Ⅰ. INTRODUCTION

Italian ryegrass (Lolium multiflorum Lam.) is native to the Mediterranean region and was originally cultivated in northern Italy. It was later introduced to the United Kingdom and has since been widely grown in temperate regions (Kim, 1990). It is a leafy, highly palatable forage crop that adapts well to cool and moist conditions but grows poorly in hot and dry summers (Bagg, 2014). In Korea, Italian ryegrass was first introduced from the United States in 1955. It now accounts for more than 80% of the domestically produced winter forage crops due to its high productivity, feed value, and ease of incorporation into cropping systems. Its cultivation area has been increasing every year.

The expansion of cultivation has led to a growing demand for Italian ryegrass seeds. Various cultivars suited to local growing conditions are now being developed and distributed domestically. As of 2021, imported varieties accounted for about 69%, while domestically developed varieties made up around 31% (NIAS, 2022). However, domestic seed production remains minimal.

Due to Korea’s climatic conditions, domestically developed varieties are often contract-produced overseas and then re-imported for distribution. Although several factors contribute to this situation, one major reason is the lack of established seed production technologies. In particular, the rainy season in June hinders harvesting and drying operations, making it difficult to produce high-quality seeds. As a result, some seed production is being conducted in southern regions, but expansion remains limited. Moreover, as seen in recent cases, overseas seed production faces potential risks such as import restrictions due to quarantine issues. This could lead to serious difficulties in securing a stable seed supply (NIAS, 2022).

Fortunately, various studies related to the domestic production of Italian ryegrass seeds have recently been conducted, particularly in the southern and Gangwon regions. In particular, the development of ultra-early maturing cultivars that allow for earlier seed harvesting (Ji et al., 2018) has led to a diversification of research in seed production. Comparative studies have been conducted on the seed and straw productivity of the ‘Greencall’ variety based on harvest time (Li et al., 2024), nitrogen fertilization rate (Yu et al., 2024), row spacing (Li et al., 2022), and seeding rate (Jeong et al., 2022). Additionally, in the mountainous areas of Gangwon, comparative studies have been carried out on seed productivity of spring-sown Italian ryegrass with different row spacings (Jeong et al., 2021), cultivars (Jeong et al., 2020), and seeding rates (Jeong et al., 2021).

However, no research has been conducted on seed production techniques for fall-sown Italian ryegrass in the mountainous areas of Gangwon. Therefore, the present study was conducted to investigate the effects of harvest timing on the seed and straw productivity of an ultra-early maturing Italian ryegrass variety sown in the fall in the mountainous regions of Gangwon.

Ⅱ. MATERIALS AND METHODS

1. Cultivation of italian ryegrass

The field experiment to determine the optimal harvest time for Italian ryegrass seed production in the Gangwon region was conducted at the experimental plots of Seoul National University's Pyeongchang Campus, located in Pyeongchang (N 35°19′58″, E 128°35′01″). Italian ryegrass was sown on September 23, 2021. The previous crop grown on the field was corn.

The soil exhibited slightly acidic properties (pH 6.48), with a relatively high organic matter content (73.53 g/kg) but a low total nitrogen content (0.19%). The available phosphorus concentration was 232 mg/kg, which was somewhat higher than that typically observed in paddy soils (Table 1).

For seed production, the Italian ryegrass variety 'Greencall,' developed by the National Institute of Animal Science (NIAS), was used. Cultivation followed standard practices: 20 kg of seeds per hectare were seeding at 20 cm row spacing. Fertilization was conducted on the day of sowing (September 23, 2021). Phosphorus and potassium fertilizers were applied evenly across the entire field at a rate of 120 kg/ha. Nitrogen fertilizer was applied at 90 kg/ha, split evenly between the sowing date and the following spring. Each plot measured 6 m² (2 m × 3 m), and the experiment was arranged in a randomized complete block design with three replications.

2. Harvesting of italian ryegrass

The Italian ryegrass for seed production was harvested at 30, 40, 50, and 60 days after heading. Before seed harvest, agronomic traits such as plant height, overall growth status, disease resistance, lodging resistance, and overwintering rate were investigated. Harvesting was carried out by excluding the border rows and collecting the central four rows to measure yield. Disease and lodging resistance were assessed visually using a 1 to 9 scale, where 1 represented the strongest resistance and 9 the weakest.

The harvested samples were immediately separated into seeds and straw, and the yield of each was measured. The seeds were spread out and dried in the shade, while the straw was dried in a 65 °C forced-air drying oven for 72 hours to determine dry matter content. Dry matter yield was calculated by multiplying the measured yield by dry matter content and converted to a per-hectare basis.

The number of spikes per m² was determined using a 20 × 30 cm quadrat installed in each plot on the sowing day. The spike count within the quadrat was then extrapolated to per m² values.

3. Evaluation of seed characteristics

Seed characteristics were evaluated using a portion of the dried seeds. Ten individual plants were selected from each plot for analysis. The total spike length was measured from the node to the tip of the spike. The number of seeds and their weight per spike were also measured. The thousand-seed weight was determined by weighing 1,000 seeds separated from the spike. Additionally, seed dry matter content was measured after drying at 65 °C in a forced-air drying oven for 72 hours.

4. Feed value analysis

For analyzing the feed value of the straw, samples collected on the harvest day were dried for more than 72 hours at 65 °C in a forced-air drying oven. After initial grinding using an electric blender, the samples were further ground using a 20-mesh mill. The prepared samples were stored in double-sealed plastic containers, kept away from direct sunlight, and used for subsequent analysis.

Crude protein content was analyzed using the Dumas method (1826). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents were determined following the method of Goering and Van Soest (1970).

Total digestible nutrient (TDN) content was estimated using ADF content, based on the formula by Holland et al. (1990): TDN (%) = 88.9 − (0.79 × ADF %).

Relative feed value (RFV) was calculated by first estimating the digestible dry matter (DDM) using ADF content: % DDM = 88.9 − (ADF % × 0.779), and estimating dry matter intake (DMI) from NDF content: % DMI = 120 / NDF %. RFV was then calculated as: RFV = (% DDM × % DMI) / 1.29.

In vitro dry matter digestibility (IVDMD) was measured using the method of Tilley and Terry (1963), as modified by Moore (1970). Rumen fluid for the test was collected from Hanwoo cattle that were fed roughage ad libitum, prior to the morning feeding.

5. Weather conditions

Weather data (temperature and precipitation) during the experimental period are shown in Fig. 1. Overall, temperatures were similar to the average year, although January and February 2022 were colder, while March and April were warmer than usual.

Heavy rainfall occurred in early September 2021, maintaining optimal soil moisture for sowing. Precipitation during the winter months was minimal. Although rainfall was higher than average in late March and early April, overall precipitation levels were low thereafter. Notably, there was a heavy downpour of 240 mm in late June.

6. Statistical analysis

Statistical analysis was conducted using the SAS package program (version 6.12, 2003). Analysis of variance (ANOVA) was performed, and treatment means were compared using the Least Significant Difference (LSD) test.

Ⅲ. RESULTS AND DISCUSSION

1. Growth characteristics

The growth characteristics of Italian ryegrass according to harvest timing after heading in the Gangwon region are presented in Table 2. Plant height was longest at 93.0 cm when harvested 30 days after heading and tended to decrease as harvest was delayed. There was no significant difference in plant height between 30 and 40 days after heading; however, plant height significantly decreased at 50 days (82.4 cm) and 60 days (80.2 cm) compared to earlier harvests (p<0.05). Following heading, the plant shifts to reproductive growth, and assimilates are allocated to seed development, which limits further elongation of plant height.

Lodging increased with delayed harvest, and complete lodging was observed at 60 days after heading. In terms of disease resistance, no major issues were observed until 40 days after heading, but leaf blight was noted at the final harvest date. The reduced incidence of disease in Gangwon Province is likely attributable to its lower temperatures relative to the southern regions. Nevertheless, as plant growth advances and senescence sets in, disease resistance diminishes, leading to the occurrence of leaf diseases. Meanwhile, most plants were found to have overwintered successfully, indicating good winter hardiness. Li et al. (2024) reported similar findings in a southern region study, where lodging increased as time after heading progressed, with all plants lodging after 40 days.

2. Seed characteristics

The effects of harvest timing on the seed characteristics of Italian ryegrass in the Gangwon region are shown in Table 3. The average spike length was 50.72 cm, with the longest spikes observed in the plot harvested 40 days after heading and the shortest in the plot harvested 60 days after heading (p<0.05).

The number of seeds per spike decreased sharply as harvest was delayed. In particular, the 60-day harvest treatment showed a drastic reduction to 76 seeds per spike, compared to 163 seeds at 40 days after heading (p<0.05). However, there was no significant difference in seed number between the 30- and 40-day harvest treatments. According to Li et al. (2024), the decrease in seed number after heading was attributable to substantial losses from shattering. The findings of the present study are likely to be explained by the same reason.

The weight of seeds per spike was highest in the 40-day harvest group and decreased with delayed harvest. The 30-day harvest treatment showed significantly lower seed weight per spike than the 40- and 50-day treatments. This indicates that seed weight was relatively low during the initial stage of development, whereas nutrient accumulation in the later stage contributed to an increase in seed weight. In a similar harvest timing study conducted by Li et al. (2024) in the southern region, the average seed weight per spike was 0.39 g, which is lower than the result observed in this study (0.542 g).

There were no significant differences in the number of spikes per unit area according to harvest timing (p>0.05). Even at 60 days after heading, the spike density was 1,853 spikes/m², showing less variation with time compared to the southern region (763 spikes/m²).

The thousand-seed weight was highest in the 50-day harvest group at 4.628 g and lowest in the 60-day group at 2.803 g, indicating an increase in thousand-seed weight up to 50 days after heading, followed by a decline. In the southern region study on row spacing by Li et al. (2022), the thousand-seed weight at 60 days after heading was 2.1807 g, slightly lower than the 2.803 g observed in this study. Meanwhile, Yu et al. (2024) reported a thousand-seed weight of 3.6217 g for the Greencall variety harvested 30 days after heading, which is similar to the result of this study (3.701 g).

3. Seed and straw yield

Seed productivity of Italian ryegrass according to harvest timing is presented in Table 4. Seed dry matter content increased consistently with harvest delay, reaching 72.07% at 60 days after heading. Choi et al. (2025) reported that, in the southern region, when Italian ryegrass was harvested on June 11, the seed moisture content was 48.9%, and three days later (June 13), it dropped to 26%. Similarly, in this study, the moisture content at 50 and 60 days after heading was 44.71% and 27.93%, respectively, showing a comparable trend.

Ling et al. (2023), in a seed production study of the forage crop Kengyilia melanthera, observed that while seed yield increased with delayed harvest, seed moisture content decreased, and beyond 27 days after flowering peak, moisture levels dropped below 40% with minimal further change.

In terms of seed yield, productivity increased with the number of days after heading, but declined after 60 days. The average yield of air-dried seeds was 3,145 kg/ha, and the highest yield was observed at 50 days after heading (4,301 kg/ha), which was significantly higher than other treatments (p<0.05). Although seed yield increased with delayed harvest, it declined at 60 days after heading, likely as a result of losses caused by seed shattering.

Meanwhile, Li et al. (2024) reported the highest seed yield in the 30-day post-heading harvest group in a southern region trial, with an average yield of 3,405 kg/ha—slightly higher than the average in this study. However, in their study, no significant differences in yield were found between treatments (p>0.05), though the 30-day group yielded the most seeds, differing from the results of this study.

Meanwhile, the dry matter content of the seed straw increased steadily with delayed harvest; however, in the 60-day harvest group, the content slightly decreased due to rainfall. Although the fresh yield of seed straw did not show a clear trend across harvest timings, the highest yield was observed at 50 days after heading. Similarly, dry matter yield increased continuously up to 50 days after heading but decreased at 60 days. The dry matter yield at 50 days after heading was 7,778 kg/ha, indicating high productivity of seed straw even after seed harvesting.

Li et al. (2024) also reported from a southern region seed production study that the dry matter yield of seed straw increased with time after heading and reached its peak at 50 days, consistent with the findings of this study.

4. Feed value of seed straw

The feed value of the seed straw after harvest is shown in Table 5. The average contents of ADF, NDF, CP, IVDMD, and TDN were 38.98%, 66.04%, 9.23%, 55.29%, and 58.11%, respectively. As the harvest timing was delayed, the fiber content increased significantly, resulting in higher ADF and NDF values. In contrast, CP (crude protein), IVDMD (in vitro dry matter digestibility), and TDN (total digestible nutrients) contents significantly decreased (p<0.05).

Consequently, the relative feed value (RFV) was highest in the 30-day post-heading harvest group at 99 and declined steadily over time, dropping to 71 in the 60-day harvest group. Similarly, Li et al. (2024) reported in their southern region harvest timing trial that RFV decreased with delayed harvesting, with an average RFV of 91. Wang et al. (2024), in a nitrogen fertilization study in the southern region, also found that the RFV of seed straw harvested around 30 days after heading was 97, showing results consistent with those of this study.

The feed value of seed straw after harvest is shown in Table 5. As harvest was delayed, the fiber content increased significantly, resulting in a notable rise in ADF and NDF contents, while CP (crude protein), IVDMD (in vitro dry matter digestibility), and TDN (total digestible nutrients) contents significantly decreased (p<0.05).

Consequently, the relative feed value (RFV) was highest at 99 in the plot harvested 30 days after heading and declined steadily with time, reaching as low as 71 in the 60-day harvest group. Similarly, in a harvest timing study conducted in the southern region, Li et al. (2024) reported that RFV decreased with delayed harvest, with an average value of 91. Wang et al. (2024) also reported comparable findings in a nitrogen fertilization study in the southern region, where the RFV of seed straw harvested around 30 days after heading was 97— results consistent with those of the present study.

Ⅳ. CONCLUSIONS

This study was conducted to determine the optimal harvest time for seed production of the ultra-early maturing Italian ryegrass variety ‘Greencall’ in the Gangwon region. The results showed that harvesting around 50 days after heading yielded the highest seed production as well as the highest yield of seed straw. Therefore, based on these findings, it can be concluded that the optimal harvest time for fall-sown Italian ryegrass for seed production in the mountainous areas of Gangwon is 50 days after heading.