Ⅰ. INTRODUCTION

Italian ryegrass (Lolium multiflorum L.) is a waterloggingtolerant annual or biennial forage crop cultivated in cropping after rice harvest in Korea, with high palatability for livestock and high feed value (Kim et al., 2016). However, in recent years, damage to Italian ryegrass productivity has increased due to the rise in abnormal climate events. Representative cases include waterlogging damage caused by frequent rainfall during the autumn sowing period, cold damage accompanied by strong winds in February after overwintering, and drought damage caused by dry winter and spring climates (Kim et al., 2015). Abnormal climate events have been intensifying seasonally in East Asia due to global warming, and the Korean peninsula is also inevitably affected by the complex interactions between the Asian continent and the Pacific Ocean (Suh et al., 2016). This increase in abnormal climate events is expected to further increase damage to domestic forage productivity (Shin, 2025). Recently, the National Institute of Animal Science conducted surveys on optimal cultivation areas and changes in yield for forage crops, along with climate impact vulnerability assessments, to ensure a stable forage supply for livestock farms. Recently, Jung (2024) reported the results of a survey on suitable agro-climatic zones and changes in forage productivity under climate conditions, and assessed the impact and vulnerability of forage to climate conditions (Phase 1) for the development of detailed implementation plans for climate change adaptation strategies for forage crops, for which a basic climate impact vulnerability assessment was conducted for both summer and winter forage crops. However, studies and reports on forage crops remain relatively scarce compared with major staple crops such as rice, and productivity-related literature and report data show large variability depending on region and cultivation timing, with low reliability (Chung et al., 2019;Shin et al., 2023;Shin, 2025). Therefore, in this study, to further supplement the climate exposure index for the climate impact vulnerability assessment results obtained in the previous study, we incorporated additional Italian ryegrass productivity data, including both recently published literature and field experimental results. Using these data, we calculated a more robust climate exposure index through correlation analyses between individual climate factors and productivity.

Ⅱ. MATERIALS AND METHODS

1. Italian ryegrass cultivation

Field experiment was conducted from 2017–2019 at the Gyeongsang National University Livestock Farm in Jinju and the experimental field in Jangheung. The experimental plot size was 6 m² (2 × 3 m), and the test cultivar Kowinearly was sown by drilling at a seeding rate of 30 kg/ha. Sowing dates were Sep 29, 2017, and Oct 11, 2018, in Jinju, and Sep 28, 2017, and Oct 23, 2018, in Jangheung. Basal fertilization was applied at a rate of N-P-K 140-120-120 kg/ha, with 30% of nitrogen applied at sowing and 70% after overwintering, and phosphorus and potassium each split equally, 50% at sowing and 50% after overwintering. No irrigation was applied. Plant height measurement and harvesting were carried out on May 25, 2018, and May 28, 2019, in Jinju, and on May 29, 2018, and May 30, 2019, in Jangheung. Fresh yield was measured in each plot, dried at 65°C for more than 72 hours to determine dry matter content, and dry matter yield was calculated by multiplying fresh yield by dry matter content.

2. Collection of Italian ryegrass productivity and climatic data

Nationwide Italian ryegrass productivity data from 1993– 2021 were provided by the Grassland and Forage Division of the National Institute of Animal Science, and data from 2021– 2023 were collected through literature review. Field experiment data were then added, and correlation analysis between Italian ryegrass productivity and climatic factors was conducted (n = 315). Nationwide meteorological data were obtained from the Automated Synoptic Observing System (ASOS) of the Korea Meteorological Administration. In cases where no weather station was located in the corresponding region, data from the nearest station within a 20 km radius were used.

3. Statistical analysis

Field experiment and published literature-based productivity data were considered as an individual sample and analyzed using Pearson’s product-moment correlation coefficient. and one-way ANOVA (Duncan, p<0.05) were performed using IBM SPSS Statistics (IBM SPSS Statistics for Windows, Version 25.0, Armonk, NY, USA).

Ⅲ. RESULTS AND DISCUSSION

1. Comparison of correlation analysis and Italian ryegrass field experiment results

To improve and refine the previously developed climate exposure indicator, this study aimed to verify whether the newly conducted correlation analysis accurately reflects actual cultivation conditions. Therefore, the results of the correlation analysis were compared with the results of Italian ryegrass field experiments conducted over two years in Jinju and Jangheung. The correlation analysis results are presented in Table 1, and the field experiment results in Table 2. The field experiment results indicated that plant height, fresh yield, and dry matter yield of Italian ryegrass significantly increased in 2018–2019 compared to 2017–2018 (Table 2). This result is considered to the relatively higher precipitation in Sep, Oct, Nov, Dec, Feb, and May in both regions during 2018–2019 compared to 2017– 2018 (Table 3, Table 4). Furthermore, the correlation analysis results also showed significant positive correlations between precipitation in Oct, Dec, Feb, and Mar and productivity. Drought during winter and spring, as well as waterlogging in autumn, have been reported to reduce Italian ryegrass productivity (Kim et al., 2015). However, waterlogging during the early growth stage can, in some cases, promote Italian ryegrass growth (Kim et al., 2022;Kim et al., 2024). Autumn precipitation has been reported to affect Italian ryegrass yield through temperature mediation, with these effects differing according to field type (paddy or upland) (Kim and Sung, 2019). The influence of autumn precipitation on Italian ryegrass growth appears to result from complex interactions with the field environment, and further investigation is required to clarify the growth mechanisms and their interactions with environmental factors.

The significant increase in Italian ryegrass production in 2018 –2019 compared to 2017–2018 is considered to be due not only to increased precipitation but also to the higher mean temperatures in Nov, Dec, Jan, and Feb (Table 5), the higher mean minimum temperatures (Table 6), and the increased growing degree days in Nov, Dec, and Feb (Table 7) compared to the previous year. Furthermore, the correlation analysis results showed significant positive correlations between productivity and the following climatic factors: mean temperature and mean minimum temperature in Oct, Dec, Jan, Feb, Mar, and Apr, as well as growing degree days in Oct, Dec, Jan, Feb, and Mar. In addition, the previous study also reported significant positive correlations between growing degree days from Jan to Apr and productivity (Jung, 2024). Temperature increase generally accelerates crop growth and affects phenology, which can lead to either increased or decreased yield (Rangaswamy et al., 2021;Rezaei et al., 2023). Therefore, the increase in winter temperatures is considered to have promoted the growth of Italian ryegrass, a winter crop with low cold tolerance (Choi et al., 2008), thereby contributing to increased productivity.

2. Climate exposure indicator derivation

The correlation analysis results were compared and validated with the field experiment results, from which the following climate exposure indicators were derived (correlation coefficient ≥ 0.4 and a p-value < 0.05) (Fig. 1). These derived indicators are considered to be applicable for Italian ryegrass climate impact vulnerability assessment.

Ⅳ. CONCLUSIONS

Italian ryegrass productivity showed a close positive correlation with precipitation before and during overwintering, temperatures in winter and spring, and growing degree days. However, some results were challenging to analyze due to complex interactions between climatic factors and field environments, and further research is needed. The climate exposure indicators derived in this study are useful basis for assessing climate impact vulnerability in Italian ryegrass, and further refinement will enable more accurate and reliable vulnerability assessments.