Land suitability studies for paddy cultivation in Dadahup Swampy Irrigation Area

The Dadahup Swampy Irrigation Area is crucial in the government’s Food Estate initiative to enhance food security in Indonesia. Following extensive infrastructure improvements, including network rehabilitation and gate construction between 2020 and 2022, a pilot project was initiated in block A5. However, rice yields in this area still need to improve, primarily due to inadequate land management practices. This study evaluates and maps land suitability for paddy cultivation in the Dadahup Swamp Irrigation Area, employing a combination of laboratory data and field research integrated with geographic information system (GIS) technology. Various parameters were considered, such as climate factors (temperature and water availability), soil characteristics (drainage, texture, depth), peatland attributes (thickness, maturity), nutrient content (CEC, base saturation, pH, C-organic), available nutrients (nitrogen, phosphorus, potassium), salinity, alkalinity, pyrite depth, and inundation levels during planting. Then, thematic raster mapping was conducted using the Inverse Distance Weighted (IDW) method, followed by reclassification based on Food and Agriculture Organization (FAO) standards for land evaluation. The result categorized Block A5 into three suitability classes: S1 (highly suitable), S2 (moderately suitable), and S3 (marginally suitable). Approximately 22.5% of Block A5 is highly suitable (S1), 39.5% is moderately suitable (S2), and around 38% is marginally suitable (S3).


Introduction
One of the National Strategic Programs launched by the government of Indonesia in food security referring to the 2020-2024 National Medium-Term Development Plan is a program to increase the national food supply, known as the Food Estate [1].One of these food estate areas is the Dadahup Swampy Irrigation Area (DIR Dadahup) in Kapuas Regency, Central Kalimantan Province.
Based on data compiled by the Directorate of Irrigation and Swamp (2020), The potential land area within DIR Dadahup is 21,226 hectares, with 6,111 hectares currently in use, while the remaining 15,115 hectares need restoration or redevelopment [2].Between 2020 and 2022, 2,195.21km of irrigation canals were rehabilitated, including 507.41 km of primary canals, 41.97 km of auxiliary primary canals, 444.82 km of secondary canals, 80.18 km of collector canals, 338.86 km of tertiary canals, as well as 781.95 km of quarter channels and 226 units of built sluice gates.
The Dadahup Swampy Irrigation Area consists of 17 blocks of land.One of them is Block A5, which was selected as the location for the irrigation system trial for a demonstration rice planting plot.Nevertheless, the rice yields here are relatively low, ranging from 1.5 to 2 tons per hectare.This level of agricultural productivity is significantly lower when compared to irrigated rice fields, which typically yield 8 tons per hectare [3].Based on this data, conducting a land suitability study in the Dadahup Swampy Irrigation Area is deemed necessary, which Block A5 will represent.A decrease in crop production can be attributed to several factors, one of which is inadequate land management [4].
Land handling errors are expected to be resolved through land suitability evaluation.Land suitability is the level of suitability of a plot of land for a particular use [5].In rice farming, land suitability is defined as the level of suitability of land used for rice farming, where the suitability of the land can be assessed for current conditions (actual land suitability) or after improvements have been made (potential land suitability) [5].A hierarchical system of different orders and classes generally expresses it [6].
Land suitability evaluation is a vital decision-making tool in land use planning.Multi-criterion evaluation (MCE) is the pivotal approach employed in land suitability analysis [7].Multi-criteria decision-making (MCDM) techniques and Geographic Information Systems (GIS) are utilized to systematically assess land and make informed decisions about its optimal use.Moreover, Spatial analysis is the primary technique used to evaluate the quality of the alternatives selected and sorted using MCE.
In this study, the matching method and geospatial technique have been used for the identification of suitable sites for paddy cultivation, especially in the swampy area, using different parameters such as climatic factors (temperature and rain), root media (drainage, texture, coarse material, and soil depth), peat (thickness and maturity), nutrient retention (soil CEC, base saturation, Ph, C-Organic), available nutrients (nitrogen, phosphorus, potassium), salinity, alkalinity, pyrite depth, and inundation height during planting.GIS techniques are utilized to compile and integrate diverse data layers comprising various parameters, culminating in the creation of the paddy suitability map for the DIR Dadahup area.This study aims to provide an overview of the existing conditions of the Dadahup both from the climatic aspect and from the physical and chemical characteristics of the soil, especially on peatlands.
This study is expected to be a reference in land handling, network operation and maintenance, and sustainable development plans at DIR Dadahup.In summary, the novelty of this research paper lies in its integrated and comprehensive approach to land suitability evaluation in a swampy area, with a specific focus on peatlands, and its practical relevance in supporting sustainable agriculture and food security goals in Indonesia.

Study Area
The Dadahup Swamp Irrigation Area is located in Kapuas Regency, Central Kalimantan Province, with a potential area of 21,226 ha and a functional site of 6,111 ha.The water system is influenced by three rivers: the Barito River to the east, the Mangkatip River to the west, and the Kapuas Murung River to the south.DIR Dadahup is located in zones II-b and III [8], where parts of the area are affected by tides in freshwater without any saltwater intrusion.
The primary locus in this study is the Right A5 Block.The Right A5 Block is a pilot project and demonstration plot location for a water management trial from the food estate program in DIR Dadahup.This area has an area of ±800 ha with secondary canals along ±3,300 m and five right tertiary canals with a length of each tertiary canal of ±2,500 m.Besides that, there is also a quarter channel with a length of each channel ± 3.3000 m.Block A5 Right has a range of land elevations ranging from + 0.83 ~ +1.74 m.
The water system in block A5 on the right is a controlled closed water system on the secondary and tertiary channels.The water irrigation on the right, Block A5, depends on rainfall.During the rainy season, tertiary and secondary channels function as drains or wasters.Meanwhile, the existing rainwater is accommodated in the quarter, tertiary, and secondary channels for extended storage during the dry season.In more detail, the location of Block A5 Right can be seen in Figure 1.

Data Source
Data for the current research project were gathered from a variety of sources, as detailed in Table 1, encompassing both primary and secondary data.To evaluate the suitability of paddy cultivation, a series of thematic layers were generated using GIS software, such as QGIS (Figure 2).These layers encompassed various factors, including temperature, water availability, root media characteristics (such as drainage, soil texture, coarse material, and soil depth), peat attributes (thickness and maturity), nutrient retention indicators (such as soil CEC, base saturation, pH, and organic carbon content), available nutrients (nitrogen, phosphorus, potassium), salinity, alkalinity, pyrite depth, and inundation height during the planting phase.

Generation of different thematic layers for land suitability evaluation for paddy cultivation
Making thematic maps is carried out for each land suitability parameter, which spatially only covers the right A5 block in the raster map.

A. Data layers of climatic factors.
Generally, soil temperature and humidity affect plant growth [9].The temperature thematic layer was created using the IDW tool in QGIS using average temperature data for the last five years, 2018-2022 (Figure 3a).The thematic layer representing water availability was created using QGIS software, employing the IDW (Inverse Distance Weighting) tool and utilizing rainfall data spanning the last five years, from 2018 to 2022 (Figure 3b).Data pertaining to root media, including information on drainage, soil texture, coarse material content, and soil depth, were gathered from seven sample locations within the study area.Direct measurements and tests are carried out with land sector experts in the field.The thematic layers of these parameters are then created using the help of the IDW tool in QGIS using the GPS position of the seven sample points (Figure 4).The thematic layers of peat consist of two critical parameters: peat thickness and peat maturity [10].The peat thickness and maturity thematic layer of Blok A5 right was then generated using the DIR.Dadahup peat thickness and maturity map obtained from the Kalimantan River Basin Office II (Figure 5).Data related to nutrient retention parameters, such as soil CEC, base saturation, pH, and C-Organic (as indicated in Figure 6), as well as nutrient availability, including nitrogen (N), phosphorus (P2O5), and potassium (K2O) (as presented in Figure 7), were collected from seven specific sample sites within our study area.Soil samples were carefully gathered from these sites and analyzed in the laboratory.Following the laboratory assessments, we used the IDW tool in QGIS to create thematic maps for these parameters, considering the precise GPS coordinates associated with the seven sample sites.

E. Data layers of salinity and alkalinity.
Data regarding salinity and alkalinity were acquired from seven designated sample sites within our study area.Following laboratory analysis, we utilized the IDW tool in QGIS to construct thematic maps representing these parameters (Figure 7).

F. Data layers of pyrite depth.
Inland suitability evaluation, one of the parameters that need to be considered in assessing land quality is the depth of sulfidic or pyrite (FeS2) [10].The depth of pyrite significantly affects the decrease in soil pH [11].Pyrite depth data is obtained through direct measurements in the field.Measurements were made at the same 7 sample sites.The results of these measurements are then used as a thematic layer of pyrite depth using the IDW tool in QGIS based on GPS points from 7 sample sites (Figure 7f).The data is obtained through direct checking in the field, which is then made into a thematic layer using the help of QGIS (Figure 8).The thematic maps for each land suitability parameter are then classified into a suitability map for each parameter using the matching method with land use requirements [12].The suitability map of each parameter has been classified into three classes, namely 'highly suitable' (S1), 'moderate suitable' (S2), 'marginally suitable' (S3), and land area [6].The classification process is carried out using the Raster Classification tool in QGIS.Furthermore, the raster map will be converted into a vector map, and lastly, we are converting it into a tertiary land block map.

B. Land suitability map for paddy cultivation.
The land suitability parameter map will then be overlaid with the scoring method, which results in a land suitability map for paddy cultivation in the Right A5 Block (Equation 1).The land suitability map for paddy cultivation will be classified into three classes, namely 'highly suitable' (S1), 'moderate suitable' (S2), and 'marginally suitable' (S3

Results and Map Analysis of Land Suitability Parameters.
The initial phase of this process involves the creation of a paddy cultivation suitability map, which relies on mapping the various factors that influence land suitability.To achieve this, a systematic process is employed to align the specific criteria associated with land suitability with those criteria detailed in Temperature and rainfall are interrelated climatic factors that directly impact paddy cultivation.The temperature across the spatial distribution of DIR Dadahup averages 27°C (Figure 3a).This temperature data has been collected from open-access records made available by Indonesia's Meteorology, Climatology, and Geophysics Agency (BMKG) over the past five years, from 2018 to 2022.Based on the criteria in Table 2, the range of temperature from 25 to 28 °C is classified as highly suitable (S1) for paddy cultivation.So, based on the matching results, it was found that overall (100%), the suitability of temperature is highly suitable (S1).Rainfall is a crucial element in the success of rice cultivation.Without sufficient rainfall, rice cultivation in a region becomes impractical.However, in the land suitability criteria for swampy lowlands in Table 2, it can be observed that one of the criteria for rainfall is the duration of the dry period, which is the number of consecutive dry months in a year with a total rainfall of less than 60 mm [10].The rainfall data has been collected from BBWS Kalimantan II over the past five years, 2018-2022.The dry period across the spatial distribution of DIR Dadahup is three months (Figure 3b).Based on the matching results with the criteria in Table 2.It was found that overall (100%), the suitability of dry period is highly suitable (S1).In summary, the result shows that in terms of climate, the Right A5 Block is very suitable for rice cultivation.The parameters of root media consist of drainage, soil texture, coarse material, and soil depth.Drainage is the influence of the rate of water percolation into the soil-on-soil air aeration [10].In land suitability classification in Table 3, drainage is categorized into four classes.Class S1 represents drainage with criteria that are hindered and very hindered.Class S2 represents drainage with somewhat hindered criteria and moderately good conditions.Class S3 signifies drainage with good criteria and somewhat rapid conditions, while class N indicates drainage with fast criteria.Primary drainage data is collected directly in the field by visually assessing soil color [10].Based on field investigation of the soil, this region is composed mainly of clay, whose colour is greyish.Based on the drainage level criteria, the soil in this region has a hindered drainage [10], as we can see in Fig. 4a.Based on the matching result with the criteria in Table 3, the drainage is highly suitable (S1) for paddy cultivation in all areas (100%) of the Right A5 Block.Because the region is composed mainly of clay, the soil texture is categorized as smooth [10], as we can see in Fig. 4b.Based on the matching result with the criteria in Table 3, the soil texture is highly suitable (S1) for paddy cultivation in all areas (100%) of the Right A5 Block.Coarse material is a modifier of soil texture determined by the percentage of gravel, cobbles, or rocks in each soil layer [10].Based on field investigation of the soil, this region has the percentage of gravel, cobbles, or rocks in each soil layer that is less than 3% (Figure 4c).Based on the matching result with the criteria in Table 3, the coarse material is highly suitable (S1) for paddy cultivation in all areas (100%) of the Right A5 Block.The variation in soil depth extended from 29 to 89 cm (Figure 4d).Based on the matching result with the criteria in Table 3, the suitability of soil depth is 33% or 288 ha of Right A5 Block are highly suitable (S1) with soil depth more than 50 cm, 50% or 437 ha of Right A5 Block are moderately suitable (S2) with soil depth around 40 to 50 cm, and 17% or 151 ha are marginally suitable (S3) for paddy cultivation with soil depth around 25 to 40 cm.

C. Land suitability of peat.
The parameter of peat consists of two sub-parameters: peat thickness and peat maturity.This peat map was collected from BBWS Kalimantan II.The variation in peat thickness extended from less than 50 cm to 100 cm (Figure 5a).Based on the matching result with the criteria in Table 3, the suitability of peat thickness is 30% or 261 ha of Right A5 Block is highly suitable (S1) with peat thickness less than 50 cm, and 70% or 615 ha of Right A5 Block are moderately suitable (S2) with peat thickness around 50 to 100 cm.The spatial distribution of peat maturity (Figure 5b) shows that all the region is sapric, which means peat soil is considered mature when it has undergone weathering to the extent that the original material can no longer be recognized, with its coarse organic material content being less than one-third of its composition [10].

D. Land suitability of nutrient retention and nutrient availability.
Nutrient retention consists of soil CEC, base saturation, pH H 2 O, and C-Organic.The data of Soil CEC and base saturation were obtained through soil investigation and lab assessment.The primary attribute of organic matter is determined by the cation exchange capacity (CEC), which retains nutrient cations essential for plant growth and development [7].The variation in soil CEC extended from 44 to 67% (Figure 6a).Based on the matching result with the criteria in Table 3, the soil CEC is highly suitable (S1) for paddy cultivation in all areas (100%) of the Right A5 Block.Base saturation is the percentage of base cations (Ca, Mg, K, and Na) that can be exchanged for their CEC value [10].The base saturation value is low in peat soils due to the low quantity of base cations.When base saturation is low, it can result in a low pH level, which, in turn, reduces soil fertility.The variation in base saturation extended from 2 to 7% (Figure 6b).Based on the matching result with the criteria in Table 3, the base saturation is marginally suitable (S3) for paddy cultivation in all areas (100%) of the Right A5 Block.The variation in pH H 2 O extended from 3 to 6 (Figure 6c).Based on the matching result with the criteria in Table 3, The suitability of pH H 2 O is 18%, or 157 ha are highly suitable (S1) with pH around 5.5 to 7, 11% or 98 ha are moderately suitable (S2) with pH around 5 to 5.5, and 71% or 620 ha of Right A5 Block are marginally suitable (S3) for paddy cultivation with pH less than 5. Organic carbon (C-organic) impacts the quality of mineral soil because its content contains nutrients available to plants, thus playing a crucial role in determining soil fertility.The variation in C-Organic extended from 1 to 6% (Figure 6d).Based on the matching result with the criteria in Table 3, C-Organic suitability is 87% or 760 ha is highly suitable (S1), and 13%, or 115 ha of the Right A5 Block, is moderately suitable (S2) for paddy cultivation.
Available nutrient parameters consist of three sub-parameters: total Nitrogen (N), Phosphorus (P2O5), and Potassium (K 2 O).Data for these sub-parameters are obtained through laboratory testing.The variation in nitrogen extended from 0.07 to 0.179% (Figure 7a).Based on the matching result with the criteria in Table 3, The suitability of nitrogen is 38 %, or 335 ha is moderately suitable (S2) with nitrogen around 0.1 to 0.2% or low, and 62%, or 541 ha, of the Right A5 Block is marginally suitable (S3) for paddy cultivation, with nitrogen less than 0.1% or very low.The variation in phosphorus extended from 10.2 to 49.6% (Figure 7b).Based on the matching result with the criteria in Table 3, The suitability of Phosphorus (P 2 O 5 ) is 50% or 437.5 ha highly suitable (S1), with phosphorus around 21 to 41% or average, and 50 % or 437.5 ha of Right A5 Block is moderately suitable (S2), with phosphorus around 10-20% or low for paddy cultivation.The variation in potassium extended from 3 to 8% (Figure 7c).Based on the matching result with the criteria in Table 3, The suitability of Potassium (K 2 O) is 100% all the areas of the Right A5 Block are marginally suitable (S3) for paddy cultivation with potassium less than 10% which is very low.From these results, it can be concluded that this region lacks soil nutrients.However, it's important to note that these limitations can be addressed through the use of fertilizers.

E. Land suitability of salinity and alkalinity.
Data for these parameters are obtained through laboratory testing.The variation in salinity in this region is 0.2 ds/m (Figure 7d).Based on the matching result with the criteria in Table 3, the suitability of salinity is 100% all the Right A5 Block areas are highly suitable (S1) for paddy cultivation.From these results, it can be concluded that this region is not influenced by saltwater at all.The variation in alkalinity in this region is around 1 to 6% (Figure 7e).Based on the matching result with the criteria in Table 3, the suitability of alkalinity is 100% all the Right A5 Block areas are highly suitable (S1) for paddy cultivation with alkalinity less than 20%.

F. Land suitability of pyrite depth.
The parameter "sulfidic hazard" considers the depth of pyrite within the soil.The variation of pyrite depth in this region is 31 to 99 cm (Figure 7f).Based on the matching result with the criteria in Table 3, the suitability of pyrite depth is 11% or 93 ha is moderately suitable (S2) with pyrite depth around 75 to 100 cm, and 89% or 782 ha of the Right A5 Block is marginally suitable (S3) for paddy cultivation with pyrite depth around 40 to 75 cm In some parts of this region, there is still an issue with the depth of pyrite, which can impact soil fertility.This issue is crucial to consider, and land management should aim to prevent pyrite oxidation to address this issue.

G. Land suitability of inundation height during planting.
As the last parameter to consider in land suitability in swampy area, the data of inundation height during planting is obtained through field observation and interviews with the farmers.The variation of inundation during planting in this region could be maintained in 20 cm height (Figure 8).Based on the matching result with the criteria in Table 3, the suitability of Inundation height during planting is 100% all the areas of Right A5 Block are highly suitable (S1) for paddy cultivation.However, these results need to be further evaluated with hydraulic experimentation models.

Land suitability map for paddy cultivation.
Land suitability analysis holds substantial significance in agricultural development and future planning.In this study, a set of 20 geographical datasets was chosen by implementing a multi-decision approach.These datasets encompass various factors, including climatic variables (temperature and precipitation), root characteristics (drainage, texture, coarse materials, and soil depth), peat properties (thickness and maturity), nutrient retention (soil CEC, base saturation, pH, and organic carbon content), available nutrients (nitrogen, phosphorus, potassium), salinity, alkalinity, pyrite depth, and inundation levels 12 during planting.The land suitability map for paddy cultivation was generated using a math calculator tool in QGIS using mathematical equation 1.The score results are then divided into three classes using a distribution equation to find the interval of each class.Based on the classification result (Figure 9), the land suitability of paddy cultivation is 23% or 197 ha are highly suitable (S1), 39% or 345 ha are moderately suitable (S2), and 38% or 333 ha of the Right A5 Block area are marginally suitable (S3).The analysis reveals that a significant expanse of the region is classified as marginally suitable (S3) for paddy cultivation.This suitability is compromised due to constraints related to factors such as soil depth, pH levels, soil nutrient composition, including nitrogen, phosphorus, and potassium, and shallow pyrite depth in select areas.

Conclusions
In the present study, we try to solve the problem of decreasing rice productivity by showing aspects that influence rice cultivation in irrigated swamp areas.Through this study, we have used GIS and matching techniques to form a map that can be used to determine climatic, physical, and chemical aspects of soil, peat, nutrient retention, and available nutrients, as well as pyrite depth with spatial units per quarter plot.From the mapping results, it was found that this location has excellent potential to be used for paddy cultivation.While nearly 40% of the area is classified as marginally suitable, it's important to note that spatial-based treatments have been developed to address this limitation.Based on the discussion results, the limitations in this region can be addressed through specific treatments, such as adding fertilizers to the land to increase Nitrogen, Phosphorus, and Potassium levels.Concerning pyrite depth, it is crucial to pay close attention during land management to prevent excessive oxidation, which can increase pH values.Additionally, further analysis of the water management system in DIR Dadahup is necessary through hydraulic simulations to assess the effectiveness of the existing water management system.Hopefully, this study can be used as a reference for the government in providing improvement and planning initiatives to increase agricultural productivity at DIR Dadahup.

Figure 1 .
Figure 1.Location of study area

Figure 3 .
Figure 3. Thematic data layer representing.a. temperature, b.Water availability B. Data layers of root media.Data pertaining to root media, including information on drainage, soil texture, coarse material content, and soil depth, were gathered from seven sample locations within the study area.Direct measurements and tests are carried out with land sector experts in the field.The thematic layers of these parameters are then created using the help of the IDW tool in QGIS using the GPS position of the seven sample points (Figure4).

5 Figure 4 .
Figure 4. Thematic data layer representing.a. drainage, b.Soil texture, c.Coarse material, d.Soil depth C. Data layers of peat.The thematic layers of peat consist of two critical parameters: peat thickness and peat maturity[10].The peat thickness and maturity thematic layer of Blok A5 right was then generated using the DIR.Dadahup peat thickness and maturity map obtained from the Kalimantan River Basin Office II (Figure5).

Figure 8 .
Figure 8.The thematic data layer of Inundation height during planting 2.4.Generation of land suitability map (LSM) A. Land suitability parameters thematic map.The thematic maps for each land suitability parameter are then classified into a suitability map for each parameter using the matching method with land use requirements[12].The suitability map of each parameter has been classified into three classes, namely 'highly suitable' (S1), 'moderate suitable' (S2), 'marginally suitable' (S3), and land area[6].The classification process is carried out using the Raster Classification tool in QGIS.Furthermore, the raster map will be converted into a vector map, and lastly, we are converting it into a tertiary land block map.

Figure 9 .
Figure 9. Land suitability map for paddy cultivation in Right A5 Block

Table 2 .
This alignment ensures that the map accurately reflects the compatibility of the study area for paddy cultivation based on the established criteria outlined in the table.
A. Land suitability of climatic factors.