Ⅰ. INTRODUCTION

In South Korea, forage crops are broadly classified into summer and winter crops, with winter crops accounting for approximately 80% of the total cultivated area (NIAS, 2022). Summer forage crops, such as sudangrass and corn, are typically grown during the warmer months. However, their cultivation period overlaps with that of rice, the country’s staple food crop, making large-scale summer forage production impractical in the context of Korea’s rice-centered agricultural system. In contrast, winter forage crops are cultivated from late autumn to the following spring after rice harvest, enabling the effective use of fallow paddy fields. This system allows for extensive winter forage production, making winter crops the dominant component of Korea's forage crop structure. Among these, Italian ryegrass (Lolium multiflorum Lam.) is the most widely grown, with a cultivation area of 79,000 hectares as of 2024. Italian ryegrass is highly favored among Korean livestock producers due to its excellent overwintering ability, high productivity, and superior feed quality. Its strong shade tolerance also makes it ideal for cropping after rice, utilizing fallow paddies efficiently (Xu et al., 2020;Oh et al., 2021). Consequently, it plays a pivotal role in ensuring a stable forage supply for the livestock industry and is expected to become even more important in the future. To date, 26 cultivars of Italian ryegrass have been developed domestically, and they are classified by maturity group into extremely early, early, medium, and late maturing types. Among these, ‘Kowinearly’ (Choi et al., 2011) is reported to have the largest cultivation share due to its high productivity, excellent feed value, and strong cold tolerance. However, in response to climate change, securing cultivars across various maturity groups is increasingly critical, and it is essential to conduct comparative cultivation trials to identify superior varieties. In particular, extremely early-maturing cultivars are valuable for optimizing crop rotation systems due to their short growth duration. Extremely early-maturing cultivars developed in Korea include ‘Greenfarm’ (Ji et al., 2011), ‘Greenfarm2ho’ (Ji et al., 2013), ‘Greenfarm3ho’ (Ji et al., 2015), ‘Green call’ (Ji et al., 2018), and ‘Earlybird’ (Woo et al., 2024). Among these, ‘Greenfarm2ho’, ‘Green call’, and ‘Earlybird’ are characterized by exceptionally short maturity periods. However, since environmental factors such as soil and climate conditions can influence cultivation performance, it is crucial to evaluate these cultivars under diverse growing environments.

Therefore, the objective of this study was to investigate the agronomic traits of three extremely early-maturing Italian ryegrass cultivars (‘Greenfarm2ho’, ‘Green call’, and ‘Earlybird’) and to analyze the cultivation performance and soil physicochemical properties, in order to identify the most promising cultivar under Korean growing conditions.

Ⅱ. MATERIALS AND METHODS

This study was conducted to scientifically compare and analyze key agronomic traits such as growth characteristics and yield of extremely early-maturing Italian ryegrass cultivars developed in South Korea, and to clearly identify differences and superiority among the cultivars. The field trials were carried out over two growing seasons from September 2023 to May 2025 at the experimental forage field of the Forages Production Systems Division, National Institute of Animal Science (NIAS), located in Cheonan, Chungcheongnam-do, South Korea (latitude 36°55′54.1″N, longitude 127°06′21.9″E). The experimental materials consisted of three extremely-early maturing Italian ryegrass cultivars developed domestically: ‘Greenfarm2ho’, ‘Green call’, and ‘Earlybird’. The experiments were conducted over three years (2023–2025), maintaining identical conditions each year to ensure fair comparisons among cultivars. The experimental field consisted of fertile loam soil. Prior to sowing, the field was improved and weeded to ensure uniform growing conditions. Seeds were sown in separate plots (1 × 3 m) for each cultivar at a seeding rate of 30 kg/ha, with row spacing of 20 cm. A randomized complete block design was used with three replications. Immediately after sowing, soil firming was performed to ensure good seed-soil contact for successful establishment before winter. During the growing period, no chemical herbicides were applied; instead, weeds were removed manually. Fertilization was based on N–P₂O₅–K₂O at a rate of 200–150–150 kg/ha. Nitrogen was split-applied 50% as basal fertilizer and 50% at early spring regrowth. Phosphorus and potassium were applied entirely as basal fertilizer prior to sowing.

1. Measurement of growth characteristics and productivity

Plant height was measured in centimeters from the ground level to the highest tip of the leaf or stem. Heading date was recorded as the day when more than 40% of the tillers had emerged spikes, based on daily observations at 9 a.m. Cold tolerance, lodging resistance, and seedling establishment were rated using a 1–9 scale, where a lower value indicated better performance. Cold tolerance was assessed based on overwinter survival and regrowth; lodging resistance was evaluated during the rapid growth stage in spring; and seedling establishment was evaluated based on emergence and early growth within three weeks after sowing.

Forage productivity was assessed by harvesting the entire plot and converting fresh yield into kilograms per hectare. Dry matter yield was calculated using samples (300–400 g) collected randomly from each plot on the harvest day. The samples were dried in a forced-air oven at 65°C for 72 hours or longer to determine dry matter content. Dry matter yield was calculated using the following formula:

2. Feed value and soil chemical properties

Crude protein (CP) content of the ryegrass was analyzed using the method described by AOAC (1990). Total digestible nutrients (TDN) were calculated using the formula of Menke and Huss (1980). Acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents were determined based on the methods of Goering and Van Soest (1970). Dry matter intake (DMI), digestible dry matter (DDM), and relative feed value (RFV) were calculated using the following formulas (Goering and Van Soest, 1970):

Soil samples were collected from a depth of 20 cm, passed through a 2 mm sieve, and analyzed for pH, total nitrogen (T/N), electrical conductivity (EC), available phosphorus (P₂O₅), and organic matter content, following the standard protocols of the Rural Development Administration (1988). Soil pH and EC were measured using a pH meter and EC meter (Orion 3-Star, Thermo Scientific), respectively. Total nitrogen content was determined using the Kjeldahl method with an automatic Kjeldahl analyzer (System 1035 Analyzer). Available phosphorus was measured by the molybdenum blue method using a UV-Vis spectrophotometer (UV-1800, Shimadzu, Japan). For exchangeable cations, 5 g of soil was extracted with 50 mL of 1 N ammonium acetate solution (pH 7.0), and the solution was analyzed using an inductively coupled plasma optical emission spectrometer (ICP-OES; iCAP 7000 Series, Thermo Scientific, Cambridge, UK).

3. Statistical analysis

All statistical analyses were performed using SPSS software (ver. 12.0; SPSS Inc., Chicago, IL, USA). Continuous variables are expressed as means ± standard error of the mean (SEM). Differences among treatment means were assessed using Duncan’s multiple range test. Statistical significance was declared at p<0.05.

Ⅲ. RESULTS AND DISCUSSION

1. Weather conditions and soil characteristics

The study was conducted from September 2023 to May 2025. Meteorological data during the experimental period were compared with the 10-year historical average and are summarized in Table 1. Soil physicochemical properties of the experimental field are presented in Table 2. Monthly average temperature and total precipitation were obtained from the Agricultural Weather Information Service (RDA).

Throughout the experimental period, air temperatures were generally higher than the historical average. In particular, the average temperatures in September and October 2023 were 1.4°C and 0.2°C higher, respectively. A similar trend of elevated temperatures was observed from September to November 2024. Precipitation patterns were irregular, with significant deviations recorded. For instance, total rainfall in September increased by 40 mm in 2023 and 178 mm in 2024 compared to the historical average.

In winter forage crop systems, rainfall immediately after sowing and during early spring regrowth is known to be crucial for plant development. During the overwintering recovery period (February to March), precipitation was significantly higher than the historical average. Such abnormal conditions, including warmer temperatures and excessive rainfall, may have negatively affected plant growth, underscoring the importance of analyzing cultivar responses under varying climatic conditions.

2. Growth characteristics

Growth traits of the three cultivars (‘Earlybird’, ‘Green call’, and ‘Greenfarm2ho’) are summarized in Table 3. All cultivars showed excellent cold tolerance, disease resistance, and insect resistance, with no significant differences observed.

However, significant differences were found in lodging resistance and plant height (p<0.05). ‘Earlybird’ exhibited the strongest lodging resistance (1.00) and the tallest plant height (114 cm), both significantly superior to the other cultivars. In contrast, ‘Green call’ and ‘Greenfarm2ho’ had lodging resistance ratings of 4.33 and 4.00, respectively, and shorter plant heights of 97.0 cm and 97.7 cm.

3. Forage productivity

Forage yield was measured across two cropping seasons (2023 –2024 and 2024–2025) and are shown in Table 4. Although numerical differences were observed among cultivars, none were statistically significant. For example, in the first year, ‘Earlybird’ recorded the highest fresh yield (52,439 kg/ha), exceeding ‘Green call’ and ‘Greenfarm2ho’ by 4,666 and 4,110 kg/ha, respectively. In the second year, fresh yield differences were smaller, but ‘Earlybird’ again ranked highest (51,823 kg/ha), resulting in the highest average fresh yield across years.

Dry matter yield followed a similar trend. ‘Earlybird’ recorded dry matter yields of 10,454 kg/ha and 10,212 kg/ha in the two years, with a mean of 10,333 kg/ha. ‘Green call’ and ‘Greenfarm2ho’ recorded average dry matter yields of 10,005 kg/ha and 9,981 kg/ha, respectively. Although Ji et al. (2013) reported a higher dry matter yield (11,452 kg/ha) for ‘Greenfarm2ho’, the difference is likely attributable to variations in weather and cultivation conditions. Dry matter yield is a critical indicator that reflects moisture content and storability and is directly tied to practical benefits such as reduced logistics cost and improved feed quality. As reported by Choi et al. (2006), dry matter yield of Italian ryegrass can vary significantly by region.

The consistent performance of ‘Earlybird’ across years suggests its suitability for stable production in regions with variable climatic conditions, particularly in the central and southern regions in South Korea.

4. Feed value

The value of a forage crop is determined not only by yield but also by its nutritional composition. The feed quality of the three cultivars was assessed using CP, NDF, ADF, CA, DMI, DDM, and RFV (Table 5). ‘Earlybird’ outperformed the others across most parameters. It recorded the highest CP content (10.8%), which was significantly higher than the other cultivars (p<0.05). This is beneficial for ruminant growth and maintenance. Ertekin et al. (2021) reported CP values for Italian ryegrass ranging from 7.0% to 13.0%, depending on nitrogen fertilization, which aligns with our findings. ‘Earlybird’ also had significantly lower NDF (54.7%) and ADF (32.2%) contents, indicating higher palatability and digestibility (p<0.05). ADF is closely related to digestibility; Alemayehu et al. (2020) reported ADF ranges of 24.7% to 34.7% for Italian ryegrass, consistent with our results. ‘Earlybird’ also had the highest DMI (2.19%) and DDM (63.8%), leading to the highest RFV (109), significantly outperforming the others (p<0.05). RFV is a key indicator of forage quality, with values above 100 indicating superior nutritional quality. While rye typically scores below 100 in Korea (Li et al., 2019), ‘Green call’ achieved higher values than rye, although it remained inferior to the other two cultivars. ‘Greenfarm2ho’ showed intermediate values: CP at 10.2%, ADF at 33.0%, and RFV at 101. Crude ash ranged from 6.71% to 7.45% across cultivars, with no significant differences, though ‘Greenfarm2ho’ had the highest value, possibly influenced by soil and fertilization conditions.

Overall, ‘Earlybird’ demonstrated superior nutritional composition with high protein and low fiber content, making it a highly promising cultivar for high-quality forage production. ‘Green call’ showed lower feed value, which may limit its competitiveness unless yield is improved. ‘Greenfarm2ho’ presented balanced traits, suitable for specific production objectives.

Ⅳ. CONCLUSIONS

This study evaluated and compared the growth characteristics, forage productivity, and feed value of three extremely early-maturing Italian ryegrass cultivars (‘Earlybird’, ‘Green call’, and ‘Greenfarm2ho’) developed in South Korea, over a three-year period from 2023 to 2025. Among the cultivars, ‘Earlybird’ showed outstanding agronomic performance. It had the strongest lodging resistance and the greatest plant height, and it also recorded the highest fresh and dry matter yield. Furthermore, it exhibited superior nutritional quality, including the highest crude protein content, the lowest fiber content, and the highest relative feed value. These characteristics collectively indicate high palatability and digestibility. Overall, ‘Earlybird’ demonstrated consistent and excellent performance across all evaluation metrics, making it a promising candidate for highquality forage production in Korean livestock systems. In contrast, ‘Greenfarm2ho’ showed a balanced profile in terms of productivity and nutritional traits, making it suitable for systems seeking overall stability. Meanwhile, ‘Green call’, which showed relatively lower yield and feed value, may require more precise cultivation management to achieve optimal performance.