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ISSN : 2287-5824(Print)
ISSN : 2287-5832(Online)
Journal of The Korean Society of Grassland and Forage Science Vol.45 No.3 pp.162-169
DOI : https://doi.org/10.5333/KGFS.2025.45.3.162

Impact of Nitrogen Application on Seed and Straw Productivity of Italian Ryegrass (Lolium multiflorum Lam.) ‘GreenCall’ in Gangwon Region

Wu Li Zhuang1, Xaysana Panyavong1, Yan Fen Li1, Ki Jun Choi2, Jong Geun Kim1,2*
1Graduate School of International Agricultural Technology, SNU, Pyeongchang 25354, Republic of Korea
2Research Institute of Eco-friendly Livestock Science, GBST, SNU, Pyeongchang 25354, Republic of Korea
* Corresponding author: Kim Jong Geun, Graduate School of International Agricultural Technology and GBST, Seoul National University, Pyeongchang 25354, Republic of Korea. Tel: +82-33-339-5728, Fax: +82-33-339-5727, E-mail: forage@snu.ac.kr
August 11, 2025 September 24, 2025 September 24, 2025

Abstract


The experiment was conducted to determine the effects of nitrogen fertilizer levels on seed production of Italian ryegrass (Lolium multiflorum Lam.) in mountainous regions of Gangwon Province. The 'Green Call' variety of Italian ryegrass was sown in Pyeongchang, Gangwon in September 2021. The experiment consisted of three nitrogen application levels (100, 120, and 140 N kg/ha) and was arranged in a randomized complete block design with three replications. Harvest was carried out on June 28. The plant height was tallest in the 140 N kg/ha treatment, but the difference was not statistically significant. Lodging resistance, disease resistance and winter hardiness showed no significant differences among treatments, although severe lodging occurred in all plots. The average spike length was 54.77 cm, with no significant difference among treatments, while the number of seeds per spike was highest in the 100 N kg/ha treatment. Seed yield increased with higher nitrogen levels, with an average of 2,820 kg/ha (based on air-dry weight). The average dry matter content of seeds and straw was 56.70% and 38.80%, respectively, with no significant differences among treatments. The average dry matter yield of residual straw after seed harvest was 4,144 kg/ha, with the highest yield observed in the 120 N kg/ha treatment. Meanwhile, the feed value of the harvested straw did not differ significantly among treatments. The average contents of ADF, NDF, CP, IVDMD, and TDN were 43.04%, 70.63%, 8.65%, 52.77%, and 54.88%, respectively. In conclusion, the optimal nitrogen fertilization level for Italian ryegrass seed production through autumn sowing in the mountainous areas of Gangwon Province was found to be 120 N kg/ha.


Green Call , Nitrogen application , Italian ryegrass , Quality , Seed yield

초록

    Ⅰ. INTRODUCTION

    The localization of Italian ryegrass seed production, which is currently largely dependent on imports, can not only reduce foreign currency expenditure but also enhance adaptability to local environmental conditions, leading to more stable production. Recently, due to its high productivity and feed value, the cultivation area of Italian ryegrass has been steadily increasing, now accounting for approximately 80% of all winter forage crops (NIAS, 2017). As a result, the demand for seeds is also rising. However, domestic seed production is limited for various reasons, leading to reliance on imports.

    Efforts are underway to overcome this limitation, particularly through the development of extremely early-maturing varieties, which allow seed harvesting to take place before the monsoon season, making domestic production more feasible. Although new varieties with various maturities are being developed, it has been widely believed that domestic seed production is unfeasible because the seed harvest period typically overlaps with the monsoon season. However, the development of extremely early-maturing varieties has cautiously raised the possibility of shifting the seed harvest period to before the monsoon, thus enabling domestic seed production.

    Nitrogen is one of the most essential nutrients for plant growth (Cameron et al., 2013). Nitrogen application contributes to increased yield per unit area and enhances seed production in most annual crops. However, excessive nitrogen use can increase production costs and negatively impact the environment. Therefore, determining the optimal nitrogen application rate is crucial for sustainable agriculture (Rochester et al., 2007;2009;Zhang et al., 2012).

    Research on nitrogen fertilization for seed production has been conducted, including studies on optimal nitrogen levels for Italian ryegrass seed production in southern regions (Yu et al., 2024), seed yield of tall fescue (Lee et al., 2015), and nitrogen requirements at different planting densities of Italian ryegrass (Kim et al., 2013). Internationally, various studies have also been conducted, such as on optimal nitrogen application rates (Bae et al., 2021), spring nitrogen application for Italian ryegrass seed production (Simic et al., 2012), autumn nitrogen fertilization for timothy seed production (Shi et al., 2017), and the effect of nitrogen rates on seed productivity of Italian ryegrass (Tim et al., 2017). Based on these studies, it was determined that research on the optimal nitrogen rate for seed production of extremely early-maturing Italian ryegrass varieties is necessary in Korea.

    Therefore, this study was conducted to determine the optimal nitrogen application rate for seed production of extremely early-maturing Italian ryegrass varieties in the Gangwon region.

    Ⅱ. MATERIALS AND METHODS

    1. Cultivation of Italian ryegrass

    The experiment to determine the optimal nitrogen application rate for seed production of Italian ryegrass was conducted at the Pyeongchang Campus of Seoul National University, located in Pyeongchang, Gangwon Province (N 35°19′58″, E 128°35′0 1″). The same field used in the study by Kim et al. (2025) was used for this trial, where maize had been grown previously. Italian ryegrass was sown on September 23, 2021, and seed harvest was conducted on June 28, 2022.

    The physicochemical properties of the soil showed a slightly acidic pH (6.48), with a relatively high organic matter content of 73.53 g/kg and a low total nitrogen content of 0.19%. Available phosphorus was 232 mg/kg, which was slightly higher than that typically found in paddy soils (Table 1).

    The Italian ryegrass used for seed production was the ‘GreenCall’ cultivar, developed by the National Institute of Animal Science. The sowing method followed a seeding rate of 20 kg/ha with a row spacing of 20 cm using drill sowing. Nitrogen fertilizer was applied at three levels—100, 120, and 140 kg/ha—on the sowing date (September 23, 2021). Phosphorus and potassium fertilizers were each applied at 120 kg/ha evenly across the entire field. Nitrogen fertilizer was split: half applied at sowing and the remaining half in 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

    Italian ryegrass for seed production was harvested on June 28. Before harvesting, growth characteristics were assessed, including plant height, growth status, disease resistance, lodging resistance, and winter survival rate. For yield measurement, the central four rows of each plot were harvested, excluding the borders. Resistance to disease and lodging was evaluated visually using a 1 to 9 scale, where 1 indicated the strongest resistance and 9 the weakest.

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

    The number of spikes per square meter was estimated by placing a 20 × 30 cm quadrat in each plot on the sowing day, counting the spikes within the quadrat at harvest, and converting the count to per square meter.

    3. Evaluation of seed characteristics

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

    4. Forage value analysis

    For the analysis of straw forage value, samples collected on the harvest day were dried in a 65°C forced-air oven for more than 72 hours, then ground first using an electric mixer, followed by a 20-mesh mill. The ground samples were stored in double-capped plastic containers, kept away from direct sunlight, and used for analysis.

    Crude protein (CP) content was analyzed by the Dumas method (1826). NDF (neutral detergent fiber) and ADF (acid detergent fiber) were determined following the method of Goering and Van Soest (1970). Total digestible nutrients (TDN) were estimated based on ADF content using the formula by Holland et al. (1990):

    • TDN (%) = 88.9 − (0.79 × ADF %).

    Relative feed value (RFV) was calculated by estimating digestible dry matter (DDM) and dry matter intake (DMI) as follows:

    • % DDM = 88.9 − (ADF % × 0.779),

    • % DMI = 120 / NDF %,

    • RFV = (% DDM × % DMI) / 1.29.

    In vitro dry matter digestibility (IVDMD) was measured using the modified method of Tilley and Terry (1963), as revised by Moore (1970). Rumen fluid used in the analysis was collected from Hanwoo cattle fed freely on roughage, sampled before morning feeding.

    5. Weather conditions

    The weather conditions (temperature and precipitation) during the experimental period are shown in Fig. 1. Temperatures were generally close to the average, though January and February 2022 were colder, while March and April were warmer than usual. In early September 2021, heavy rainfall ensured adequate soil moisture at sowing. There was minimal precipitation during the winter. Rainfall was higher than average in late March and early April, but was limited thereafter. Notably, there was a torrential downpour of 240 mm in late June.

    6. Statistical analysis

    Statistical analysis was performed using the SAS software package (Version 8, 2003). Analysis of variance (ANOVA) was conducted, 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 under different nitrogen application rates are presented in Table 2. Plant height was not significantly affected by nitrogen levels, with an average height of 87.6 cm. The heading date was April 18, showing no differences among the nitrogen treatments. There were also no significant differences in lodging resistance, disease resistance, or winter hardiness among treatments (p>0.05). However, at the time of seed harvest, the average lodging resistance score was 6.8, indicating that most plants had lodged.

    Similar findings were reported by Yu et al. (2024) in a study on optimal nitrogen rates for seed production of Italian ryegrass in southern regions, where no significant differences were found in plant height, heading date, lodging, disease resistance, or winter hardiness—thus supporting the conclusions of this study. However, the average plant height in the southern region study was 95.8 cm, which was taller than that observed in the Gangwon region.

    In general, plant height tends to increase with higher nitrogen application. Muhammad et al. (2022) reported that in wheat, plant height increased with nitrogen application rates ranging from 0 to 300 kg/ha, compared to the control, with no further increase beyond 225 kg/ha. Similar trends have been observed in nitrogen application studies across various grass species, where plant height increased with higher nitrogen levels (Back et al., 2013;Kim et al., 2015;Tomple et al., 2021).

    2. Seed characteristics

    The effects of nitrogen application rates on seed characteristics are shown in Table 3. There were no significant differences in spike length among nitrogen treatments (p>0.05), with an average spike length of 54.77 cm. The shortest spikes were observed in the 140 kg/ha treatment. The number of seeds per spike decreased as nitrogen application increased, and seed weight per spike was also lowest at the highest nitrogen level. However, these differences were not statistically significant (p>0.05).

    The thousand-seed weight (TSW) was highest in the lower nitrogen treatments (100 and 120 kg/ha), while the number of spikes per unit area was lowest in these lower nitrogen treatments. In the nitrogen application trial conducted by Yu et al. (2024) in the southern region, spike length was also shortest in the 140 kg/ha treatment, although the differences among treatments were not significant. The highest number of seeds per spike was observed in the 120 kg/ha treatment, and seed weight was lowest at 140 kg/ha, which is consistent with the results of this study.

    In contrast, Shi et al. (2017) reported that in a Leymus chinensis seed production trial, the number of inflorescences and thousand-seed weight increased with higher nitrogen application in autumn, whereas spring nitrogen application had no significant effect on inflorescence number. However, in this study, the number of spikes per square meter was highest in the lowest nitrogen treatment (100 kg/ha), and the thousandseed weight was also greater in this treatment.

    Ryu et al. (2016), in their study on rye seed production, reported that spike length increased with higher nitrogen application, which contrasts with our findings. However, they also observed that the number of spikes per unit area increased with nitrogen level, which is consistent with the present study.

    Wang et al. (2022), in a seed production study of Elymus sibiricus in the Xinjiang region of China, reported that the thousand-seed weight increased with nitrogen levels from 0 to 120 kg/ha but peaked at 90 kg/ha before decreasing. Similarly, in this study, the 100 kg/ha treatment produced the heaviest seeds, while the 120 and 140 kg/ha treatments resulted in lighter seeds, showing a comparable trend.

    3. Productivity of seed and straw

    Seed productivity under different nitrogen application rates is presented in Table 4. The average seed dry matter (DM) content at harvest was 56.70%, with no significant differences among treatments. Fresh and dry seed yields averaged 4,341 kg/ha and 2,453 kg/ha, respectively. Although seed yield tended to increase with higher nitrogen application, the differences were not statistically significant (p>0.05). On an air-dried basis, the highest seed yield was observed in the 140 kg/ha treatment (2,960 kg/ha), while the lowest was in the 100 kg/ha treatment (2,718 kg/ha).

    In a nitrogen application trial in the southern region by Yu et al. (2024), seed yield (adjusted to 13% moisture content) significantly increased with nitrogen rate, although there was no significant difference between 120 and 140 kg/ha treatments. In this study, no significant difference was found between the 100 and 120 kg/ha treatments. Similarly, Shi et al. (2017) reported that seed productivity of Leymus chinensis increased with nitrogen level, particularly when nitrogen was applied in autumn rather than spring.

    Simic et al. (2012), in a nitrogen application study for Italian ryegrass seed production in Siberia, found that the highest seed yield was achieved with a spring top-dressing of 50 kg/ha nitrogen (with 80 kg/ha applied in autumn). Increasing nitrogen beyond 100–150 kg/ha did not improve seed yield. In fact, higher nitrogen caused lodging and seed drop, leading to reduced harvestable yield. Bae et al. (2021), using a regression model based on a reclaimed land trial, estimated the maximum seed yield at 102 kg/ha nitrogen application, with yields declining beyond that point, recommending approximately 100 kg/ha as the optimal rate.

    Characteristics of the straw remaining after seed harvest are shown in Figs. 2 and 3. The average dry matter content of the straw was 38.80%, with a tendency to increase as nitrogen rate increased, though not significantly (p>0.05). Dry matter yield was significantly higher in the 120 kg/ha treatment (14,112 kg/ha) and lowest in the 100 kg/ha treatment (8,560 kg/ha). The overall average DM yield was 4,144 kg/ha, with the 120 kg/ha treatment yielding significantly more (p>0.05).

    In Yu et al. (2024), the dry matter content of straw decreased with increasing nitrogen, with an average of 62.19%, which is higher than in the present study. Simic et al. (2012) also reported a wide annual variation in straw yield, ranging from 1,856 to 6,746 kg/ha, with a trend toward higher yield under greater nitrogen application. However, in this study, straw yield in the 140 kg/ha treatment was lower than that in the 120 kg/ha treatment.

    Hejduk and Macháč (2019) reported that the post-harvest straw of Italian ryegrass had a dry matter content ranging from 40.82% to 43.64%, with productivity at 6.00 ± 1.76 t/ha, indicating higher dry matter content and yield than in the present study.

    4. Forage value of straw

    The residual straw generated as a by-product after seed production of Italian ryegrass has good potential as a forage resource. The forage value of the post-harvest straw under different nitrogen application rates in the Gangwon region is shown in Table 5. The average values for ADF, NDF, CP, IVDMD, TDN, and RFV were 43.04%, 70.63%, 8.65%, 52.77%, 54.88%, and 73, respectively.

    ADF and NDF contents were higher than those reported in the southern region trial by Yu et al. (2024), while crude protein content, in vitro dry matter digestibility (IVDMD), and TDN content were lower, indicating reduced forage quality. Consequently, the TDN and RFV values, which are estimated based on ADF and NDF contents, were also lower—54.88% and 73, respectively.

    The average IVDMD was 52.77%, which is lower than the values reported in other studies (Yu et al., 2024;Li et al., 2022;Jeong et al., 2022). The RFV was also relatively low.

    Table 5 The content of crude protein (CP), ADF (acid detergent fiber), NDF (neutral detergent fiber), IVDMD (in vitro dry matter digestibility), TDN (total digestible nutrient) and RFV (relative feed value) depending on the nitrogen fertilizer application

    Ⅳ. CONCLUSIONS

    This study was conducted to determine the optimal nitrogen fertilizer level for seed production of the ultra-early maturing Italian ryegrass variety ‘Greencall’ in the Gangwon region. The results showed that nitrogen fertilizer application did not significantly affect seed production, but straw production was highest at 120 N kg/ha. Therefore, based on these results, 120 N kg/ha is recommended as the optimal nitrogen fertilizer rate for fall-sown Italian ryegrass seed and straw production in the mountainous Gangwon region.

    Ⅴ. ACKNOWLEDGEMENTS

    This study was financially supported by the Cooperative Research Program for Agriculture Science & Technology Development (Project No. RS-2023-00228804).

    Figure

    KGFS-45-3-162_F1.jpg

    Monthly meteorological data around the experimental periods in Pyeongchang.

    KGFS-45-3-162_F2.jpg

    Dry matter content of straw depending on the nitrogen application rate.

    KGFS-45-3-162_F3.jpg

    Fresh and dry matter yield of straw depending on the nitrogen application rate.

    Table

    Chemical properties of soil in experimental field

    * OM : Organic matter, TN : Total nitrogen, CEC : Cation exchange capacity.

    The agronomic characteristics of Italian ryegrass depending on the nitrogen application rate

    * 1: good(strong), 9: bad(weak).
    * NS : not significant.

    The characteristics of the spikes and the seed depending on the nitrogen application rate

    * NS : not significant.

    Fresh and dry matter(DM) yield of seed depending on the nitrogen application rate

    * NS : not significant, Air-dry : 13% moisture basis.

    The content of crude protein (CP), ADF (acid detergent fiber), NDF (neutral detergent fiber), IVDMD (in vitro dry matter digestibility), TDN (total digestible nutrient) and RFV (relative feed value) depending on the nitrogen application rate

    * NS : not significant.

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