Ⅰ. INTRODUCTION

Alfalfa (Medicago sativa L.) hay remains a cornerstone forage for ruminant production systems because of its high crude protein and digestible fiber, but the success of haymaking hinges on the ability to dry cut forage quickly and predictably in the field. Classic and contemporary evaluations of hay systems emphasize that field-drying rate is dominated by weather—especially solar radiation—followed by vapor pressure deficit (temperature and relative humidity), wind, and soil moisture. These factors interact with crop management (conditioning, tedding, and windrow inversion) to determine both time to safe baling moisture and the magnitude of mechanical and weather-induced losses (Rotz and Chen, 1985).

In Korea, where producers increasingly seek to expand home-grown forage, haymaking is uniquely challenged by a humid climate that brings frequent rainfall and elevated humidity from late June into July–early August, followed by a secondary rainy period in mid-August to early September. Such seasonality compresses practical haymaking windows and elevates the risk of re-wetting, leaf dropout, and color degradation, particularly after midsummer (Ball et al., 2008;Koech et al., 2016). Beyond the timing of rains, climatological syntheses describe hot, humid summers with high relative humidity and heavy precipitation concentrated in June–September—conditions that are generally unfavorable for rapid field drying.

Mechanical swath manipulation can sometimes offset adverse weather by exposing wetter layers and reducing swath density. Tedding typically accelerates early drying, but its benefits are situation-dependent, while windrow inversion can increase day-of-treatment drying rates with comparatively gentle handling. However, both practices can increase leaf loss if performed at low plant moisture (Idowu et al., 2013). These global patterns are well documented in field trials and reviews from North America and Europe. (Ball et al., 2008)

Despite Korea’s rapid progress in forage agronomy, peerreviewed work quantifying alfalfa field-drying dynamics under Korean weather remains relatively limited and fragmented. Prior domestic studies have reported June field-drying periods of roughly four days and showed that conditioner use reduced drying time by about one day (Seo et al 2001;Kim et al., 2004;Park et al., 2013). Other work assessed species effects and tedding frequency in spring annuals, and compared conditioner types and tedding timing. Yet, comprehensive, season-spanning evaluations that explicitly test how dry matter yield and the frequency of tedding influence both drying trajectory and leaf dropout across Korea’s pre- and post-rainy climate periods are scarce. Therefore, this study was conducted to examine the effects of dry matter yield and tedding in seasonal hay production of alfalfa produced for an annual year.

Ⅱ. MATERIALS AND METHODS

1. Experimental design

This experiment was conducted in 2024, and alfalfa seeded in the fall of 2023. Alfalfa (SW 5615) was cultivated in the field Department of Animal Resources Development, National Institute of Animal Science Animal Science, located in Cheonan, Chungcheongnam-do, Republic of Korea. In a 1 ha alfalfa field sown at a rate of 20 kg/ha. A 3 × 3 factorial experimental design was used. The three treatment plots were dry matter yield at 3 ton/ha (3 TON), 5 ton/ha (5 TON), and 7 ton/ha (7 TON). The three tedding plots included no tedding (CON), tedding once daily (OT), and tedding twice daily (TT).

2. Alfalfa dry pattern and leaf dropout

Alfalfa was harvested at the early flowering stage in May, June, August, September, and October of 2024. Samples (1 m²) were collected before harvest to determine moisture content, and dry matter yields were calculated for 3 ton/ha (3 TON), 5 ton/ha (5 TON), and 7 ton/ha (7 TON). After harvest, 6 m2 area (2 × 3 m) was randomly designed to each plot for the experiment. From the harvested material, a 1 kg sample was collected was a 100 × 100 cm mesh net. A fixed weight was loaded for each plot, and each sample net was put in the intermediate pile of loaded alfalfa to measure the weight over time. Weights were measured every 10:00, 14:00, and 17:00 to check the dry pattern. OT was conducted tedding once at 14:00. TT was conducted tedding at 10:00 and 17:00 twice. After tedding, samples were struck 10 times with long bars for measurement of leaf dropout rate by tedding. After 100 h drying time, the tedding was stopped. In the issue of unusual matters such as rain, weight measurement was not conducted, and the experiment was performed for 4 days. After the dry pattern experiment was completed, the leaf dropout rate was determine by weighing of the leaves dropped from the mesh net.

3. Statistical analysis

Statistical analysis was conducted to Tukey test (p<0.05) using the PROC ANOVA SAS program (v. 9.4 program, 2013) for significant differences between each treatment. For the interaction effects, data were analyzed as a 3 × 3 factorial design using the PROC MIXED SAS program (v. 9.4 program, 2013).

Ⅲ. RESULTS AND DISCUSSION

1. Weather condition

Fig. 1 compares the 2024 monthly mean air temperature and precipitation with the climate normal for 1991–2020. Relative to the climate normal, the 2024 monthly mean temperature was similar in May (17.2 vs. 17.5°C) and June (22.7 vs. 21.8°C), but higher in August (27.6 vs. 25.2°C) and September (24.4 vs. 20.2°C). During the 2024 harvest period, mean precipitation was lower than the climate normal in August (66.4 vs. 299.7mm) but higher in September (318.0 vs. 146.4mm).

Fig. 2 shows differences in sunshine duration and humidity. Sunshine duration in 2024 exceeded the climate normal in May (258.1 vs. 211.6 h), June (273.7 vs. 207.3 h), and August (237.6 vs. 184.0 h). The average relative humidity in 2024 was also higher than the climate normal. Within the 2024 harvest period, the mean minimum relative humidity was low in May and June (approximately 19% and 22%), but higher in August and September (45% and 41%), with October reaching 29% (units for humidity are reported as “% in the source dataset).

2. Field dry pattern

Fig. 3 summarizes seasonal changes in the drying pattern of alfalfa stands as a function of dry matter yield, and Fig. 4 depicts changes in the drying pattern attributable to tedding. In May and June, favorable drying weather enabled the crop to reach <20% moisture (wet basis) within 100 h. According to Seo et al. (2001), the field-drying period for alfalfa harvested in June in Korea was approximately four days, and the use of mechanical conditioning shortened the drying period by at least one day. By contrast, the average of seasonal all samples during August (57.5%), September (55.0%), and October (61.9%), moisture content did not fall below 50%, indicating conditions unfavorable for producing dry hay. When contrasted on a common 100-h benchmark, season effects dominate (May–June <20% vs. August–October ≥50%), whereas yield effects are generally modest except when re-wetting events occur (August), which amplify between-yield separation (Rotz, 1993). Within each season, tedding frequency shows minimal effect under fast-drying conditions (May–June) but detectable divergence under humid or re-wet conditions (August–September), aligning with prior findings that mechanical manipulation expresses benefits early in drying or after dew/rain (Pattey et al., 1988;Kim et al., 2004). These results suggest that managers should prioritize seasonal timing and weather windows first, then adjust tedding intensity only where humidity, cloud cover, or rainfall slow evaporation.

When drying patterns were analyzed by dry matter yield, no statistically significant seasonal differences were detected except for August. The August anomaly appears to reflect rainfall events occurring just before 24 h and 76 h, which re-wetted the swaths, temporarily raising moisture content before subsequent re-drying and, consequently, amplifying between-group differences. According to Rotz (1993) and Hendry (2023), the effects of swath width and swath height on field drying are pronounced. In the present study, we focused on dry matter yield and did not explicitly control or standardize swath width or height; therefore, any yield-related effects on the drying pattern may have appeared attenuated.

Pattey et al. (1988) reported that, in alfalfa and timothy (Phleum pratense L.), differences attributable to mechanical treatments such as tedding were generally not significant. However, they also noted that early in the drying period and following rainfall or heavy dew the benefit of tedding became evident. For the tedding comparison, no statistically significant differences between each season were observed except in August and October. In August, precipitation resulted in significant treatment effects, and in October, the TT treatment showed the lowest moisture content among treatments. Notably, the only clear moisture advantage for tedding appears under cooler, drier October conditions, when brittleness is lower and solar exposure still favors evaporation, a setting in which gentle tedding can expose damp layers without excessive shatter (Pattey et al., 1988;Rotz and Shinners, 2007;Hendry, 2023). This study infers that low relative humidity, together with longer sunshine duration in May and June facilitated rapid, uniform drying, minimizing treatment contrasts. Conversely, under higher humidity and shorter sunshine duration, the effect of tedding on drying became more pronounced. These results are consistent with Kim et al. (2004), who reported that, in spring annual legumes and grasses, increasing the tedding frequency produced little additional reduction in moisture content during field drying.

3. Leaf dropout

Fig. 5 summarizes seasonal patterns of leaf dropout (leaf shatter) in alfalfa as affected by dry matter yield (TON) and tedding (TED). In May, a dry matter yield (TON) effect was detected on leaf dropout (TON; 20.2 vs. 18.0 vs. 15.5%; p = 0.050). In June (TED; 16.9 vs. 19.0 vs. 30.5%; p = 0.004) and September (TED; 24.3 vs. 26.3 vs. 29.7%; p = 0.027), a significant tedding effect was observed. Considering the pronounced June TED effect, this study infers that under favorable drying weather the susceptibility of alfalfa to leaf shatter can increase; however, because no TED effect was detected in May, this interpretation warrants further investigation.

Across seasons, TT often resulted in greater leaf dropout than CON, specifically in some 5 TON cases and in all 7 TON cases (p<0.05). Thus, higher dry matter yield appears to magnify the tedding-induced leaf shatter. Overall, these results suggest that tedding, although intended to accelerate field drying, may confer little benefit on drying time when drying conditions are suboptimal, while increasing leaf dropout.

According to Rotz and Shinners (2007), leaf shatter can be minimized when swath manipulation (e.g., inversion/raking) is performed while the forage is still relatively wet around 35–40% moisture rather than when it is near baling dryness; when handled too dry, leaf losses on alfalfa can approach ~20%. In this study, May–June swaths typically reached 35–40% moisture, whereas from August onward, moisture often failed to drop below ~50%; nevertheless, high leaf dropout was observed. We infer that rainfall and generally unfavorable drying conditions (including re-wetting) likely increased dry matter losses and exacerbated leaf shatter, consistent with prior reports that rain and late/over-dry handling markedly elevate leaf and dry matter losses during field drying.

4. Considered strategy

In our study, tedding had little effect on accelerating drying under favorable spring conditions (May–June), when low relative humidity and ample sunshine allowed the crop to approach <20% moisture within ~100 h even without tedding, yet tedding consistently increased leaf loss, with the magnitude of loss amplified at higher dry matter yields (7 ton/ha). By contrast, in October, when higher humidity and shorter sunshine duration impeded drying, the effect of tedding became apparent only after 28 h, indicating a limited, conditional benefit under humid, slow-drying environments. Taken together, these patterns suggest that the drying advantage of tedding is frequently outweighed by leaf shatter and DM loss, especially as yield and handling intensity increase. Taken together, these results suggest a “minimal-necessary tedding” strategy: (i) do not ted once leaves have entered the brittle zone (<40–45% moisture), (ii) avoid tedding during/just after re-wetting, when mechanical agitation accelerates leaf detachment, and (iii) prioritize single-pass, early-day tedding only under humid conditions where a measurable exposure benefit exists, especially at moderate yields (Pattey et al., 1988;Ball et al., 2001;Rotz and Shinners, 2007). Under May–June conditions, omitting tedding generally does not lengthen time-to-bale yet reduces leaf loss and helps retain green color. As swath moisture approaches 35–45%, alfalfa leaves become increasingly brittle; additional mechanical manipulation at lower moisture can drive shatter losses approaching 20% in the literature (Rotz and Shinners, 2007;Ball et al., 2001). Under August–October humidity and intermittent re-wetting, any tedding should be limited to a single, gentle pass while swath moisture remains roughly 50–60%, primarily to lift and aerate the lower swath layer. Repeated passes provide diminishing drying gains but compound mechanical losses (Pattey et al., 1988;Rotz, 1993). In high-yield fields, where swath density is high and handling losses escalate, avoid multi-pass tedding and instead manage for exposure at mowing.

Ⅳ. CONCLUSIONS

This study was conducted within an ongoing research effort in Korea on hay production, storage, and utilization technologies. Also, specifically investigated how seasonal variation in alfalfa dry matter yield and the number of tedding affect the field-drying pattern and leaf dropout. The effect of dry matter yield on the drying pattern was minimal in May and June, likely because low relative humidity and ample sunshine duration provided favorable drying conditions. By contrast, in October, when higher humidity and shorter sunshine duration impeded drying, the effect of tedding became evident after ~28 h of drying. In addition, higher dry matter yield was associated with greater leaf dropout across tedding treatments (TED; 24.3 vs. 26.3 vs. 29.7%, p = 0.027). Therefore, under hay-favorable weather in May–June, even at high yields, it is feasible to produce hay at ~20% moisture in about four days without performing tedding; considering leaf shatter losses and green color retention, omitting tedding is a viable option. For post-June harvests, when drying conditions are generally less favorable, ensiling is likely to be the more advantageous conservation method.