D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127 121
the future improvement of FPR on soil erosion? The survey information was analyzed and reported.
3. Results and discussion
3.1. Soil loss from high-value contour hedgerows erosion-runoff plots
In the researcher-managed site, annual soil loss measured from the high-value contour hedgerows
treatment 45.4 Mg ha
− 1
was lower by 30 compared to the conventional practice of up-and-down culti-
vation 65.3 Mg ha
− 1
. This suggests that high-value contour hedgerows are effective measures to minimize
soil erosion on steepland vegetable systems. Poudel et al. 1999b discussed in detail the effectiveness
of high-value contour hedgerows in minimizing soil movement down the slope, and the management of
natural terraces formed in between contour hedgerows. Annual soil loss measured on farmers’ plots ranged
from 1.4 Mg ha
− 1
to 52.5 Mg ha
− 1
with an average of 21.2 Mg ha
− 1
Table 3. There was a good agreement between measured and simulated soil losses. One of
the farmer-managed erosion-runoff plots plot 5 rep- resented an unplanted plot fallow-fallow-fallow and
lost 23.7 Mg ha
− 1
year
− 1
, equivalent to establishment
Table 4 Selected chemical properties of original soil surface 0–15 cm, eroded sediment, and final soil surface 0–15 cm on contour hedgerows
treatment in researcher-managed erosion-runoff plots in the Manupali watershed, Mindanao, the Philippines n = 6 Total-N
Organic C pH-H
2
O P
Ca Mg
K g kg
− 1
g kg
− 1
mg kg
− 1
cmol
c
kg
− 1
cmol
c
kg
− 1
cmol
c
kg
− 1
1. Original 4.2 0.5
a
54 5.5 5.3 0.1
3.9 0.9 2.6 0.6
1.5 0.2 1.0 0.1
2. Eroded soil First cropping season
2.6 0.9 68 4.6
5.3 0.1 9.5 1.5
6.3 0.8 1.7 0.2
0.7 0.1 Second cropping season
4.9 0.5 66 6.4
4.9 0.2 6.1 1.6
NA
b
NA 1.1 0.1
Third cropping season 4.3 0.2
76 2.6 4.8 0.1
11.7 1.2 5.3 0.8
2.0 0.3 0.9 0.1
Fourth cropping season 4.1 0.3
57 4.5 4.7 0.1
10.9 1.1 NA
NA 0.6 0.1
Fifth cropping season 3.4 0.7
67 5.1 4.3 0.1
15.7 1.8 5.0 1.4
0.8 0.2 0.7 0.0
Sixth cropping season 1.5
c
63 4.3
15.7 2.3
0.1 0.63
Seventh cropping season 2.8 0.2
56 2.8 4.0 0.1
22.7 4.8 2.8 0.5
0.8 0.1 0.3 0.0
3. Final soil
d,e
2.3 0.2
∗∗
43 3.1ns 3.7 0.1
∗∗∗
8.4 1.2
∗
2.5 0.4ns 0.7 0.1
∗∗
0.3 0.0
∗∗∗ a
Figures in paranthese are standard error of mean.
b
Not available.
c
Sample size n = 1.
d
Student-t test for the similarity of the means between the initial properties versus final properties.
e ∗,∗∗,∗∗∗
Significant at 0.05, 0.01, and 0.001 probability level, respectively, with student t-test. ns indicate not significantly different at 0.05 probability level by student t-test.
of a natural fallow. Most soil loss was during the first unplanted season when rainfall was high. This farmer
cooperator could not plant a crop in his erosion plot due to ill health. The farmer cooperator managing
Plot 8 established additional contour hedgerows in the plot and planted trees along the hedgerows which
resulted in extremely low amounts of annual soil loss 1.4 Mg ha
− 1
. 3.2. Impacts of soil erosion on soil fertility
Impacts of soil erosion on soil fertility were ev- ident by the end of the experiment on both the
researcher-managed experiment and farmer-managed erosion-runoff plots. In the researcher-managed con-
tour hedgerows erosion-runoff plots, total-N, soil pH, Mg, and K were significantly lower at the end
of the experiment compared to the original values Table 4. Although statistically not significant, or-
ganic C values decreased from an average of 54 g kg
− 1
at the start of the experiment to 43 g kg
− 1
at the end of the experiment. This decline in organic C may af-
fect the sustainability of these production systems as organic C affects not only soil physical and chemical
properties but also microbial activity in soils. There was a significant increase in available P at the end
of the experiment. Available P increased from its
122 D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127
Table 5 Selected soil properties of the final soil surface 0–15 cm at the upper, and the lower slope positions of 20 m long farmer-managed
erosion-runoff plots in the Manupali watershed, Mindanao, the Philippines n = 12 Total-N g kg
− 1
Organic C g kg
− 1
pH P mg kg
− 1
Upper 2.4 0.2
a
49 5.3 4.5 0.1
11.8 4.9 Lower
2.7 0.2 63 5.9
4.8 0.1 13.0 4.4
Difference lower–upper
b
0.3 0.2ns 14 4.9
∗
0.3 0.1
∗∗
1.2 1.7ns
a
Figures in paranthese are standard error of mean.
b ∗,∗∗,∗∗∗
indicate significantly different at 0.05, 0.01, and 0.001 probability level by paired-comparison t-test. ns indicate not significantly different at 0.05 probability level by paired-comparison t-test.
average value of 3.9 to 8.4 mg kg
− 1
. However, eroded soils showed consistently higher values for P com-
pared to original soil surface Table 4. Since P is one of the yield limiting nutrients in these soils Poudel
and West, 1999, unwarranted removal of P from the field requires immediate attention.
In farmer-managed erosion-runoff plots, notable differences in crop establishment and soil qualities
between the upper and the lower portions of 20 m long erosion-runoff plots were observed during the
study. Soil pH and organic C in the lower portions of the erosion-runoff plots were significantly higher
compared to that of upper slope position Table 5. The lower slope positions showed, on average, 7
greater soil pH and 28 greater organic C. Although statistically not significant, total-N and available P
in the lower portions were higher compared to that of the upper portions. Similar results were found in
researcher-managed
erosion-runoff plots
Poudel et al., 1999b. These differences in soil fertility gra-
dient across the slope positions suggest the need for a
Table 6 Means, standard deviations SD, and root mean square errors RMSE of measured and simulated annual soil loss and runoff values for
the selected cropping sequences in the Manupali watershed, Mindanao, the Philippines Cropping
Size Natural Annual
Annual sequence
n slope
soil loss runoff
Mean SD Measured Simulated
RMSE Measured Simulated
RMSE Mean
SD Mean
SD Mean SD
Mean SD Mg ha
− 1
Mg ha
− 1
Mg ha
− 1
Mg ha
− 1
mm mm mm mm Cabbage-tomato-corn
a
2 41.5
2.5 38.9
16.9 33.1
6.0 23.6
58 12
52 3
17 Corn-cabbage-tomato
2 41.5
1.5 53.5
12.3 53.2
6.1 6.3
51 2
48 2
3 Fallow-fallow-potato
3 54.3
13.1 19.7
2.5 23.0
3.7 7.0
– –
109 16
– Cabbage-fallow-tomato 2
23.5 7.5
12.5 4.0
8.5 2.5
4.2 –
– 40
17 –
a
The first, second and the third crops represent January, May and September plantings, respectively.
variable management strategy to improve soil fertility on these sloping lands.
3.3. Effects of cropping sequence on soil erosion The simulated annual soil loss for the four repli-
cated cropping sequences under high-value contour hedgerows were reasonably close to measured val-
ues Table 6. The cropping sequence of cabbage- tomato-corn showed a relatively larger RMSE value
due to a large difference in actual 55.8 Mg ha
− 1
versus simulated annual soil loss 27.1 Mg ha
− 1
for one of its two replicates. This replicate plot 23 in researcher-managed site had a soil loss of
66 Mg ha
− 1
during the first cropping season, while its counterpart Plot 1 in researcher-managed site
lost only 2 Mg ha
− 1
of eroded soil. This large differ- ence in soil loss between the two replicates of the
cabbage-tomato-corn cropping sequence is attributed to a greater digging of soils in one of the replicates
Plot 23 in researcher-managed site while setting up
D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127 123
Table 7 Simulated average annual soil loss and runoff for 15, 25, 35,
45, 55, and 65 slope under different cropping sequences in the Manupali watershed, Mindanao, the Philippines
Cropping sequence Soil loss
Runoff Mg ha
− 1
mm I. Single cropping
Tomato-fallow-fallow
a
3.1 59.5
Cabbage-fallow-fallow 6.8
59.5 Fallow-cabbage-fallow
96.6 47.3
II. Double cropping Tomato-corn-fallow
53.5 49.1
Fallow-corn-cabbage 61.3
47.2 III. Triple cropping
Tomato-corn-cabbage 52.8
47.3 Cabbage-tomato-corn
44.9 49.0
Cabbage-corn-tomato 61.3
48.3 Tomato-cabbage-tomato
98.3 46.2
Cabbage-tomato-cabbage 28.1
46.1 Corn-cabbage-tomato
71.5 45.2
a
The first, second and the third crops represent January, May and September plantings, respectively.
plots. Several large stones were dug out and trees were uprooted from this plot. Simulated annual soil loss
for fallow-fallow-fallow sequence was 22.9 Mg ha
− 1
as opposed to the 23.7 Mg ha
− 1
measured value. With a single vegetable crop per year, average soil
loss was least Table 7 when a fallow was established well before the most erosive time of the year Septem-
berOctober. However, if not constrained by capital or labour, farmers would be unlikely to leave land in
fallow during the rainy season, the season when crop- ping is favoured under the essentially rain-fed system.
If a single crop was taken in the summer period, fal- low was not sufficiently well established to control soil
erosion by SeptemberOctober. If, however, the fallow followed corn as seen in the double cropping, the soil
loss was considerably less than if following cabbage.
Not all multiple cropping sequences were equally effective in reducing soil erosion Table 7. The crop-
ping sequence of tomato-cabbage-tomato 98.3 Mg ha
− 1
resulted in nearly three times more soil loss than that of cabbage-tomato-cabbage 28.1 Mg ha
− 1
. Hence, consideration must be given to the crops and
planting seasons when designing a multiple crop- ping pattern to minimize erosion on steeplands. The
reason for low annual soil loss from the cabbage- tomato-cabbage cropping sequence is attributed to
greater canopy cover by cabbage than tomato Poudel et al., 1999b during erosive rainfall events that
generally occur in the months of March–May and August–October. The importance of canopy cover to
minimize soil loss, especially during the months of September–October, was also manifested by the sim-
ulated soil loss for the cabbage-tomato-corn sequence Table 7. Poudel et al., 1999b reported a greater
canopy cover for corn than tomato and cabbage.
Fig. 2 shows the effect of selected multiple-cropping sequences on annual soil loss for different slope cat-
egories. It shows that the difference in the amount of soil loss between cropping sequences increases as
slope increases. These data support the suggestion by Phillips et al. 1993 that on gentle slopes, cropping
sequences have less influence on soil erosion than on steeper slopes.
As for measured soil loss in researcher-managed site Poudel et al., 1999b, on average, two-thirds of
the total soil loss across all cropping sequence x slope simulations occurred during September–December,
whereas one-third occurred during May–August data not shown. Emphasis should be given to those crop-
ping sequences that include less erosive crops in their September plantings. Simulation results indicated that
Fig. 2. Simulated annual soil loss in tomato-cabbage-tomato, cabbage-corn-tomato, and cabbage-tomato-cabbage cropping se-
quence in the Manupali watershed, Mindanao, the Philippines.
124 D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127
Table 8 Simulated seasonal soil loss with 42 natural slope for May and
September plantings of corn, tomato, and cabbage in the Manupali watershed, Mindanao, the Philippines
Cropping seasons Soil loss
Mg ha
− 1
I. May–August Corn after cabbage
23.4 Cabbage after tomato
20.2 Corn after tomato
17.8 Tomato after cabbage
9.2 II. September–December
Tomato after cabbage 55.4
Tomato after corn 24.1
Cabbage after corn 24.4
Corn after tomato 27.8
in-crop erosion can be affected by the prior crop in the sequence. Table 8 presents simulated soil loss for
different crops in their May and September plant- ings at 42 natural slope. The September planting of
tomatoes after cabbage showed 130 greater soil loss 55.4 Mg ha
− 1
compared to that of planting tomatoes after corn 24.1 Mg ha
− 1
. This relatively lower soil loss after corn compared to that after cabbage is at-
tributed to the differences on the root systems of the preceding crops. Tan and Fulton 1985 reported the
total root length of corn to be twice that of tomato, with a much greater spatial density. This greater root
system of corn probably holds soil more strongly, re- sulting in a reduced soil erodibility. Soil loss in tomato
is also believed to have been aggravated by the prac- tice of earthing up twice, i.e. taking soil from between
the tomato rows forming deep furrows between them, and applying that soil to the base of the tomato plants.
This was done only once in corn and cabbage. Earth- ing up apparently increases the erodibility of the soils
by lowering the surface bulk density and breaking aggregates. Such soil disturbance would be expected
to enhance entrainment and re-entrainment in sloping tomato fields. Rose 1988 described entrainment and
re-entrainment of the deposited sediments as impor- tant processes in erosion in sloping lands. Hence,
minimizing soil disturbance i.e. minimal tillage to reduce soil erodibility appears to be a valid erosion
reduction practice in these landscapes.
Predicted annual runoff values for three cropping sequences:
tomato-cabbage-tomato, cabbage-corn-
Fig. 3. Simulated annual runoff for tomato-cabbage-tomato, cabbage-corn-tomato, and cabbage-tomato-cabbage cropping se-
quence in the Manupali watershed, Mindanao, the Philippines.
tomato and cabbage-tomato-cabbage are presented in Fig. 3. Although soil loss differed between the
three cropping sequences, annual runoff for each was very similar. This suggests that different cropping
sequences with a relatively low runoff volume may not reduce soil erosion on sloping lands. As there
was no relationship between runoff and soil erosion across cropping sequences, factors other than runoff
e.g. gravity loss, soil disturbance, root distribution were responsible for the soil loss differences between
cropping sequences.
On average, runoff quadrupled as the slope in- creased from 15 to 65 Fig. 3. This trend suggests
that farmers on steeper slopes should adopt practices, such as mulching, to conserve water in their vegetable
fields.
3.4. Future prospects of FPR on soil conservation The farmer cooperators’ survey indicated a good fu-
ture prospect of FPR on soil conservation. Impacts of the participatory research were evident by the end of
the experiment, as most of the farmer cooperators had already started replicating their contour hedgerows in
their nearby vegetable fields. Pineapple was the most preferred hedgerow species. However, limited avail-
ability of planting materials constrained its widespread and rapid extension. At least one farmer cooperator
D.D. Poudel et al. Agriculture, Ecosystems and Environment 79 2000 113–127 125
integrated pineapple with trees in his farm land. As- paragus had poor growth in most farmer’s plots, while
pigeon pea suffered from insect pest damage. Lemon- grass was a good hedgerow in all erosion-runoff
plots.
Based on the survey results, this participatory research helped farmer cooperators in learning the
benefits of contour hedgerows 9 out of 12 and of planting in contour 6 out of 12 for soil conservation.
Ten out of 12 farmer cooperators mentioned that they had gained a quantitative impression of the soil loss
from their vegetable fields. Most farmer cooperators considered the participatory research approach as
an effective tool for technology transfer 11 out of 12. But, farmer cooperators also pointed out several
problems in relation to participatory erosion control research. The majority of cooperators 9 out of 12
agreed that input cost and time were the main con- straints to this research. At least two farmer coopera-
tors complained about the obstacles to the movement of their draft animals during field operations imposed
by iron sheets used in the erosion-runoff plots. Other problems related to this research included: technical-
ity in soil collection and air-dry, frustration on the part of farmer cooperators due to poor attendance of
their fellow cooperators in regular meetings, labour availability, and capital requirement for the research.
Farmer cooperators suggested several measures for the future improvement of FPR on soil conservation.
These included: careful selection of farmer coopera- tors who can spend more time for the research, finan-
cial assistance to conduct field experiments, regular visits of a farmer’s field experiment by other fellow
cooperators, farmer-to-farmer technology transfer, a clear agreement between the researchers and farmers
about the use of research materials after the comple- tion of the research, regular meetings, detailed plan
of activities, and a strong monitoring of the program.
4. Conclusions
