Delineation, Characterization of Physical Conditions
Delineation, Characterization of Physical Conditions of On-Farm Trial Site on Alluvial Soils Vo Quang Minh1, Le Quang Tri 1 and Ryuichi Yamada2 1: Department of Soil Science & Land management, College of Agricultural, Cantho University, Vietnam 2: Japan International Research Center For Agricultural Sciences, Japan Tel : 84-71-831005, Fax : 84-71-830814, EMAIL :[email protected] ; [email protected], [email protected]
Abstract In soil science, a map is generally used to present the spatial distribution of soil variables. The aim of the soil survey is to examine, describe, classify, and map the soils occuring in the buffer zone. A soil survey is not an end in itself, but a tool for agricultural development. There is a need for a further stage – the evaluation of soils, vegetation, climate, hydrology, and other factors in relation to the requirements of diferent types of land use. Agricultural environments in the humid and sub-humid tropics have very high spatial complexity. Efforts to classify this variability into homogeneous ecological units to facilitate the transfer of technologies across geographical areas, encounter serious constraints. It is not difficult to identify mappable criteria that will separate farm areas into distinct units. However, it is challenging to specify the relevant criteria that influence the adaptation of particular technologies, and to use the spatial data that is available to make efficient extrapolation judgements. This activity is often constrained by limited data and insufficient knowledge of how the data can be used. In the Mekong Delta, soils and hydrology play important roles for agricultural practices, therefore, the characterization and delineation of physical conditions based on the soil and hydrological characteristics are the first steps in land evaluation and land use planning. Tan Phu Thanh village was selected as a case of alluvial soisl for ground truth survey, characterization, delineation in this study. The village classified into 13 soil units, in which nearly half of area is home or gardent (1176,94 ha or 45% of the village). In the rest, the developed alluvial soils are found, which alluvial material accumulated on the topsoil. Some soils have pyritic material occurred from 80 to 120 or greater than 120 cm from the soil surface. The top soil thickness ranged from 20 to 40 cm., and inundation depth ranged from 60-80 cm.
1. Introduction The prioritization of agricultural research among environments relies on reasonably useful and accurate information on what those environments are, and how much agricultural area and production are distributed among them. To date the agricultural resource allocalation debate has been limited to relatively broad ecosystem distinctions, ie. Irrigated, rainfed lowland, upland, and deepwater (Herdt and Riely, 1987). There has been progress during the past decade in developing more practical agroecological classifications at continental and national scales (Higgins and Kassam, 1987) Most of the food needs of the increasing population in rice growing and consuming countries will have to come from these lowlands as there is little scope for increasing the irrigated are in thenfuture. In order to formulate research strategies for increased rice production, characterizaitization and delineation of area under difference subecosystem or mapping unit are required.
2. Description of the village Tan Phu Thanh village located in the South of Chau Thanh district, neighbors in the North is Nhon Nghia village, in the East is Thanh Dong, in the Western-South is Thanh Xuan village. Total area is 2,604.44 ha,
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with 7 hamplets, inlduding Tan Thanh Dong, Tan Thanh Tay, Phu Loi, Phu Thanh, , Thanh Loi, Thanh Phu, Thanh My, Tan An, Tan Phu, and Long An.
3. Methodology The research had been done based on following steps: Step 1 : Research outline, secondary data collection. Step 2 : Field data collection (socioeconomic, soil, hydrological data collection) Step 3 : Data, map digitizin, processing (ILWIS, MAPINFO software used) Step 4 : Map delineation and characterization (using GIS and ecosystems criteria) 3.1. Method of survey Generation of an accurate database is the most important part of this methodology. The process begins with the selection of appropriate map of the research area which created by land administration department (cadastral map), which located exact each pacel on the map for easy to recognized in the field. Ground truth is carried out to collect the information on soil type, occurrence of sulfidic and sulfuric horizone in the profile, depth of surface horizone, depth of inundation, length of inundation, and duration of inundation. Soil samples are also collected at each soil type for amalyzing of pH, EC, total N, total P, available P, extractable K, Ca, Na, and Mg, percent of organic matter,.. The actual precise area and administration map of the studied area is collected from the Cadastral sector of Chau thanh district (at scale 1:2,000). Based on these references, as many transects were crossed over the survey area. A total amount of 145 soil survey locations were identified. The soil survey activity has been done from May to June, 2001. Three survey groups were formed and the survey was done based on the pre-defined observation points and field truth measurements. Methodology of data analysis The intepretation of the data provides thematic maps, which integrated by using GIS, based on the generation of different combination, delineate the area into different mapping units or subecosystems. These database will be used for suitability assesment and land use planning for next paper. The spatial heterogenity and temporal variability of biophysical parameters, used as criteria for classification of subecosystems or mapping unit, make the characterization of the units complex and restrict the validity of the maps only to the year of survey. This situation makes it difficult to select a site representative of an subecosystem or mapping unit. Even the repeated mapping does not capture the realistic scenario. Data were classified on the basis of the sub-ecological zones in term of typical land use types. Four steps in the data analysis are used as follows: Transferring data from questionnaire to paper sheets Processing & checking data on paper sheets Input data in computer, map compilation and data digitizing Arranging files, map and data analysis/procesing. GIS used as tools in map and data manipulation.
4. Results 4.1. Climatic conditions of Tan Phu Thanh Village Tan Phu Thanh village belong to Chau thanh district, Cantho province, the climatic conditions are similar to the condition of the district or province, which distinguse season, dry and rainy seasons. The dry season starts from January to May, while the rainy season starts from May to December. Total rainfall of the region about 1952 mm/year, however most of rainfall concentrated in the rainy season, while there are no rain in February and March, high rainfall concentrated from May (113.3 mm) to December (153 mm), amount of rainfall is highest in September (439.2 mm). Depending on table 1 and
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figure 6, in the rainy season, there are no drought spell occurrence, which harmful for cropping season because there are not enough water for irriagtion. However, the hydrology conditions of the village are quite suitable for agricultural eventhouth drought spell occurred. Temperature of the village is nearly stabilized in the year, average temperatute is about 27.3 oC, highest Temp. is in May (29.6oC), and lowest is in December (25.3oC). The village has high air humidity, specially in the rainy season, highest is in September (91%), and lowest is in the dry season (79 – 82%). Generally, the climatic conditions of Tan Phu Thanh village are the same as the conditions of the districts or province, it is belong to the climatic regime of the region, which suitable for the agricultural development. Especially, the land use parterns diversity in the village is very high, which conforming for the suitable of the villlage for agricultural production. OF TANPHUTHANH (1998) the climatic conditions of Tan Phu VILLAGE Thanh villages (1998) FigureCILMATIC 1: ShowingCONDITIONS (Source : Statistical year book 1998, Statistical office of Chauthanh district, 1999)
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Rainfall (mm)
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Rainfall (days)
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Temp. oC Air. Hu. (%)
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Rainfall (mm)
300 250 200 150 100 50 0
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4.2. Hydrological conditions of Tan Phu Thanh village The inundation depth will effect to the type of crops, cropping system, and also the development of fishery. The inundation of Tan Phu Thanh village is affected by the tidal regime and receive water from Hau river, about 10 km from Hau river. Since maximum depth of inundation is high, ranging from 40 to 80 cm.
4.3. Present land use of Tan Phu Thanh village According to the map, there were 13 land use patterns in the village, in which double rice crops is dominated in most of the hampletes. However, fruit crops and perenial are concentrated with a very large area along the river and national highway, in which Tan Phu and Long An hampletes have the largest area of fruit gardent and upland crops, the other land uses occupied a few hectars including mixed garden, church, cemetory, house, which located along the river or national highway or local paths, canal, river,.. Double rice, fruit garden, and perenial are the dominated land uses in the village and distributed in most of the hampletes, it showing that the village has the potential in deleloping the fruit crops such as oranges, rambutant, longan, mangove,..as reported by the farmer and the goverment. while double rice is now shifting to triple rice as practiced at some places in the village. This is showing the highly suitability of crops in the area.
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4.4. Proximity to main river In Tan Phu Thanh village, Balang river is the main river of the village, which the farmers can use for transpotation of their product to the market, and also for their local transpotation. The distance from the main river will effect to the time to transport their product to the market for consumtion ,and also the time of transpotation.. Depending on the area and the location of the main river, more than 50 % area of Tan Phu Thanh village has the distance less than 1000 m from the main river. 4.5. Proximity to main road In Tan Phu Thanh village, National high way is the main road located in the village, which the farmers can use for transpotation of their product to the market, and also for their local transpotation. The proximity to the main road will effect to the time to transport their product to the market for consumtion ,and also the time of transpotation.. Depending on the area and the location of the main road , more than 50 % area of Tan Phu Thanh village has the distance less than 1000 m from the main road. 4.6. Proximity to main market In the village, most of farmer production are for local consumtion, which the farmer sell their product in local market, since, it will be very easy for local cumsumtion if their field very near to the local market. In Tan Phu Thanh village, there are two main market located in the village (including Xeo vong, So 10, and Cai Tac makets), and the proximity of farmer fields to local market ranging from 500 to more than 4000 m, in which most of distance concentrated within 1000 to 3000 m. If farmers produce more product they used to sel their product in Cantho or Cairang market 4.7. Proximity to elementary school In Tan Phu Thanh village, there are 11 elementary schools located in the village, since, it is very suitable for student to study. Most of distance from farmer houses to the elementary schools raning from less than 500 m to 2000 m, which concentrated within the distance from 500 to 1500 m. Therefore, the student can go to school by walk or bicycle or by boat. 4.8. Proximity to secondary school There are 2 secondary school located in Tan Phu Thanh village (including Tan Phu Thanh and Tam vu 2 secondary schools), if considered within the village, the student have to go far by walk or bicycle or by boat to the school, because it is far from school to their house, the distance raning from less than 500 m to 7000 m, and the distance concentrated from 500 to 5000 m. However, because there is an other secondary school in Cai rang, which very near for student located in the hamplet of Tan Thanh Dong, and Tan Thanh Tay and Phu Thanh, they can study in these school intead of studying local secondary school. 4.9. Soils of Tan Phu Thanh village 4.9.1. Soil formation According to Nguyen Huu Chiem (1992), the Mekong delta, in which Tan Phu Thanh village located, the formation of the recent Holocence seiments of the delta began about 11,000 years B.P. As for older seiemnts, Bosum et al (1971) have interpreted an aeromagnetic map covering the Mekong delta as suggesting that the metamorphosed lower Paleozoic deposits found in the plateau area Northest of the delta and in Cambodia to the Northwest of the delta constitute the basement of the delta. The thickness of 3 to 5 km of the sediments suggested by magnetic interpretation means that they could include any parts of the section ranging from the Permian limstones to the Quaternary alluvium. According to Tran Kim Thach (1980), during the Terriary the delta was covered by a thick layer of old sediments consisting of marine,
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brackish and alluvial sediments. Especially during the late Pleistocene era, when the sea fell to 68 meters below its present level (Biswa, 1973), sediments of the Mekong river covered all the delta. In the Holocene regression, the sea gradually receded. Sediments of a transitional to subaqueous fan-delta were formed. These sediment contain relatively few pollents (either freshwater, mangrove or brackish). Total sulfur and water soluble salt contents are low. EC value varies from 0.2 to 0.6 ms/cm, pHxo and pHw are mostly above 3.5. Toward the sea, the holocene sediments become thicker. The deepest layer of Holocence sediments contains small shells. The pHw and pHox are mostly above 7. EC value is high *4ms/cm). Polen is completely absent. These indicators show that the layer represents a marine environemnt and was deposited during the Holocene transgression. In the subsequent marine regression, sandy clay layer with laminated structure, relatively high EC value (2-4 ms/cm), low contents of total sulfur, water soluble sulfate, pyrite, and pollen, in which illite mineral was transformation to vermiculite or kaolinite, was deposited on the marine sediments. This layer represents a tidal flat environment. The continuation of the marine regression toward the South China sea subsequently led to the development of a coastal landform. The coastal complex consists of many sand ridges, coastal flats, inter-ridges and mangrove swamps. Coastal flats have moderate relief, lying about 1 to 1.5 meters above mean sea level. Mangroves are distributed along the coastline and the mouth of the Mekong river. Many kinds of mangrove species thrive in these swamps. Very new potential acid sulfate soils have formed there. When sea receded far from the former coast, the recent alluvial sediments were drained. In the high floodplin and the tide-affected floodplain, a large amount of recent sediments were deposited. The coarse sediments such as sand and silt were carried by violent plug-flow and deposited along the river banks, forming natural levees, while clay was deposited behind the levees and formed the backswamps. Three areas, namely, the open floodplain. The closed floodplain and the broad depression are located far from the river and received only small quantities of new accretion. There, the mangrovw sediment layer can be found very cloase to the topsoil. The soil formation of Tan Phu Thanh village is the same as the formation of the Mekong Delta, the formation mostly by the sediments of the Mekong River during Holocene period. During this period of sedimentation, the sea level has raised and lowered many times. In the rainfed areas, seawater intrudes far inside the Delta during the dry season and the affected areas cover more than 1 million hectares. In the rainy season, although the soil surface is flushed and freshened, the shallow groundwater still remains saline. In the past, as the river changed its course, several river branches in low landscape had been formed and deposits with high sulphur content and organic matter have been deposited. 4.9.2. Soil types of Tan Phu Thanh village There are 6 major soil types in Tan Phu Thanh village, and large area are potential acid sulfate soil, in which sulfidic horizon often occurred at the depth more than 80 cm from soil surface. the pyritic material indicated in the field by oxidation of H2O2, which will oxidize pyritic material and bring soil pH down, if pyritic material presented, soil pH will down to lower than 2. These soil types presently not harmfull for crops, but if it exposed to the surface such as for raised bed, pond making,.. it will be oxidized and released a lot of toxicity as Al3+, Fe2+, total acid, and low pH (soil types code 3,4,5 and 6). Besides these, most of the soil receive a lot of alluvial materal from river, deposited on the top soil to form a Fluvic phase, which indicate the accumulation of aluvial material on the topsoil. However, due to the accumuation of organic matter on the surface during crop cultivation, the soil surface have a dark color to form the umbric phase. There are no occurrence of pyritic material in the horizon in other soil types (code 1 and 2), these soil types are favorable for most of the crops. Table 9: Chemical characteristics of deposited alluvial soil 10
Horizon
pH
EC Ms/cm
Ptotalú %
Pavai Mg/100g
K
1 2 3 4
H3 LA 0 – 30 H3 LA 30 – 95 H3 LA 95 – 110 H3 LA > 110
5.87 6.85 6.44 4.97
0.29 0.26 0.41 1.47
0.03 0.03 0.05 0.05
1.25 13.77 14.45 13.73
0.30 0.75 0.68 0.92
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Na Mg (meq/100g) 1.72 2.74 2.80 3.28
9.83 10.07 9.46 10.17
Ca
CEC meq/100g
OM
Nttotal %
13.14 4.55 4.92 3.88
20.77 15.87 25.25 17.87
6.07 0.89 1.58 2.68
0.27 0.07 0.09 0.09
(Source : Vo quang Minh, Le quang Tri (2000)) This soil type received the alluvial material from the river, which content a large amount of nutrition for crops, especially the high content of available P, Ca and Mg, (available P raning from 1 to 14 mg/100g at the top soils. Soil pH is relatively nutural raning from 5 to 7. Generally, the soil chemical properties are quite favorable for crops. Table 10: Chemical characteristics of Typical alluvial soil No
Horizon
pH
EC Ptotalú Pavai ms/cm % mg/100g 1 V11 0 - 10 5.64 0.21 0.03 3.59 2 V11 10 - 35 5.68 0.23 0.03 2.20 3 V11 35 - 50 5.43 0.53 0.07 9.45 4 V11 50 - 80 3.32 1.59 0.05 4.87 5 V11 >80 6.88 0.82 0.07 28.72 (Source : Vo quang Minh, Le quang Tri (2000))
CEC Na Mg Ca meq/100g (meq/100g) 0.82 5.62 9.11 15.20 0.66 4.26 8.70 15.14 0.86 4.75 11.62 17.06 1.13 5.77 5.70 11.17 1.83 10.01 7.81 21.70
K 0.23 0.29 0.43 0.42 0.21
OM
Nttotal
4.81 2.95 6.87 9.28 3.02
0.20 0.16 0.27 0.26 0.09
This soil type is the same as above soil type, but soil could not received alluvial material from the river, since the nutrients in the soil are lower , especially the content of available P, raning from 2 to 9 mg/100g at the top soils. Soil pH is relatively nutural, raning from 5 to 6. Other parameters are quite suitable for crops. Table 11: Chemical characteristics of typical developed alluvial soil No
Horizon
pH
EC Ptotalú Pavai ms/cm % mg/100g 1 V4 0 – 15 5.31 0.21 0.05 3.29 2 V4 15 – 50 5.67 0.25 0.02 1.75 3 V4 50 – 120 5.63 0.14 0.03 1.25 4 V4 > 120 5.53 0.28 0.04 3.12 (Source : Vo quang Minh, Le quang Tri (2000))
K 0.21 0.24 0.58 0.70
Na Mg (meq/100g) 0.71 4.82 1.09 6.99 11.19 9.08 1.41 9.62
Ca 11.70 12.18 5.81 5.96
CEC meq/100g 19.23 22.04 19.93 20.43
OM % 4.12 4.47 1.30 1.23
Nttotal % 0.33 0.22 0.09 0.08
This soil type is more developed than above soil types, and located in the higher land. Since the soil nutrients are fewer than about soils. Especially, the content of available P is very low, which need to be applied fertilizer, Ca and Mg are also lower than above soil types. However, soil pH is still normal. If this soil type is used for cultivation, it need to be applied fertilizer to increase the crop production. 4.9.3. Depth of topsoil layer in Tan Phu Thanh village Depth of top soil layer determine the root zone which favorable for crops growth, and supply nutrient, water for crops. If this layer is thin, it is difficult for crops to stand or absorb soil nutrient, water. The thickness of top soil layer will also depend on the characteristics of the subsoil layer, which can be caused by soil pan, sub soil compacknessm, or the accumulation of soil toxicity in the subsoil, causing root can not penetrate into this layer. In Tan Phu Thanh village, more than half of area, the depth of top soil layer from 20 to 50 cm. The extent of depth of top soil layer in Tan Phu Thanh village is showed in table 12. 4.9.4. Beginning of pyritic layer in Tan Phu Thanh village The depth of occurrence of pyritic layer will effect to the development of root, in which very high content of pyritic material.This layer now under reduced condition, and will release high content of toxicity and low pH when it oxidized. Depending on the occurrence of pyritic layer, the this map can be subdivided in to 4 zone, in which half of area there is no occurrence of pyritic material in the soil profile, the occurrence of pyritic layer in the rest areas is from 80 to 120 cm from the soil surface. In cultivation, it should be mentioned to prevent the oxidation of this layer.
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4.9.5 Land mapping units Land mapping units are employed as a basis for land evaluation in this study. These units are based on combinations of depth of inundation, depth of sulfidic layer occurenc and depth of topsoil layer. There are 13 soil mapping units identified in Tan Phu Thanh village. The description and extent of land mapping units showed as follows: •
Depth of maximum innundation classes 1. 20 - 40 cm 2. 40 - 60 cm 3. 60 - 80 cm
•
Depth of pyritic layer occurence classes 1. Non-pyritic material 2. 80 - 120 cm 3. > 120 cm
•
Depth of topsoil classes 1. 0 - 20 cm 2. 20 - 50 cm 3. > 50 cm 4. 120 - 150 cm 5. > 150 cm
5. Conclusion •
Twelve land mapping units were identified in Tan Phu Thanh based on the combination of depth of inundation, depth of sulfidic layer occurenc and depth of topsoil layer.
•
Most of land characteristics of Tan Phu Thanh were suitable for selected land use types. The only limited factors were the depth of maximum flooding and the depth of pyritic layer ocurrence. However, upgrading for land suitability classification by construction of dike to protect from floodding, the limitation of flooding hazard were solved.
References Biswas, B. 1973. Quaternary changes in Sea level in the South China Sea. Geol. Soc. Malaysia. Bull. 6 : 229-256 Furukawa, H. 1992. Coastal Wetlands of Indonesia - Environment, Subsistance, Reclamation. Tokyo : Keiso-Shobo. Herdt, Robert W. and Frank Z. Riely, Jr. 1987. International rice research priorities : Implication for biotechnolgy initiatives. Paper prepared for the Rockefeller Workshop on Allocating Resources for Developing Country Agricultural Research, Bellagio, Italy, July 6-10, 1987. Higgins, G.M, A.H. Kassam, H. T. Van Velthuizen and M. F. Purnell. 1987. Pages 171-183 in Bunting, A. H (ed.) Agricultural environments – Characterization, classification and mapping. Proceedings of the Rome workshop on agroecological characterization, classifcation, and mapping, 14-18 april 1986.C.A.B International, Wallingford, Oxon OX 10 8 DE, U.K Nguyen Huu Chiem. 1993. Geo-Pedological study of the Mekong delta. Southest Asian Studies, Vol. 31, No. 2. September 1993. Statistical office of Chauthanh district, 1999. Statistical year book 1998. Tran Kim Thach. 1980. Sedimental Geology of the Mekong delta. General University of Ho Chi Minh City. (Unpublished) Vo Quang Minh, Le Quang Tri. 2000. Classification of land mapping units based on soils and hydrological characteristics of Tan Phu Thanh village, Chau thanh district, Cantho province. In: Development of new technologies and their practice for sustainable farming systems in the Mekong Delta. Proceedings of the 2000 annual workshop of Jircas Mekong delta project. Jircas-CTU-CLIRRI.
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Figure 2 : Location of Tan Phu Thanh village in Cantho Province.
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Figure 3: Soil map of Tan Phu Thanh village (Soil Taxonomy)
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Figure 4 : Depth of topsoil layer in tan phu Thanh village
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Figure 5 : Inundation depth in Tan Phu Thanh village.
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Figure 6 : Beginning of pyritic layer in Tan Phu Thanh village
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Figure 6 : Proximity to main road
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Figure 7 : Proximity to main river
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Figure 8 : Proximity to main market
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Figure 9 : Proximity to elementary school
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Figure 10 : Proximity to secondary school
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Abstract In soil science, a map is generally used to present the spatial distribution of soil variables. The aim of the soil survey is to examine, describe, classify, and map the soils occuring in the buffer zone. A soil survey is not an end in itself, but a tool for agricultural development. There is a need for a further stage – the evaluation of soils, vegetation, climate, hydrology, and other factors in relation to the requirements of diferent types of land use. Agricultural environments in the humid and sub-humid tropics have very high spatial complexity. Efforts to classify this variability into homogeneous ecological units to facilitate the transfer of technologies across geographical areas, encounter serious constraints. It is not difficult to identify mappable criteria that will separate farm areas into distinct units. However, it is challenging to specify the relevant criteria that influence the adaptation of particular technologies, and to use the spatial data that is available to make efficient extrapolation judgements. This activity is often constrained by limited data and insufficient knowledge of how the data can be used. In the Mekong Delta, soils and hydrology play important roles for agricultural practices, therefore, the characterization and delineation of physical conditions based on the soil and hydrological characteristics are the first steps in land evaluation and land use planning. Tan Phu Thanh village was selected as a case of alluvial soisl for ground truth survey, characterization, delineation in this study. The village classified into 13 soil units, in which nearly half of area is home or gardent (1176,94 ha or 45% of the village). In the rest, the developed alluvial soils are found, which alluvial material accumulated on the topsoil. Some soils have pyritic material occurred from 80 to 120 or greater than 120 cm from the soil surface. The top soil thickness ranged from 20 to 40 cm., and inundation depth ranged from 60-80 cm.
1. Introduction The prioritization of agricultural research among environments relies on reasonably useful and accurate information on what those environments are, and how much agricultural area and production are distributed among them. To date the agricultural resource allocalation debate has been limited to relatively broad ecosystem distinctions, ie. Irrigated, rainfed lowland, upland, and deepwater (Herdt and Riely, 1987). There has been progress during the past decade in developing more practical agroecological classifications at continental and national scales (Higgins and Kassam, 1987) Most of the food needs of the increasing population in rice growing and consuming countries will have to come from these lowlands as there is little scope for increasing the irrigated are in thenfuture. In order to formulate research strategies for increased rice production, characterizaitization and delineation of area under difference subecosystem or mapping unit are required.
2. Description of the village Tan Phu Thanh village located in the South of Chau Thanh district, neighbors in the North is Nhon Nghia village, in the East is Thanh Dong, in the Western-South is Thanh Xuan village. Total area is 2,604.44 ha,
1
with 7 hamplets, inlduding Tan Thanh Dong, Tan Thanh Tay, Phu Loi, Phu Thanh, , Thanh Loi, Thanh Phu, Thanh My, Tan An, Tan Phu, and Long An.
3. Methodology The research had been done based on following steps: Step 1 : Research outline, secondary data collection. Step 2 : Field data collection (socioeconomic, soil, hydrological data collection) Step 3 : Data, map digitizin, processing (ILWIS, MAPINFO software used) Step 4 : Map delineation and characterization (using GIS and ecosystems criteria) 3.1. Method of survey Generation of an accurate database is the most important part of this methodology. The process begins with the selection of appropriate map of the research area which created by land administration department (cadastral map), which located exact each pacel on the map for easy to recognized in the field. Ground truth is carried out to collect the information on soil type, occurrence of sulfidic and sulfuric horizone in the profile, depth of surface horizone, depth of inundation, length of inundation, and duration of inundation. Soil samples are also collected at each soil type for amalyzing of pH, EC, total N, total P, available P, extractable K, Ca, Na, and Mg, percent of organic matter,.. The actual precise area and administration map of the studied area is collected from the Cadastral sector of Chau thanh district (at scale 1:2,000). Based on these references, as many transects were crossed over the survey area. A total amount of 145 soil survey locations were identified. The soil survey activity has been done from May to June, 2001. Three survey groups were formed and the survey was done based on the pre-defined observation points and field truth measurements. Methodology of data analysis The intepretation of the data provides thematic maps, which integrated by using GIS, based on the generation of different combination, delineate the area into different mapping units or subecosystems. These database will be used for suitability assesment and land use planning for next paper. The spatial heterogenity and temporal variability of biophysical parameters, used as criteria for classification of subecosystems or mapping unit, make the characterization of the units complex and restrict the validity of the maps only to the year of survey. This situation makes it difficult to select a site representative of an subecosystem or mapping unit. Even the repeated mapping does not capture the realistic scenario. Data were classified on the basis of the sub-ecological zones in term of typical land use types. Four steps in the data analysis are used as follows: Transferring data from questionnaire to paper sheets Processing & checking data on paper sheets Input data in computer, map compilation and data digitizing Arranging files, map and data analysis/procesing. GIS used as tools in map and data manipulation.
4. Results 4.1. Climatic conditions of Tan Phu Thanh Village Tan Phu Thanh village belong to Chau thanh district, Cantho province, the climatic conditions are similar to the condition of the district or province, which distinguse season, dry and rainy seasons. The dry season starts from January to May, while the rainy season starts from May to December. Total rainfall of the region about 1952 mm/year, however most of rainfall concentrated in the rainy season, while there are no rain in February and March, high rainfall concentrated from May (113.3 mm) to December (153 mm), amount of rainfall is highest in September (439.2 mm). Depending on table 1 and
2
figure 6, in the rainy season, there are no drought spell occurrence, which harmful for cropping season because there are not enough water for irriagtion. However, the hydrology conditions of the village are quite suitable for agricultural eventhouth drought spell occurred. Temperature of the village is nearly stabilized in the year, average temperatute is about 27.3 oC, highest Temp. is in May (29.6oC), and lowest is in December (25.3oC). The village has high air humidity, specially in the rainy season, highest is in September (91%), and lowest is in the dry season (79 – 82%). Generally, the climatic conditions of Tan Phu Thanh village are the same as the conditions of the districts or province, it is belong to the climatic regime of the region, which suitable for the agricultural development. Especially, the land use parterns diversity in the village is very high, which conforming for the suitable of the villlage for agricultural production. OF TANPHUTHANH (1998) the climatic conditions of Tan Phu VILLAGE Thanh villages (1998) FigureCILMATIC 1: ShowingCONDITIONS (Source : Statistical year book 1998, Statistical office of Chauthanh district, 1999)
500
Rainfall (mm)
450
Rainfall (days)
400
Temp. oC Air. Hu. (%)
350
Rainfall (mm)
300 250 200 150 100 50 0
1
2
3
4
5
6
7
8
9
10
11
12
Months
4.2. Hydrological conditions of Tan Phu Thanh village The inundation depth will effect to the type of crops, cropping system, and also the development of fishery. The inundation of Tan Phu Thanh village is affected by the tidal regime and receive water from Hau river, about 10 km from Hau river. Since maximum depth of inundation is high, ranging from 40 to 80 cm.
4.3. Present land use of Tan Phu Thanh village According to the map, there were 13 land use patterns in the village, in which double rice crops is dominated in most of the hampletes. However, fruit crops and perenial are concentrated with a very large area along the river and national highway, in which Tan Phu and Long An hampletes have the largest area of fruit gardent and upland crops, the other land uses occupied a few hectars including mixed garden, church, cemetory, house, which located along the river or national highway or local paths, canal, river,.. Double rice, fruit garden, and perenial are the dominated land uses in the village and distributed in most of the hampletes, it showing that the village has the potential in deleloping the fruit crops such as oranges, rambutant, longan, mangove,..as reported by the farmer and the goverment. while double rice is now shifting to triple rice as practiced at some places in the village. This is showing the highly suitability of crops in the area.
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4.4. Proximity to main river In Tan Phu Thanh village, Balang river is the main river of the village, which the farmers can use for transpotation of their product to the market, and also for their local transpotation. The distance from the main river will effect to the time to transport their product to the market for consumtion ,and also the time of transpotation.. Depending on the area and the location of the main river, more than 50 % area of Tan Phu Thanh village has the distance less than 1000 m from the main river. 4.5. Proximity to main road In Tan Phu Thanh village, National high way is the main road located in the village, which the farmers can use for transpotation of their product to the market, and also for their local transpotation. The proximity to the main road will effect to the time to transport their product to the market for consumtion ,and also the time of transpotation.. Depending on the area and the location of the main road , more than 50 % area of Tan Phu Thanh village has the distance less than 1000 m from the main road. 4.6. Proximity to main market In the village, most of farmer production are for local consumtion, which the farmer sell their product in local market, since, it will be very easy for local cumsumtion if their field very near to the local market. In Tan Phu Thanh village, there are two main market located in the village (including Xeo vong, So 10, and Cai Tac makets), and the proximity of farmer fields to local market ranging from 500 to more than 4000 m, in which most of distance concentrated within 1000 to 3000 m. If farmers produce more product they used to sel their product in Cantho or Cairang market 4.7. Proximity to elementary school In Tan Phu Thanh village, there are 11 elementary schools located in the village, since, it is very suitable for student to study. Most of distance from farmer houses to the elementary schools raning from less than 500 m to 2000 m, which concentrated within the distance from 500 to 1500 m. Therefore, the student can go to school by walk or bicycle or by boat. 4.8. Proximity to secondary school There are 2 secondary school located in Tan Phu Thanh village (including Tan Phu Thanh and Tam vu 2 secondary schools), if considered within the village, the student have to go far by walk or bicycle or by boat to the school, because it is far from school to their house, the distance raning from less than 500 m to 7000 m, and the distance concentrated from 500 to 5000 m. However, because there is an other secondary school in Cai rang, which very near for student located in the hamplet of Tan Thanh Dong, and Tan Thanh Tay and Phu Thanh, they can study in these school intead of studying local secondary school. 4.9. Soils of Tan Phu Thanh village 4.9.1. Soil formation According to Nguyen Huu Chiem (1992), the Mekong delta, in which Tan Phu Thanh village located, the formation of the recent Holocence seiments of the delta began about 11,000 years B.P. As for older seiemnts, Bosum et al (1971) have interpreted an aeromagnetic map covering the Mekong delta as suggesting that the metamorphosed lower Paleozoic deposits found in the plateau area Northest of the delta and in Cambodia to the Northwest of the delta constitute the basement of the delta. The thickness of 3 to 5 km of the sediments suggested by magnetic interpretation means that they could include any parts of the section ranging from the Permian limstones to the Quaternary alluvium. According to Tran Kim Thach (1980), during the Terriary the delta was covered by a thick layer of old sediments consisting of marine,
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brackish and alluvial sediments. Especially during the late Pleistocene era, when the sea fell to 68 meters below its present level (Biswa, 1973), sediments of the Mekong river covered all the delta. In the Holocene regression, the sea gradually receded. Sediments of a transitional to subaqueous fan-delta were formed. These sediment contain relatively few pollents (either freshwater, mangrove or brackish). Total sulfur and water soluble salt contents are low. EC value varies from 0.2 to 0.6 ms/cm, pHxo and pHw are mostly above 3.5. Toward the sea, the holocene sediments become thicker. The deepest layer of Holocence sediments contains small shells. The pHw and pHox are mostly above 7. EC value is high *4ms/cm). Polen is completely absent. These indicators show that the layer represents a marine environemnt and was deposited during the Holocene transgression. In the subsequent marine regression, sandy clay layer with laminated structure, relatively high EC value (2-4 ms/cm), low contents of total sulfur, water soluble sulfate, pyrite, and pollen, in which illite mineral was transformation to vermiculite or kaolinite, was deposited on the marine sediments. This layer represents a tidal flat environment. The continuation of the marine regression toward the South China sea subsequently led to the development of a coastal landform. The coastal complex consists of many sand ridges, coastal flats, inter-ridges and mangrove swamps. Coastal flats have moderate relief, lying about 1 to 1.5 meters above mean sea level. Mangroves are distributed along the coastline and the mouth of the Mekong river. Many kinds of mangrove species thrive in these swamps. Very new potential acid sulfate soils have formed there. When sea receded far from the former coast, the recent alluvial sediments were drained. In the high floodplin and the tide-affected floodplain, a large amount of recent sediments were deposited. The coarse sediments such as sand and silt were carried by violent plug-flow and deposited along the river banks, forming natural levees, while clay was deposited behind the levees and formed the backswamps. Three areas, namely, the open floodplain. The closed floodplain and the broad depression are located far from the river and received only small quantities of new accretion. There, the mangrovw sediment layer can be found very cloase to the topsoil. The soil formation of Tan Phu Thanh village is the same as the formation of the Mekong Delta, the formation mostly by the sediments of the Mekong River during Holocene period. During this period of sedimentation, the sea level has raised and lowered many times. In the rainfed areas, seawater intrudes far inside the Delta during the dry season and the affected areas cover more than 1 million hectares. In the rainy season, although the soil surface is flushed and freshened, the shallow groundwater still remains saline. In the past, as the river changed its course, several river branches in low landscape had been formed and deposits with high sulphur content and organic matter have been deposited. 4.9.2. Soil types of Tan Phu Thanh village There are 6 major soil types in Tan Phu Thanh village, and large area are potential acid sulfate soil, in which sulfidic horizon often occurred at the depth more than 80 cm from soil surface. the pyritic material indicated in the field by oxidation of H2O2, which will oxidize pyritic material and bring soil pH down, if pyritic material presented, soil pH will down to lower than 2. These soil types presently not harmfull for crops, but if it exposed to the surface such as for raised bed, pond making,.. it will be oxidized and released a lot of toxicity as Al3+, Fe2+, total acid, and low pH (soil types code 3,4,5 and 6). Besides these, most of the soil receive a lot of alluvial materal from river, deposited on the top soil to form a Fluvic phase, which indicate the accumulation of aluvial material on the topsoil. However, due to the accumuation of organic matter on the surface during crop cultivation, the soil surface have a dark color to form the umbric phase. There are no occurrence of pyritic material in the horizon in other soil types (code 1 and 2), these soil types are favorable for most of the crops. Table 9: Chemical characteristics of deposited alluvial soil 10
Horizon
pH
EC Ms/cm
Ptotalú %
Pavai Mg/100g
K
1 2 3 4
H3 LA 0 – 30 H3 LA 30 – 95 H3 LA 95 – 110 H3 LA > 110
5.87 6.85 6.44 4.97
0.29 0.26 0.41 1.47
0.03 0.03 0.05 0.05
1.25 13.77 14.45 13.73
0.30 0.75 0.68 0.92
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Na Mg (meq/100g) 1.72 2.74 2.80 3.28
9.83 10.07 9.46 10.17
Ca
CEC meq/100g
OM
Nttotal %
13.14 4.55 4.92 3.88
20.77 15.87 25.25 17.87
6.07 0.89 1.58 2.68
0.27 0.07 0.09 0.09
(Source : Vo quang Minh, Le quang Tri (2000)) This soil type received the alluvial material from the river, which content a large amount of nutrition for crops, especially the high content of available P, Ca and Mg, (available P raning from 1 to 14 mg/100g at the top soils. Soil pH is relatively nutural raning from 5 to 7. Generally, the soil chemical properties are quite favorable for crops. Table 10: Chemical characteristics of Typical alluvial soil No
Horizon
pH
EC Ptotalú Pavai ms/cm % mg/100g 1 V11 0 - 10 5.64 0.21 0.03 3.59 2 V11 10 - 35 5.68 0.23 0.03 2.20 3 V11 35 - 50 5.43 0.53 0.07 9.45 4 V11 50 - 80 3.32 1.59 0.05 4.87 5 V11 >80 6.88 0.82 0.07 28.72 (Source : Vo quang Minh, Le quang Tri (2000))
CEC Na Mg Ca meq/100g (meq/100g) 0.82 5.62 9.11 15.20 0.66 4.26 8.70 15.14 0.86 4.75 11.62 17.06 1.13 5.77 5.70 11.17 1.83 10.01 7.81 21.70
K 0.23 0.29 0.43 0.42 0.21
OM
Nttotal
4.81 2.95 6.87 9.28 3.02
0.20 0.16 0.27 0.26 0.09
This soil type is the same as above soil type, but soil could not received alluvial material from the river, since the nutrients in the soil are lower , especially the content of available P, raning from 2 to 9 mg/100g at the top soils. Soil pH is relatively nutural, raning from 5 to 6. Other parameters are quite suitable for crops. Table 11: Chemical characteristics of typical developed alluvial soil No
Horizon
pH
EC Ptotalú Pavai ms/cm % mg/100g 1 V4 0 – 15 5.31 0.21 0.05 3.29 2 V4 15 – 50 5.67 0.25 0.02 1.75 3 V4 50 – 120 5.63 0.14 0.03 1.25 4 V4 > 120 5.53 0.28 0.04 3.12 (Source : Vo quang Minh, Le quang Tri (2000))
K 0.21 0.24 0.58 0.70
Na Mg (meq/100g) 0.71 4.82 1.09 6.99 11.19 9.08 1.41 9.62
Ca 11.70 12.18 5.81 5.96
CEC meq/100g 19.23 22.04 19.93 20.43
OM % 4.12 4.47 1.30 1.23
Nttotal % 0.33 0.22 0.09 0.08
This soil type is more developed than above soil types, and located in the higher land. Since the soil nutrients are fewer than about soils. Especially, the content of available P is very low, which need to be applied fertilizer, Ca and Mg are also lower than above soil types. However, soil pH is still normal. If this soil type is used for cultivation, it need to be applied fertilizer to increase the crop production. 4.9.3. Depth of topsoil layer in Tan Phu Thanh village Depth of top soil layer determine the root zone which favorable for crops growth, and supply nutrient, water for crops. If this layer is thin, it is difficult for crops to stand or absorb soil nutrient, water. The thickness of top soil layer will also depend on the characteristics of the subsoil layer, which can be caused by soil pan, sub soil compacknessm, or the accumulation of soil toxicity in the subsoil, causing root can not penetrate into this layer. In Tan Phu Thanh village, more than half of area, the depth of top soil layer from 20 to 50 cm. The extent of depth of top soil layer in Tan Phu Thanh village is showed in table 12. 4.9.4. Beginning of pyritic layer in Tan Phu Thanh village The depth of occurrence of pyritic layer will effect to the development of root, in which very high content of pyritic material.This layer now under reduced condition, and will release high content of toxicity and low pH when it oxidized. Depending on the occurrence of pyritic layer, the this map can be subdivided in to 4 zone, in which half of area there is no occurrence of pyritic material in the soil profile, the occurrence of pyritic layer in the rest areas is from 80 to 120 cm from the soil surface. In cultivation, it should be mentioned to prevent the oxidation of this layer.
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4.9.5 Land mapping units Land mapping units are employed as a basis for land evaluation in this study. These units are based on combinations of depth of inundation, depth of sulfidic layer occurenc and depth of topsoil layer. There are 13 soil mapping units identified in Tan Phu Thanh village. The description and extent of land mapping units showed as follows: •
Depth of maximum innundation classes 1. 20 - 40 cm 2. 40 - 60 cm 3. 60 - 80 cm
•
Depth of pyritic layer occurence classes 1. Non-pyritic material 2. 80 - 120 cm 3. > 120 cm
•
Depth of topsoil classes 1. 0 - 20 cm 2. 20 - 50 cm 3. > 50 cm 4. 120 - 150 cm 5. > 150 cm
5. Conclusion •
Twelve land mapping units were identified in Tan Phu Thanh based on the combination of depth of inundation, depth of sulfidic layer occurenc and depth of topsoil layer.
•
Most of land characteristics of Tan Phu Thanh were suitable for selected land use types. The only limited factors were the depth of maximum flooding and the depth of pyritic layer ocurrence. However, upgrading for land suitability classification by construction of dike to protect from floodding, the limitation of flooding hazard were solved.
References Biswas, B. 1973. Quaternary changes in Sea level in the South China Sea. Geol. Soc. Malaysia. Bull. 6 : 229-256 Furukawa, H. 1992. Coastal Wetlands of Indonesia - Environment, Subsistance, Reclamation. Tokyo : Keiso-Shobo. Herdt, Robert W. and Frank Z. Riely, Jr. 1987. International rice research priorities : Implication for biotechnolgy initiatives. Paper prepared for the Rockefeller Workshop on Allocating Resources for Developing Country Agricultural Research, Bellagio, Italy, July 6-10, 1987. Higgins, G.M, A.H. Kassam, H. T. Van Velthuizen and M. F. Purnell. 1987. Pages 171-183 in Bunting, A. H (ed.) Agricultural environments – Characterization, classification and mapping. Proceedings of the Rome workshop on agroecological characterization, classifcation, and mapping, 14-18 april 1986.C.A.B International, Wallingford, Oxon OX 10 8 DE, U.K Nguyen Huu Chiem. 1993. Geo-Pedological study of the Mekong delta. Southest Asian Studies, Vol. 31, No. 2. September 1993. Statistical office of Chauthanh district, 1999. Statistical year book 1998. Tran Kim Thach. 1980. Sedimental Geology of the Mekong delta. General University of Ho Chi Minh City. (Unpublished) Vo Quang Minh, Le Quang Tri. 2000. Classification of land mapping units based on soils and hydrological characteristics of Tan Phu Thanh village, Chau thanh district, Cantho province. In: Development of new technologies and their practice for sustainable farming systems in the Mekong Delta. Proceedings of the 2000 annual workshop of Jircas Mekong delta project. Jircas-CTU-CLIRRI.
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Figure 2 : Location of Tan Phu Thanh village in Cantho Province.
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Figure 3: Soil map of Tan Phu Thanh village (Soil Taxonomy)
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Figure 4 : Depth of topsoil layer in tan phu Thanh village
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Figure 5 : Inundation depth in Tan Phu Thanh village.
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Figure 6 : Beginning of pyritic layer in Tan Phu Thanh village
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Figure 6 : Proximity to main road
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Figure 7 : Proximity to main river
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Figure 8 : Proximity to main market
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Figure 9 : Proximity to elementary school
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Figure 10 : Proximity to secondary school
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