THE USE OF GEOGRAPHIC INFORMATION SYSTEMS FOR SOIL SURVEY AND LAND EVALUATION

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1 Page 1 of 8 THE USE OF GEOGRAPHIC INFORMATION SYSTEMS FOR SOIL SURVEY AND LAND EVALUATION Mr. INTHAVONG Thavone, Deputy head of Soil Survey and Land Use Planning Division; GIS specialist National Agriculture and Forestry Research Institute Soil Survey and Land Classification Center Soil Survey and Land Use Planning Division Abstract: Geographic Information System (GIS) plays an important role in soil survey and land evaluation for land use planning in the Lao.P.D.R nowadays. The model of the use of Geographic Information System conducted for rainfed lowland rice, cash crops and fruit trees suitability assessment in the Central Part of the Lao.P.D.R. The main objectives of the study are to look for the suitability rating for different type of crops in different parts of the Country or in different soil physical factors and other factors. It will be valuable data for agricultural development of the country in the future. The methodology of this study proceeds by converting land characteristics into a set of land qualities that are relevant for the land utilization type. The Geographic Information Systems provides the digital soil map, comprising digitized polygons of soil units, which linked to an attribute table of quantitative soil properties. Each land quality is determined by assessing the appropriate land characteristics, the user specifies the criteria for assessing suitability and match the land quality with the land use requirement for specific crops for evaluation (based on bio-physical considerations) by using Automation Land Evaluation System (ALES) and map results using GIS. The results of land suitability assessment from this study area indicate that the most areas evaluated are moderately (S3) to slightly limitation (S2) for rainfed lowland rice, cash crops and fruit crops due to most severe limitation factors in production are the limited available nutrient content and soil reaction. Consistent yield improvements can be expected by a proper choice of crops or alternative land uses and/or by concentrating on an appropriate management on liming and fertilizer application. INTRODUCTION The Lao P.D.R has been endorsed with abundant natural resources i.e. forest, land and water. In the year s , the forest cover of Laos was about 70 of territory, people lived in equilibrium with ecosystem. Nowadays, the ecosystem is not the same; the main cause of this ecosystem change is well known under the term of deforestation. Deforestation is due to shifting cultivation practice: in upland area where lived families or 1.5 million of ethnic peoples practicing this mode of cultivation so forest has been destroyed around hectares per annum; another reason is due to increasing pressure from agricultural expansion, illegal logging and by custom and traditional living condition, large areas are burning for hunting and /or for other purposes. In order to solve this problem, Party and Lao Government had lead out a land use policy, which aim to protect, conserve, and rehabilitate land and forest resources. Forest and Soil resources inventory and the assessment of land suitability classification is one of the main strategy of Land use policy thus, Soil Survey and Land Classification Center have to paid more attention on this context, soil survey and land evaluation of physical environment has becomes essential. At present, the soil survey at a reconnaissance scale has been completed throughout the country. However, most of the survey areas were concentrated on the areas of low-relief, which normally have slopes less than 55 percent. At the same time, number of the semi-detailed and detailed soil surveys were also made to serve the needs of soil interpretation for agriculture planning from various government agencies. Soil Survey and Land Classification Center now recognized about 16 soil groups and more than 20 soil units in the Lao P.D.R. Unfortunately, these are many soils defined in such a way that the users lacking a soil science background find it difficult to understand them. Therefore one of the main priority of SSLCC has been the establishment of the soil interpretation for agriculture use, which can help other agencies in making more meaningful use of soil and land resource management.

2 Page 2 of 8 OBJECTIVE: The objective of this study is to present an approach to establishing GIS techniques in conjunction with other land computerized land evaluation tools to generate land suitability maps from soil-crop suitability maps and their integration for land resource management. MATERIALS AND METHODS 1. Soil study: The study area is located in Paksan, Bolikhamxay province in the Central part of the Lao P.D.R and it lies on longitudes E and latitudes N, the topography is flat or almost flat with 2-8 slope to steep land with slope more than 55. Climatologically the area has a dry period from November to May and wet period from June to October. The average annual rainfall in growing period is about 1700 mm and mean temperature in growing period is 28C. The system of soil classification used by the soil survey and land classification center (SSLCC) is derived from the FAO/UNESCO s legend soil map of the world, 1989 revised legend. There are two categories: soil groups and subgroups (units). Classification is based on soil properties (diagnostic horizons and properties) observed in the field or inferred from those observation or on laboratory measurements. A soil group consists of soils that are developed on similar materials and similar environment conditions (physiography, topography, and slopes and drainage condition). As for soil subgroups are differentiated from one to another accordingly to the chemical-physical properties of soils and/or soil diagnostic properties. The treatment of materials from field survey and from laboratory for map compilation included the following: Delineation of soil unit boundary (on a topographical map at 1/ scale, produced by Russia with Gauss projection) by transferring with the help of each aerial photograph interpretation unit and the result of field survey and elements of the interpretative situation from the aerial photograph on to the base map; each mapping unit should bear the index of mapping unit featuring soil group, soil subgroups etc. The soil pattern of this study area includes 6 soil groups: Arenosol, Regosols, Alisols, Acrisols, Luvisols and Cambisols with associated soil units: Haplic Arenosols, Dystric Regosols, Gleyic Alisols, Ferric Alisols etc as show in the legend of soil map below. Land mapping units are presented on the map by soil profile code which referred to dominant soil group in capital letters and subgroups (soil units) by small letter, and combined with soil depth class, soil texture, slopes class and soil fertility. The full combination of the associated is given by these examples: P 120: LPd-R-SL-b (M) LP -Soil group where: LP -LEPTOSOLS LPd -Soil unit LPd -Dystric LAPTOSOLS R -Soil Depth R -Rock out crop(> 0-30cm depth) SL -Soil texture class SL -Sandy loam texture b -Slopes class b -Undulating with slopes ranges 2-8 M -Soil fertility M -Medium fertility

3 Page 3 of 8 Figure 1. Land mapping units identified in the study area. 2. Application to Land Suitability Evaluation for Cropping System: This land evaluation methodology proceeds by converting land characteristics or primary land attributes that are recorded by a soil survey, into a set of land qualities that are relevant for the land utilization type. Land qualities are important for determining the physical land suitability for growing crops; these are nutrient availability, nutrient retention, erosion hazard, moisture availability, temperature regime and rooting condition. These land qualities can be ranked according to the following classes: S1- Lands very well suited for crop production; having no significant limitations that restrict their use for this land use alternative. S2- Land well suited for crop production; having slight limitation that restrict their use for this land alternative. S3- Land moderately well suited for crop production; having moderate limitations that reduce the choice of crops and/or require special land management for this land use alternative. N- Lands not suited for crop production, having very severe limitations that preclude their use for this land use alternative.

4 Page 4 of 8 Flowchart of the operations needed to create a map of suitability classes for crops using FAO land evaluation procedures Each land quality is defined by specific combination of selected land characteristics (flowchart) i.e. nutrient availability can be derived directly from the soil properties ( organic matter, available phosphorus, available potassium and soil reaction phh20); rooting condition and erosion hazard can be considered from soil information (effective soil depth, slope class, soil texture) and moisture availability refers to the water requirement in growing period can be derived from rainfall and temperature regime can be derived from mean temperature in growing period. The way in which these combinations are performed must be specified by the user and expressed in the form of decision trees. A decision tree is basic component of the model. The decision tree can be a severity level or a subclass decision tree. The severity level decision trees allow one to place each land unit into one of the defined suitability classes, based on how good the LURs of each LUT are met by the prevailing land characteristics. The subclass decision tree assigns specific physical suitability subclasses as a final output of the decision procedure, indicating the major limitations. The tabulated land use requirements for a list of crops (Qualitative Land Evaluation 1995; SSLCC) have been used for specific suitability rate for each crops and figure below shows a simple decision tree for land use type rainfed lowland rice and land use requirement nutrient retention. Table 1: LAND USE REQUIREMENT OF SOME LAND USE TYPES Land use types Land Quality Diagnostic factor Suitability rate Units S1 S2 S3 N 1. Rice - Temperature - Mean temp. in growing period C >35 - Moisture avail. - Nutrient avail. - Av.annual rainfall - organic matter - P(available) - K2O(available) - Soil_pH (Soil Reaction) mm ppm mg/100g reaction >1500 >3 >25 > <1 <10 < >35 <800 >8.5 - Nutrient reten. - CEC.total (meq/100g) - Base saturation() meq/100g >15 > <5 <35 <4.0 - Rooting Condi. - Erosion hazard - Effective soil depth - Slope - Soil texture cm class >50 a Sc,C,Cl b Scl,Sil,Si c Ls,Sl <15 >c gravels,sand -Oxygen avail. - Soil drainage class 1,2, Corn - Temperature - Mean temp. in growing period C >35 <16 -Moisture avail. - Water requirement in growing period Mm <300 - Nutrient avail. - organic matter - P (available) - K2O (available) - Soil_pH (Soil Reaction) ppm mg/100g reaction >2.5 >25 > <1.0 <6 < >8.5 <4.5 - Nutrient reten. - CEC.total (meq/100g) - Base saturation() meq/100g >15 > <50 <3 - Rooting Condi - Erosion hazard - Effective soil depth - Slope - Soil texture cm class >100 ab Sl,L,Sil,Cl c d <25 >d - Oxygen avail. - Soil drainage class 5, ,2 1. Citrus - Temperature - Mean temp. in growing period C >35 <13 - Moisture avail. - Av.annual rainfall mm >3000 < Nutrient avail. - organic matter - P (available) ppm >2.5 > <1.0 <6

5 Page 5 of 8 - K2O (available) - Soil_pH (Soil Reaction) mg/100g reaction > < >8.4 <4.5 - Nutrient reten. - CEC.total (meq/100g) - Base saturation() meq/100g >10 > <35 <5 - Rooting Condi. - Erosion hazard - Effective soil depth - Slope - Soil texture cm class >100 a,b,c Sl,L,Sil,Si,vf Sl d e >e - Oxygen avail. - Soil drainage class 5, ,2 Nutrient Retention (nr) > CECe-c (CEC by sum of basses+extr.acidity,topsoil) meq/100g]... : 3 (Moderate) meq/100g]... : = meq/100g] > Bases/c(Basaturation) 1.vl (Very Low) [0-25 ]...: 2.sl [25-35 ]... : 3.l (Low) [35-50 ]... : 4.m (Medium) [50-75 ]... : 5.h (High) [ ]... : meq/100g]... : =2(Slightly) meq/100g] > Bases/c (Basaturation) 1.vl (Very Low) [0-25 ]...:2.sl [25-35 ]... : 3.l (Low) [35-50 ]...: 4.m (Medium) [50-75 ]... : 5.h (High) [ ]... : meq/100g] > Bases/c (Basaturation) 1.vl (Very Low) [0-25 ]...: 2.sl [25-35 ]......: 3.l (Low) [35-50 ].....: 4.m (Medium) [50-75 ]...: 5.h (High) [ ]...: 3(Moderate) =1 =2(Slightly) =1 =1 3 (Moderate) =1 2(Slightly) none none 3 (Moderate) 2(Slightly) 2(Slightly) none none Figure 2. Example of a severity level decision tree for land use type rainfed low land rice and land use requirement nutrient retention. The graphs, the land use requirement " Nutrient Retention" is evaluated through an assessment of cation exchange capacity by sum of basses plus extr. Acidity (CECe) and basaturation (Bases). A first level decision is made on the basis of the cation exchange capacity by sum of basses plus extr. acidity, with additional subdivisions related to the amount of basaturation (Bases). RESULTS The Automation Land Evaluation System (ALES) are used to compute and present the result of land suitability classification. The land suitability for each one of the lands mapping units of a survey area can be demonstrated in the table 2 below. This table shows mapping code and approximate extent of those mapping units suitable for rainfed lowland rice, cash crops and fruit crops. Land mapping units are grouped into classes according to degree of limitation in use or risk of damage when used. Thus, the most serious degree of limitation determines the suitability classes and classes are indicated by numeric 1 to 4 increasing order of suitability and each class are subdivided into subclass according to dominant kinds of limitation. Small case letter following the class number indicates the dominant limitation. The overall suitability of the study area for the Rainfed lowland rice, Cash crops and Fruit trees is illustrated in fig. 2, 3 and 4.

6 Page 6 of 8 Figure 2. Suitability map of the study area for rainfed low land rice Figure 3. Suitability map of the study area for Mungbean

7 Page 7 of 8 Figure 4. Suitability map of the study area for Citrus The results of land suitability classification in this study area indicated that: the most areas evaluated are moderately limitation (S3) to slightly limitation (S2) for rainfed low land rice, cash crops and fruit crops due to most severe limitation factors in production are the limited available nutrient content (na) and soil reaction (ph). Thus, an appropriate management on water supply, drainage arrangement, liming and fertilizer application should take into consideration. Generally, there are a lots of land use types in the study area in which some land use type answer the goals of development, some land use types not. Thus, it is necessary to select suitable land use types. The principle of select suitable land use types was based primarily on information gathered from the soil and land capability maps i.e. soils are grouped in term of their response to the same productivity level and/or their requirement common and similar management practices for specific use or crops cultivation. Optimum prospective land use of Thabok, Bolokhamxay province was classified in accordance with 9 land utilization types as the table 3 below: Table 3: Proposed Land Utilization Types Mapping legend Land Utilization Types(LUT) LUT-1 Rp (Rainfed low land Rice) S3(na,n,ph,s) Land Suitability Rating LUT-2 (Co,Mb,Sb,Tob);(Cot,Man,Su) S2(na,c,ph,m,n);S3(na,ph,m,c) LUT-3 (Mb,Tob);(Ci,Co,Cot,Man,Sb,Su) S2(na,n,ph,m);S3(na,ph,n,m,c) LUT-4 (Mb,Tob);(Co,Cot,Sb,Su);(Man) S2(na,n,ph,m,rc);S3(na,ph,m,c,rc),N(rc,m) LUT-5 (Tob);(Ci,Co,Cot,Man,Mb,Sb,Su) S2(na,n,ph,m,s);S3(na,ph,n,m,c,s) LUT-6 (Tob);(Ci,Co,Cot,Man,Mb,Sb,Su) S2(na,ph,m);S3(na,ph,m,c),N(na,m) LUT-7 (Ci,Co,Cot,Man,Mb,Sb,Su,Tob) S3(na,ph,n,m,c) LUT-8 (Ci,Co,Cot,Man,Mb,Sb,Su,Tob) S3(na,ph,n,m,c),N(na,m,ph) LUT-9 (Ci,Co,Cot,Mb,Sb,Su,Tob)(Man) S3(na,ph,n,m,c,rc,s),N(rc,m,ph) STP Reservation forest Land Utilization Types (LUT) Rp-Rainfed lowland rice Cash crops: Co-Corn, Cot-Cotton, Mb-Mungbean, and Sb-Soy bean, Tob-Tobaco, Su-Sugar cane Fruit crops: Ci-Citrus, Man-Mango

8 Page 8 of 8 Figure 5. Optimum prospective land use map of the study area CONCLUSION AND DISCUSION The use of Geographic Information System in conjunction with other land computerized land evaluation tools to generate land suitability assessment has both advantages and drawbacks. However, the advantages are comparatively greater. The main advantages include that: models can be built based on local expert knowledge, available data and specific objectives, enhancing a better use of local experience to solve local problems and output can be integrated with a GIS to produce required maps. The main drawbacks include that: a strictly user defined approach is followed to assign severity levels to combinations of land characteristics values, giving way to some subjectivity in the decision. Although the land suitability classification system in the Lao.P.D.R has been developed nowadays, there are still some problems that limit its use. Some problems and reaction to the system can be summarized as follows: Although the agronomic data and other observations of crop performance are essential for classifying the land in suitability, they have been used to a limit extent for developing the system. The reason is that there are not so many rigorous research investigations on crop response to soil in the Lao.P.D.R. Some limitation being used for the determination of classes or subclasses are rather difficult to visualize. For instance flooding regime, moisture stress and erodibility are difficult ones. REFERENCES: Soil survey and Land Classification Center (SSLCC), 1995 Qualitative Land Evaluations. Soil survey and Land Classification Center (SSLCC) " Methodology of soil Survey and Land Classification" P.A BURROUGH " Principle of Geographic Information System for Land Resources Assessment" Food and Agriculture Organization of the United Nation " Land Evaluation for Development" Rossiter and Van Wambeke, 1989 ALES: Automation Land Evaluation System. ALES User s manual, version 2.2, Dep. of Agronomy, Cornell University, NY. Dr. Ty PHOMMASACK, Land Use/Land cover change overall land use policy in the Lao P.D.R