Effects of Harvest Time on the Yield and Forage Value of Winter Forage Crops in Reclaimed Lands of Korea

This research was conducted to select the most suitable winter forage crop varieties for silage in reclaimed land located in the Midwest of Korea by investigating the soil environment, crop growth characteristics, dry weight, and forage value according to growth stage. The slightly alkalescent soil was characterized by a pH of 7.41–7.84, by an electrical conductivity (EC) of 1–2.5 dS/m, and by 440–934 mg/kg of available phosphate. Barley showed the highest chlorophyll content in the heading stage and milk stages, while oats and triticale reached the highest content in the milk and dough stage. In both years, triticale achieved the highest leaf area index (LAI), reaching 4.3–4.8. In addition, triticale showed the highest percentage of dry matter and the highest dry weight in the milk stage. Forage value was the best in the heading stage for all cereal crops; however, its quality decreased as the growth stage proceeded. This study suggests cultivating triticale, which showed high adaptability to reclaimed soil and climatic conditions, as well as good growth and dry weight when harvested between the milk and dough stages. These results indicate that triticale can be cultivated all year round in salty soil and these data can be useful to increase forage production in reclaimed soil.


Introduction
Soil salinization is a global environmental problem that negatively affects crop yield and thus poses a threat to the world's food security [1]. Soil salinity is a major global problem because it negatively affects agricultural productivity and sustainability. In addition, soil salinity is spreading worldwide in over 100 countries, and no continent is entirely free from salinity [2]. Since mountains cover 65% of Korean territory, the cultivable land area is relatively small. For this reason, a land reclaiming project was launched as part of the national economic development plan in the 1960s, turning into a large-scale development system later in the 1970s [3].
During prolonged dry weather, water in the soil evaporates, and the salt contained in lower layers comes up to the soil's surface by capillarity and eventually damages crops. Furthermore, the soil's lack of chemical components and decreased air permeability and transmissibility make soil drainage difficult [4]. With increased irrigation, growth gets better, but a constant lack of water leads to water stress, with water absorption in the roots not being able to catch up with stomatal transpiration of leaves, which leads to a cessation of root growth and a decreased efficiency in nutrient absorption [5]. In addition, an increase in soil Na + and Mg 2+ content damages the structure of plant cells and impairs photosynthesis, inhibiting the production of chlorophyll [6]. In addition, an excessive concentration of various ions combined with high salinity causes enzyme inhibition, changing the metabolism and physiological functions of the plant. Salinity also increases competitive absorption between Na and K [7,8].

Agronomy
From October 2018 to May 2020, this experiment progressed for two years in Seokmun reclaimed land, Songsan-myeon, Dangjin-si, Chungcheongnam-do (36 • 58 45 N, 126 • 39 55 E). The cereal crops used in this experiment were artificially crossbred by the National Institute of Crop Science and fostered by the pedigree breeding method. As a result, the cereal crops used in the investigation were salinity tolerant compared to other crops and resistant to cold weather. For this reason, barley, triticale, and oats, were selected (Table 1) because they are cultivatable in winter on reclaimed land. The experiment was conducted on 16 October 2018 and 17 October 2019, respectively, in an area of 0.1 ha, and each cereal crop was planted through drill seeding at a concentration of 220 kg/ ha. As for the fertilizer, the amount for barley cultivation on paddy fields, N-P 2 O 5 -K 2 O = 91-74-39 kg/ha, was the standard. In addition, phosphorus and potassium were added as basal fertilizer for each field, and no pesticides and herbicides were used. The harvesting period in 2019 was April 26, May 3, and May 16, and in 2020 it was April 29, May 7, and May 14. Each crop was planted in three replicates of 1 m 2 area each.

Plant and Soil Sampling and Analysis
Three replicates were collected from the same soil (0-20 cm from the surface). When harvesting crops, they were naturally dried for a week, and passed through a 2 mm-hole siege were used for analysis. The soil's physical and chemical analysis were done according to NIAST, 2000, by the Rural Development Administration. As for soil chemical analysis, pH and electrical conductivity (EC), 5 g of soil and 25 mL of distilled water (1:5 ratio) were measured by a pH meter (CP-500 L, iSTEK, Seoul, Korea) and EC meter(Beckman). Exchangeable cations Ca, K, Mg, and Na were leached by distilled water and 1N-NH 4 OAc (pH 7.0), and the cations in the leachate were analyzed by ICP (Varian Vista-MPX, Varian, Palo Alto, CA, USA). Available phosphate was determined by the Lancaster method, organic matter (OM) by the Tyurin method, and cation exchange capacity (CEC) by the IN-ammonium acetate method. T-N was analyzed using organic elemental analysis (Vario MAX CNS, Elementar, Germany).

Measurement of Chlorophyll and LAI
Chlorophyll content of the leaves was measured utilizing a portable chlorophyll meter (SPAD-502Plus, Konica Minolta Sensing Americas, Inc, Ramsey, NJ, USA) which measures chlorophyll by light absorption rate of red light. The flag leaf and third leaf were measured in ten replicates, and the average was considered as the result. Leaf area index (LAI) was calculated using an LI-3100 Area Meter (Lincoln, NE, USA) with three replicates collected in from a 1 m 2 area. The dry matter percentage represents the percentage of nutrients present, excluding water content, and was determined using the following formula: percentage of dry matter (%) = (dry weight/fresh weight) × 100.

Statistical Analysis
Experimental data were statistically processed using the statistical analysis program, R Ver.4.1.2 (R Core Team, 2021). Two-way ANOVA analysis was carried out to determine the interaction between cereal crops and growth stage, and Duncan's multiple range test was used for post verification. A significance level of p < 0.05, was chosen, and each analysis was executed at least three times.

Weather and Field Condition
During the cultivation of cereal crops, temperature and precipitation data were collected from the Korea Meteorological Administration; the data are shown in Figure 1. In the middle latitudes temperate zone, Korea is characterized by cold and dry winters because of cold and dry continental anticyclones. In the central district, the experiment was conducted in Seokmun reclaimed land in Dangjin, Chungcheongnam-do. The mean air temperature in the first year was 12. = DDM (%) × DMI (%)/1.29, using digestible dry matter (DDM) and dry matter intake (DMI) from DDM (%) = 88.9 − (ADF (%) × 0.779), DMI (%) = 120/NDF (%).

Statistical Analysis
Experimental data were statistically processed using the statistical analysis program, R Ver.4.1.2 (R Core Team, 2021). Two-way ANOVA analysis was carried out to determine the interaction between cereal crops and growth stage, and Duncan's multiple range test was used for post verification. A significance level of p < 0.05, was chosen, and each analysis was executed at least three times.

Weather and Field Condition
During the cultivation of cereal crops, temperature and precipitation data were collected from the Korea Meteorological Administration; the data are shown in Figure 1 Field crop cultivation was possible because of some desalting. Table 2 shows data about the soil's characteristics before seeding and by harvesting time. The experimental soil's pH was between 7.41 and 7.84, which makes it alkalescent, and the EC average declined 1.5 times from 2.5 dS/m in 2019, to 1 dS/m in 2020. In both years, available phosphate was 440-934 mg/kg, higher than the appropriate amount, and the same applied to exchangeable cations such as K, Ca, and Ma. OM is matter in which organic substances are combined, and helps the plant sprout easily in soil with nutrients from feces and the remains of organisms. The average OM was 3.18% in 2019 and 2.92% in 2020, which are within the appropriate range based on reclaimed land. Field crop cultivation was possible because of some desalting. Table 2 shows data about the soil's characteristics before seeding and by harvesting time. The experimental soil's pH was between 7.41 and 7.84, which makes it alkalescent, and the EC average declined 1.5 times from 2.5 dS/m in 2019, to 1 dS/m in 2020. In both years, available phosphate was 440-934 mg/kg, higher than the appropriate amount, and the same applied to exchangeable cations such as K, Ca, and Ma. OM is matter in which organic substances are combined, and helps the plant sprout easily in soil with nutrients from feces and the remains of organisms. The average OM was 3.18% in 2019 and 2.92% in 2020, which are within the appropriate range based on reclaimed land.   Table 3 shows the data for barley, triticale, and oats collected in two years divided by the growth stage. In both years a significant difference (p < 0.05) was found in the tiller number and productive tiller in cereal crops, but both growth stage and interaction were statistically insignificant. Oats showed the highest values for tiller number and productive tiller. In the year 2019, the tiller number was 551.2, the productive tiller was 526.2, and in the year 2020, the tiller number was 672, and the productive tiller was 616. In the case of culm length and panicle length, a significant difference was found by growth stage and cereal crops, with it being within p < 0.05 for both years; interaction between these two factors was also found. Culm length was the highest in barley for both years, with 90.6 cm in 2019 and 84.5 cm in 2020, while oats had the greatest panicle length in both years, with 16.4 cm in 2019 and 9.9 cm in 2020. Triticale panicle length was also high, with 9.6 cm in 2020. In addition, excluding oats, barley and triticale showed the highest panicle and culm length during the milk stage.  As for chlorophyll content, no significant statistical difference was shown in cereal crops in 2019, but there was a significant difference (p < 0.05) by growth stage. Barley showed the highest values in the flag leaf at 46.6, and triticale had the highest in third leaf a 39.1. Overall, flag leaf and third leaf values were the highest during the heading stage in all cereal crops, but oats sometimes showed the highest value of flag leaf during the milk stage. As for chlorophyll content in 2020, a significant difference (p < 0.05) was found between cereal crops, but no significant difference was found in flag leaf by growth stage, while there was a substantial difference in the third leaf. Oats had the highest values, with 37.6 for the flag leaf and 31.9 for the third leaf. While barley showed the highest values during the heading and milk stages, triticale and oats showed the highest during the milk and dough stages.

Growth and Development Characteristics
Triticale's LAI was the highest at 4.3 in 2019, and all cereal crops showed the highest LAI during the milk stage. No significant difference was found between cereal crops in 2020, but there was a significant difference (p < 0.05) by growth stage. In addition, triticale was the highest with 4.8, and all cereal crops showed the highest LAI during the heading stage.

Dry Weight and Percentage of Dry Matter
( Figure 2) shows the data regarding dry weight and percentage of dry matter of cereal crops by growth stage, collected over the two years.
while there was a substantial difference in the third leaf. Oats had the highest values, with 37.6 for the flag leaf and 31.9 for the third leaf. While barley showed the highest values during the heading and milk stages, triticale and oats showed the highest during the milk and dough stages.
Triticale's LAI was the highest at 4.3 in 2019, and all cereal crops showed the highest LAI during the milk stage. No significant difference was found between cereal crops in 2020, but there was a significant difference (p < 0.05) by growth stage. In addition, triticale was the highest with 4.8, and all cereal crops showed the highest LAI during the heading stage.

Dry Weight and Percentage of Dry Matter
( Figure 2) shows the data regarding dry weight and percentage of dry matter of cereal crops by growth stage, collected over the two years. Triticale showed the highest dry weight in all growth stages and was exceptionally high during the milk stage at 1223 g/m 2 . Regarding the percentage of dry matter, triticale showed the highest with 44.8% during the dough stage. As for dry weight in 2020, there was a significant difference within p < 0.05 between cereal crops, but there was no significant difference according to the growth stage. Triticale's dry weight was high during the heading and milk stages, but barley's dry weight was the highest during the dough stage with 540 g/m 2 , followed by triticale with 516 g/m 2 . Triticale showed the highest percentage of dry matter, with 39% during the dough stage. Oats had the highest values for both years with 683 g/m 2 and 392 g/m 2 during the dough stage, but the dry weight was significantly lower than in barley and triticale. Table 4 shows data about the forage value of cereal crops by growth stage collected over the two years. We conducted a two-way analysis of variance to investigate the difference between groups.

Chemical Analysis
As a result of conducting a two-way analysis of variance to find out the difference between groups, a significant difference (p < 0.05) between cereal crops and growth stage was found for both years with interactions, except for the growth stage of NDF in 2019.  Triticale showed the highest dry weight in all growth stages and was exceptionally high during the milk stage at 1223 g/m 2 . Regarding the percentage of dry matter, triticale showed the highest with 44.8% during the dough stage. As for dry weight in 2020, there was a significant difference within p < 0.05 between cereal crops, but there was no significant difference according to the growth stage. Triticale's dry weight was high during the heading and milk stages, but barley's dry weight was the highest during the dough stage with 540 g/m 2 , followed by triticale with 516 g/m 2 . Triticale showed the highest percentage of dry matter, with 39% during the dough stage. Oats had the highest values for both years with 683 g/m 2 and 392 g/m 2 during the dough stage, but the dry weight was significantly lower than in barley and triticale. Table 4 shows data about the forage value of cereal crops by growth stage collected over the two years. We conducted a two-way analysis of variance to investigate the difference between groups. Cereal crops ** ** *** *** *** *** Growth stage *** *** *** *** *** *** C × G ** NS *** *** *** *** Cereal crops ** *** *** *** *** *** Growth stage *** *** *** *** *** *** C × G *** *** *** *** * *** Growth stages (heading stage: HS, milk stage: MS, dough stage: DS), Abbreviations: crude protein (CP); neutral detergent fiber (NDF); acid detergent fiber (ADF); total digestible nutrient (TDN); relative feed value (RFV). *** p value < 0.001, ** p value < 0.01, * p value < 0.05, ns: non-significant.

2019-2020
As a result of conducting a two-way analysis of variance to find out the difference between groups, a significant difference (p < 0.05) between cereal crops and growth stage was found for both years with interactions, except for the growth stage of NDF in 2019.
The data confirmed that CP decreased as the days elapsed after the heading stage in all cereal crops. The mean CP value of triticale was the highest, at 10.4, in 2019, and barley's CP value was the highest, at 9.1, in 2020. Regarding CP, triticale showed the highest values, with 16.4% during the heading stage in 2019, and barley had the highest, with 9.3% in the milk stage and 6.7% in the dough stage. On the other hand, barley had the highest in 2020, with 13.4% in the heading stage and 8.9% in the milk stage. Oats had the highest with 6.5% during the dough stage.
NDF and ADF are cell wall components that form the structure of plants, making livestock feel full when ingested. Therefore, they are important indicators of feed quality, forage intake and digestibility. In 2019, the mean of NDF was the lowest in triticale, and ADF was the lowest in barley, but in 2020, both NDF and ADF were the lowest in oats. The lower these values, the better the quality of the coarse fodder. As for NDF, triticale had the lowest value in 2019 with 60.9% in the heading stage, while barley had the lowest with 64.4% in the milk stage; triticale showed the lowest with 62.8% in the dough stage.
Barley had the lowest ADF at 22.4% during the heading stage, while triticale at 29.9% had the lowest during the milk stage and barley at 34.5% during the dough stage. In 2020, the lowest NDF was detected in oats during the heading stage and milk stage at 43% and 57.2% respectively, while triticale had the lowest during the dough stage at 56.7%. As for ADF, during the heading and milk stages, oats had the lowest at 20.2% and 26.2%, while barley had the lowest at 30.5% during the dough stage.
The RFV is an index of potential digestible energy and is also used as an indicator for the ranking of grass forages based on the amount of intake, by using the quality class of dry grass as a standard. Usually, if it is over 100, the forage value is considered good. All cereal crops showed the highest result during the heading stage and quality steadily decreased as the growth stage proceeded. In 2019, the highest was shown in triticale at 94.5 during the milk stage, followed by barley at 89.2 and oats at 87.0. In 2020, oats had the highest at 111.3, followed by barley at 105.2 and triticale at 101.5; triticale's value was high at 102.8 even in the dough stage.

Discussion
This research was carried out to provide useful information regarding forage value and winter cultivation of cereal crops in relation to the increased utilization of fallow land in winter times in reclaimed land. In a country with limited national territory, such as Korea, farm income can be increased by maximizing the yield per unit area through efficient land application and a double-cropping system. In addition, an increase in forage quality can be expected by selecting the proper harvesting time to improve the forage's efficiency, which enhances the preference of livestock by satisfying the requirements for digestion and absorption.
In general, the soil pH values were within the optimal range for barley production, with average values ranging between 6.0 and 6.6 [26]; however, it was confirmed that the pH of reclaimed soil in our study was 7.41-7.84, which was higher than the mean values. Nonetheless, crop growth was still possible. EC was 1-2.5 dS/m, and organic matter was 2.92-3.18%. Available phosphate was higher than the appropriate range at 440-934 mg/kg, and the exchangeable cations K, Ca, and Mg were also higher than the minimum amount. In general, it was observed that the structural stability was reduced due to the low organic matter in soil affected by salinity [27]. Accordingly, compost, manure, and fertilizer were applied to enhance the soil quality and yield of crops, and the yield was increased under the condition of salinity stress and soil remediation [28,29]. The effectiveness of fertilizer, manure, and other additions has been proved in various studies, which also report that in reclaimed land in Korea, fertilizer and manure addition are part of the conventional farming method carried out before cultivating crops. Judging from their presence in conventional agricultural soils, there is a high probability that both available phosphate and exchangeable cation K, Ca, and Mg have been accumulated for a long period of time. According to [30], when organic matters such as livestock compost were applied in excessive amounts, or used for a long time, effective phosphoric acid was excessively accumulated in the topsoil with a maximum of 1547 mg/kg −1 and an average of 554 mg/kg −1 . In addition, exchangeable cations were higher than the appropriate range, with 8.9 of Ca, 0.89 of K, and 2.0 of Mg. Similar results were found in this experiment.
Usually, drought conditions in saline soils adversely affect crop growth due to negative effects on plant water relations [31]. In saline soil, during rainfall the salinity decreases, but otherwise the salinity increases. Therefore, high-salinity pastures show that crops can be competitive if the soil is high in moisture [32]. During the experiment, the temperature in the year 2020 was 1.2 • C higher than in 2019. The precipitation in 2020 was reduced to 80 mm, which was half the amount of 2019, but precipitation reached a peak of 100-120 mm of rainfall in November and May, showing a wide range of weather differences. In the case of culm length, panicle length, and LAI, growth was better in 2020 than in 2019 during the heading stage. However, growth was reduced during the milk and the dough stages due to the dramatic increase in temperature in May and concentrated rainfall. According to a study by [33], it was confirmed that DM (dry matter) depended heavily on the environment, such as soil conditions and high temperatures. Similar to the study of [34], the results showed that if the temperature increases by 1 • C during wheat cultivation, the production decreased by 3-10%. Another study [9] also confirmed that crops are highly dependent on soil salinity and climate, and crop yield changes according to seasonal dynamics. In the case of triticale, reaction to pH was the lowest since triticale has a higher tolerance compared to barley, and the result of this research was partly consistent with studies in which yield varied widely among crops over the years [35]. In addition, compared to the growth period of the first planting, it was observed that rainfall was halved during the second growth period, and more severe stress conditions were imposed due to high air temperature, leading to a decrease in yield [36,37].
In 2019, triticale showed the highest values for both panicle length and culm length at 11.8 cm and 99.5 cm, respectively, during the milk stage. In 2020, barley culm length was the highest at 87.7 cm in the heading stage, and oats panicle length was the highest at 12.5 cm in the dough stage. Since oats reach maturation later than other cereal crops, it is better to harvest them in June rather than May to obtain the best yield [38]. It was also confirmed in this research that as the oat growth stage proceeded and growth gradually increased, it reached the highest in the dough stage. In general, leaf growth is reduced compared to root growth in dry soil with high salinity due to factors related to water stress rather than salt-specific effects [5]. In many crops, leaf chlorophyll content and its indirect assessment via soil plant analysis development (SPAD) have been demonstrated to be heritable traits related to leaf physiology, yield, and quality of the crop [39].
In this experiment, in 2019, when the chlorophyll content was between 30 and 50, on average, for flag leaves and third leaves, the LAI averaged 3.7-4.3 for each of the three varieties, and in triticale it was the highest at 4.5 during the milk stage, which is the growth stage. In addition, in 2020, when the chlorophyll content was between 20 and 40, the LAI averaged 4.6-4.8, which was relatively higher than in 2019. In the milk stage, the LAI was the highest in triticale at 4.2. As leaf chlorophyll is a major pigment for leaf photosynthesis in the chloroplast, leaf chlorophyll concentration is very important in the production of biomass in plant leaves [40]. In other words, improving the photosynthetic ability of plants by increasing the amount of chlorophyll is one of the strategies for improving the growth and yield of crops [41]. In this experiment, considering dry weight and percentage of dry matter, triticale showed a higher value with respect to the other two crops, particularly during the milk stage. According to the research results of [42], wheat had the greatest dry matter, followed by triticale, barley, with oat showing the lowest. Triticale showed the lowest reaction to pH, since it has a higher tolerance compared to barley, and the results of this research were consistent with other studies where the yield was very diverse each year [35]. Five types of barley were harvested at three stages of maturity (bloom, milk, and dough), with the same results as in other studies where dry weight was the highest in the bloom and milk stage [43]. A study by [44] suggested that not all crops grow at the same speed and pattern, and that the best stage to harvest them is the soft dough stage.
In this study, results were consistent with those of a study reporting an increase in dry weight of cereal crops and a decrease in forage value as the growth stage proceeded [45]. It was observed that as the growth stage proceeded, CP of all the cereal crops decreased; the same results were reported in other existing studies [45,46]. This is believed to be due to the increased proportion of stems to total dry weight by harvesting time after the heading stage. NDF and ADF values were the lowest during the heading stage in both years, but in barley and oats these values increased from the ripening milk stage to the dough stage. This is consistent with a research result showing that forage barley's NDF increased as the maturity stage of whole-crop cereal proceeded [46]. On the other hand, triticale's NDF decreased as the maturation came close to the dough stage, in agreement with other research results where NDF usually stayed the same or decreased as maturity proceeded [47,48]. According to [33], it seems that as the seed ratio increases rapidly in triticale after harvest and increase of seed ratio leads to an accumulation of starch. Accordingly, it is inferred that this contributes to lowering the NDF and ADF contents, and also the TDN content. In another study [49], the relationship between maturity stage and NDF was different between cereal forages, suggesting that this could have an effect on determining the optimal harvest season.

Conclusions
Although pH and EC were higher than the reference values, barley, triticale, and oats could be cultivated in this experiment. However, precipitation and temperature had a significant impact on the growth of three cereal crops, and although there were many differences in the growth and dry weight between 2019 and 2020, consistent results were Attained between each of the three cereal crops. Forage value was the best during the heading stage, but it decreased considerably as the growth period went on. In addition, regarding the growth and dry weight of all three cereal crops, the yield was expected to increase during the milk and dough stages rather than the heading stage. Considering all the results, it was determined that triticale is the most adaptable crop to the environment of reclaimed land in central western Korea, and the crop which shows the highest dry weight. However, due to lack of consistency in crop yields and climate each year, more diverse types of research are needed in the future. Hence, multilateral research is required to draw conclusions, and additional follow-up studies are necessary. Furthermore, research comparing the yield of crops when converting rice paddies to field cultivation is also needed.