Ⅰ. INTRODUCTION
Italian Ryegrass (IRG) is a winter forage crop with early growth, high forage production and feed value, and high palatability (Choi et al., 2018). Like these characteristics, IRG is a representative forage crop, accounting for 83% of winter forage crops cultivated in Korea (MAFRA, 2022).
According to the National Institute of Meteorological Sciences (NIMS, 2018), Korea has reported that temperatures have increased by 1.4℃ and precipitation has increased by 124mm over the past 30 years (1990-2018) from the beginning of the 20th century (1912-1941). These climate changes can have an impact on changes in agricultural ecology, such as the growth period and growth characteristics of crops (Lee et al., 2008). In addition, due to these climate changes, abnormal climate tends to increase the occurrence frequency (Shim et al., 2008), which is judged to affect the forage production.
The study on the calculated damage considering abnormal climate was conducted by applying the World Meteorological Organization (WMO) standard using the machine learning model (Jo et al., 2021;Kim et al., 2022). This calculated only the damage to whole crop maize, a representative summer forage crop in Korea (Jo et al., 2021;Kim et al., 2022). So, it is necessary to calculate the damage to IRG, a winter forage crop that accounts for most of the domestic forage supply. In addition, it is believed that the calculated damage can be visually presented through a map and effectively show the damage amount of IRG to the user.
Therefore, this research was conducted to calculate the IRG damage consideration of the abnormal climate caused by the WMO scenario using a machine learning model, and the predicted damage was presented as a map.
Ⅱ. MATERIALS AND METHODS
1. Data collection
A total of 1,384 data sources of IRG were collected from the research papers in Journal of the Korean Society of Grassland and Forage Science (KSGFS), an adaptability test of imported varieties of grasses and forage crops operated by National Agricultural Cooperative Federation (NACF), the research reports on livestock experiments operated by Korean National Livestock Research Institute, and the Journal of Korean Society of Crop Science (Table 1). Table 2 shows The IRG data collected from 1986 to 2020 were the cultivation area, sowing date, harvest date, and the Dry matter yield (DMY).
The climate data used in this study collected data from 102 Automated Synoptic Observing System (ASOS) from the Weather data service-Open MET data portal (data.kma.go.kr) of the Korea Meteorological Administration. The collection of climate data is a 40-year period from 1979 to 2018 when the matched IRG data and data were collected on an hourly basis from January to December every year.
2. Processing climate data
The climate data processing for use in the yield prediction model excluded two regions (Daegu(Gi) and Gangjin-gun) with hour-unit data did not exist; five regions (Gwanaksan, Muan, Bukchuncheon, Sejong, and Hongseong)with operating under 5 years from 1986 to 2020; 8 regions (Bukgangneung, Bukchangwon, Juam, Cheomchalsan, Gochang-gun, Gosan, Seongsan, and Seongsanpo) applied close to City Hall and county offices area due to existing over 2 station in same regions. The 87 weather station data were used out of a total of 102 weather station data (Table 3).
Among the IRG cultivation areas, the data from the nearest cultivation site were applied to the place where there was no cultivation site. The climate data were used from September 1 to May 31 considering the growth period of IRG. The climate factors considered in this study were temperature, precipitation, and wind speed (Table 4). The missing value of the climate factor was supplemented by inputting the average of the time before and after the missing.
3. Yield prediction model construction
The constructed yield prediction model learned the DMY of climate conditions according to the growth period and cultivation area of IRG and can calculate DMY under various climate conditions. Eight machine learning techniques were used to construct yield prediction models: Linear, FM (Factorization Model), Deep, Deep Crossing, Wide & Deep, DeepFM, CIN (Compressed Interaction Network), and xDeepFM.
In this study, the R2 value was the highest, and the lowest Root Mean Square Error (RMSE) value was chosen to select a yield prediction model.
The climate data increased the number of data by abnormal weather, adjusted to a level similar to the number of data by normal weather, and used in the yield prediction model.
Data by abnormal weather was selected for the year in which the average of climate factors for one year deviated from the standard deviation ± 2 times of normal weather by region. Of the total 408 abnormal weather data, 390 data by abnormal weather were repeatedly learned seven times (n=2,730), which removed overlapping data (n=18), to a similar level to the data by normal weather (n=2,618). Python and Tensorflow were used to constructed yield prediction models through machine learning.
4. Calculating damage by abnormal climate
The DMY damage (Damage) according to abnormal climate was calculated through the difference between the predicted DMY in normal climate (DMYnormal) and in abnormal climate (DMYabnormal) through the yield prediction model. The damage calculation process is as follows.
Where, the normal and abnormal climate for calculating DMYnormal and DMYabnormal of IRG was set in the following way. The normal climate by region was set as the average (40-year average) of weather data by year by the IRG data collection year (1986-2020).
The abnormal climate by region was set by giving fluctuation values to climate factors (temperature, precipitation, and wind speed) in normal weather. The fluctuation value of abnormal weather was calculated after the mean and standard deviation (SD) for each climate factor and set to four levels (-2, -1, +1, and +2 times SD) of ± 1 and ± 2 times SD (Park et al., 2015). The SD by climate factor varied by region, with temperature, precipitation, and wind speed ranging from 0.28 to 1.10℃, 0.02 to 0.32 mm, and 0.04 to 0.80 m/s, respectively.
5. Mapping as damage of abnormal climate
The map was made using the QGIS (Quantum Geographic Information System) and was expressed by dividing it by domestic administrative districts. The amount of damage was divided into five classes by the level, and the more it was, the darker it was.
Among the areas for calculating the amount of damage, areas close to the city hall and county office were applied to areas where administrative districts overlap. In this process, Gosan, Gochang-gun, Bukgangneung, Bukchangwon, Seongsan, Seongsanpo, Juam, and Cheomchalsan were replaced to the Jeju, Gochang, Gangneung, Changwon, Seogwipo, Seogwipo, Suncheon, and Jindo, under map preparation, respectively.
The final area where the map of abnormal climate damage was presented was 87 areas. The damage to IRG by abnormal climate was divided into five classes by standard deviation and shown on the map.
Ⅲ. RESULTS AND DISCUSSION
1. Calculated dry matter yield of IRG by abnormal climate level
Based on the eight machine learning models, the R2 and RMSE of the yield prediction model varied from 0.6300 to 0.6758 and 0.1581 to 0.1689, respectively (Table 5). The yield prediction model used in this study was xDeepFM, which had the highest R2 and the lowest RMSE compared to other models. The DMYnormal calculated by xDeepFM ranged from 5,678 to 15,188 kg/ha and varied by region (Fig. 1). In abnormal temperatures, abnormal precipitation, and abnormal wind speed, the DMYabnormal ranged from 5,227 to 15,853 (Fig. 1A), 5,676 to 15,189 (Fig. 1B), and 4,964 to 15,511 (Fig. 1C) kg/ha, respectively, and varied by region and level.
2. Calculated damage of IRG by abnormal climate level
The damage of IRG due to abnormal temperature, abnormal precipitation, and abnormal wind speed ranged from -1,380 to 1176, -3 to 2465, and -830 to 962 kg/ha, respectively (Fig. 2). The maximum damage caused by the abnormal temperature level exceeded 1,176 kg/ha when the hourly temperature decreased (-2 level) in Gochang (Fig. 2A). As the temperature increased, the DMY of IRG tended to increase, which was the same result as Jung et al. (2020). IRG is vulnerable to cold (Choi et al., 2005), so it assumes that DMY has decreased because it is hard to over-winter under low temperatures in winter. The maximum damage caused by the abnormal precipitation was 2,465 kg/ha when the hourly precipitation increased and decreased in Daejeon (Fig. 2B). Except for some sites, such as Daejeon and Jangsu, most of the sites suffered no damage. It is judged to have little impact on precipitation when cultivating IRG, which is thought to be similar to Choi et al. (2018).
The maximum damage caused by the abnormal wind speed was 962 kg/ha when the hourly wind speed decreased (–2 level) in Gunsan (Fig. 2C). The tendency of DMY by the level of abnormal temperature and abnormal wind speed increased as the abnormal climate level increased. The amount of precipitation in which the maximum damage occurred was 0% of the DMYnormal in areas other than Jangsu and Daejeon.
It is guessed that the damage in Jangsu and Daejeon was affected by factors other than abnormal climate. In addition, it is necessary to examine whether abnormal climate using the WMO method is a weather condition that damages the DMY of IRG. Therefore, it is judged that abnormal climate needs to be set in a different method to compare and evaluate the WMO method.
3. Mapping of the damage by abnormal climate level
The map presented the DMYnormal (Fig. 3) and damage by abnormal climate using WMO methods by the level (Fig. 4). As a result of converting the damage of IRG by abnormal climate in each region into the ratio of DMYnormal, the damage was in the range of 0 to 22%. When the map of the results of this study was presented separately by the administrative district, the damage was not calculated, so there was a blank (white) area. Therefore, the maximum damage in accordance with the WMO scenario calculated by the xDeepFM-based yield prediction model was 2,465 kg/ha. In addition, as the level of abnormal temperature and abnormal wind speed increases, the DMY of Italian ryegrass increases. As for the damage to IRG, administrative districts with ASOS weather data were presented as maps (Fig. 4). In this study, it is required to review whether the damage of IRG caused by abnormal climate is significant. In the future, research on the calculation of damage to IRG needs to be additionally conducted considering the search for more abnormal climate cases and the growth stage of IRG. In addition, to compensate for the gap in the blank area, more detailed damage can be calculated by using the automatic weather system (AWS), which provides more data at points than the ASOS, although there is much-missing data and device malfunction.