trend over time, as described at Ban Bo Muang Noi (Fig. 7.5a), even with the higher
observed rainfall amounts in 2010 (Table 7.3). The decline in soil loss between the
first and second year in the Arachis treatment in Chieng Khoi was more drastic than
in Ban Muang Noi. Although measured annual soil loss rates showed a high
variability, as depicted by large standard errors of the means, and statistical analysis
revealed the influence of SCT in reducing soil loss in the first year of the field trial.
Field observations indicated that the described pattern was most probably related to
a slow development of soil coverage at an early stage of the field trial. Nevertheless,
the impact of SCT was most effective for the cover crop (Arachis pintoi) treatment
in combination with minimum tillage, reducing annual soil loss rates on average by
15.5 Mg ha
À1 when compared to farmers’ own practices in 2009, and to a negligible
amount in 2010.
7.3.3 Performance of Maize Yields, as Affected by Soil
Conservation Treatments
SCT and fertilizer application significantly (p < 0.01) affected maize grain yields
in Ban Bo Muang Noi, Thailand (Fig. 7.6a). However, the effect of both changed
over time, leading to a significant (p < 0.05) interaction. The highest maize grain
yields (5.5 Mg ha
À1 ) were reported 3 years after establishment of the control plot
without hedgerows and with fertilizer applied, and in the same year, the lowest
maize grain yields (2.0 Mg ha
À1 ) were obtained on plots using ruzi grass barriers
but without fertilizer application. The use of contour hedge rows significantly
reduced maize grain yields (p < 0.01), by up to 39 % in the second year and
47 % in the third year, as compared to the control plot without hedges. This decline
in maize grain yields was much higher than the reduction by almost 17 % in the
cropping area, as compared to the control plot without hedgerows. The control
plots, regardless of fertilizer application levels, showed a strong yield increase from
the first to the second year, but then the increase was lower in the third year after
fertilizer was applied (Fig. 7.6b). The cumulative grain yield over 3 years amounted
to 10.7 Mg ha
À1 in the control plot without hedgerows/barriers (average fertilizer
treatments), 1.3 times higher than under the soil conservation treatments.
The performance of maize grain yields in Chieng Khoi, Vietnam showed a
different behavior to those in Ban Bo Muang Noi in Thailand (Fig. 7.6c). In the
first year, the yield response in Chieng Khoi was almost twice as high as in Ban Bo
Muang Noi, being in the range 5.5–6.5 Mg ha
À1 . This difference was probably
associated with the different maize hybrid varieties and fertilizers used in each case
study. The treatment using Arachis pintoi as a cover crop, in combination with
minimum tillage, outperformed farmers’ practices by 1.5 Mg ha
À1 in 2009, as
compared to the trials using Panicum maximum as a grass barrier and relay cropping
using Phaseolus calcaratus. The positive grain yield trend previously observed in
Ban Bo Muang Noi under SCT could not be confirmed for the experimental trials
7 Soil Conservation on Sloping Land: Technical Options and Adoption Constraints
245
observed rainfall amounts in 2010 (Table 7.3). The decline in soil loss between the
first and second year in the Arachis treatment in Chieng Khoi was more drastic than
in Ban Muang Noi. Although measured annual soil loss rates showed a high
variability, as depicted by large standard errors of the means, and statistical analysis
revealed the influence of SCT in reducing soil loss in the first year of the field trial.
Field observations indicated that the described pattern was most probably related to
a slow development of soil coverage at an early stage of the field trial. Nevertheless,
the impact of SCT was most effective for the cover crop (Arachis pintoi) treatment
in combination with minimum tillage, reducing annual soil loss rates on average by
15.5 Mg ha
À1 when compared to farmers’ own practices in 2009, and to a negligible
amount in 2010.
7.3.3 Performance of Maize Yields, as Affected by Soil
Conservation Treatments
SCT and fertilizer application significantly (p < 0.01) affected maize grain yields
in Ban Bo Muang Noi, Thailand (Fig. 7.6a). However, the effect of both changed
over time, leading to a significant (p < 0.05) interaction. The highest maize grain
yields (5.5 Mg ha
À1 ) were reported 3 years after establishment of the control plot
without hedgerows and with fertilizer applied, and in the same year, the lowest
maize grain yields (2.0 Mg ha
À1 ) were obtained on plots using ruzi grass barriers
but without fertilizer application. The use of contour hedge rows significantly
reduced maize grain yields (p < 0.01), by up to 39 % in the second year and
47 % in the third year, as compared to the control plot without hedges. This decline
in maize grain yields was much higher than the reduction by almost 17 % in the
cropping area, as compared to the control plot without hedgerows. The control
plots, regardless of fertilizer application levels, showed a strong yield increase from
the first to the second year, but then the increase was lower in the third year after
fertilizer was applied (Fig. 7.6b). The cumulative grain yield over 3 years amounted
to 10.7 Mg ha
À1 in the control plot without hedgerows/barriers (average fertilizer
treatments), 1.3 times higher than under the soil conservation treatments.
The performance of maize grain yields in Chieng Khoi, Vietnam showed a
different behavior to those in Ban Bo Muang Noi in Thailand (Fig. 7.6c). In the
first year, the yield response in Chieng Khoi was almost twice as high as in Ban Bo
Muang Noi, being in the range 5.5–6.5 Mg ha
À1 . This difference was probably
associated with the different maize hybrid varieties and fertilizers used in each case
study. The treatment using Arachis pintoi as a cover crop, in combination with
minimum tillage, outperformed farmers’ practices by 1.5 Mg ha
À1 in 2009, as
compared to the trials using Panicum maximum as a grass barrier and relay cropping
using Phaseolus calcaratus. The positive grain yield trend previously observed in
Ban Bo Muang Noi under SCT could not be confirmed for the experimental trials
7 Soil Conservation on Sloping Land: Technical Options and Adoption Constraints
245