†These authors contributed equally.
Academic Editor: Graham Pawelec
Background: Changes in dietary patterns have led to a decrease in rice consumption, raising demands for the cultivation of alternative crops that meet the current requirements. Potatoes are highly productive and can be stored for a relatively long period, thereby ensuring adequate income for farmers; however, optimal cultivation is necessary to maximize yield. Objective: This study proposes optimal cultivation regions for potato considering climate and soil conditions. Materials and methods: The CLIMEX model was developed to evaluate climatic suitability, while the soil suitability was scored based on five soil characteristics. The final areal suitability for potato cultivation was classified into 4 levels: very suitable, suitable, marginal, and unsuitable. Results: Overall, 36.5% of South Korea had very suitable climate, but areas with the best values for soil conditions were approximately 10% of the climatically suitable areas. When considering the climate and soil conditions simultaneously, climatic suitability and soil condition were inversely related, resulting in only 1.2% of optimal areas with Jeju Island as the most suitable area. Conclusions: Because both climate and soil conditions need to be suitable for growing crops, this study can provide potential paddy-cultivation areas for potato cultivation and a method for evaluating suitable areas for crop cultivation.
Annual rice consumption in South Korea and other rice cultivation areas have consistently decreased due to climate change, and changes in household eating habits [1]. Overall, arable land utilization has steadily decreased since 1970, leading to cultivation areas constituting only 16.9% of the total land area [2, 3]. However, there is a disparity between rice supply and demand because of an increase in rice production. Hence, there has been an effort to flexibly use paddy fields for stable rice supply and enhance food self-sufficiency by producing (or rotating) other crops in paddy fields [4]. For example, feed value, harvesting time, and sowing period were compared under forage cropping systems [5, 6]. Other studies of cropping systems investigated productivity and income of potato-corn in fields and paddies [7], sesame seed [8], and optimal forage crops in paddy fields in summer and winter [9]. Potential areas for apple cultivation have also been investigated [10, 11]. Moreover, suitable areas for growing Italian ryegrass have been predicted in Gangwon-do [12] using a spatial distribution model [13]. Because climate change affects crops and their cultivation area [14], suitable growing areas have been identified for southern-type garlic [15], black raspberry [16], and teff and barley [17]. In this analysis, a geographic information system (GIS)-based analytic hierarchy process was used [16, 18]. Studies concerning upland-paddy rotation has evaluated the effect of growth and yield on reclaimed tidal land [19], and on foxtail millet, proso millet, sorghum, and rice [4].
Various alternative crops for rice have been proposed, such as sweet potatoes, potatoes, and corn [14]. Among them, potatoes are favored as an alternative crop for rice by farmers because of advantages of relatively easy cultivation, long-term storage capacity and high productivity. Nevertheless, both quantity and quality of potatoes are greatly affected by climate and soil conditions [2, 20, 21]. Hence, it is necessary to consider both these factors while identifying potential areas for potato cultivation.
The CLIMEX model, a species distribution modeling tool specialized for climate-based prediction, can project potential distributions of a species by identifying climatically suitable areas [22, 23, 24], and has been widely applied to predict the climatic suitability of plants such as prickly acacia [25], common bean [26], and potato [27, 28]. Soil suitability for crop cultivation is known to be a function of variables that define texture, drainage class, and slope [11, 12]. A previous study predicted suitable cultivation regions for medicinal plants [29], while [30] reported major environmental factors affecting the geographical distribution and quality of Scutellaria baicalensis. In addition, there are some studies which predicted suitable areas for plant inhabitation, such as Panax notoginseng under various climatic conditions [31], habitat suitability modeling of Perilla frutescens [32], and prediction of current and future cultivation areas of Carthamus tinctorius [33].
The suitability of climate and soil for potato cultivation in South Korea can be evaluated using the CLIMEX model and the maximum limiting characteristic method [34]. This study aims to investigate the suitability of the climate and soil of paddy-cultivation areas for potato cultivation, and to propose an optimal area for field potato cultivation in South Korea based on the evaluation.
South Korea is geographically located in the mid-latitude temperate zone (N
33
Five soil variables were used to determine the soil suitability (N
Soil characteristics (Grade) | Poor (5) | Normal (10) | Proper (15) | Good (20) |
Soil texture | Sandy | Clayey | Clay loam | Sandy loam |
Silty clay loam | Silty sandy loam | |||
Drainage class | Poor | Excessively well | Moderately | Well |
Slope (%) | 7–15 | 2–7 | 0–2 | |
Effective soil depth (cm) | 20 |
50 |
||
Gravel content (%) | 10–35 |
The CLIMEX (version 4.0, Hearne software, Australia) model predicts the
potential distribution of a target species based on meteorological information
and estimated model parameters from biological information. The possibility of
species distribution is quantified using the Ecoclimatic Index (EI), which is a
representative of climatic suitability resulting from the growth index (GI) and
stress index (SI) [22, 40]. Potatoes are generally not exposed to stressful
climates because they are predominantly cultivated in favorable climates. Hence,
the EI for potato was determined based only on the parameter related to GI,
meaning that EI and GI values were the same, because SI could not be calculated
for potato. Thus, climatic suitability (N
Temperature Index (TI), Moisture Index (MI), and Light Index (LI) were among
seven indices necessary for calculating GI, and were used by considering data
availability. In addition, CLIMEX calculates minimum degree-days required to
complete a generation by using a parameter of population degree day (PDD). TI has
four parameters from DV0 to DV3, and DV0 and DV3 designate the lower and upper
threshold temperature of the target species. MI includes four parameters from SM0
to SM3, representing the lower and upper threshold soil moisture, respectively,
and determined by the amount of precipitation in a specific area. The CLIMEX
parameters of potato were employed from a previous study [24], and adjusted for
the growing conditions for major Korean potatoes such as Superior, suggested by
the RDA [30] (Table 2). The RDA reported that the suitable temperature range for
growing potato was 14–23
Parameters | Code | Previous values | Adjusted values | |
Temperature | ||||
Limiting low temperature ( |
DV0 | 4 | 4 | |
Lower optimal temperature ( |
DV1 | 16 | 14 | |
Upper optimal temperature ( |
DV2 | 25 | 24 | |
Limiting high temperature ( |
DV3 | 40 | 30 | |
PDD | 950 | 950 | ||
Moisture | ||||
Limiting low soil moisture | SM0 | 0.05 | 0.2 | |
Lower optimal soil moisture | SM1 | 0.2 | 0.4 | |
Upper optimal soil moisture | SM2 | 0.8 | 1.6 | |
Limiting high soil moisture | SM3 | 1.5 | 2.5 | |
Light | ||||
Daylength at no growth | LT1 | 10 | 10 | |
Daylength at maximum growth | LT0 | 16 | 16 |
The final suitable sites for cultivation of potato (S
The crop yields are related to physical properties of the soil, and they affect growth differently depending on the crop [43]. Even for the same variety, potatoes show differences in growth and quality depending on the soil type, and are sensitive to climate, suggesting the necessity for proposing areas for its cultivation by considering both climatic and soil conditions [44].
Among the soil variables, soil texture had the highest value, with an average of
17.3, whereas the slope showed the lowest average score of 8 (a high value means
that there are many suitable areas for growing potatoes). Approximately 90% of
the soil texture at the calculated suitability points was either optimal or
suitable, while only 1.2% of the area was scored as inadequate (Fig. 1A, Table 3). In general, plant length and yield have been reported to be long and high,
respectively, in the order clay loam, loam, and sandy loam [45, 46]. Considering
the above criteria, South Korea had a very suitable environment for potato
cultivation; in this study, approximately 50% of the regions were found to be
sandy loam. In addition to potatoes, soybean [47], broadleaf liriope [48], Asian
lizard’s tail [49], and sesame [50] grow well in sandy loam soils, indicating
that South Korean soil is suitable for cultivating various crops. In contrast,
the values for slope indicated unfavorable conditions; high slopes are unsuitable
for potato cultivation. Approximately 65% of the areas scored based on the slope
were evaluated to be unsuitable, while 20% of the areas were above suitable.
Consequently, N
Maps showing (a) soil, (b) climate, and (c) soil + climate suitability for cultivating potato.
Factors | Ratio of optimal area (%) | Ratio of suitable area (%) | Ratio of marginal area (%) | Ratio of unsuitable area (%) | *Ratio of etc. (%) | Average score of suitability (SD) |
Drainage class | 32.3 | 7.6 | 45.7 | 10.8 | 3.6 | 13.2 (5.3) |
Texture | 49.7 | 40.4 | 4.1 | 1.2 | 4.6 | 17.3 (3.2) |
Effective depth | 18.2 | 37.8 | 21.8 | 18.6 | 3.6 | 12.9 (5.0) |
Gravel contents | 31.7 | 34.8 | - | 29.9 | 3.6 | 13.6 (6.1) |
Slope | 9.0 | 10.9 | 11.0 | 65.5 | 3.6 | 8.0 (5.0) |
Growth Index | 37.6 | 45.7 | 16.7 | 0 | 23.1 (3.7) | |
* This ratio means that proportion not analyzed in the model. |
When analyzing the soil variable score and overall suitability, approximately 50% of areas in South Korea were classified as unsuitable for potato cultivation, while only 16% of the area was suitable or optimal. The Jeju-do region was found to have the best soil for potato cultivation (Fig. 2A). Jeju-do and Gwangju scored the best and worst drainage classes, respectively. In addition, Gwangju had the lowest score for soil texture in South Korea, while Sejong showed the highest score. The effective soil depth and gravel content were higher in Sejong than in any other region, but Daegu scored the lowest. A high gravel content may increase the incidence of physiological disorders in potato [54]. According to a previous study [39], reported that field crops yield high gravel content; suitable levels of gravel facilitate good drainage, which is advantageous for growth [55]. An effective soil depth is the depth at which crops can reach roots and absorb air, water, and nutrients [46]. Accordingly, the deeper the effective soil depth, the better the crop growth. In particular, the maximum yield was confirmed at 75 cm or more in sandy loam and 100 cm in loam and loam soil. However, at a lower effective soil depth, the soil volume for storing water and nutrients is small, resulting in poor growth of the roots and reduced yield [46]. For this reason, it is worthwhile to project a potential distribution of potatoes using effective soil depth and gravel content because high potato yield can be obtained with suitable site classified by the effective soil depth. In this study, an effective soil depth of more than 50 cm was found in 56% of the total area in South Korea, while in approximately 44% of the area, it was 50 cm or less. Incheon and Gangwon had the most and least suitable slope, respectively, for potato cultivation. In general, the soil conditions for potato cultivation were relatively more suitable in Sejong, Jeju-do, Incheon, and Seoul compared to other regions.
Ratio of (a) soil, (b) climate, and (c) soil + climate suitability to cultivate potato in 17 administrative districts.
In terms of the ratio of suitable cultivation areas, the Jeju-do region, which scored the highest soil suitability, had 35% of the optimal areas for potato cultivation, while Ulsan, with 4% of suitable areas, had the lowest score. The ratio of suitable and marginal areas was high in Sejong and Daejeon, and the least favorable scores were mainly observed in the eastern region, including Daegu, which showed the lowest soil suitability for potato cultivation. In contrast, only 9% of the unsuitable areas were found in Jeju-do, which was the lowest score among the different regions in South Korea.
Most regions in South Korea were predicted to be suitable for potato
cultivation, particularly in regions with high elevation and low temperatures
(Fig. 1B). However, the N
Potatoes vary considerably in yield and quality depending on the environmental conditions, but the most influential factor is temperature [20, 56, 57]. However, it was reported that annually harvested crops, such as potato, rarely suffer from the effects of external temperatures as they grow only during climatically favorable conditions [58]. In this study, only GI was used to predict climatic suitability, excluding SI, because most of the potatoes were sown and planted at specific times, indicating that it is not generally exposed to external climatic stresses. In contrast, SI needs to be considered in addition to GI in wild plants (e.g., wild ginseng). Some crops are constantly exposed to unfavorable conditions, causing climatic stresses. In CLIMEX, an SI of 100 or higher indicates an impossible condition for plant grow, so SI can be useful for finding a suitable cultivation area even though it was not used in for potato due to the above reason.
Favorable scores for N
The ratio of areas very suitable for potato cultivation based on climate and
soil conditions (S
Previous study established that there was considerable variation in crop
cultivation to bioclimatic factors in current scenarios, showing direct influence
on areas where potato cultivation in mountainous areas between 2000 and 4000
meters above sea level [61]. In South Korea, there was a region-wide difference
in N
Previous studies which predicted the growth, production, and distribution of potatoes were reported, such as global potential potato production according to climate change [27], and the potential amount of potato yield in suitable sites by seasons [62]. Most studies were modeled by analyzing climate and soil conditions [27, 51, 62], while this study related scores of five soil variables and the climate suitability of potatoes using CLIMEX. For this reason, we expect that this study provides detail information necessary for potato cultivation. In particular, since CLIMEX uses time-series climate data (monthly average temperature and rainfall), this result has demonstrated the climatic suitability of potatoes based on scientific evidence compared to the potential distribution of potatoes in previous studies [11, 13, 27]. For example, a previous study used annual climate data to confirm the potential distribution of potatoes [27], so it is difficult to obtain a dynamic potential distribution considering monthly variation of climates. In contrast, CLIMEX is a semi-dynamic model that calculates monthly temperature, precipitation, and duration of light to derive regional suitability of species, suggesting detail response to climatic condition compared to existing studies [22, 27].
Climatic conditions in South Korea are known to be unfavorable for potato
cultivation [63, 64]. Rainy season begins at the harvest time for spring potatoes
in South Korea, causing poor quality due to a high amount of precipitation, while
heat damage during sowing time of autumn potato has been observed [63, 64, 65].
Similarly, this study evaluated that approximately 80% of regions were marginal
suitable or unsuitable even though this study focused on geographic suitability
rather than time-climate relationship during cultivation [28]. However, as this
study used soil and climatic conditions which were major factor determining the
suitable area of potato cultivation, the selected regions (S
A suitable area with high climate and soil suitability for crop cultivation is important to enhance crop productivity, and both factors must be considered for field cultivation. This study investigated suitable paddy-cultivation areas for the field cultivation of potatoes in South Korea by simultaneously considering climate and soil conditions. The current results proposed that optimal potato cultivation depended mainly on soil conditions rather than climate and Jeju Island as the most suitable area having the best climate and soil conditions in South Korea. This result can be used as information for selecting potato cultivation sites with less risk and high productivity to a farmer with fallow land. Even though non-environmental factors, such as economic concerns, transportation, and distance from local markets, must be taken into consideration to choose an optimal cultivation area, this study can function as a basic evaluation because climate and soil are the most important determinants. In the future, the aforementioned non-environmental factors may be included in the evaluation step so that the most optimal and practical potato cultivation areas can be proposed.
J-YS and J-MJ equally participated in the design, analysis, and writing the manuscript. W-HL supervised the study and revised manuscript.
Not applicable.
Not applicable.
This work was supported by the Rural Development Administration (RDA) (Grant number. PJ01533101) and the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2021R1I1A3050757).
The authors declare no conflict of interest.