# Land Suitability Assessment for Apple (Malus domestica) Production in Sentele Watershed in Hadiya Zone, Southern Ethiopia

Authors: Getachew Beyene; Nigussie Dechassa; Alemayehu Regasa; Lemma Wogi
Journal: Applied and Environmental Soil Science
 (2022)

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## Abstract

Apple (Malus domestica) is cultivated in Southern Ethiopia. However, the crop is being grown in without affirming the suitability of the land for its cultivation. Therefore, this research was conducted to assess the suitability of the land of Sentele Watershed for apple production in Southern Ethiopia. Integrating GIS and analytic hierarchy process (AHP) method, which is widely used in multi-criteria decision-making for tackling multi-attribute decision-making problems in real situations, was used in this study. In the application techniques, most attributes that determine apple growth, climate, edaphic, topography, and current land use/land cover were combined. In determining the weights of the attributes, the opinions of experts and experienced apple orchard workers were considered, and an agricultural land suitability map was produced as highly suitable, moderately suitable, marginally suitable, and least suitable. The methodology was based on the land evaluation developed by FAO (1976) that suggests biophysical diagnostic factors, which most strongly influenced the cultivation of apples. Criteria were defined, background information was gathered, and a raster surface was created. The layers are reclassified, weighed, and then the output layers are overlaid with the background information such as a map of topography to see the best potential sites and to prepare the final suitability map. The final apple suitability map showed that only 2.2% of the total land is highly suitable, 32% is moderately suitable, and 52.1% is marginally suitable, and it requires detailed investigation and careful decision over other land uses to invest in it. 13.7% is the least suitable for apple cultivation. It is concluded that about 34% of the total land of the study area is suitable for apple production, and about 66% is unsuitable. The results imply that it is necessary to take improvement measures such as irrigation, species selection, removing leaves (defoliation), and appropriate land-use planning in most of the land of the watershed before investing in apple cultivation and production, and it is necessary to expand apple production in the future only in areas that are highly and moderately suitable for producing the crop in the study area.


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## Body

## 1. Introduction

Land suitability analysis evaluates the factors responsible for the suitability of crops in a given area. The concept of land evaluation is the assessment of land performance when used for a specific purpose, involving the execution and interpretation of surveys and studies of topography, climate, soil, vegetation, and other aspects of land [1]. Land suitability analysis provides information on the constraints and opportunities for the use of land and, therefore, guides decision on optimal utilization of resources. Also, such a kind of analysis allows for identifying the major limiting factors for agricultural production and enables decision-makers to develop a crop management scheme able to overcome such limitations and increase productivity [2]. The primary objective of land suitability evaluation [3] is the prediction of the inherent capacity of the land to support a specific land use for a long time without deterioration and with minimum costs of socioeconomic and environmental values.The knowledge on apple cultivation was acquired from literature, local experts, development agents, and farmers engaged in apple production and land use/land cover (LULC). Each factor has some degree of contribution towards the suitability for apple cultivation. The temperature has a profound effect on all aspects of apple tree physiology; at extremes, high or low temperatures can cause death, while, at intermediate temperatures, all physiological processes are affected [4]. Soil properties are one of the most important factors in agricultural land suitability assessment [5]. Apple grows best on well-drained, loam soils having a depth of above 60 cm and a pH range of 5.6 to 6.8 [6], which is rich in organic matter free from hard substrata and water-logged conditions. Extreme soil pH values result in nutrient tie-up or toxicity and poor tree and fruit development. High yields are obtained on freely drained soils where water is not limited [7].In Southern Ethiopia, where this research was conducted, no similar research had been undertaken with research on land suitability assessment for apple production. Some studies have been conducted in different regions that focus on land suitability assessment for apple production [8–11]. These researches are restricted to a few areas and give inadequate information to utilize resources in Sentele Watershed, characterized at a small scale with high-level generalization, and locally adopted evidence such as climatic, edaphic, topographic, and current land use/land cover is needed for decision-making on proper resource utilization. Thus, there is an urgent need for land suitability assessment for sustainable apple production in the area.Several procedures have been used for land suitability assessment [1], ranging from expert knowledge based on farmers’ experience to process-oriented simulation methods. The evaluation process requires contributions from different fields such as natural science, the technology of land use, economics, and sociology [12]. Torrieri and Batà [13] mentioned that land managers and land-use planners are encouraged to use multi-criteria decision-making tools in combination with GIS for integrating and managing numerous and heterogeneous factors. The analytical hierarchy process (AHP) developed by Saaty [14] is also widely used for solving a variety of problems based on complex parameters across various levels where the interaction among parameters is common characteristics [15]. Saaty and Vargas [16]; AHP is a widely used method in decision-making and developed for selecting the best from several alternatives to several criteria. Thus, AHP is a mathematical method that established a hierarchal model for solving highly complex problems of land management with the best alternatives [17]. Experts and scientific knowledge were weighted with analytic hierarchy (AHP) (Dadeoğlu and Dengiz) [18]; the weight assignment approach was used [19]. The GIS method is a technique that provides greater flexibility and accuracy for handling digital spatial data.Therefore, in this study the analytical hierarchy process (AHP) integrated with the geographic information system (GIS) was applied to delineate suitable apple(Malus domestica) cultivation locations in Sentele Watershed, Southern Ethiopia, using the relevant variables of climatic condition (temperature, rainfall), soil parameters (pH, drainage, texture), topographic characteristics (elevation, slope, aspect), and land use/land cover that have been analyzed, and a land suitability map was produced. The map generated is hoped to provide information for apple-growing farmers, extension agents, experts, and researchers along with the valuable information on the suitability of the land for growing apples based on important land conditions and considering the quality of land characteristics on scientific bases on future.


## 2. Materials and Methods

### 2.1. Description of the Study Area

This study was carried out in the Sentele Watershed located in Hadiya Zone, Southern Ethiopia, about 245 km southwest of the capital of Ethiopia (Figure1), at 7°36′00″ to 7°39′30″ N and 37°48′24″ to 37°50′522″ E, with an elevation of 2270 to 2680 meters above sea level. Sentele Watershed has slopes of 2 to 30 percent. The total annual rainfall in the area is 1178 mm, and the mean annual maximum and minimum temperatures are 22.8°C and 9.2°C, respectively (Figure 2). As the area is located at higher elevations, it enjoys a temperate climate with three distinct seasons, namely Bega, Belg, and Kremt. Climatic data used for evaluating the climatic characteristics of the study area were obtained from Ethiopian Meteorological Agency data registered from Hossaina Station. The data set comprises maximum and minimum temperatures and rainfall (Figure 2). The geology of the studied watershed is Phanerozoic quaternary period volcanic with associated sediments revealing basaltic ignimbrite parent material. Therefore, it exposes rocks of the Cenozoic era mostly formed during the quaternary period as a result of the widespread volcanism induced by extensive fracturing and subsequent faulting [20].Figure 1
Location map of study area.Figure 2
Climate data collected from Hossaina, a center nearest to the study site (1991–2018).Agriculture is the main source of livelihood for the community, and subsistence-type mixed crop-livestock systems characterize the farming system. Mixed agriculture has been a dominant economic activity in the area. Like many parts of Ethiopia, Hadiya Zone is mainly characterized by rain-fed mixed farming with traditional technologies. Both crops and livestock production systems are the mainstays of the livelihood in the area.


### 2.2. Materials Used and Methods of Data Collection

After having the preliminary site visit, the topographic map with a semi-detailed scale (1 : 50,000) was obtained from the Ethiopian Mapping Agency and used to generate DEM layers. The global positioning system (GPS) records the watershed boundary points. To develop the land use and land cover map, Landsat 8 images were obtained from the USGS website and accessed using Earth Explorer viahttps://earthexplorer.usgs.gov. Cloud-free images of the area were acquired on October 10, 2021. Climate data for the last 29 consecutive years were taken from the Ethiopian Meteorological Agency. The data for this research were conducted using a survey method to determine land conditions. Sample points were done based on homogeneous land units from an overlay of maps, and soil sampling was carried out from pedons excavated at each land mapping unit. The topographic characteristics, soil parameters, climatic condition, and land use/land cover of the area are considered the most important determinant factors of land suitability analysis for apple cultivation in this study [8, 9]. Therefore, land suitability assessment was done by comparing site conditions with the apple requirement concerning the characteristics of topographic characteristics (slope, altitude, aspect), soil parameters (depth, drainage, soil pH, texture), climate condition (mean temperature, growing period temperature, and rainfall), and land/use land cover (LULC). Rainfall and temperature point data were converted into polygon using the Thiessen polygon in ArcGIS. After that, they were converted into raster using the conversion tool.


### 2.3. Field Work

Data on the area were collected including a topographic map (1 : 50,000), climatic data, and land-use requirements for apple growth. With the aid of a location map to identify land units, a free survey method was used and the identified land units were geo-referenced using a global positioning system (GPS). Four land units were identified, and in each land unit, a profile pit was excavated. At each LMU, pedons having 2 m × 2 m × 1.5 m were excavated, which represents that land units and soil samples were collected from each identified genetic horizons of the soil profiles, starting from the lowest to the uppermost, to prevent cross-contamination. 15 soil composites from four profiles pits were taken for physical and chemical analysis of soil parameters.Soil data used for evaluating the soil characteristics of the study area were obtained from field identification and soil samples analyzed at the SNNPR Bureau of Agriculture Hawassa Soil Testing Laboratory. There were four major types of soils identified in the studied area according to WRB [21] soil classification. These are Chromic Luvisols, Silandic Andosols, Rhodic Nitisols, and Vertic Luvisols, which were formed as a result of elevation, slope, soil attributes, land use, and landforms on which land suitability assessment was based.


## 2.1. Description of the Study Area

This study was carried out in the Sentele Watershed located in Hadiya Zone, Southern Ethiopia, about 245 km southwest of the capital of Ethiopia (Figure1), at 7°36′00″ to 7°39′30″ N and 37°48′24″ to 37°50′522″ E, with an elevation of 2270 to 2680 meters above sea level. Sentele Watershed has slopes of 2 to 30 percent. The total annual rainfall in the area is 1178 mm, and the mean annual maximum and minimum temperatures are 22.8°C and 9.2°C, respectively (Figure 2). As the area is located at higher elevations, it enjoys a temperate climate with three distinct seasons, namely Bega, Belg, and Kremt. Climatic data used for evaluating the climatic characteristics of the study area were obtained from Ethiopian Meteorological Agency data registered from Hossaina Station. The data set comprises maximum and minimum temperatures and rainfall (Figure 2). The geology of the studied watershed is Phanerozoic quaternary period volcanic with associated sediments revealing basaltic ignimbrite parent material. Therefore, it exposes rocks of the Cenozoic era mostly formed during the quaternary period as a result of the widespread volcanism induced by extensive fracturing and subsequent faulting [20].Figure 1
Location map of study area.Figure 2
Climate data collected from Hossaina, a center nearest to the study site (1991–2018).Agriculture is the main source of livelihood for the community, and subsistence-type mixed crop-livestock systems characterize the farming system. Mixed agriculture has been a dominant economic activity in the area. Like many parts of Ethiopia, Hadiya Zone is mainly characterized by rain-fed mixed farming with traditional technologies. Both crops and livestock production systems are the mainstays of the livelihood in the area.


## 2.2. Materials Used and Methods of Data Collection

After having the preliminary site visit, the topographic map with a semi-detailed scale (1 : 50,000) was obtained from the Ethiopian Mapping Agency and used to generate DEM layers. The global positioning system (GPS) records the watershed boundary points. To develop the land use and land cover map, Landsat 8 images were obtained from the USGS website and accessed using Earth Explorer viahttps://earthexplorer.usgs.gov. Cloud-free images of the area were acquired on October 10, 2021. Climate data for the last 29 consecutive years were taken from the Ethiopian Meteorological Agency. The data for this research were conducted using a survey method to determine land conditions. Sample points were done based on homogeneous land units from an overlay of maps, and soil sampling was carried out from pedons excavated at each land mapping unit. The topographic characteristics, soil parameters, climatic condition, and land use/land cover of the area are considered the most important determinant factors of land suitability analysis for apple cultivation in this study [8, 9]. Therefore, land suitability assessment was done by comparing site conditions with the apple requirement concerning the characteristics of topographic characteristics (slope, altitude, aspect), soil parameters (depth, drainage, soil pH, texture), climate condition (mean temperature, growing period temperature, and rainfall), and land/use land cover (LULC). Rainfall and temperature point data were converted into polygon using the Thiessen polygon in ArcGIS. After that, they were converted into raster using the conversion tool.


## 2.3. Field Work

Data on the area were collected including a topographic map (1 : 50,000), climatic data, and land-use requirements for apple growth. With the aid of a location map to identify land units, a free survey method was used and the identified land units were geo-referenced using a global positioning system (GPS). Four land units were identified, and in each land unit, a profile pit was excavated. At each LMU, pedons having 2 m × 2 m × 1.5 m were excavated, which represents that land units and soil samples were collected from each identified genetic horizons of the soil profiles, starting from the lowest to the uppermost, to prevent cross-contamination. 15 soil composites from four profiles pits were taken for physical and chemical analysis of soil parameters.Soil data used for evaluating the soil characteristics of the study area were obtained from field identification and soil samples analyzed at the SNNPR Bureau of Agriculture Hawassa Soil Testing Laboratory. There were four major types of soils identified in the studied area according to WRB [21] soil classification. These are Chromic Luvisols, Silandic Andosols, Rhodic Nitisols, and Vertic Luvisols, which were formed as a result of elevation, slope, soil attributes, land use, and landforms on which land suitability assessment was based.


## 3. Data Analysis of Research

### 3.1. Establishing Evaluation Criteria

Expert information on apple crop cultivation was collected through interviews with key informants. The key informants were chosen according to their professional career and knowledge developed through experience in apple cultivation. Therefore, this study established 11 key criteria organized into four groups (climate, soil, topographic characteristics, and land use/land cover) [22] and key informant opinions.


### 3.2. Creation of Thematic Maps

Thematic maps in this study include climate maps (growing period temperature, mean annual temperature, and rainfall), soil maps (soil depth, drainage, soil texture, pH), topographic maps (slope, elevation, aspect), and land use/land cover (Figure3). These thematic maps were created and edited, overlaid, and visualized based on the suitability analysis using ArcGIS software of ESRI. The application of GIS for overlaying thematic layers to establish land databases requires that the layer maps are converted into a common coordinate system. This involves a stepwise arrangement and organization of acquired data in a manner that is appropriate for analysis. All these maps were again reclassified into four classes of suitability as defined in the growth condition requirement table of apple. The reclassification of each thematic map generates the individual suitability map of each parameter that is further used for evaluating the final suitability map of apple using AHP (Figure 4).Figure 3
Suitability maps of criteria.
(a)(b)Figure 4
Flow chart of data collection and data analysis.


### 3.3. Assigning Weights of Factors and Variables

The results from the key informant interviews were used to derive the relative importance of one criterion to another using the analytical hierarchy process (AHP) [23], which has been used in a pairwise comparison technique to assign individual parameter weights for each factor. So, the analytical hierarchy process is adjusted to weight various factors and variables effectively, setting relatively higher values for more important factors based on the opinions of key informants [9]. The weighted overlay tool applies one of the most used approaches for overlay analysis to solve multi-criteria problems and suitability models. As land suitability analysis requires both spatial and attribute data in many data layers, GIS can be used to combine biophysical and socioeconomic characteristics for land evaluation and a multi-criteria evaluation tool can be developed to support the decision-makers the balance among different stakeholders’ interests. Then, integration of GIS and AHP combines decision support methodology with powerful visualization, mapping, and analyzing capabilities.According to Saaty [23], there are three steps to process the AHP technique: the first step of the AHP technique is to structure the overall goal (land suitability) into several criteria and sub-criteria in a hierarchy. The second step of the AHP technique involves a comparison of the alternatives, criteria, and sub-criteria. They are compared in pairs for each factor of the next higher level. The third step of the AHP technique is to synthesize the comparisons to get the priorities of the alternatives for each criterion and the weights of each criterion to the goal (Table 1).GPT = growth season temperature; LULC = land use/land cover.Table 1
Pairwise comparison matrix of the criteria and their weights.
AspectDrainageElevationGPTLULUpHRainfallSlopeSoil depthTempTextureAspect111/71/511/31/31/31/31/51Drainage111/51/3111/31/31/31/31Elevation75113333335GPT53115333335LULU111/31/511/31/51/31/31/51pH311/31/3311/311/31/31/3Rainfall331/31/3531331/35Slope331/31/3311/311/31/33Soil depth331/31/3331/3311/33Temp531/31/35333315Texture111/51/511/31/51/31/31/51The consistency ratio was calculated according to the matrix that was formed for the significance level of the analytic hierarchy process (AHP) parameters, and the result was found to be 0.09 < 0.1. According to this consistency ratio, the weight values obtained in Table2 were used in the weighted overlay analysis. The ratings of the sub-parameters of each parameter were also used in the analysis.Table 2
Eigenvector of weights.
Aspect0.0258Drainage0.0397Elevation0.2037GST0.1895LULC0.9339pH0.0578Rainfall0.1142Slope0.0640Soil depth0.0884Temperature0.1402Texture0.0428GST = growing season temperature; LULC = land use/land cover.


### 3.4. Land Suitability Analysis for Apple Using Weighted Overlay

The weighted linear combination (WLC) class of map combination (overlay) was used to prepare a map of suitability. Simple additive weighting is based on the concept of a weighted average in which continuous criteria are standardized to a common numeric range and then combined using a weighted average [24]. The decision-maker assigns the weights of relative importance directly to each attribute map layer. The total score (Table 3) for each alternative is obtained by multiplying the importance of weight assigned to each attribute by the scaled value given for that attribute to the alternative and then summing the product’s overall attributes [25].Table 3
Weights of the parameters and scores of sub-parameters.
CriteriaOptimal valuesEigenvector weightWeightSuitabilityElevation2500–27000.203720.37S12300–2500S22100–2300S31900–2100S4Slope0–100.06406.4S18–18S218–28S328–58S4Aspect359–2560.02582.58S1256168S2168–89S389– (−1)S4pH5.52–5.80.05785.78S15.8–5.83S25.83–6.15S36.15–6.30S4LULCGrassland0.03393.39S1Agricultural landS2Open landS3SettlementS4Mean annual temperature9–110.140214.02S111–14S214–16S316–18S4The temperature during the growing season15–15.50.189518.95S115.5–16S216–17S317–17.5S4Rainfall1500–20000.114211.42S12000–1500S21500–1000S31000–500S4TextureClay loam0.04284.28S1ClayS2Soil depth200–1500.08848.84S1150–100S2100–70S3<70S4DrainageWell-drained0.03973.97S1Moderately drainedS2GST = growing season temperature; LULC = land use/land cover.


### 3.5. WLC Is Computed as H = ∑wixi

where H is the composite suitability score, xi is factor scores (cells), wi is weights assigned to each factor, and ∑ is the sum of weighted factors.For the assessment of land suitability for apple production in the study area, eleven factors that influence apple growth were selected and prioritized. From these factors, the possibilities and constraints for apple production were evaluated. These were elevation, slope, aspect, GPT, mean temperature, rainfall, soil depth, soil pH, drainage, current land use, and land cover and soil texture (Table4).Table 4
Land suitability criteria classification for apple cultivation [8, 9, 51].
CriteriaUnitLand suitability classesS1S2S3S4ElevationMeter a.s.l2500–27002300–25002100–23002900–3100Slope%0–88–1818–2828–40AspectDirection359–256256–168168–8989-(-1)GPT°C15–1717–1919–2121–23Mean temp°C9–1111–1414–1616–18RainfallMm1000–12001200–1300, 800–10001300–1400, <800>1400Soil depthcm150–200100–15070–100<70pH-log (H+)6.0–6.55.7–6.05.6–5.7<5.6Drainage%Well-drainedModerately drainedLULCTypeGrasslandAgricultural landOpen landSettlementSoil textureTextureLoamy clayClaym.a.s.l = meter above sea level; GPT = growth season temperature; LULC = land use/land cover.


## 3.1. Establishing Evaluation Criteria

Expert information on apple crop cultivation was collected through interviews with key informants. The key informants were chosen according to their professional career and knowledge developed through experience in apple cultivation. Therefore, this study established 11 key criteria organized into four groups (climate, soil, topographic characteristics, and land use/land cover) [22] and key informant opinions.


## 3.2. Creation of Thematic Maps

Thematic maps in this study include climate maps (growing period temperature, mean annual temperature, and rainfall), soil maps (soil depth, drainage, soil texture, pH), topographic maps (slope, elevation, aspect), and land use/land cover (Figure3). These thematic maps were created and edited, overlaid, and visualized based on the suitability analysis using ArcGIS software of ESRI. The application of GIS for overlaying thematic layers to establish land databases requires that the layer maps are converted into a common coordinate system. This involves a stepwise arrangement and organization of acquired data in a manner that is appropriate for analysis. All these maps were again reclassified into four classes of suitability as defined in the growth condition requirement table of apple. The reclassification of each thematic map generates the individual suitability map of each parameter that is further used for evaluating the final suitability map of apple using AHP (Figure 4).Figure 3
Suitability maps of criteria.
(a)(b)Figure 4
Flow chart of data collection and data analysis.


## 3.3. Assigning Weights of Factors and Variables

The results from the key informant interviews were used to derive the relative importance of one criterion to another using the analytical hierarchy process (AHP) [23], which has been used in a pairwise comparison technique to assign individual parameter weights for each factor. So, the analytical hierarchy process is adjusted to weight various factors and variables effectively, setting relatively higher values for more important factors based on the opinions of key informants [9]. The weighted overlay tool applies one of the most used approaches for overlay analysis to solve multi-criteria problems and suitability models. As land suitability analysis requires both spatial and attribute data in many data layers, GIS can be used to combine biophysical and socioeconomic characteristics for land evaluation and a multi-criteria evaluation tool can be developed to support the decision-makers the balance among different stakeholders’ interests. Then, integration of GIS and AHP combines decision support methodology with powerful visualization, mapping, and analyzing capabilities.According to Saaty [23], there are three steps to process the AHP technique: the first step of the AHP technique is to structure the overall goal (land suitability) into several criteria and sub-criteria in a hierarchy. The second step of the AHP technique involves a comparison of the alternatives, criteria, and sub-criteria. They are compared in pairs for each factor of the next higher level. The third step of the AHP technique is to synthesize the comparisons to get the priorities of the alternatives for each criterion and the weights of each criterion to the goal (Table 1).GPT = growth season temperature; LULC = land use/land cover.Table 1
Pairwise comparison matrix of the criteria and their weights.
AspectDrainageElevationGPTLULUpHRainfallSlopeSoil depthTempTextureAspect111/71/511/31/31/31/31/51Drainage111/51/3111/31/31/31/31Elevation75113333335GPT53115333335LULU111/31/511/31/51/31/31/51pH311/31/3311/311/31/31/3Rainfall331/31/3531331/35Slope331/31/3311/311/31/33Soil depth331/31/3331/3311/33Temp531/31/35333315Texture111/51/511/31/51/31/31/51The consistency ratio was calculated according to the matrix that was formed for the significance level of the analytic hierarchy process (AHP) parameters, and the result was found to be 0.09 < 0.1. According to this consistency ratio, the weight values obtained in Table2 were used in the weighted overlay analysis. The ratings of the sub-parameters of each parameter were also used in the analysis.Table 2
Eigenvector of weights.
Aspect0.0258Drainage0.0397Elevation0.2037GST0.1895LULC0.9339pH0.0578Rainfall0.1142Slope0.0640Soil depth0.0884Temperature0.1402Texture0.0428GST = growing season temperature; LULC = land use/land cover.


## 3.4. Land Suitability Analysis for Apple Using Weighted Overlay

The weighted linear combination (WLC) class of map combination (overlay) was used to prepare a map of suitability. Simple additive weighting is based on the concept of a weighted average in which continuous criteria are standardized to a common numeric range and then combined using a weighted average [24]. The decision-maker assigns the weights of relative importance directly to each attribute map layer. The total score (Table 3) for each alternative is obtained by multiplying the importance of weight assigned to each attribute by the scaled value given for that attribute to the alternative and then summing the product’s overall attributes [25].Table 3
Weights of the parameters and scores of sub-parameters.
CriteriaOptimal valuesEigenvector weightWeightSuitabilityElevation2500–27000.203720.37S12300–2500S22100–2300S31900–2100S4Slope0–100.06406.4S18–18S218–28S328–58S4Aspect359–2560.02582.58S1256168S2168–89S389– (−1)S4pH5.52–5.80.05785.78S15.8–5.83S25.83–6.15S36.15–6.30S4LULCGrassland0.03393.39S1Agricultural landS2Open landS3SettlementS4Mean annual temperature9–110.140214.02S111–14S214–16S316–18S4The temperature during the growing season15–15.50.189518.95S115.5–16S216–17S317–17.5S4Rainfall1500–20000.114211.42S12000–1500S21500–1000S31000–500S4TextureClay loam0.04284.28S1ClayS2Soil depth200–1500.08848.84S1150–100S2100–70S3<70S4DrainageWell-drained0.03973.97S1Moderately drainedS2GST = growing season temperature; LULC = land use/land cover.


## 3.5. WLC Is Computed as H = ∑wixi

where H is the composite suitability score, xi is factor scores (cells), wi is weights assigned to each factor, and ∑ is the sum of weighted factors.For the assessment of land suitability for apple production in the study area, eleven factors that influence apple growth were selected and prioritized. From these factors, the possibilities and constraints for apple production were evaluated. These were elevation, slope, aspect, GPT, mean temperature, rainfall, soil depth, soil pH, drainage, current land use, and land cover and soil texture (Table4).Table 4
Land suitability criteria classification for apple cultivation [8, 9, 51].
CriteriaUnitLand suitability classesS1S2S3S4ElevationMeter a.s.l2500–27002300–25002100–23002900–3100Slope%0–88–1818–2828–40AspectDirection359–256256–168168–8989-(-1)GPT°C15–1717–1919–2121–23Mean temp°C9–1111–1414–1616–18RainfallMm1000–12001200–1300, 800–10001300–1400, <800>1400Soil depthcm150–200100–15070–100<70pH-log (H+)6.0–6.55.7–6.05.6–5.7<5.6Drainage%Well-drainedModerately drainedLULCTypeGrasslandAgricultural landOpen landSettlementSoil textureTextureLoamy clayClaym.a.s.l = meter above sea level; GPT = growth season temperature; LULC = land use/land cover.


## 4. Results and Discussion

### 4.1. Factors Affecting Apple Growth

Every crop has its requirements for growth. Various geo-environmental factors influence the suitability of the land for different agricultural products [26]. The importance of each factor, namely elevation, growing period temperature (GPT), mean annual temperature, rainfall, soil depth, slope, soil reaction (pH), soil texture, drainage, land use/land cover, and aspect, was identified (Table 5). Each factor has been represented by limits and degree of suitability to apple production in each unit of area based on experts’ judgment and different literature.Table 5
Evaluation criteria and land area under different land suitability classes.
CriteriaAreaS1 Highly suitableS2 Moderately suitableS3 Marginally suitableS4 Least suitable%Ha%Ha%Ha%HaElevation16.4308.831.9600.726.5499.025.2474.5GTP3.667.827.9525.453.41005.515.1284.3Mean temp14.4271.231.6595.042.9807.811.1209.0Rainfall13.5254.236.2681.721.5404.828.8542.3Soil depth30.5574.331.9600.721.4403.016.2305.0Slope29.4553.632.5612.026.3495.211.8222.2pH6.6124.334.8655.348.2907.610.4195.8Soil type66.21,246.633.8636.4--Drainage43.5819.156.51,063.9--LULC22.1416.125.6482.126.3495.226.0489.6Aspect26.9506.533.0621.428.0527.212.1227.9Source: calculated from scores of suitability maps and AHP technique.


#### 4.1.1. Elevation

The elevation is an important factor affecting any plant growth due to its role in temperature change [27]. Whence, elevation has got a high weight value of 0.2037. In the study area, the elevation suitability map shows that about 1/6th of the land has an elevation of 2500–2700 meters above sea level, which is highly suitable, and about 1/3rd of the land has an elevation range of 2300–2500 m.a.s.l, which is moderately suitable, while about 1/4th of the land has an elevation range of 2100–2300 meters above sea level, which is marginally suitable for apple cultivation, and the other 1/4th of the land has an elevation range of 1900–2100 meters above sea level, which is least suitable (Table 5). The results indicated that more than half of the land is not suitable for apple cultivation from an elevation point of view. The elevation is an important factor affecting any plant growth due to its role in temperature changes and thus in a variation of plant cover [27]. At the high altitudes in the tropics, average temperatures are lower, which allows easier reaching of chilling conditions, but seasonal amplitudes remain low [28]. Apple can be grown at an elevation ranging between 1800 and 2700 m.a.s.l. However, altitude ranges from 2500 to 2700 meters above sea level, which is highly suitable for apple cultivation because the apple gets its chilling requirement fulfilled at a temperature below 7°C to overcome its dormancy [29]. Therefore, the chilling requirement of the apple can be satisfied by the higher elevation of the watershed. In this study, after browsing through literature and experts’ opinions, the elevation parameter has been given the highest priority weight in preparing the land suitability map of apple for the study area.


#### 4.1.2. The Temperature during the Growing Season

The temperature during the growing season is another environmental factor affecting the growth of apples after elevation, and it has got the second-highest priority of 0.1895. During the growing period (October to January) in the studied area, temperatures average around 15–23°C (Figure2). However, the most suitable temperatures required for apple growth during this period are 15–17°C [9]. Thus, only 3.6% of the land has a temperature during the growing season of 15–17°C, which is highly suitable for apple development. About 1/6th of the land has an average temperature of 17–19°C, which is moderately suitable. However, about half of the land has an average temperature ranging between 19 and 21°C, which is marginally suitable for apple production, whereas about 1/6th of the land has an average temperature of 21–23°C, which is the least suitable for apple production during the growth period. This result indicated that no land in the study area is highly suitable, and more than 2/3rd of the land is not suitable for apple production. Apple is very sensitive to temperature during early growth, which greatly affects final fruit size [30]. Therefore, it is considered one of the criteria for land suitability assessment and was assigned the priority weight of 0.1895. The studied variety “Anna” requires 120 days of development period on MM106 [31].


#### 4.1.3. Mean Annual Temperature

Temperature affects the net carbon exchange, carbon balance, and carbon partitioning in the apple tree [32]. Mean annual temperature has got the third-highest priority of 0.1402. Apple trees require a cool temperature for proper growth and development. The yearly mean maximum temperature of the study area is 22.8°C, and the yearly mean minimum temperature is 9.2°C. The results showed that about 1/7th of the land has a temperature condition of 9–11°C, which is highly suitable for apple production, whereas about 1/3rd of the land has a temperature range between 12 and 14°C, which is moderately suitable for apple production. However, about 3/7th (42.9%) of the land has a yearly average temperature of 14–16°C, which is marginally suitable for apple production. However, it was found that about 1/10th of the land has 16–18°C, which is the least suitable for apple production. The results implied that more than half of the land has a yearly average temperature not suitable for apple cultivation. The apple tree requires a temperate climatic regime for growth and fruit development [33]. Low temperature is the most significant factor in affecting dormancy completion [34]. Temperature is a main environmental factor affecting the net carbon exchange, carbon balance, and carbon partitioning in the apple tree [35]. The buds of the apple tree may not bloom or may be uneven if the chilling requirements are not satisfied [36]. Hester and Cacho [37] stated that temperature affects both photosynthesis and respiration of the apple.


#### 4.1.4. Rainfall

Rainfall is one of the most important factors affecting the growth of plants. Both highest rainfall and lowest rainfall are harmful to plant growth. Excessive rainfall is harmful to plant growth, and also, its deficit causes a serious effect on plant growth. Rainfall has got the fourth highest priority weight of 0.1142. The meteorological data (1991–2018) obtained from the area revealed that the lowest and highest annual rainfall in the area ranged between 914 and 1499 mm (Figure2). The optimum range of annual rainfall for apple production is 1000–1250 mm [38]. The results indicated that about 1/8th of the land has rainfall ranging between 1100 and 1200 mm, which is highly suitable for apple production, whereas about 1/3rd of land receives about 1200–1300 mm of annual rainfall, which is moderately suitable for apple production. About 1/5th of the land has rainfall ranging between 1300 and 1400 mm, which is marginally suitable for apple production. However, more than 1/4th of the land has rainfall of <800 mm and >1400 mm, which is least suitable for apple production. In general, about half of the area has received rainfall not suitable for apple production.


#### 4.1.5. Soil Depth

Soil depth is also one of the important factors affecting apple growth. It has got the fifth priority of 0.0884. The results indicated that about 1/3rd of the land has a soil depth of more than 150 cm, which is highly suitable for apple production, and about 1/3rd of the land has soil depth ranging between 100 and 150 cm, which is considered moderately suitable. However, about 1/5th of the land has a soil depth ranging between 70 and 100 marginally suitable cm depth. However, about 1/6th of the land has <70 cm soil depth, which is least suitable for apple production (Table5). Soil depth determines root growth, as well as the presence of volumes of water and air in the soil [39], and the roots of cultivated plants can reach and use the available water and nutrients [40]. Soil depth is the most important soil property affecting the hydrologic properties of soils. According to Fu et al. [41], variation in soil and depth is connected with soil formation processes, loss of materials through weathering and transportation, and deposition of soil through erosion.


#### 4.1.6. Slope

The slope is an important indicator of land suitability since it influences drainage, irrigation, and soil erosion [42]. An increase in slope degree slows down the development of soils and decreases soil depth and fertility [43]. The slope has been given the priority of 0.0640. The growth of apples is determined by slope, and it was determined using the digital elevation model (DEM). Each land mapping unit is described according to its respective slope classes. The results indicated that about 1/4th of the land has a slope of less than 10%, which is considered highly suitable for apple production, and about 1/3rd of the land has a slope ranging between 10% and 20%, which is moderately suitable. However, about 1/4th of the land has a slope ranging between 20 and 30%, which is marginally suitable for apple production, and about 1/10th of the land has a slope of above 30%, which is as least suitable for apple production. Therefore, about 62% of the land in the study is suitable in terms of slope for apple production, whereas about more than 38% is not suitable for apple production. Sites with higher degrees of slope should be avoided as they cause problems with equipment used for apple cultivation [44].


#### 4.1.7. Soil pH

Soil pH provides information about the solubility and thus potential availability of elements for crop growth and subsequently specifies the soil suitability for the specific crop [45]. Soil pH has got a priority of 0.0578. In the soils of the study area, pH value ranges from 5.6 to 6.41. According to the [46] rating, the soils of the study Watershed rated as moderately to slightly acidic. Apple can be grown in a wide range of soil pH; however, it performs best with a pH of 6.0–6.5 [47]. Thus, the results show that about 1/15th of the land has a soil pH range between 6.0 and 6.5, which is highly suitable for apple cultivation, and about 1/3rd of the land has a soil pH range between 5.8 and 6.0, which is moderately suitable, and about half of the land has pH value range between 5.6 and 5.8, which is marginally suitable for apple cultivation. However, about 1/10th of the land has pH values below 5.6, which is least suitable for apple production. The results indicated that about 4/7th of the land soils have pH, which is not suitable for apple production, while 3/7th of the land is suitable for apple growing from a pH point of view. Soil pH provided information about the solubility and potential availability of nutrients for crops and then identifies soil suitability for the specific crop grown [48]. Soil pH below 5.5 and greater than 7.5 growth limitations has been observed.


#### 4.1.8. Soil Texture

Soil texture is one of the important soil parameters and major soil physical characteristics determining plant growth [48]. Apple should be grown on soils that have good drainage, aeration, and permeability. Therefore, soil texture has got a priority of 0.0428. The thematic soil texture map of the study area showed that 2/3rd of the land has clay loam soil texture, which is highly suitable for apple cultivation, whereas about 1/3rd of the land has clay textured soil, which is moderately suitable for apple production. Therefore, soil texture is not a limiting factor for apple production in the study area since clay loam and clay soil characteristics are classified as the most suitable and moderately suitable soil textures for apple production (Table 5). Soil texture is a controlling factor of soil reaction, nutrient availability, water-holding capacity, soil porosity, air-water circulation, soil density, and root growth [49].


#### 4.1.9. Soil Drainage

Apple tree needs well-drained and not too wet soil. Soil drainage has got a priority value of 0.0397. Based on the results of the drainage suitability map, the drainage classes of the study area were classified into two soil permeability property classes: well-drained and moderately drained. Thus, about 3/7th of the land has well-drained soils, which are highly suitable for apple production. However, about 4/7th of the land has moderately drained soils, which are moderately suitable for apple production. Thus, the soils of the study area are well-drained and moderately drained due to clay loam and clay soil properties and have no limitation in drainage. The assessment of the soil drainage requirement is a critical characteristic in selecting land for crop production because it permits the normal growth of plants. Chattopadhyay [50] stated that the apple requires a well-drained soil for its growth. Well-drained soils are regarded as the best for apple cultivation [51].


#### 4.1.10. Land Use/Land Cover

Land use is the different uses of land made by human beings, and land cover is the physical material at the part of the Earth’s surface. Land use/land cover (LULC) has been considered one of the influencing factors for apple cultivation and has got a priority of 0.0339. For this study, LULC was classified into four classes: grassland as highly suitable, agricultural land as moderately suitable, open land as marginally suitable, and settlement as least suitable for apple production. Therefore, about 1/5th of the land was covered with grass, which is highly suitable for apple production because of its possibility to cultivate apples, and about 1/4th of the land was used as an agricultural field, which is moderately suitable for apple production, while about 1/4th of the land is covered by vegetation, which is marginally suitable for apple cultivation, and about 1/4th of the land is used as a settlement, which is considered as least suitable for apple production. Thus, more than half of the land is not suitable for apple production from the current land use/land cover point of view. The increment of settlement vegetation decreases the chance of expansion.


#### 4.1.11. Aspect

The aspect of an area is one of the important factors affecting the crop growth as it determines how much sunlight will be available for the growth of a particular crop; thus, the aspect is considered an assessment criterion for land suitability assessment for apple cultivation and has got a priority of 0.0258. The results showed that the east-facing slope has about 1/4th of the land, which is highly suitable for apple production, and about 1/3rd of the land has a southeast-facing slope, which is moderately suitable for apple production. However, about 1/4th of the land has a slope facing to the west and southwest aspect, which is marginally suitable, and 1/10th of the land has a slope facing to the north, northeast, and northwest direction, which is least suitable for apple production. The spatial variation of aspects had important effects on apple yield and quality. Aggelopoulou et al. [52] suggested that changes in topography and aspect had important effects on apple yield and quality. To maintain their physiological activities, apples need sun exposure at certain intervals. Light and apple fruit quality are strongly associated [53]. 30% of total light is needed to ensure quality fruit [54]. Thus, more than half of the land has an aspect suitable for apple production.


### 4.2. Final Suitability Map of Apple

With the help of individual thematic maps and their apple growth-influencing percentage, the final suitability map of apples has been prepared (Figures3 and 5). The thematic maps are climatic maps (GPT, mean temperature, and rainfall), soil maps (depth, pH, texture, and drainage), topographic maps (elevation, slope, and aspect), and land use/land cover maps (LULC). The weight values of each selected parameter calculated in the analytic hierarchal process (AHP) and designated scores of sub-criterion were used in weighted overlay analysis to generate the final suitability map of apple in Sentele Watershed Southern Ethiopia. The final suitability map as shown in Figure 5 stipulated small patches of sites into four suitability categories: most suitable, moderately suitable, marginally suitable, and least suitable. The result showed that 2.2% of the land is most favorable and the best biophysical, climatic, soil, and land use/land cover condition for apple cultivation, and 32% moderately suitable land for apple cultivation indicates a secondary priority, which also bears all the favorable conditions but not as the highly suitable. However, more than half (52.1%) of the land is marginally suitable, which indicates that the third priority class for apple cultivation needs detailed scrutiny of all influencing factors and decides on the feasibility of the investment over other land use options. The other 13.7% of the land is least suitable for apple cultivation and represents currently unsuitable for apple cultivation.Figure 5
Final land suitability map of study areas for apple cultivation.


## 4.1. Factors Affecting Apple Growth

Every crop has its requirements for growth. Various geo-environmental factors influence the suitability of the land for different agricultural products [26]. The importance of each factor, namely elevation, growing period temperature (GPT), mean annual temperature, rainfall, soil depth, slope, soil reaction (pH), soil texture, drainage, land use/land cover, and aspect, was identified (Table 5). Each factor has been represented by limits and degree of suitability to apple production in each unit of area based on experts’ judgment and different literature.Table 5
Evaluation criteria and land area under different land suitability classes.
CriteriaAreaS1 Highly suitableS2 Moderately suitableS3 Marginally suitableS4 Least suitable%Ha%Ha%Ha%HaElevation16.4308.831.9600.726.5499.025.2474.5GTP3.667.827.9525.453.41005.515.1284.3Mean temp14.4271.231.6595.042.9807.811.1209.0Rainfall13.5254.236.2681.721.5404.828.8542.3Soil depth30.5574.331.9600.721.4403.016.2305.0Slope29.4553.632.5612.026.3495.211.8222.2pH6.6124.334.8655.348.2907.610.4195.8Soil type66.21,246.633.8636.4--Drainage43.5819.156.51,063.9--LULC22.1416.125.6482.126.3495.226.0489.6Aspect26.9506.533.0621.428.0527.212.1227.9Source: calculated from scores of suitability maps and AHP technique.


### 4.1.1. Elevation

The elevation is an important factor affecting any plant growth due to its role in temperature change [27]. Whence, elevation has got a high weight value of 0.2037. In the study area, the elevation suitability map shows that about 1/6th of the land has an elevation of 2500–2700 meters above sea level, which is highly suitable, and about 1/3rd of the land has an elevation range of 2300–2500 m.a.s.l, which is moderately suitable, while about 1/4th of the land has an elevation range of 2100–2300 meters above sea level, which is marginally suitable for apple cultivation, and the other 1/4th of the land has an elevation range of 1900–2100 meters above sea level, which is least suitable (Table 5). The results indicated that more than half of the land is not suitable for apple cultivation from an elevation point of view. The elevation is an important factor affecting any plant growth due to its role in temperature changes and thus in a variation of plant cover [27]. At the high altitudes in the tropics, average temperatures are lower, which allows easier reaching of chilling conditions, but seasonal amplitudes remain low [28]. Apple can be grown at an elevation ranging between 1800 and 2700 m.a.s.l. However, altitude ranges from 2500 to 2700 meters above sea level, which is highly suitable for apple cultivation because the apple gets its chilling requirement fulfilled at a temperature below 7°C to overcome its dormancy [29]. Therefore, the chilling requirement of the apple can be satisfied by the higher elevation of the watershed. In this study, after browsing through literature and experts’ opinions, the elevation parameter has been given the highest priority weight in preparing the land suitability map of apple for the study area.


### 4.1.2. The Temperature during the Growing Season

The temperature during the growing season is another environmental factor affecting the growth of apples after elevation, and it has got the second-highest priority of 0.1895. During the growing period (October to January) in the studied area, temperatures average around 15–23°C (Figure2). However, the most suitable temperatures required for apple growth during this period are 15–17°C [9]. Thus, only 3.6% of the land has a temperature during the growing season of 15–17°C, which is highly suitable for apple development. About 1/6th of the land has an average temperature of 17–19°C, which is moderately suitable. However, about half of the land has an average temperature ranging between 19 and 21°C, which is marginally suitable for apple production, whereas about 1/6th of the land has an average temperature of 21–23°C, which is the least suitable for apple production during the growth period. This result indicated that no land in the study area is highly suitable, and more than 2/3rd of the land is not suitable for apple production. Apple is very sensitive to temperature during early growth, which greatly affects final fruit size [30]. Therefore, it is considered one of the criteria for land suitability assessment and was assigned the priority weight of 0.1895. The studied variety “Anna” requires 120 days of development period on MM106 [31].


### 4.1.3. Mean Annual Temperature

Temperature affects the net carbon exchange, carbon balance, and carbon partitioning in the apple tree [32]. Mean annual temperature has got the third-highest priority of 0.1402. Apple trees require a cool temperature for proper growth and development. The yearly mean maximum temperature of the study area is 22.8°C, and the yearly mean minimum temperature is 9.2°C. The results showed that about 1/7th of the land has a temperature condition of 9–11°C, which is highly suitable for apple production, whereas about 1/3rd of the land has a temperature range between 12 and 14°C, which is moderately suitable for apple production. However, about 3/7th (42.9%) of the land has a yearly average temperature of 14–16°C, which is marginally suitable for apple production. However, it was found that about 1/10th of the land has 16–18°C, which is the least suitable for apple production. The results implied that more than half of the land has a yearly average temperature not suitable for apple cultivation. The apple tree requires a temperate climatic regime for growth and fruit development [33]. Low temperature is the most significant factor in affecting dormancy completion [34]. Temperature is a main environmental factor affecting the net carbon exchange, carbon balance, and carbon partitioning in the apple tree [35]. The buds of the apple tree may not bloom or may be uneven if the chilling requirements are not satisfied [36]. Hester and Cacho [37] stated that temperature affects both photosynthesis and respiration of the apple.


### 4.1.4. Rainfall

Rainfall is one of the most important factors affecting the growth of plants. Both highest rainfall and lowest rainfall are harmful to plant growth. Excessive rainfall is harmful to plant growth, and also, its deficit causes a serious effect on plant growth. Rainfall has got the fourth highest priority weight of 0.1142. The meteorological data (1991–2018) obtained from the area revealed that the lowest and highest annual rainfall in the area ranged between 914 and 1499 mm (Figure2). The optimum range of annual rainfall for apple production is 1000–1250 mm [38]. The results indicated that about 1/8th of the land has rainfall ranging between 1100 and 1200 mm, which is highly suitable for apple production, whereas about 1/3rd of land receives about 1200–1300 mm of annual rainfall, which is moderately suitable for apple production. About 1/5th of the land has rainfall ranging between 1300 and 1400 mm, which is marginally suitable for apple production. However, more than 1/4th of the land has rainfall of <800 mm and >1400 mm, which is least suitable for apple production. In general, about half of the area has received rainfall not suitable for apple production.


### 4.1.5. Soil Depth

Soil depth is also one of the important factors affecting apple growth. It has got the fifth priority of 0.0884. The results indicated that about 1/3rd of the land has a soil depth of more than 150 cm, which is highly suitable for apple production, and about 1/3rd of the land has soil depth ranging between 100 and 150 cm, which is considered moderately suitable. However, about 1/5th of the land has a soil depth ranging between 70 and 100 marginally suitable cm depth. However, about 1/6th of the land has <70 cm soil depth, which is least suitable for apple production (Table5). Soil depth determines root growth, as well as the presence of volumes of water and air in the soil [39], and the roots of cultivated plants can reach and use the available water and nutrients [40]. Soil depth is the most important soil property affecting the hydrologic properties of soils. According to Fu et al. [41], variation in soil and depth is connected with soil formation processes, loss of materials through weathering and transportation, and deposition of soil through erosion.


### 4.1.6. Slope

The slope is an important indicator of land suitability since it influences drainage, irrigation, and soil erosion [42]. An increase in slope degree slows down the development of soils and decreases soil depth and fertility [43]. The slope has been given the priority of 0.0640. The growth of apples is determined by slope, and it was determined using the digital elevation model (DEM). Each land mapping unit is described according to its respective slope classes. The results indicated that about 1/4th of the land has a slope of less than 10%, which is considered highly suitable for apple production, and about 1/3rd of the land has a slope ranging between 10% and 20%, which is moderately suitable. However, about 1/4th of the land has a slope ranging between 20 and 30%, which is marginally suitable for apple production, and about 1/10th of the land has a slope of above 30%, which is as least suitable for apple production. Therefore, about 62% of the land in the study is suitable in terms of slope for apple production, whereas about more than 38% is not suitable for apple production. Sites with higher degrees of slope should be avoided as they cause problems with equipment used for apple cultivation [44].


### 4.1.7. Soil pH

Soil pH provides information about the solubility and thus potential availability of elements for crop growth and subsequently specifies the soil suitability for the specific crop [45]. Soil pH has got a priority of 0.0578. In the soils of the study area, pH value ranges from 5.6 to 6.41. According to the [46] rating, the soils of the study Watershed rated as moderately to slightly acidic. Apple can be grown in a wide range of soil pH; however, it performs best with a pH of 6.0–6.5 [47]. Thus, the results show that about 1/15th of the land has a soil pH range between 6.0 and 6.5, which is highly suitable for apple cultivation, and about 1/3rd of the land has a soil pH range between 5.8 and 6.0, which is moderately suitable, and about half of the land has pH value range between 5.6 and 5.8, which is marginally suitable for apple cultivation. However, about 1/10th of the land has pH values below 5.6, which is least suitable for apple production. The results indicated that about 4/7th of the land soils have pH, which is not suitable for apple production, while 3/7th of the land is suitable for apple growing from a pH point of view. Soil pH provided information about the solubility and potential availability of nutrients for crops and then identifies soil suitability for the specific crop grown [48]. Soil pH below 5.5 and greater than 7.5 growth limitations has been observed.


### 4.1.8. Soil Texture

Soil texture is one of the important soil parameters and major soil physical characteristics determining plant growth [48]. Apple should be grown on soils that have good drainage, aeration, and permeability. Therefore, soil texture has got a priority of 0.0428. The thematic soil texture map of the study area showed that 2/3rd of the land has clay loam soil texture, which is highly suitable for apple cultivation, whereas about 1/3rd of the land has clay textured soil, which is moderately suitable for apple production. Therefore, soil texture is not a limiting factor for apple production in the study area since clay loam and clay soil characteristics are classified as the most suitable and moderately suitable soil textures for apple production (Table 5). Soil texture is a controlling factor of soil reaction, nutrient availability, water-holding capacity, soil porosity, air-water circulation, soil density, and root growth [49].


### 4.1.9. Soil Drainage

Apple tree needs well-drained and not too wet soil. Soil drainage has got a priority value of 0.0397. Based on the results of the drainage suitability map, the drainage classes of the study area were classified into two soil permeability property classes: well-drained and moderately drained. Thus, about 3/7th of the land has well-drained soils, which are highly suitable for apple production. However, about 4/7th of the land has moderately drained soils, which are moderately suitable for apple production. Thus, the soils of the study area are well-drained and moderately drained due to clay loam and clay soil properties and have no limitation in drainage. The assessment of the soil drainage requirement is a critical characteristic in selecting land for crop production because it permits the normal growth of plants. Chattopadhyay [50] stated that the apple requires a well-drained soil for its growth. Well-drained soils are regarded as the best for apple cultivation [51].


### 4.1.10. Land Use/Land Cover

Land use is the different uses of land made by human beings, and land cover is the physical material at the part of the Earth’s surface. Land use/land cover (LULC) has been considered one of the influencing factors for apple cultivation and has got a priority of 0.0339. For this study, LULC was classified into four classes: grassland as highly suitable, agricultural land as moderately suitable, open land as marginally suitable, and settlement as least suitable for apple production. Therefore, about 1/5th of the land was covered with grass, which is highly suitable for apple production because of its possibility to cultivate apples, and about 1/4th of the land was used as an agricultural field, which is moderately suitable for apple production, while about 1/4th of the land is covered by vegetation, which is marginally suitable for apple cultivation, and about 1/4th of the land is used as a settlement, which is considered as least suitable for apple production. Thus, more than half of the land is not suitable for apple production from the current land use/land cover point of view. The increment of settlement vegetation decreases the chance of expansion.


### 4.1.11. Aspect

The aspect of an area is one of the important factors affecting the crop growth as it determines how much sunlight will be available for the growth of a particular crop; thus, the aspect is considered an assessment criterion for land suitability assessment for apple cultivation and has got a priority of 0.0258. The results showed that the east-facing slope has about 1/4th of the land, which is highly suitable for apple production, and about 1/3rd of the land has a southeast-facing slope, which is moderately suitable for apple production. However, about 1/4th of the land has a slope facing to the west and southwest aspect, which is marginally suitable, and 1/10th of the land has a slope facing to the north, northeast, and northwest direction, which is least suitable for apple production. The spatial variation of aspects had important effects on apple yield and quality. Aggelopoulou et al. [52] suggested that changes in topography and aspect had important effects on apple yield and quality. To maintain their physiological activities, apples need sun exposure at certain intervals. Light and apple fruit quality are strongly associated [53]. 30% of total light is needed to ensure quality fruit [54]. Thus, more than half of the land has an aspect suitable for apple production.


## 4.1.1. Elevation

The elevation is an important factor affecting any plant growth due to its role in temperature change [27]. Whence, elevation has got a high weight value of 0.2037. In the study area, the elevation suitability map shows that about 1/6th of the land has an elevation of 2500–2700 meters above sea level, which is highly suitable, and about 1/3rd of the land has an elevation range of 2300–2500 m.a.s.l, which is moderately suitable, while about 1/4th of the land has an elevation range of 2100–2300 meters above sea level, which is marginally suitable for apple cultivation, and the other 1/4th of the land has an elevation range of 1900–2100 meters above sea level, which is least suitable (Table 5). The results indicated that more than half of the land is not suitable for apple cultivation from an elevation point of view. The elevation is an important factor affecting any plant growth due to its role in temperature changes and thus in a variation of plant cover [27]. At the high altitudes in the tropics, average temperatures are lower, which allows easier reaching of chilling conditions, but seasonal amplitudes remain low [28]. Apple can be grown at an elevation ranging between 1800 and 2700 m.a.s.l. However, altitude ranges from 2500 to 2700 meters above sea level, which is highly suitable for apple cultivation because the apple gets its chilling requirement fulfilled at a temperature below 7°C to overcome its dormancy [29]. Therefore, the chilling requirement of the apple can be satisfied by the higher elevation of the watershed. In this study, after browsing through literature and experts’ opinions, the elevation parameter has been given the highest priority weight in preparing the land suitability map of apple for the study area.


## 4.1.2. The Temperature during the Growing Season

The temperature during the growing season is another environmental factor affecting the growth of apples after elevation, and it has got the second-highest priority of 0.1895. During the growing period (October to January) in the studied area, temperatures average around 15–23°C (Figure2). However, the most suitable temperatures required for apple growth during this period are 15–17°C [9]. Thus, only 3.6% of the land has a temperature during the growing season of 15–17°C, which is highly suitable for apple development. About 1/6th of the land has an average temperature of 17–19°C, which is moderately suitable. However, about half of the land has an average temperature ranging between 19 and 21°C, which is marginally suitable for apple production, whereas about 1/6th of the land has an average temperature of 21–23°C, which is the least suitable for apple production during the growth period. This result indicated that no land in the study area is highly suitable, and more than 2/3rd of the land is not suitable for apple production. Apple is very sensitive to temperature during early growth, which greatly affects final fruit size [30]. Therefore, it is considered one of the criteria for land suitability assessment and was assigned the priority weight of 0.1895. The studied variety “Anna” requires 120 days of development period on MM106 [31].


## 4.1.3. Mean Annual Temperature

Temperature affects the net carbon exchange, carbon balance, and carbon partitioning in the apple tree [32]. Mean annual temperature has got the third-highest priority of 0.1402. Apple trees require a cool temperature for proper growth and development. The yearly mean maximum temperature of the study area is 22.8°C, and the yearly mean minimum temperature is 9.2°C. The results showed that about 1/7th of the land has a temperature condition of 9–11°C, which is highly suitable for apple production, whereas about 1/3rd of the land has a temperature range between 12 and 14°C, which is moderately suitable for apple production. However, about 3/7th (42.9%) of the land has a yearly average temperature of 14–16°C, which is marginally suitable for apple production. However, it was found that about 1/10th of the land has 16–18°C, which is the least suitable for apple production. The results implied that more than half of the land has a yearly average temperature not suitable for apple cultivation. The apple tree requires a temperate climatic regime for growth and fruit development [33]. Low temperature is the most significant factor in affecting dormancy completion [34]. Temperature is a main environmental factor affecting the net carbon exchange, carbon balance, and carbon partitioning in the apple tree [35]. The buds of the apple tree may not bloom or may be uneven if the chilling requirements are not satisfied [36]. Hester and Cacho [37] stated that temperature affects both photosynthesis and respiration of the apple.


## 4.1.4. Rainfall

Rainfall is one of the most important factors affecting the growth of plants. Both highest rainfall and lowest rainfall are harmful to plant growth. Excessive rainfall is harmful to plant growth, and also, its deficit causes a serious effect on plant growth. Rainfall has got the fourth highest priority weight of 0.1142. The meteorological data (1991–2018) obtained from the area revealed that the lowest and highest annual rainfall in the area ranged between 914 and 1499 mm (Figure2). The optimum range of annual rainfall for apple production is 1000–1250 mm [38]. The results indicated that about 1/8th of the land has rainfall ranging between 1100 and 1200 mm, which is highly suitable for apple production, whereas about 1/3rd of land receives about 1200–1300 mm of annual rainfall, which is moderately suitable for apple production. About 1/5th of the land has rainfall ranging between 1300 and 1400 mm, which is marginally suitable for apple production. However, more than 1/4th of the land has rainfall of <800 mm and >1400 mm, which is least suitable for apple production. In general, about half of the area has received rainfall not suitable for apple production.


## 4.1.5. Soil Depth

Soil depth is also one of the important factors affecting apple growth. It has got the fifth priority of 0.0884. The results indicated that about 1/3rd of the land has a soil depth of more than 150 cm, which is highly suitable for apple production, and about 1/3rd of the land has soil depth ranging between 100 and 150 cm, which is considered moderately suitable. However, about 1/5th of the land has a soil depth ranging between 70 and 100 marginally suitable cm depth. However, about 1/6th of the land has <70 cm soil depth, which is least suitable for apple production (Table5). Soil depth determines root growth, as well as the presence of volumes of water and air in the soil [39], and the roots of cultivated plants can reach and use the available water and nutrients [40]. Soil depth is the most important soil property affecting the hydrologic properties of soils. According to Fu et al. [41], variation in soil and depth is connected with soil formation processes, loss of materials through weathering and transportation, and deposition of soil through erosion.


## 4.1.6. Slope

The slope is an important indicator of land suitability since it influences drainage, irrigation, and soil erosion [42]. An increase in slope degree slows down the development of soils and decreases soil depth and fertility [43]. The slope has been given the priority of 0.0640. The growth of apples is determined by slope, and it was determined using the digital elevation model (DEM). Each land mapping unit is described according to its respective slope classes. The results indicated that about 1/4th of the land has a slope of less than 10%, which is considered highly suitable for apple production, and about 1/3rd of the land has a slope ranging between 10% and 20%, which is moderately suitable. However, about 1/4th of the land has a slope ranging between 20 and 30%, which is marginally suitable for apple production, and about 1/10th of the land has a slope of above 30%, which is as least suitable for apple production. Therefore, about 62% of the land in the study is suitable in terms of slope for apple production, whereas about more than 38% is not suitable for apple production. Sites with higher degrees of slope should be avoided as they cause problems with equipment used for apple cultivation [44].


## 4.1.7. Soil pH

Soil pH provides information about the solubility and thus potential availability of elements for crop growth and subsequently specifies the soil suitability for the specific crop [45]. Soil pH has got a priority of 0.0578. In the soils of the study area, pH value ranges from 5.6 to 6.41. According to the [46] rating, the soils of the study Watershed rated as moderately to slightly acidic. Apple can be grown in a wide range of soil pH; however, it performs best with a pH of 6.0–6.5 [47]. Thus, the results show that about 1/15th of the land has a soil pH range between 6.0 and 6.5, which is highly suitable for apple cultivation, and about 1/3rd of the land has a soil pH range between 5.8 and 6.0, which is moderately suitable, and about half of the land has pH value range between 5.6 and 5.8, which is marginally suitable for apple cultivation. However, about 1/10th of the land has pH values below 5.6, which is least suitable for apple production. The results indicated that about 4/7th of the land soils have pH, which is not suitable for apple production, while 3/7th of the land is suitable for apple growing from a pH point of view. Soil pH provided information about the solubility and potential availability of nutrients for crops and then identifies soil suitability for the specific crop grown [48]. Soil pH below 5.5 and greater than 7.5 growth limitations has been observed.


## 4.1.8. Soil Texture

Soil texture is one of the important soil parameters and major soil physical characteristics determining plant growth [48]. Apple should be grown on soils that have good drainage, aeration, and permeability. Therefore, soil texture has got a priority of 0.0428. The thematic soil texture map of the study area showed that 2/3rd of the land has clay loam soil texture, which is highly suitable for apple cultivation, whereas about 1/3rd of the land has clay textured soil, which is moderately suitable for apple production. Therefore, soil texture is not a limiting factor for apple production in the study area since clay loam and clay soil characteristics are classified as the most suitable and moderately suitable soil textures for apple production (Table 5). Soil texture is a controlling factor of soil reaction, nutrient availability, water-holding capacity, soil porosity, air-water circulation, soil density, and root growth [49].


## 4.1.9. Soil Drainage

Apple tree needs well-drained and not too wet soil. Soil drainage has got a priority value of 0.0397. Based on the results of the drainage suitability map, the drainage classes of the study area were classified into two soil permeability property classes: well-drained and moderately drained. Thus, about 3/7th of the land has well-drained soils, which are highly suitable for apple production. However, about 4/7th of the land has moderately drained soils, which are moderately suitable for apple production. Thus, the soils of the study area are well-drained and moderately drained due to clay loam and clay soil properties and have no limitation in drainage. The assessment of the soil drainage requirement is a critical characteristic in selecting land for crop production because it permits the normal growth of plants. Chattopadhyay [50] stated that the apple requires a well-drained soil for its growth. Well-drained soils are regarded as the best for apple cultivation [51].


## 4.1.10. Land Use/Land Cover

Land use is the different uses of land made by human beings, and land cover is the physical material at the part of the Earth’s surface. Land use/land cover (LULC) has been considered one of the influencing factors for apple cultivation and has got a priority of 0.0339. For this study, LULC was classified into four classes: grassland as highly suitable, agricultural land as moderately suitable, open land as marginally suitable, and settlement as least suitable for apple production. Therefore, about 1/5th of the land was covered with grass, which is highly suitable for apple production because of its possibility to cultivate apples, and about 1/4th of the land was used as an agricultural field, which is moderately suitable for apple production, while about 1/4th of the land is covered by vegetation, which is marginally suitable for apple cultivation, and about 1/4th of the land is used as a settlement, which is considered as least suitable for apple production. Thus, more than half of the land is not suitable for apple production from the current land use/land cover point of view. The increment of settlement vegetation decreases the chance of expansion.


## 4.1.11. Aspect

The aspect of an area is one of the important factors affecting the crop growth as it determines how much sunlight will be available for the growth of a particular crop; thus, the aspect is considered an assessment criterion for land suitability assessment for apple cultivation and has got a priority of 0.0258. The results showed that the east-facing slope has about 1/4th of the land, which is highly suitable for apple production, and about 1/3rd of the land has a southeast-facing slope, which is moderately suitable for apple production. However, about 1/4th of the land has a slope facing to the west and southwest aspect, which is marginally suitable, and 1/10th of the land has a slope facing to the north, northeast, and northwest direction, which is least suitable for apple production. The spatial variation of aspects had important effects on apple yield and quality. Aggelopoulou et al. [52] suggested that changes in topography and aspect had important effects on apple yield and quality. To maintain their physiological activities, apples need sun exposure at certain intervals. Light and apple fruit quality are strongly associated [53]. 30% of total light is needed to ensure quality fruit [54]. Thus, more than half of the land has an aspect suitable for apple production.


## 4.2. Final Suitability Map of Apple

With the help of individual thematic maps and their apple growth-influencing percentage, the final suitability map of apples has been prepared (Figures3 and 5). The thematic maps are climatic maps (GPT, mean temperature, and rainfall), soil maps (depth, pH, texture, and drainage), topographic maps (elevation, slope, and aspect), and land use/land cover maps (LULC). The weight values of each selected parameter calculated in the analytic hierarchal process (AHP) and designated scores of sub-criterion were used in weighted overlay analysis to generate the final suitability map of apple in Sentele Watershed Southern Ethiopia. The final suitability map as shown in Figure 5 stipulated small patches of sites into four suitability categories: most suitable, moderately suitable, marginally suitable, and least suitable. The result showed that 2.2% of the land is most favorable and the best biophysical, climatic, soil, and land use/land cover condition for apple cultivation, and 32% moderately suitable land for apple cultivation indicates a secondary priority, which also bears all the favorable conditions but not as the highly suitable. However, more than half (52.1%) of the land is marginally suitable, which indicates that the third priority class for apple cultivation needs detailed scrutiny of all influencing factors and decides on the feasibility of the investment over other land use options. The other 13.7% of the land is least suitable for apple cultivation and represents currently unsuitable for apple cultivation.Figure 5
Final land suitability map of study areas for apple cultivation.


## 5. Conclusion

The study has delineated the potentially suitable land areas for apple cultivation in Sentele Watershed and drew special attention to the need of evolving an appropriate land planning. It can be inferred from the final land suitability maps that about 2.2% and 32% of the land are highly suitable and moderately suitable for apple cultivation, respectively. However, about 52.1% and 13.7% of the land are marginally suitable and least suitable for apple cultivation, respectively. From the actual suitability view, the main limitations to apple production were found to be rainfall, land use/land cover (LULC), and elevation and growing period temperature. From the total land area, more than half is moderately suitable. From the suitability maps of potentiality, some limitations can be improved with the application of soil amendments, irrigation, species selection, and removing leaves (defoliation). The output enables the users to select management options to alleviate the identified limitations. The techniques and methods of this study can be also applied to land suitability of other important crops in the study area and elsewhere with additional and more refined parameters. The apple suitability map can serve as a basis for a decision support tool for policymakers, land-use planners, and farmers by providing information alike regarding the land suitability of apple production. One of the limitations to this research is the absence of published source materials concerning the major characteristics such as climate, topography, and soil. The other limitation was the knowledge gap on apple cultivation among experts and apple-producing farmers. This study focuses only on the suitability of apple cultivation, but also further research can be conducted for determining the optimum locations for different types of crops to enhance the sustainable crop in the study area.



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*Source: 4436417-2022-06-13.xml*