25-5-soil erosion from agricultural area

8/1/2019 25-5-Soil Erosion From Agricultural Area

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ON-SITE EROSION OF UPLAND AGRICULTURE

A case study : local Thais Ban Kasai and Mien Ban La Bal Ya

of KHunsamun Watershed, NAN BASIN

Orathai Mingthipol1

1 Department of Landscape and Environmental Conservation, Faculty of Agricultural Production, Maejo

University, Thailand

Abstract

Since the upland agriculture has expanded in Khun Samun sub watershed, thesevere erosion and sedimentation has became the hazardous problem in this area.Agriculture in the upland of Mien Ban La Lao Ya village is also one of many areasthat causes this severe erosion. This preliminary study of on site erosion uses theempirical model of USLE for estimating on site erosion of upland agriculture andforest. Soil samples from nineteen upland agricultural plots and 6 forest plots of BanLa Bao Ya were selected for erodibility factor (K). This study found four interestingfindings: 1) on site erosion rate of bare land and annual cash crops was over thetolerance as the severe to very severe level due to ground coverless and, 2) the fallowareas protected soil surface better than annual cash crop and permanent cash cropsdue to dense ground cover and a high permeability of soil. 3) The soil erosion ratesin the forest areas located at similar slope gradients to those of the upland agriculturalplots was very low. These findings imply that converting forest areas to agricultural

areas increases soil erosion. 4) Dirt roads in the upland field also played a significantrole in altering near-surface hydrologic response and subsequently accelerating soil

erosion in this area.

1. Introduction

The upland agriculture has been rapidly evolving in Northern and EasternThailand from traditional systems to modern systems. The transition is influencedmainly by external socio-economic factors rather than agro-ecological determinants.As contacts to lowland markets increase, the transformation to cash-based economy

accelerates. This event also has approved among Mien people in Khun Samun. Therole of upland rice cultivation has changed as the demand for vegetables, maize andfruits from lower people increased; forests were cleared for more land for uplandproduction. According to the Land Development Department (LDD), about 17million sq. kms, or one third of the country, is subject to moderate to severe erosionhazards. (Omakupt,1991). Soil erosion removes the fertile surface soil horizon (sheeterosion); this leads to losses of organic matter and plant nutrients. Therefore, soilerosion must be viewed in relation to the general loss of soil fertility. Furthermore,soil erosion destroys the surface soil structure by separation of clay and silt texturefractions (sheet erosion). Stones are often left on the soil surface of the upper areas of a slope. Erosion destroys the relief of the soil surface (gully erosion) and leads to

siltation of water streams and reservoirs. Thus this research paper is to present thepreliminary study of Khun Samun interdisciplinary research on 1) on-site losses from

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various types of upland agriculture, and 2) preliminary discussion on the on-siteerosion and its impact.

2. Study site

Khun Samun sub watershed, the tributary of Mae Nam Nan watershed, issituated in areas with elevation varying from 300-1,100 meters from mean sea level.The morphology of this watershed consists of mountainous, hilly area, narrow riverterraces and alluvial fans on downstream.

Soil interplay of different soil forming factors, topographic features andparental materials produces a great diversity of soil group. Formally, thee soils wereclassied into two main groups: red yellow podzolic and reddish brown lateritic soils.A new taxonomy classification was done by The LDD (1982). They reported that themain soils in this areas are Clayey Tropaqualfs, Loamy Paleustults, SkeketalHaplustalfs, and Tropohumults while others are loamy Haplustalfs, and Clayeytropaqueots.

From land use map of the DLD in 1975 and from Landsat imagery in 2000,this area was mainly covered by mixed deciduous forest with small area of dryevergreen forest at the upper northwestern part. Some disturbed forests and mixedrotated farming area were situated along the lower basin with some extended areastoward upstream. Agricultural land consisted of upland rice, maize, cotton andperennial crops such as lychee, orange longan and rambutan. Most agricultural landswere cultivated within disturbed mixed deciduous forests. Paddy was cultivated insmall areas in the narrow valley of Huai Ka Sai Stream and the lower Samun Riverthat used to be upland rice and former disturbed mixed deciduous forests.

Figure 1. Khun Samun sub watershed

2



Figure 2 Land use

.

Figure 3 Typical topographic and land use characteristics for upland

agriculture

Ban La Bao Ya is a Mien village situated within C-zone reserve forest. Most farmers have 2-

4 plots of land. The agricultural fields are widespread in upland area. The agricultural in Ban

La Bao Ya was depended very much on upland rice for household consumption. They

practice a rotational system of farming, having a fallow period of 3-4 years for upland rice

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and 1-2 year for maize and cotton. Lychee, maize, cotton and recently rambutan have been

planted as cash crops. All kinds of chemical inputs were applied to cash crops and there are

few chemical fertilizers and herbicides were applied on upland rice. Most farming areas were

rainfed

3. The investigation

Historical and more recent data including topography, geology, climatic data,hydrologic data, land capability, soil properties and vegetation were compiled. Thedescription of soil profiles, field identification and environment determination wereobtained from field investigations. The problems encountered and their magnitudes inthe study area were assessed. A set of factors as identified in the USLE were studiedand reviewed.

On-site Erosion: The field investigations was carried out in May 2004, it was thebeginning of rainy season when Mien farmers were starting farming. Soil samples

from twenty-one upland agricultural plots and 6 forest plots of Ban La Bao Ya wereselected using the criteria of picking samples to cover the range of differences inphysiographic, land use and crop types. The percentage of the land use types is shownin Figure 3.

% sampled plots

11%

11%

11%

11%19%

15%

11%

11%

slashed and burnt

bare soil

upland rice

maize

permanent cashcrops

fallow area

dry everngreen forest

disturbed mixed

deciduous forest

Figure 3 The percentage of the land use types

Soil samples were collected from the selected plots of land belonging to theseland use types. Soil samples were also collected from 2 types of forest, so that thefertility and erodibility levels between the agricultural and forest areas could be

compared. At each soil sampling location, 1 composite soil sample at 15 cm depthand also 6 undisturbed soil samples to 30 cm depth, separated into three verticaldepths, 0-10 cm 10 – 20 and 20 -30 cm depths, using the thinning and coring methodfor permeable analysis (K-index) and bulk density were taken.

The soil samples were used for fertility and erodibility analysis and also somephysical determinations such as texture and tone by finger test, field observationswere also carried out.

The soil surface of most of the sampled plots were studied and it wasobserved that 1) soil surface characteristics of upland rice and maize plots were mostsimilar, it was sandy loam with coarse sand, dry and compacted, moderate topsoil

depth with very rapid of infiltrability but a low permeability that was indicated by alow permeable rate which decreases slightly with soil depth, non conservation

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measures were practised. 2) Deep topsoil was occurred in all plots of forest, morethan 10 cm depth of humus with very rapid of infiltrability and permeability. And 3)soil texture and depth of topsoil were almost similar by comparing between fallowareas and upland field crop (rice and maize). Inflitrability including permeabilityincreased gradually with period of leaving but there was non significance in depth of

topsoil as well as soil texture excepting 7 yrs fallow area was changed significantly.

During the field investigation, it was found the upland Mien farmers did notutilize any conservation practices. In addition data from the open-ended interviewsand field investigation indicated that farmers did not recognize and therefore did notrectify soil erosion problems. Farmers also perceived that soil erosion had minimaleffects on production and farmers do not rely on government cost-sharing erosioncontrol programs.

Permeability was defined as the movement of water into the interconnectedpores that form an intricate net of irregular capillary tubes. Laboratory testing of permeability used the undisturbed samples and utilized a permeameter for measuringK with a falling-head permeameter. The hydraulic conductivity was measured in thelaboratory following Klute (1965). The conversion equation for K was as follows:

K = [2.3 aL/A(t2-t1)](log H1 – logH2)

Where H1 and H2 = the values of hydraulic head at time t1 and t2, respectively.

The Khunsamun GIS database was used for interpreting land cover types,drainage pattern, percent steepness, slope length and determining the watershed

boundary. Monthly rainfall data were obtained from the Nan Horticulture ResearchStation. Soil conservation measures and agricultural activities were determined byfield observations. Soil Loss was predicted by using the Revised Universal Soil LossEquation (RUSLE) (Wischmeier and Smith, 1978), adjusted to satisfy the localconditions by an area weighting score. The RUSLE is a Windows-based model thatwill be placed in field offices for use by field conservation planning. The equation issimple arithmetic relation of various factors influencing erosion as follows:

A = RKLSCP

Where: A = Soil loss in ton /ha/year

R = Rain erosivity factor; rainfall factor (R-FAC) was determined using linear

regression equations developed by Samran (1984) and Dumronghanvitaya (1985) forthe highlands of Northern Thailand. Analysis of annual rainfall data of past 11 yearsgives the R-factor. This equation was applied where the location is lower 800 MASLas follows

R = 8.276 P – 215.058, Where R = Rainfall factor (m-ton/ha) and P = annual rainfall(cm).

Analysis of annual rainfall data of past 11 years gives the R-factor.

K -factor; soil erodibility factor (K) represents susceptibility of soil to erosion. It is ameasure of erodibility based on the nomograph.

The variables used to analyze the K-factor are % organic matter (OM), % sand, % siltand very fine sand, soil structure and the level of permeability.

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The variable % OM can reduce erodibility because when percentages are high itreduces the susceptibility of the soil to detachment, and it increases infiltration, whichreduces runoff and thus erosion. The variable soil structure affects both susceptibilityto detachment and infiltration. Permeability (K-sat) of the soil profile affects Kbecause it affects runoff.

L-factor is the slope length factor, representing the effect of slope length on erosion.Slope length is the distance from the origin of overland flow along its flow path to thelocation of either concentrated flow or deposition. Slope lengths are best determinedby visiting the site, pacing out flow paths, and making measurements directly on theground.

S-factor is the slope steepness. Represents the effect of slope steepness on erosion.Soil loss increases more rapidly with slope steepness than it does with slope length.

L factor and S factor are usually considered together. LS factors = the slope lengthfactor (L) is the effect of slope length on erosion and the slope gradient factor (S) isthe effect of slope steepness on erosion.

The L and S factors in each plot were measured from the site and can be expressed interms of a mathematical equation based on data analyses by Wischmier and Smith(1978) as follows:

S = (0.43 + 0.30s + 0.04s2)/6.617L = (λ / 22.1) m

where S = Percent slope

λ = Slope length (m),

and M = 0.5, if s ≤ 12%= 0.6, if s > 12%

C-factor is the cover-management factor. The C-factor is used to reflect the effect of cropping and management practices on erosion rates. The C-factor indicates how theconservation plan will affect the average annual soil loss and how that soil-losspotential will be distributed in time during construction activities, crop rotations orother management schemes.P-factor is the soil conservation practice factor which reflects the impact of supportpractices and the average annual erosion rate.

Cropping and soil conservation factor (CP) was obtained from the Land DevelopmentDepartment, LDD (1996).

When the equation was used for computing soil loss from agricultural areas, allfactors except the rainfall factor were modified to increase computational efficiency.

4. Results

Generally, the soils in the upland and highland areas are complex soils due tothe characteristics such as erosive texture, complex structure, low productivity andlow capability of the land. Where the surface soil characteristics have a shallowtopsoil, rock fragments, a scattering of boulders and the topography is steep slopes,the natural soil fertility is low to medium. Hence, most of these soils are classified aserosive soils (LDD, 1983). These areas are generally unsuitable for agriculturalregarding to the high rates of erosion where the soils have been disturbed. It isrecommended that these soils are left under forest cover for watershed protectionpurposes.

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The landform and surface characteristics, factors influencing soil erosion wereused to evaluate the on-site erosion including on-site prediction value (Table 1-2).

Onsite erosion of Bare land

In the uplands, it was found most farmers left their land as bare land afterharvesting, some were slashed and burnt and some were started preparing at thebeginning of the rainy season (figure 4). Agricultural practices like these and also thesoil properties and slope gradient tend to increase the energy of raindrop impact andthe velocity of runoff flow, thus the soil particles detach from the soil surface and aretransported to lower areas and streams.

Slashed and burnt area Bare soil area

Figure 4 bare land in Mien farming area

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Table 1. The landform and surface characteristics of sampled plots

PermePlot

No.

Crop

Type

Landform

Surface characteristics

0-10 cm

1 Bare soil Hilly area dry soil of surface; sandy loam with coarse sand ;ground cover less 7

2 Bare soil Hilly area dry and tillage soil surface, loosen bare soil ; sandy loam ; ground coverless 35

3 Bare soil Hilly area dry soil surface, compact bare soil ; sandy loam ; ground coverless 8

4 Slashed and burnt Hilly area loosen dry soil ; sandy loam38

5 Slashed and burnt Hilly area compact surface of soil , sandy loam 6

6 Slashed and burnt Hilly area compact soil; sandy loam with coarse sand and rock fragment 9

7 Upland rice(3 weeks grows)

Hilly area compact surface; sandy loam with slightly rock fragment

12

8 Upland rice (2 weeks grows)

Ridge topof the hill

slightly ground cover; shallow topsoil,sandy loam with coarse sand, slightly cementing with rock fragment andbolder 9

9 Upland rice intercrop with 2 yrsrambutan(2 weeks grows)

Steep slope compact surface; sandy loam and coarse sand with scattering of rock fragment

6

10 Maize(1 weeks grows)


ground coverless; loosen bare soil; sandy loam and coarse sand and scatteringrock fragment

21


Steep slope compact dry soil ; sandy loam with coarse sand and scattering rock fragment

6


Hilly area compact dry soil; shallow topsoil, coarse sand , a few cement of clay withrock fragment

8

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Table 1. (cont.) PermePlot

No.

Crop

Type

Landform

Surface characteristics

0-10 cm13 Rambutan (2 yrs) Moderate

slopecompact soil ;moderate deep of topsoil layer, sandy loam with coarse sand,ground coverless 12

14 Lychee (6 yrs) Hilly area compact soil; shallow topsoil; sandy loam with coarse sand and rock fragmentand bolder, ground coverless 7

15 Longan (6 yrs) Moderateslope

compact dry soil; shallow topsoil; sandy loam with coarse sand13

16 Rambutan (4 yrs) Moderateslope

compact dry soil; shallow topsoil; sandy loam with coarse sand11

17 Lychee (4 yrs) Moderateslope

compact dry soil; shallow topsoil; sandy loam with , rock fragment withscattered big bolder 6

18 Fallow area (2 yr) Very steepslope

Compact dry soil with dense weed; shallow topsoil, sandy loam with coarsesand , rock fragment with scattered big bolder 12

19 Fallow area (3 yr) Hilly area Cover with dense and height of weed; shallow topsoil; sandy loam withcoarse sand 14

20 Fallow area (5 yr) Ridge topof the hill

Cover with young bamboo and dense of weed; shallow topsoil; sandy loamwith coarse sand 23

21 Fallow area (7 yr) Very steepslope

Cover with dense of bamboo and weed; moist soil; sandy loam with coarsesand 31

22 Mixed deciduous(MDF1)

Moderateslope

Compact topsoil with moderate deep of top soil layer; moist; sandy loam ;moderate thick of litter cover 18

23 Mixed deciduous Ridge top of the hill(MDF2)

slightly litter with loosen zone, moderate deep of topsoil; sandy loam ;moderate thick of litter cover 24

24 Mixed deciduous(MDF3)

Moderateslope

thick litter with compact zone; moderate thick of topsoil; dense groundcover 15

25 Dry evergreen(DEF 1)


loosen soil; deep of topsoil ; moist; sandy loam with silt; moderate thick of litter cover, slightly of ground cover , wide and high crown 42


Very steepslope



Moderateslope




Table 2. factors influencing soil erosion and on site erosion rate

Plot Crop type

R-

factor

K-

factor*

C-

factor**

P-

factor**

LS-

factor On-site

Tolerance

goal**** O

No. ton/ha/yr to1 bare soil (1) 229.92 0.31 0.9 1 15.68 1006.84 over limit

2 bare soil (2) 229.92 0.29 0.9 1 15.29 917.54 over limit

1 bare soil (3) 229.92 0.34 0.9 1 12.46 876.63 over limit

3 slashed and burnt (1) 229.92 0.26 0.45 0.9 19.34 468.23 over limit



4 upland rice (3 weeks) 229.92 0.33 0.24 0.9 13.49 221.08 over limit



8Maize (1 week grown) 229.92 0.31 0.24 0.9 10.46 161.04 over limit

9 Maize(2 weeks) 229.92 0.27 0.24 0.9 15.7 210.52 over limit 10 Maize(2 weeks) 229.92 0.29 0.24 0.9 13.2 190.11 over limit

11 rambutan (2 yr) 229.92 0.38 0.22 0.9 6.89 119.19 over limit

12 lychee (6 yr) 229.92 0.38 0.19 0.9 11.24 167.93 over limit

13 longan(6 yr) 229.92 0.41 0.12 0.9 8.95 91.12 over limit

14 rambutan (4 yr) 229.92 0.36 0.14 0.9 8.44 88.02 over limit

15 lychee (4 yr) 229.92 0.38 0.13 0.9 8.34 85.25 over limit

16 Fallow area (1 yr) 229.92 0.32 0.013 0.9 18.00 5.49 acceptable




20 MDF (1) 229.92 0.32 0.004 0.9 11.24 2.98 acceptable

21 MDF (2) 229.92 0.33 0.004 0.9 15.34 4.19 acceptable

22 MDF (3) 229.92 0.25 0.004 0.9 13.41 2.77 acceptable

23 DEF (1) 229.92 0.25 0.001 0.9 14.56 0.75 acceptable

24 DEF (2) 229.92 0.21 0.001 0.9 18.34 0.80 acceptable

25 DEF (3) 229.92 0.26 0.001 0.9 14.56 0.78 acceptable

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DMDF = Disturbed mixed deciduous forest ; DEF = Dry evergreen forest in upper of Khun Samun Watershed

*K- factor is analyzed by nomograph ** C-P factor is categorized from LDD list (1996)

*** Global Tolerance rate = 12.5 ton ha-1yr-1 (USDA, 1964)**** Soil erosion classification of Thailand (ton rai-1yr-1 ) : < 1.00 = very slight; 1.01 – 5.00 = slight ; 5.01 – 20.00 = moderat

100.01 = very severe



On-site erosion rates in this area were higher than the erodibility class whichwas classified by LDD (1983) as very severe for bare soil (Table 2) and severe forslashed and burnt area. Reference to the U.S. Department of Agriculture (USDA,1964) classification, indicates that all plots are over the limit of tolerance.

Bare Soil

0

20

40

60

80

100

120

140

160

180

o n s

i t e e

r o s i o n (

t o n / r a i / y r )

bare soil (1)

bare soil (2)

bare soil (3)

acceptable

Slashed and burnt area

0

20

40

60

80

100

slash and burnt

o n s

i t e

e r o s i o n (

t o n / r a i / y r )

slashed and burnt (1)



acceptable

Figure 5 on-site erosion of plots of slashed and burnt ( n = 3) and bare soil ( n = 3)

Soil erosion rates in annual cash crops (upland rice and maize)

The upland rice and maize areas of Mein La Bao Ya were scatteredwidespread on both of moderated to steep slope in the middle of Khunsamun subwatershed. The most were rotation system as farmers do preparing and planting.manually, herbicide and fertilizer was applied on those fields.

On-site erosion rate in these areas were also higher than the erodibility classthat was classified by LDD (1983) as severe (figure 6) and lower than bare landrelatively. Reference to the U.S. Department of Agriculture (USDA, 1964)classification, indicates that all plots are over the limit of tolerance.

Upland rice

0

10

20

30

40

50

1

o n s

i t e

e r o s i o n ( t

o n / r a i / y r )

upland rice (3 weeks)



acceptable

Maize

0

10

20

30

40

1

o n s

i t e

e r o s i o n (

t o n / r a i / y r )

Maize (1 week grown)

Maize(2 weeks)

Maize(2 weeks)

acceptable

Figure 6 the on-site erosion of plots of upland rice ( n = 3) and maize ( n = 3)

During the field investigation, rill erosion and small gullies were found on thesurface in these plots. The upland soils were observed to be compacted soils with amoderate topsoil of sandy loam and coarse sand, rock fragments and with a low

1



permeability, there was no topsoil mulching, low ground cover and no conservationpractices were utilized as shown in the Figure 7. This situation let runoff erosionoccurred whenever the intensity of rainfall exceeds the infiltration rate at the groundsurface.

Figure 7 Rill erosion on upland rice field

The CP-factor represents the effects of plant cover, soil cover, soil biomass,soil disturbance activities and soil conservation practices. From the conservationpoint of view, limited ground cover can be increased soil particle detachability. Thisfactor is very important at the beginning of the rainy season when the soils are dryand the particles easily detached. At the start of the rainy season when soils are

poorly saturated the soils do not store water and have a low rainfall infiltrationcapacity because all macro pores are destroyed at the beginning of rainstorm.Therefore most rainfall becomes overland flow and this has a greater potential fordetaching and transporting the top soil to the lower slope areas (Lane et al., 1996).

Soil erosion rates of the permanent cash crop areas

Some upland cash crop areas were changed to the permanent cash crops suchas longan, lychee, orange and rambutan, which were recently fruit trees. Mienfarmers selected the moderated steep plots or the plots nearby the Khun Samun riverfor fruit tree planting. This agricultural system has been transferred from low land

people since 1992 by high farming income reason.The soil erosion rate for some plot of permanent cash crops were over the

tolerance goal but it was moderate as the Thai erosion class (Table 2, Figure 8). On-site erosion rates were highly variable, ranging from 13.64 to 26.87 ton rai-1 yr-1 (85.25 to 167.93 ton ha-1 yr-1). The highest rates of on-site erosion occurred in the 4yrs lychee due to high values of slope gradient and very high of K factor. The soils inthis area were sandy loam, shallow topsoil’s which were compacted and had lowpermeability; there was no topsoil mulching, low ground cover (C-Factor) and noutilisation of conservation practices (P-factor). This characteristic is highly importantin the rainy season because the soils are poorly saturated and they have a low rainfall

infiltration capacity due to destruction of the macro pores by rainfall impact.Therefore, the same process of soil erosion as described for the upland soils wouldoccur in the upland orchard soils under the conditions described above.

2



Permanent cash crops

0

10

20

30

1

o n s

i t e

e r o s i o n (

t o n / r a

i / y r )

rambutan (2 yr)

lychee (6 yr)

longan(6 yr)

rambutan (4 yr)

lychee (4 yr)

acceptable

Figure 8 the on-site erosion of plots of permanent cash crops ( n = 5)

Soil erosion rates of the fallow areas

The on-site erosion of the sampled plots from the fallow area were lower thanthat from the upland rice and permanent cash crops as the acceptable rate (Figure 9).This result indicated that dense ground cover plays highly significance on C and Pfactor.

Fallow area

0

1

2

3

1

o n s

i t e

e r o s i o n (

t o n / r a i / y r )

Fallow area (1 yr)

Fallow area (3 yr)

Fallow area (5 yr)

Fallow area (7 yr)

acceptable

Figure 9 the on-site erosion of fallow areas ( n = 4) and 5 yr fallow area

By the indigenous knowledge, most farmers usually leave some plots of

unfertile land as fallow areas for recovery the fertilization. Recently, the fallow

period rapidly decreases due to the population and economic pressures. This event

can be implied that the rotation farming may be ignored in the near future.

The ecological view points, land can recover its fertility by its own natural

succession process.

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Forest soil erosion rates

In the steep slope of the upper northeast of Mien village soils from two typesof forest, disturbed mixed deciduous and dry evergreen forest, were taken. Comparedwith the forest area, the soil erodibility factor (K) of the two forest soils was slightly

lower than the soils in the agricultural areas. The top layer of the forest soil wascomposed of silt loam on top layer with sandy loam in lower layer, and a very thick layer of litter. The permeability of the forest area was relatively high and decreasedonly slightly with increasing depth, so runoff would be decreased. Where denseground cover exists and a thick layer of litter the potential soil particle detachabilityand transportability due to raindrop impact and runoff would be much lower than thatin the agricultural soils. From the above factors, the soil erosion rate of the forestarea was very slight and less than rate of tolerance and the LDD erosion class.

The dry evergreen forest characteristics on the upper northeast of the MienVillage consisted of big trees and dense ground cover, indicating the potential of soilerosion control. The depths of the forest soils were greater than the depth of the

agricultural soils even the disturbed mixed deciduous, and in the former soils therewas a very thick and loose layer of litter. Soil properties such as these mean that thesoils have high water storage potentials and low surface runoff rates. On the otherhand, on- site erosion rate of disturbed mixed deciduous seems to be higher than dryevergreen forest soils, due to poor ground cover and opened crown canopy. Howeverthe on site erosion rate of these forest were used as the preferable value of thisresearch study.

Forest areas

0

1

2

3

1

o n s

i t e

e r o s i o n (

t o n / r a i / y r )

MMD (1) MMD (2)

MMD (3) DEF (1)

DEF (2) DEF (3)

acceptable

Figure 10 the on-site erosion of forest areas ( n = 6) and dry evergreen forest

5. DISCUSSION

Accelerated deforestation, production of annual food crops, and transitionfrom long to short fallows or continuous cropping as well as cropping in new niches,such as steep slopes, result in soil erosion, removal of natural vegetation andperennials from landscapes, and eventually in watershed degradation, and loss of biodiversity. In South and Southeast Asia, about 16 % of all the land used is seriouslydegraded. Estimates of the annual economic loss of the agricultural GDP due to soil

degradation range from 7 to 11 % (IFPRI, 1999).

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Erosion has several disadvantages associated with the productivity of land aswell as several off-site problems such as siltation, drainage disruption, gullying of roads, euthrophication, loss of wildlife habitats, damage to public health, plusincreased water treatment costs. Of the 75 x 109 tons of soil eroded world-wide eachyear, about two-thirds come from agricultural land. This loss costs the world about $

400 billion per year, including losses due to nutrient loss, water loss and off-siteimpacts (Pimentel et al., 1995). More over, Loss of soil loss covers soil degradationdue to it looses of productivity and leads to becoming desertification as far as noplants are unable to grow on such a land.

The major determinants of water erosion are rainfall, soil type, topography,particularly steepness and length of slope, and plant cover. Most soil loss occursfrom soils with steep slopes and with little soil surface cover. Actual losses areloosely related to the character and maturity of different agricultural crops, i.e. theerosion risk varies during the growing season or during the lifetime of a plantation.

Soil loss from cropping systems including annual crops, particularly crops havingwide row-spacing and requiring regular weeding (e.g. cassava, maize and vegetables)(Anon, 1996; Aina, et al., 1977; Barker, 1990; Lanh, 1994), is more severe thanlosses from cropping systems including perennial crops and/or trees (Hashim et al.,1995; Leigh, 1973 & 1982; Sombatpanit, 1995; Soong, 1980). Rates of erosion underforest cover vary with soil types but are generally low (Anon, 1996; Leigh, 1973 &1982; Putjaroon, 1987), whereas rates of erosion in freshly logged over areas can beextremely high (Anon, 1996).

The impact of soil erosion have been widely investigated in many regions bySamapuddhi & Suvanakorn (1962), Chunkao et al. (1979), Pairintra (1982),Preechapanya (1984) and Suksawang (1991), their main findings were as follows:

• Erosion from natural forest even in the heavy rainfall area in the South isquite low, less than 1.0 ton ha-1 yr-1.

• Fire induced soil erosion in the forest in about 2-10 times greater than that ina natural forest depending upon forest type and fire intensity.

• Agroforestry systems such as growing coffee in hill-evergreen forests withnarrow terraces, reforestation on medium or steep slopes can keep topsoil onthe site to the same degree as natural forests.

• Traditional upland crop cultivation such as rice, corn, beans and samepractices on slopes steeper than 35 percent produced soil loss higher than thetolerance limit (12.5 ton ha-1 yr-1).

• Erosion control measures such as grass-strips, intercropping and hillsidesditches can effectively reduce soil erosion to much less than the tolerancelimit.

• Roads also play a significant role in altering near-surface hydrologicresponse and subsequently accelerating soil erosion in mountainous areas of Southeast Asia; however, it is not clearly understood how the hydrologicaland geomorphological impacts of roads compare to those resulting fromother human activities, such as vegetation removal for agriculture. Althougherosion and sedimentation in highland areas of northern Thailand have beenaccelerated by extensive deforestation and changes in agricultural patternsthat have taken place over the last several decades

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Fallowing with appropriate cover crops is also important in restoration of eroded and degraded lands, e.g. improvement of soil fertility and maintenance of organic matter content.

Biological methods of soil conservation, such as buffer strips1 of grass orherbaceous vegetation may be more effective and economical than terraces for

controlling erosion and reducing runoff velocity. Placing deep-rooted perennialshrubs at regular intervals may provide the barrier needed to decrease runoff velocityand encourage sedimentation. Vegetative barriers may be easy to plant, and effectiveat controlling erosion, but require a level of management input not characteristic of many slash-and-burn agro-ecosystems.

Soil loss threatens the long-term sustainability of farmers’ livelihood. Soilconservation techniques are less readily acceptable if they only give positive resultsseveral years after implementation, thus, efficient soil conservation can be mostrapidly implemented when based on the modification of indigenous measures, ratherthan implementation of imported ones. Farmers will select a conservation technique

based on the efficiency to control erosion, the short-term benefit (yield, fertility), andthe ease in implementation (time, labors, costs).

It has been demonstrated that the upland agriculture in Khun Samun hasaccelerated soil erosion. This adverse impact has been felt in both upland andlowland areas. The agricultural land-use practices generated the rapid runoff of rainwater which in turn resulted in soil erosion problem in upland areas reducing thefertility of the soil.

The investigation of on-site erosion in upland agricultural areas in the KhunSamun watershed aimed to determine and compare the erosion rates within andamong different characteristics of landform and also farming practices. The main

findings can be summarized as follows:• Besides on-site erosion previously mentioned, farming has led to increased

erosion rates in the uplands due to the morphological characteristics. Inaddition, the higher rate of on-site erosion occurred while the value of slopegradient in this area increases.

• The fallow areas protected soil surface better than annual cash crop andpermanent cash crops due to dense ground cover and a high permeability of soil.

• The soil erosion rates in the forest areas located at similar slope gradients tothose of the upland agricultural plots was very low. These findings implythat converting forest areas to agricultural areas increases soil erosion.

1 A buffer strip are strips of grass or herbaceous vegetation that are grown along terraces forcontrolling erosion and reducing runoff velocity

6



Table 3. Overview of on-site erosion from various landforms in Song

Watershed

Landform

type

Number

of

samples

Number of

Samples in

severe

category

Number of

Samples

over

tolerance

rate

Fraction

over

tolerancerate

% of

samples

over

tolerance

rate

Bare soil 3 3 3 3/3 100Slashed andburnt

3 3 3 3/3 100

Upland rice 3 3 3 3/3 100Maize 3 3 3 3/3 100Permanentcash crops

5 1 1 1/5 100

Fallow area 4 0 0 0/4 0

Mixeddeciduous

0/3 0

Dryevergreen

6 0 0 0/3 0

6. CONCLUSIONS

Most farmers did not recognise and correct soil erosion problems, most didnot practice any conservation measures. Many farmers perceived that soil erosion

had minimal effects on production than economic pressure. During the investigation,informal interviews with farmers highlighted that the farmers tended to rely ongovernment cost-sharing programs of soil erosion control or entire budgets supportedby the government.

Where cultivation of easily eroded land cannot be avoided, then soilmanagement techniques that prevent direct raindrop impact on a bare soil surfaceshould be used, i.e. techniques that help keep water infiltration rates high enough toreduce runoff to a negligible level (the cover approach). On steep slopes, practicesthat permit safe disposal of runoff water from the field when rainfall exceeds theinfiltration capacity of the soil should be implemented (the barrier approach).

References

Aina, P.O., Lal, R. and Taylor, G.S. (1977). Soil erosion from tropical arable lands and its

control. SCSA Publ. 21: 75-84. In Lal, R. 1984. Advances in Agronomy 37: 183-248.

Anon. 1996. Guidelines for the prevention and control of soil erosion and sedimentation inMalaysia. Department of Environment, Ministry of Science, technology and theEnvironment, Malaysia. Chap. 2. http://www.jas.sains.my/ doe/new/index.html

Barker, T. C. 1990. Agroforestry in the tropical highlands. pp. 195-227. In: Agroforestry,classification and management. (ed) K.G. MacDicken and N.T. Vergara, New York,

NY, Wiley.

7



Chunkao,K.,P.Kurat,S.Bonyawat,P. Dhammanondh and N. Panbrana. 1979. Soil and waterlosses from Mae Huad Forest in Lampang, Kog Ma. WS. Res. Bul. No. 28, Fac. of Forestry Univ., 31 pp. (in Thai with English abstract).

Dumronghanvitaya, W. 1985. An Estimation of Soil Erosion in Chiangmai Province by usingUniversal Soil Loss Equation. M.S. thesis, Kasetsart Univ., Bangkok. (in Thai)

IFPRI .1999. Soil degradation: A threat to developing-country food security by 2020? Food,Agriculture, and the Environment Discussion Paper 27. Sara J. Scherr (ed),International Food Policy Research Institute, Washington D.C. 63 p.

Hashim, G.M., Ciesiolka, C.A.A., Yusoff, W.A., Nafis, A.W., Mispan, M.R., Rose, C.W. andCoughlan, K.J. 1995. Soil erosion processes in sloping land in the east coast of peninsular Malaysia. Soil Technology 8: 215-233.

Janmahasatien, R. (1986) Soil and water losses from the terraced reforestation at AngkhangHighland, Chiangmai, M.S. Thesis, Kasetsart Univ. (in Thai with English abstract)

Klute, A .1965b. Laboratory measurement of hydraulic conductivity of saturated soil, pp. 210– 221. In Methods of Soil Analysis. Amer. Soc. Agron. Monograph NO.9.

Kottama, W. 1998. Soil erosion of Huaijo Low Hill Water , Chiangmai Basin. M.S. Thesis,Kasetsart Univ. (in Thai with English abstract)

Land Development Department. (1983) Guidelines of Erosion Classification of Thailand. .Ministry of Agricuture and Co orperatives, Bangkok. 182 p .(inThai)

Land Development Department. (1996) Application of the Universal Soil Loss Equation andSoil Consevation Measures. Ministry of Agricuture and Co orperatives, Bangkok. 226p .(inThai)

Lane,L.J.,M.H. Nichols and G.B. Paige. (1996) Modeling Erosion on Hillslopes: Concept,Theory and Data.USDA-ARS, Southwest Watershed research Center, Tucson, AZ.USA.

Lanh, L.V. (1994) Establishment of ecological models for rehabilitation of degraded barrenmidland land in northern Vietnam. Journal of Tropical Forest Science 7(1): 143-156.

Leigh, C.H. (1973) Area 5: 213-217. In: Lal, R. 1984. Soil erosion from tropical arable landsand its control. Advances in Agronomy 37: 183-248.

Leigh, C.H. (1982) Geogr. Ann. A. 64A(3-4): 171-180. In: Lal, R. 1984. Soil erosion fromtropical arable lands and its control. Advances in Agronomy 37: 183-248.

L. A. Bruijnzeel and W. R. S. Critchley, Environmental Impacts of Logging Moist TropicalForests. International Hydrological Programme, no. 7 (1994); and A. D. Ziegler and T. W.Giambelluca, "Importance of Rural Roads as Source Areas for Runoff in Mountainous Areasof Northern Thailand," Journal of Hydrology (in press).

Pairintra, C., K. Boonproma and C. Mongkolsawat. (1982) Surface runoff and soil loss fromshifting cultivated area. Paper presented in 1982 National Seminar on Soil and WaterConservation. Role of soil and water conservation on National Development,

Bangsean Hotel, Chonburi, May 24-29. 1982 (inThai)

8



Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K., Kurz, D., McNair, M., Crist, S.,Shpritz, L., Fitton, L., Saffouri, R. and Blair, R. (1995) Environmental and economiccosts of soil erosion and conservation benefits. Science 267: 1117-1123.

Preechapanya, P. (1984) Soil and water losses from agro-forestry systems: A case study of coffee plantation under hill evergreen forest at Doi Pui, Chiangmai, M.S. thesis,Kasetsart Univ., (in Thai with English abstract)

Samapuddhi,K. and P. Suvanakorn. DATE A study on the effect of shifting cultivation onforest soils. Tech. Report No. r 51, Royal Forest Department, Ministry of Agricultureand Co operatives.

Sombatpanit, S., Rose, C.W., Ciesiolka, C.A. and Coughlan, K.J. 1995. Soil and nutrient lossunder rozelle (Hibiscus subdariffa L. var. altissima) at Khon Kaen, Thailand. SoilTechnology 8: 235-241.

Soong, N.K., Haridas, G., Yeoh, C.S. and Tan, P.H. (1980). Soil erosion and conservation inPeninsular Malaysia. Rubber Research Institute of Malaysia: Kuala Lumpur. In:

Guidelines for the prevention and control of soil erosion and sedimentation inMalaysia. 1996. Department of Environment, Ministry of Science, technology and theEnvironment, Malaysia. Appendix B. http://www.jas.sains.my/doe/new/index.html

Suksawang, S. (1991) Impact of Selective Logging System on Water Yield on a SmallTropical Watershed in Thailand. Ph.D Dissertation, Graduate School, Univ. of thePhilippines at Los Banos.

Thainoogul, W and other 13 Authors. A comparative study of soil erosion affected by rubberand other plant covers . Progressive report for 1981. No. 2-09-04-20-02. AgriculturalTechnical Dept, Ministry of Agriculture and Cooperative, 25 pp (in Thai).

Takahashi, T.,K Nagahori,C. mongkosawat and M. Losirikul. (1983) Runoff and Soil Loss.

In: Shifting Cultivation-An Experiment at Nam Phrom, Northeast Thailand, J. ForestryVol.9, No.3,pp 112 – 136.

Wischmeier, W.H and D.D Smith (1978) Predicting Rainfall- erosion loss. Agri. ResearchService Handbook No. 282. USDA, Washington, D.C. 48 p.

25-5-soil erosion from agricultural area

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