The field trials were established using bounded run-off plots (for further
explanations, see also Sect. 7.4) with a width of 4 m and a length of 18 m
downslope, and with side walls of 0.20 m in height to prevent run-on water.
Maize (Zea mays) was used in all treatments as a representative local cropping
system. In the case of Ban Muang Bo Noi, trials were established in April 2003 and
fields laid out using a split-plot design and with fertilizer application as the main
variable factor (no fertilizer, and 60 kg N ha
À1 plus 14 kg P ha
À1 ), soil conservation
as the subfactor, and with two replicates. In total, 16 monitoring plots were
established, and a collection device for run-off water and eroded soil was installed
at the lower end of each plot. Subfactor treatments were: (1) vetiver grass (Vetiveria
zizanioides) barriers, (2) ruzi grass (Brachiaria ruziziensis) barriers, (3) leucaena
(Leucaena leucocephala) hedges, and (4) a control without a hedgerow (all under
minimum tillage). Leucaena, ruzi grass and vetiver grass were planted in three 1 m
wide barriers at intervals of 6 m, occupying about 17 % of the total plot area. Maize
was relay cropped with Jack beans (Canavalia ensiformis) starting in September
2003. Jack beans were planted 1 month prior to maize harvest. Maize stover and all
Jack bean materials were left on the plots as mulch to protect the soil from erosion
and suppress weed growth the following growing season. Plots with hedgerows or
grass barriers were pruned three to six times per year, with pruning spread evenly
over the alley. In all treatments, weeding was done by hand when necessary, which
defined the trial set-up as a minimum tillage system (Young 1996).
In the case of Chieng Khoi, field trials were chosen based on a participatory
selection process in cooperation with local farmers and extension officers, resulting
in four treatments, namely: (1) maize cropping following farmers’ normal practice
(hoeing, weeding, burning, animal plowing and hoeing), (2) maize with Panicum
maximum as a grass barrier, (3) maize under minimum tillage with Arachis pintoi as
a cover crop, and (4) maize under minimum tillage, relay cropped with a leguminous bean Phaseolus calcaratus. Trial plots were installed as a randomized complete block design with three replicates, receiving a total fertilizer rate of 158, 17.5
and 58.6 kg ha
À1 of N, P, and K respectively. Panicum maximum grass barriers were
planted in June 2009 and Arachis pintoi was transplanted in June 2009. Phaseolus
calcaratus was sown in all years 1 month after maize planting. In both years, maize
was sown in mid-May and harvested at the end of September. In the case of Ban Bo
Muang Noi, maize was harvested at the beginning of October in 2003, 2004 and
2005. As a common approach in both field trials, harvested maize plants were
separated into grain and stover and oven-dried at 70
C to determine the dry weight.
Soil loss and run-off data were collected after every rainfall event using a series
of collecting tanks or buckets, which directly measured run-off volumes. Soil loss
amounts were calculated based on the collected heavier sediment found at the
bottom of the plot in the collection device, and the suspended sediment fractions.
Suspended sediment fractions were collected through run-off samples of approximately 1 L, as taken from the tanks or buckets after stirring and filtering. After
filtration, particles collected on the filter were oven-dried at 105
C for 24 h to
determine the amount of sediment found in suspension.
242
T. Hilger et al.
explanations, see also Sect. 7.4) with a width of 4 m and a length of 18 m
downslope, and with side walls of 0.20 m in height to prevent run-on water.
Maize (Zea mays) was used in all treatments as a representative local cropping
system. In the case of Ban Muang Bo Noi, trials were established in April 2003 and
fields laid out using a split-plot design and with fertilizer application as the main
variable factor (no fertilizer, and 60 kg N ha
À1 plus 14 kg P ha
À1 ), soil conservation
as the subfactor, and with two replicates. In total, 16 monitoring plots were
established, and a collection device for run-off water and eroded soil was installed
at the lower end of each plot. Subfactor treatments were: (1) vetiver grass (Vetiveria
zizanioides) barriers, (2) ruzi grass (Brachiaria ruziziensis) barriers, (3) leucaena
(Leucaena leucocephala) hedges, and (4) a control without a hedgerow (all under
minimum tillage). Leucaena, ruzi grass and vetiver grass were planted in three 1 m
wide barriers at intervals of 6 m, occupying about 17 % of the total plot area. Maize
was relay cropped with Jack beans (Canavalia ensiformis) starting in September
2003. Jack beans were planted 1 month prior to maize harvest. Maize stover and all
Jack bean materials were left on the plots as mulch to protect the soil from erosion
and suppress weed growth the following growing season. Plots with hedgerows or
grass barriers were pruned three to six times per year, with pruning spread evenly
over the alley. In all treatments, weeding was done by hand when necessary, which
defined the trial set-up as a minimum tillage system (Young 1996).
In the case of Chieng Khoi, field trials were chosen based on a participatory
selection process in cooperation with local farmers and extension officers, resulting
in four treatments, namely: (1) maize cropping following farmers’ normal practice
(hoeing, weeding, burning, animal plowing and hoeing), (2) maize with Panicum
maximum as a grass barrier, (3) maize under minimum tillage with Arachis pintoi as
a cover crop, and (4) maize under minimum tillage, relay cropped with a leguminous bean Phaseolus calcaratus. Trial plots were installed as a randomized complete block design with three replicates, receiving a total fertilizer rate of 158, 17.5
and 58.6 kg ha
À1 of N, P, and K respectively. Panicum maximum grass barriers were
planted in June 2009 and Arachis pintoi was transplanted in June 2009. Phaseolus
calcaratus was sown in all years 1 month after maize planting. In both years, maize
was sown in mid-May and harvested at the end of September. In the case of Ban Bo
Muang Noi, maize was harvested at the beginning of October in 2003, 2004 and
2005. As a common approach in both field trials, harvested maize plants were
separated into grain and stover and oven-dried at 70
C to determine the dry weight.
Soil loss and run-off data were collected after every rainfall event using a series
of collecting tanks or buckets, which directly measured run-off volumes. Soil loss
amounts were calculated based on the collected heavier sediment found at the
bottom of the plot in the collection device, and the suspended sediment fractions.
Suspended sediment fractions were collected through run-off samples of approximately 1 L, as taken from the tanks or buckets after stirring and filtering. After
filtration, particles collected on the filter were oven-dried at 105
C for 24 h to
determine the amount of sediment found in suspension.
242
T. Hilger et al.