Suitability Analysis for Scaling Chickpea Improved Varieties in Ethiopia

Background: Appropriate decision-making on crop production will reduce various risk factors associated with unsustainable land management. The limited available arable land be taken for granted which may turn from ‘best’ to ‘worst’ irrespective of the kind of land use and management practice without understanding its special requirements and potential use. GIS has contributed to the speed and efficiency of the overall planning process in agricultural land use suitability, since it enables quick and efficient access to large amounts of information, exhibiting relationships, patterns, and trends that are useful in monitoring land use potential and suitability evaluation. As crop’s environmental requirements vary from variety to variety, it is recommended to undertake variety specific analysis and mapping for better understand the extent of scaling-up the specific crop technology Results: GIS-based land suitability map for chickpea was generated for each variety under consideration mapped showing their percentage area coverage of suitability for each regional states in Ethiopia. Based on, the suitability analysis desi chickpea varieties Mastewal, Naatolii, Teketay and Arerti, Habru, Kasech, and Yelbey kabuli chickpea varieties classified as highly suitable that cover 0.67, 0.71, 1.4, 2.3, 1.3, 2.4 and 1.2 million ha of the country respectively. While moderately suitable areas for the same varieties cover 25.2, 11.3, 25.9, 26.4, 26.6, 9.6, 17.1 million ha. Conclusion : The suitability analysis results show that the currently available improved varieties of chickpea can be targeted for scaling out in the identified land suitability classes in Ethiopia with some caution. Amhara, Oromia, SNNP and Tigray remain the major regions with suitable areas for production of available varieties of chickpea compared to Afar, Benishangul Gumuz, Gambella, and Somali regions. However, the highly suitable areas are limited compared to moderately suitable areas, which are higher across the regions.


Background
Agriculture is a source of food and income, but, where, when, how and what to cultivate are the main issues that farmers and land managers are confronted daily (Mokarram et al. 2010).
Appropriate decision-making on crop production will reduce various risk factors associated with unsustainable land management. The limited available arable land be taken for granted which may turn from 'best' to 'worst' irrespective of the kind of land use and management practice without understanding its special requirements and potential use (FAO 1993;Biradar et al., 2019).
Land suitability classification for agriculture is very important for future planning to help decision-makers and agricultural development planners; and determine how appropriate use of the land in a location is more suitable for certain agricultural use (Singha and Swain 2016).
GIS has contributed to the speed and efficiency of the overall planning process in agricultural land use suitability, since it enables quick and efficient access to large amounts of information, exhibiting relationships, patterns, and trends that are useful in monitoring land use potential and suitability evaluation. It is useful tool for scaling proven technologies and packages of practices including the specific crops and crop varieties to address the yield and nutritional gaps (Singha and Swain 2016;Low et al., 2018). As crop's environmental requirements vary from variety to variety, it is recommended to undertake variety specific analysis and mapping for better understand the extent of scaling-up the specific crop technology (Nigussie, 2014).
The objective of the study assesses the extent and distribution of areas that are potentially suitable for chickpea (Cicer arietinum L.) varieties using Geographic Information System (GIS), and Multi-Criteria Decision-Making Analysis (MCDA) technique.

The Chickpea crop
On average, chickpea production globally consists of about 75% of desi and 25% of kabuli types (AAFC, 2004). Ethiopia is the largest chickpea producer in Africa and ranking sixth globally (http://ethioagp.org/chickpea/). According to FAO (2019), chickpea area, production, and productivity have increased between 2009-2108 respectively (Fig.1). Figure 1.Area harvested, production and productivity of chickpea in Ethiopia Source: FAO (2019) In Ethiopia, chickpea with thousand seed weight (TSW) below 200 g is considered as small; between 200-380 g is medium; and greater than 380 g is considered as large seeded. Chickpea varieties released between 1990 and 2000 showed an increase in seed weight of 31.9% and 12% for kabuli and desi, respectively. Remarkable progress has been achieved in genetic gain for seed size in the chickpea breeding program because of the primary focus on the development of largeseeded Kabulis due to world market demand (Bekele et al. 2015). Seed size is the most important quality trait for Kabuli types as larger seeds fetch higher premium price in international trade (Gaur et al. 2007).

Geospatial data used
The main factors were used in the generation of the suitability map: rainfall and temperature surface maps (during the growing period) interpolated at a resolution of about 300 m which again re sampled to 200 m to match the 200 m analysis resolution; and length of growing period (LGP) from the Ministry of Agriculture (WBISPP 2004) with a slight modification (i.e. joining the values of dependable length of period and converting to raster (pixel based). The soil types data were acquired from MoA modified by the Woody Biomass Inventory and Strategic Planning Project (WBISPP, 2004) while, the soil properties ([chemical (pH) and physical (depth, texture, and drainage)], were extracted from the Soil and Terrain Database of East Africa and gridded soil database of 250m (ISRIC, 2015). For the altitude information, the Shuttle Radar Topography Mission (SRTM) 90 m digital elevation model (DEM) database (Jarvis et al. 2008) was used and the same DEM used for topographic analysis such as for generating slope maps.
These data were re-sampled to a common spatial resolution of 200 m for the spatial analysis in the GIS domain.While administrative boundaries, and infrastructure (roads, towns, and other facilities) were used to compute statistical information and prepare the final maps respectively. However, park and lake areas were excluded (restricted) in this land suitability analysis.

Defining environmental requirements
The land suitability class boundary thresholds were mainly based on (FAO 1984;FAO 2007) employing multi-criteria evaluation technique that integrates major determinant factors that affect chickpea production in Ethiopia. The national variety trials conducted at multi-locations and multi-seasons were used to define various suitability ranges/limits. Then, environmental requirements of each variety were defined by means of a set of critical values, which determine the limits between the land suitability levels (classes) that reflect the degree of suitability (Table   1). According to FAO classification, S1 corresponds to 85-100% of optimum yield under the recommended management practices, S2 to 60-85%, S3 to 40 -60%, N1 to 25 -40% and N2 to 25 -0% (Elsheikh and Abdalla, 2016 Land having no significant limitations to sustained application of a given use, or only minor limitations that will not significantly reduce productivity and will not raise inputs above an acceptable level S2

Moderately suitable
Land having limitations which, in aggregate, are moderately severe for sustained application of a given use; the limitations will reduce productivity and increase required inputs to the extent that the overall advantage to be gained from the use, although still attractive, will be appreciably low to that expected on S1 land S3 Marginally suitable Land having limitations which, in aggregate, are severe for sustained application of a given use and will so reduce productivity or benefits, or increase required inputs, that this expenditure will be only marginally justified.

N Not suitable
Land that cannot support the land use on a sustained basis, or land on which benefits do not justify necessary inputs Source: FAO, 1976FAO, & 1993 Since the analysis is raster (pixel) based, some of the data, which were in vector format (object based), were converted to uniform raster datasets. The important GIS layers of environmental factors affecting the growth of chickpea varieties were identified and each layer's pixel values were classified and assigned weight. Following this, the environmental factor layers were compared among themselves and ranked. Based on the rate and rank assigned to each pixel, the land suitability map for each variety was computed. The classification of each layer into suitability categories was done using Reclassify by Table function in ArcGIS spatial analyst (ESRI GIS package) tool. The reclassification is implemented in the model by preparing separate tables for each factor/criteria layer and chickpea variety.

Criteria layers and overall suitability analysis
The overall suitability map is the combined result of the altitude, slope, soil types and soil properties, and the climate layers. The weighted overlay approach built on ArcGIS ModelBuilder was used for the overlay analysis to solve such multi-criteria problems of suitability. The suitability criteria layers were assigned weights to account for their relative importance and overlaid using the weighted overlay tool to produce the overall land suitability map. The purpose of weighting is to express the relative importance of each factor regarding the effects on crop production (Perveen et al. 2007). The analytic hierarchy process (AHP) was used to evaluate and calculate the weights for the different criteria (Saaty, 2008) and numerical scales of measurement were derived through comparing against the goal for importance. The pair wise comparisons scales were assigned through discussion among experts. The overall suitability is computed by multiplying the selected criteria weight (Wi) by the assigned sub-criteria score (Xi) and summing these values in the ArcGIS Model Builder (Eq.1): Where S denotes the final land suitability score, Wi denotes the weight of the corresponding suitability criteria, Xi denotes the assigned sub-criteria score of i suitability criteria and n is the total number of criteria maps. The final suitability result (maps and tabular data) including the explanatory document are prepared both in softcopy and hardcopy.

Crop varieties
Seven chickpea varieties (Mastewal, Naatolii, Teketay, Arerti, Habru, Kasech and Yelbe) were used in suitability analysis. The varieties were selected based on current production and area coverage in the technology transfer productivity earliness export and local market quality parameters (   Table 2).

Results and discussion
Area and suitability mapping GIS-based land suitability map for chickpea was adopted from (Demeke, 2018) followed by variety level land suitability map showed the percentage area coverage of suitability for each regional state computed based on their respective total area Table 3. Table 3. Area (ha) of regional administrative states in Ethiopia* Note: *The total area includes all agriculture, forest, water, town, and other lands bounded within the boundary of each regional state; Addis Abeba, Dire Dawa and Harari are city administrations with limited agricultural land for crop production.

Crop-level land suitability mapping
From the outset, it should be noted that the suitability analysis in this study does not exclude the areas occupied by non-agricultural areas such as forests, woodlands, towns (except Addis Abeba, Dire Dawa and Harari) and another non-cropland uses. It also does not account the updated cropland currently under active cultivation. The chickpea crop level suitability area showed 1.61% (highly suitable) and 19.36 % (moderately suitable) for chickpea production across the regions (Figure 2 and Error! Reference source not found.). Generally, the crop level highly suitable land areas of chickpea are still larger than the highly suitable land area for most individual varieties. This is expected because the environmental range boundaries for the different suitability class thresholds are defined considering broader ranges of adaptation to encompass the adaptation ranges of most of the varieties currently available.   (   Table 2). It is an early maturing variety and can be potentially used in double cropping in areas having a short rainy season (belg) following the harvest of the main rainy season crops. In the local market, it is preferred for its relatively larger seed size than the local varieties and for its light red color. The variety is relatively tolerant to wilt and root rot fungal diseases.
The variety level suitability analysis and mapping results for this variety are shown in Figure 3 and Table 5. When compared with the overall crop level suitability result of chickpea ( Figure 2 and Error! Reference source not found., the highly suitable lands for Mastewal are still smaller. The highly suitable lands are in the west-central highlands of Ethiopia largely in parts of Amhara and Oromia and SNNP regional states. The moderately suitable and marginally suitable areas of Mastewal variety is mainly covering most of Amhara and Oromia, and central and northern SNNPR.

Naatolii (ICCX-910112-6)
Naatolii grain yields ranged from 2.5-3.5 tons ha -1 in the research field (MoARD 2007). It is a high yielding and short duration chickpea variety resistant to fusarium wilt disease in waterlogging Vertisol areas. However, it is recommended to advance the planting date and drain excess water from the field. There are local and foreign market demands to meet producing chickpea varieties like Naatolii, although the supply is very limited, as its production has not yet expanded. It has a local market preference due to its light golden seed color and medium seed size of 240g of TSW (   Table 2).The variety level suitability analysis and mapping results for this variety are shown in Figure 4 and Table 6.
The moderately suitable and highly suitable areas for this variety cover large parts of Amhara followed by mainly central Oromia. It covers also part of central Tigray and northern SNNP to a smaller extent. Compared with the overall (crop level) suitability result of chickpea, this variety has relatively smaller coverage.  Table 6. Land area under different suitability classes for Naatolii variety in regional states

Teketay (ICCX-940002-F5-242P-1-1-1)
Teketay variety yields, on average, 2.0 to 2.7 and 1.6 to 2.2 tons ha -1 at research stations and on farmers' fields, respectively, with a medium seed size for having TSW of 310 g ( Table 2). The observed yield potential on farmers' fields during the 2015-2018 scaling project of ICARDA in potential chickpea growing areas of the country was by far higher than the yield reported for release, which was attributed to sub-optimal crop management and weather conditions in the selected test locations during nationwide testing.
The variety level suitability analysis and mapping results for this variety are shown in Figure 5 and

Arerti (FLIP 89-84C)
Arerti variety yields, on average, 1.6-5.2 and 1.8-4.7 tons ha -1 in research and farmers' fields, respectively, with 257 g of TSW (   Table 2; NSIA 2000), being medium in seed size. It is widely grown in the country and is a dominant chickpea variety under production as the result of national level pre-scaling up activities by EIAR in addition to its merits prior to 2015.
The variety level suitability analysis and mapping results for this variety are shown in Figure 6 and

Habru (FLIP-88-42C)
Habru yields, on average, 2.4 to3.2 tonsha -1 inresearch field with TSW of 319 g ( Table 2; MoARD 2004), being medium in seed size, even though it has a relatively larger seed size than chickpea varieties considered, except Yelbey, in this land suitability analysis. It has got wide adaptation and is a dominant variety as a result of national level pre-scale up activities by EIAR prior 2015 in addition to its biological merits, such as better performance in both moisture stress and mid to high altitude areas. This variety is moderately resistant to wilt.compared with the overall crop level suitability result of chickpea, shown in Figure 2 and Error! Reference source not found., the suitable areas of Habru variety (see Figure 7 and Table 9) Table 9. Land area under different suitability classes for Habru variety in regional states

Kasech (FLIP-95-31C)
Kasech variety yields, on average, 2.0 to2.5 and 1.6 to2.0 tons ha -1 in research and farmers' field, respectively, with a TSW of 375g (   Table 2; MoA 2011), which falls in medium seed size although it has the biggest seed size than the varieties included in this study. Even though it is low yielding, Kasech is an early maturing variety, which is well adapted to moisture stress areas.
The variety level suitability analysis and mapping results for this variety are shown in Figure 8 and Table 10. The variety has the largest highly suitable land (2.395 million ha) compared with both the crop and variety level suitability analysis results. These areas are found in Amhara largely followed by Oromia, Tigray and SNNP. The combined highly suitable and moderately suitable areas of the Kasech variety is, however, still smaller than the crop level suitability and other varieties considered in this analysis.   Compared with the overall crop-level suitability result of chickpea, shown in Figure 2 and Error! Reference source not found., the suitable areas of Yelbey variety are smaller than that of the crop level results, mostly covering the central highlands of the country; stretching from most of central Tigray, central and western Amhara, central Oromia, to large parts of northern SNNP ( Figure 9 and Table 11). The results show that the highly suitable areas are the fourth largest (1.22 million ha), when compared with the variety level suitability results and they are found in Amhara largely followed by Oromia and SNNP. Figure 9. Land suitability map for chickpea var. Yelbey Table 11. Land area under different suitability classes for Yelbey variety in regional states

Conclusion
• Amhara, Oromia, SNNP and Tigray remain the major regions with suitable areas for production of available varieties of chickpea compared to Afar, Benishangul Gumuz, Gambella, and Somali regions. However, the highly suitable areas are limited compared to moderately suitable areas, which are higher across the regions.
• In general, areas of the highly and moderately suitable lands for most varieties considered in this analysis are smaller than the areas of crop level suitability. This difference is expected since the crop level environmental range boundaries for the suitability class thresholds are defined to encompass the adaptation ranges of available varieties.
• Chickpea varieties considered in this analysis, the highly suitable areas are much larger than the current estimated area under chickpea production in the country. For example, some kabuli chickpea varieties such as Kasech and Arerti have close to 2.3 million ha each of highly suitable areas, which is over the estimated crop suitability areas. Overall, Arerti variety, followed by Teketay and Mastewal, have broader adaptation compared to other varieties Land suitability map for chickpea Source: Demeke (2018) Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.

Figure 3
Land suitability map for chickpea var. Mastewal Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Land suitability map for chickpea var. Naatolii Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Land suitability map for chickpea var. Teketay Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Land suitability map for chickpea var. Arerti Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Land suitability map for chickpea var. Habru Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.

Figure 8
Land suitability map for chickpea var. Kasech Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Land suitability map for chickpea var. Yelbey Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.

Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download. chickpeadata.docx