Land Characteristics and Soil Erosion in Relation to Slope by pharmphresh37

VIEWS: 284 PAGES: 9

									J. Jpn. Soc. Soil Phys.

No. 21, p. -1 ./   ,**+


 Land Characteristics and Soil Erosion in Relation to Slope
   Farming in the Highlands of Candikuning, Bali, Indonesia

     Hajime NARIOKA*, I.W. Sandi ADNYANA**, Mastur*** and Simplicio M. MEDINA****
 * Faculty of Environmental Science and Technology, Okayama University, - + + Tsushima-naka,
                                          Okayama 1** 2/-*, Japan
       ** Faculty of Agriculture, Udayana University, Jl. PB. Sudiman, Denpasar, Bali 2*,-,, Indonesia
     *** Watershed Management Technology Center, Jl. Jend. A. Yani-Pabelan, P.O. Box ,3/, Solo/1+*,,
                                           Central Java, Indonesia
 **** Farming Systems and Soil Resources Institute, College of Agriculture, University of the Philippines
                                       ˜
                                Los Banos, College, Laguna .*-+, Philippines


                                                  Abstract

         Many environmental problems, such as soil erosion, a#ect upland and hillyland agricultural
      systems. In a study conducted in Candikuning village, Bali, Indonesia, biophysical characteristics
      and soil erosion were determined in relation to slope farming.
         The area is dominated by forests and vegetables dry land with slopes ranging from moderate to
      steep. Soils in the area have medium to high fertility levels and the major soil types are Andosols
      and Regosols.
         Erosion was found to occur slightly in the forestland but was more severe in the dry and shrub
      lands especially in areas with slope more than +/       .   As such, appropriate soil and water
      conservation measures are needed to achieve sustainable farming systems in these areas.
      Key words : soil erosion, slope farming, highland, Bali, Indonesia



                                                         water resources will be degraded.
                     Introduction
                                                           This study was conducted in order to gener-
  According to the Bali Local Government                 ate basic data related to land characteristics
(+33/), population growth rate in the island is          and degree of soil erosion in sloping farmlands.
quite high during the last twenty years.                 The findings of this study can also be used as
Coupled with a limited area for cultivation of           important information or input to future re-
food crops, the need to produce more food to             search activities.
meet the demands of an increasing population
                                                                       Materials and Methods
has become highly imperative.
  Faced with this reality, farmers are forced to            The research was conducted in Candikuning
cultivate even the sloping lands, which are              village, district of Tabanan, Bali, Indonesia
oftentimes unsuitable for annual crops. The              which had an elevation between +,,** m to
intensive nature of annual crop cultivation in           ,,+** m above sea level and having coordinates
slope lands can cause soil erosion. Without              2 +. -* S to 2 +2 -* S latitude and ++/ 1 -/ E
appropriate soil conservation measures, soil             to ++/ ++ -* E longitude.      Landform units
productivity will decrease and erosion materi-           found in the village are cauldron valleys in the
als from upslope can accumulate in the low-              northern and northwestern parts, which are
lying areas as sediments. As a result, land and          undulating to rolling, and volcanic ridge in the
 38                                                   21    ,**+




                    Fig. +   Land unit map of Candikuning, Tabanan, Bali, Indonesia


south and western parts where the topography          units were identified as presented in Fig. +.
is hilly to mountainous. The soil types are              Soil sampling was done based on slope se-
Gray Brown Andosols whose parent material is          quence, slope class and land status. The soil’s
intermediary volcanic ash and Gray Regosols           physical and chemical analysis were done at
which have intermediary tu# volcanic ash as           the Laboratory of Soil Science in Udayana Uni-
parent material.                                      versity. The degree of erosion was evaluated
  Primary data on climatic characteristics,           using the Universal Soil Loss Equation (USLE)
land use, soil characteristics, topographic fea-      formulated by Wischmeier and Smith (+312)
tures, slope patterns and status of erosion were      which states that :
obtained through direct observation, soil sam-             A R K L S C P
pling and farmer interviews. Secondary data           where, A is the predicted soil loss (t ha + y +), R
was also collected. A field survey was done to         is the annual rainfall erosivity factor (MJ mm
ascertain the dominant and existing land uses         ha + h + y +), K is the soil erodibility factor
in the area. A land use map of Bedugul area           (t ha h MJ + ha + mm +), L is the slope length
produced by the local government of Bali was          factor, S is the slope steepness factor, C is the
used as a baseline map.                               cover and management factor and P is the
  The boundaries of each land use were deline-        conservation support practice factor.
ated using an air photography, topographic               Each component of the USLE as applied to
map (+ : ,/,***) and a slope map where +, land        the research site was determined based on cer-
           : Land Characteristics and Soil Erosion in Relation to Slope Farming in the Highlands of Candikuning, Bali, Indonesia   39




                      Fig. ,    Topography map of Candikuning, Tabanan, Bali, Indonesia


tain equations such that the rainfall erosion                        +321). In the research site, the months from
index (R) was calculated based on Bols’s equa-                       October to April is rainy season and May to
tion (Bols, +312). The values for of K and LS                        September are the dry months. The mean
factors were calculated based on the equation                        annual rainfall is ,,/02 mm.
according to Wischmeier and Smith (+312).                               Minimum and maximum temperatures were
Values for C and P factors were based on the                         recorded at +. and ,. , respectively. Month-
CP values published by Hammer (+32*). The                            ly evaporation was also found to be high in
tolerable soil loss as computed by Hammer                            October and low in June with a daily mean of
(+32,), was also the basis of determining the                        -., mm. The magnitude of evaporation is
magnitude of erosion from each land unit                             significantly correlated with temperature.
identified in the research site.                                      Monthly relative humidity recorded show that
                                                                     the highest occurred in March and the lowest
           Results and Discussion
                                                                     in October with daily mean of 21.3 .
Agro-climatic and Meteorological Character-                          Topography and Slope Pattern
istics                                                                  Areas with flat to undulating topography
   When monthly rainfall is less than 0* mm, it                      and having a slope of * 2 account for ,/
is dry season while rainy season is character-                       (about /0, hectares) of the research area. How-
ized by rainfall more than +** mm (Sandy,                            ever, areas with moderate to steep slopes
 40                                                  21    ,**+




                     Fig. -   Slope map of Candikuning, Tabanan, Bali, Indonesia


occupy 1/ (about +,1,2 hectares) of the total        fertility status in the area included CEC, base
area. Steep lands are usually prone to erosion       saturation and organic carbon content
and cultivation could exacerbate the problem.        (Puslittanak, +33/). As the parent material of
The topographic and slope class maps of the          these soils is intermediary volcanic ash tempo-
research area are shown in Figs. , and -, re-        rary deposited from surround volcanoes, they
spectively.                                          tend to have high nutrient content. The soil
Soil Characteristics                                 fertility status in the research area is presented
   Tables + and , present the physical and           in Table -.
chemical properties of the soil in the research        It was also found that the fertility of the soil
area, respectively. Soil texture ranges from         in the lower slope is relatively higher com-
silty loam to loamy sand, although there is a        pared to the middle and upper slopes. This is a
considerable amount of sand present. The             result of nutrient deposition in the lower slopes
dominance of sand causes some elements, par-         from the upper slopes because of erosion. As
ticularly nitrate nitrogen to decrease rapidly       consequence of advanced erosion, nutrient
either by leaching or runo#. This explains the       availability may drop in long-term.
very low availability of nitrogen.                   Land Use
   Other parameters analyzed to determine the          Candikuning village is dominated by forest
               : Land Characteristics and Soil Erosion in Relation to Slope Farming in the Highlands of Candikuning, Bali, Indonesia     41


                              Table +       Physical properties of the soil in the research area

                                                                                                                          Bulk
Samples                                    Depth Sand Silt           Clay
                 Characteristics                                                 Texture         Structure Permeability density
 Codes                                      (cm)  ( ) ( )            ( )                                     (cm s +)   (g cm -)

              Bukit Catu                    * -*     2/42      ,42      +4.   Loamy Sand          Granular        +40+ +*      -
                                                                                                                                       *430
  S+ (.)      (dry land                    -* 0*     3+4/      .42      -41   Sand                Granular        +4+3 +*      -
                                                                                                                                       *43+
              (slope : ,- ))

              Bukit Catu                    * -*     2042      14/      /41   Loamy Sand          Granular        04+3    +*   .
                                                                                                                                       *413
  S, (-)
              (dry land (+/      ))        -* 0*     0+4/     -042      +41   Sandy Loam          Granular        -4+1    +*   .
                                                                                                                                       *400

              Kembang Merta                 * -*     //42     -*4+   +.4+     Sandy Loam          Granular        -4.1    +*   .
                                                                                                                                       *42-
  S- (-)
              (dry land (++ ))             -* 0*     ,04-     /*4+   ,-40     Silty Loam          Granular        04++    +*   .
                                                                                                                                       *41,

              Kembang Merta                 * -*     -.43     //4,    .43     Silty Loam          Granular        .4/*    +*   .
                                                                                                                                       *42.
  S. (,)
              (dry land (2 ))              -* 0*     /.41     -*42   +.4/     Sandy Loam          Granular        +4,1    +*   -
                                                                                                                                       *42.

              Kembang Merta                 * -*     0/41     +04-   +24*     Sandy Loam          Granular        24,/    +*   .
                                                                                                                                       *41-
  S/ (,)
              (dry land (- ))              -* 0*     0-4*     ,340    14.     Sandy Loam          Granular        +4--    +*   -
                                                                                                                                       *410

                                            * -*     .340     .340      *42   Sandy Loam          Granular        34/2    +*   .
                                                                                                                                       *41,
  S0 (2)      Forrest land (1         )
                                           -* 0*     2.4-     +-43      +41   Loamy Sand          Granular        ,4,1    +*   -
                                                                                                                                       *41*



                              Table ,      Chemical properties of the soil in the research area

  Samples                                                                   Base
                 Depth          pH         Org. matter           CEC                         Total-N        Available-P Available-K
   codes                                                      (c mol/kg) saturation
                  (cm)         (H, *)          ( )                                             ( )            (ppm)       (ppm)
(Land unit)                                                                 ( )

                   * -*         /421             +40-           +,4++          2,410           *4*/2            20410              ,14/2
  S+ (.)
                  -* 0*         04,3             *42/           +,42*          224+-           *4*+/            -+4/3              --4,3

                   * -*         04**             -410           +140*          334/0           *4+2*            3141-              --4-+
  S, (-)
                  -* 0*         04-2             -4*+           +041.          3.41.           *4+,-            +,4+-              ,.413

                   * -*         /402             -4,1           +14+3          -.4+/           *4*2+            ,,43.              0+4,0
  S- (-)
                  -* 0*         /4,2             ,400           +34//          .04/,           *4*0.            +*421              214.-

                   * -*         /421             ,43*           +.4,1          3/4/-           *4*0*            1-4*2              ++34*0
  S. (,)
                  -* 0*         04+,             +41-           ,,4..          -+402           *4*-+             34*,              +.34/+

                   * -*         .420             -402           +34/,          //43,           *4*..            1/4.-               ,/4.3
  S/ (,)
                  -* 0*         /4.0             ,4/-           +.4.3          234/0           *4*0+            /.40*               -+40.

                   * -*         /43.             -4,2           +-422          3*43+           *4*22            +14-*               .-421
  S0 (2)
                  -* 0*         04+2             ,4/*           ,*4-,          3042.           *4*01             143+               ,1422


 Table -      Soil fertility status in the research area
                                                                         with a total area of about +,,/- hectares, dis-
                                                                         tributed in the surrounding part of Beratan
  Samples                                 Slopes        Fertility        Lake and in the western part of the village.
   codes             Location              ( )           status
(Land unit)                                                              The forest area includes parts of Mt. Pohen, Mt.
   S+   (.)      Bukit Catu                 ,-      medium               Tapak and the Botanical Garden of Bedugul.
   S,   (-)      Bukit Catu                 +/      very high               The major land use classifications in the vil-
   S-   (-)      Kembang Merta              ++      medium               lage include forest, dry land crops, settlements
   S.   (,)      Kembang Merta               2      high                 and lake. Land uses patterns and their distri-
   S/   (,)      Kembang Merta               -      very high            bution is described in Fig. .. Vegetable is the
   S0   (2)      Forrest land                1      high                 dominant dryland crop, which include cab-
 42                                                   21     ,**+




                     Fig. .   Land use map of Candikuning, Tabanan, Bali, Indonesia


bage, potato, carrot, lettuce, garlic, celery and     high. This is mainly due to the high percent-
others. Corn, sweet potato and banana are also        age of very fine sand and silt and low clay
planted in the dry lands and consist of about         content. As regards the slope length and steep-
0.- hectares.                                         ness (LS) factor, the increase in length and
Erosion                                               steepness of slope results to higher LS values
  Values for the USLE equation factors as de-         for the USLE.
termined from the research site are presented           The applied soil conservation measure in the
in Table .. Table / presents comparison be-           dryland vegetable areas was bench terrace, al-
tween the actual level of erosion and the value       though the quality of terraces in the lower
of tolerable soil loss in the research area. Based    slopes is better than those constructed in the
on these calculation, predicted soil erosion in       upper slopes. This condition caused stability
the research area was delineated in map as            of the bench terrace riser in the upper slopes is
shown in Fig. /.                                      lower than in the lower ones. Accordingly, the
  It was found out that the soil erosivity was        locations in the dryland vegetable crops with
high during the months of October to March,             +/       -*    slope, experience a severe to
which are within the rainy season. Soil ero-          very severe erosion occurrence. Aside from the
dibility was classified as moderate to very            slope, low density of vegetation contributed to
               : Land Characteristics and Soil Erosion in Relation to Slope Farming in the Highlands of Candikuning, Bali, Indonesia   43


                  Table .        Values of the USLE components as determined in the research areas

                Erosivity              Erodibility          Slope Cover and Conservation Predicted
 Land         (MJ mm ha      +
                                      (t ha h MJ +          factor management practices  soil erosion                          Level of
 unit            h + y +)              ha + mm +)                    factor    factor    (t ha + y +)                        soil erosion
                   (R)                     (EK)             (ELS)     (EC)      (EP)          (A)

   +              ,+,10                   *4*+1-              *4,-         *4.**              *4+/              /4*2         very slight
   ,              ,+,10                   *4*.+*              +4.*         *4.**              *4+/             1-4,1         moderate
   -              ,+,10                   *4*,0,              +432         *4.**              *4+/             004,,         moderate
   .              ,+,10                   *4*+2+              /4/*         *4.**              *4-/            ,304/,         severe
   /              ,+,10                   *4*-*2              34/*         *4.**              *4-/            21+4/,         very severe
   0              ,+,10                   *4*-*2              340*         *4-**              *4.*            1/.4++         very severe
   1              ,+,10                   *4*-/.              *41/         *4**/              +4**              ,42,         very slight
   2              ,+,10                   *4*-/.              ,4**         *4**/              +4**              14/-         very slight
   3              ,+,10                   *4*-/.              /4**         *4**/              +4**             +242-         slight
  +*              ,+,10                   *4*-/.              24/*         *4**/              +4**             -,4*+         slight
  ++              ,+,10                   *4*-/.             +24-+         *4**+              +4**             +-413         slight
  +,              ,+,10                   *4*-/.             --4-,         *4**+              +4**             ,/4+*         slight

 A R · EK · ELS · EC · EP


        Table /      Comparison of the predicted soil erosion and tolerable soil loss in the research areas


        Land      Soil depth        Depth factor                               Predicted             Tolerable
                                                         Resource life                                                 Degree of
        unit        (mm)             (mm y +)                                 soil erosion            soil loss
                                                             (y)                                                        erosion
                                                                              (t ha + y +)           (t ha + y)

          +           ++**                +4*                  -**                 /4*2                -401           Very slight
          ,           +*/*                +4*                  -**                1-4,1                -4/*           Moderate
          -           +,**                +4*                  -**                004,,                .4**           Moderate
          .           ++**                +4*                  -**               ,304/,                -401           Severe
          /           ++/*                +4*                  -**               21+4/,                -42-           Very severe
          0           +*/*                +4*                  -**               1/.4++                -4/*           Very severe
          1           +,**                +4*                  -**                 ,42,                .4**           Very slight
          2           ++**                +4*                  -**                 14/-                -401           Very slight
          3           +*/*                +4*                  -**                +242-                -4/*           Slight
         +*            3/*                +4*                  -**                -,4*+                -4+1           Slight
         ++           +***                +4*                  -**                +-413                -4--           Slight
         +,            2/*                +4*                  -**                ,/4+*                ,42-           Slight

        [Tolerable soil loss]         [Soil depth (mm)]          [Depth factor] / [Resource life (years)] .


the higher rates of erosion.                                             uisite to achieve sustainable farming system in
  On the other hand, the forestlands and dry                             tropical volcanic highland.
vegetable crop areas with less than - slope
                                                                                                   Conclusion
have only slight erosion. Combination be-
tween intensive soil surface protection (by veg-                           Forest and dryland vegetable crops domi-
etation canopy), e#ective soil conservation                              nate the major land use in the research area.
measures and appropriate cropping pattern in                             The main physiography in the area is volcanic,
the high risk erosion such as the dryland vege-                          with rolling to mountainous landforms. The
table area, should be established to prevent soil                        area has a moderate to steep slope. General soil
erosion and maintain soil fertility as a prereq-                         fertility status ranges from medium to high
 44                                                   21    ,**+




                     Fig. /   Erosion map of Candikuning, Tabanan, Bali, Indonesia


due to high organic matter content and base                 Bali Local Gov’t., Denpasar (In Indonesian).
saturation. Important limiting factor of soil           Bols, P.L. (+312) : The Iso-erodent Map of Java and
                                                            Madura. Soil Research Institute, Bogor, Indo-
fertility is low nitrogen. Soil texture is sandy
                                                            nesia (In Indonesian).
and has low bulk density.                               Dai, J. and Rosman (+31*) : Reconnaissance Soil
   The erosion degree in the area ranges from               Map of Bali. Soil Research Institute, Bogor,
very slight to very severe, depending on land               Indonesia (In Indonesian).
status. Erosion occurred slightly in the forest-        Hammer, W.I. (+32*) : Soil Conservation Consultant
                                                            Report. Technical Note No. 1. FAO Project
land, but it was severe in the drylands with
                                                            INS/12/**0. Center for Soil Research, Bogor,
slope more than +/ . To achieve sustainable                 Indonesia.
farming in the slope lands, e#ective conserva-          Hammer, W.I. (+32*) : Final Soil Conservation Con-
tion measures combined with soil surface pro-               sultant Report. Technical Note No. ,0. AGOF/
tection and appropriate cropping pattern                    INS/12/**0. Center for Soil Research, Bogor,
should be establish in the tropical volcanic                Indonesia.
                                                        Puslittanak Team. +33/. Technical Method for Soil
highland.
                                                            Fertility Evaluation. Tech. Report No. +/. Ver-
                  References                                sion +. Center for Soil and Agroclimate, Bogor,
                                                            Indonesia (In Indonesian).
 Bali Local Government (+33/) : Land Planning of        Sandy, I.M. +321. Regional Climate of Indonesia.
     Bali Province. In : ,*+*, Facts and Analysis.          University of Indonesia, Jakarta.
        Q : Land Characteristics and Soil Erosion in Relation to Slope Farming in the Highlands of Candikuning, Bali, Indonesia   45


Wischmeier, W.H. and D.D. Smith. +312. Predicting                            tion Planning. USDA Agric. Handbook No.
   Rainfall Erosion Losses. A Guide to Conserva-                             /-1.+.




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