cations for soil fertility was revealed. Soil profile
2 mS-2 exhibited considerably higher S-Values, because they were influenced by
calcareous conglomerates, but also had higher amounts of OM and Nt than profile
2 uS-1, as derived from sandstone. These findings indicate that a sufficient cation
supply is a prerequisite for increasing soil organic matter during fallow periods.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
101