Growth and Forage Value of Two Forage Rice Cultivars According to Harvest Time in Reclaimed Land of South Korea

Abstract

This study compares the growth of two forage rice cultivars (Oryza sativa L.), Mogwoo and Mogyang, in Midwest reclaimed land (Seongmun Tide Embankment, Korea) for two years to find the most adaptable cultivars and the appropriate harvest time. In the case of high salinity soil, it was confirmed that the influence of precipitation was relatively high on soil condition and crop growth. In Mogyang, plant height and culm length tended to decrease slightly as the precipitation increased. As for the tiller number, Mogyang was higher than Mogwoo, but the leaf area was about 1.5 to 2 times higher in Mogwoo than in Mogyang. In addition, in both cultivars, dry weight increased rapidly during the dough stage, and Mogyang was 1538 and 1815 g/m², respectively, while Mogwoo was 2090 and 2752 g/m², which was significantly higher. Mogyang had a CP of 4.8%, a TDN and RFV of 59.4%, 94.0, respectively, and Mogwoo had a CP of 9.7%, a TDN and RFV of 60.1%, 103.8, respectively, resulting in Mogwoo having higher values, and in particular Mogwoo was found to have better forage quality in the milk stage than in the dough stage. In addition, in terms of soil and climate conditions in Midwest reclaimed land, it was confirmed that the Mogwoo variety was the most suitable compared to Mogyang, and dry weight was higher in the dough stage than in the milk stage, but it was concluded that high forage quality could be obtained by harvesting during the milk stage.

1. Introduction

Globally, the problem of soil salinity is increasing, and it is occurring due to various causes in several countries. In Egypt, intensive irrigation of cultivated land in a dry climate is a major cause of secondary soil salinization, as precipitation is rare and evaporation is high [1]. In Indonesia, it is estimated that changes in rainfall patterns and rising global sea levels will reduce the total area of coastal rice fields of 291,992 ha by 2050, and affect a larger area of rice land due to saline concentration and submergence [2,3,4]. As Korea has a narrow land area, many mountainous terrains, and is surrounded by the sea on three sides, the lack of cultivated land has emerged as a big problem, and large-scale reclamation projects have been implemented. The Seosan reclamation project, Korea’s first large-scale reclamation project, began construction in 1980 and was completed in 1995, and most of the reclaimed land was developed as agricultural land, and became a habitat for migratory birds in winter when no farming was done [5]. In addition, through a national project to reclaim the whole area of Saemangeum, a 33 km-long embankment was built from the north of the West Sea to the south and a huge reclamation project was carried out for agricultural use, which is Korea’s representative Saemangeum Reclamation Project [6]. Since the soil of reclaimed land has very high salinity, it adversely affects the germination of crops and causes the growth and development of crops to decrease [7]. As such, various studies are being conducted on how environmental stress has a bad influence on the plant’s growth and development and to improve plant tolerance to various types of environmental stress [8].

Basically, the soil salinity problem occurs when salt accumulates in the root area of the crop, resulting in a decrease in soil water available to the crop [9]. Another possibility is that the evapotranspiration leads salts to accumulate in the top of the soil as shallow groundwater table exists and the salts containing water move upward. This form of secondary soil salinization is mainly due to bad drainage [1]. Salinity in the soil imposes stress conditions on plant cultivation in agriculture, which severely reduces crop production [7]. Although natural rainfall is effective in removing salt-from soils, a long time is required to achieve acceptable results [10]. Therefore, in Korea’s reclaimed land, irrigated cultivation is generally predominant to reduce salinity, and rice is a representative crop. Rice is not a salt-resistant crop, but it is easier to cultivate than other crops because salinity can be controlled through precipitation in summer and proper irrigation.

The majority of rice straw currently produced is cultivated by grinding and mixing it into paddy fields, because this is an inexpensive way to deal with rice straws and provide organic compounds that stimulate the microorganisms’ activity in paddy fields [11]. In addition, the rice straw supplementation increases soil fertility and rice production, and N, P, K, C/N, and Fe²⁺ are mostly derived from crop residues and biochar [12], and promotes environmental conditions suitable for bacteria that play a substantial role in carbon and nitrogen mineralization in the soil [13]. Besides, rice straws are the remnants of crops that farmers use as feed for ruminants in Asia. Rice straws are low in nutritional value due to their high silica content and low nitrogen content, but are suitable for use in ruminants with low nutrient requirements [14].

However, one of the rice straw’s main disadvantages as animal fodder is the low digestibility of main organic and cell wall components [15]. In general, straw composition and fiber digestibility depends considerably on the variety of rice straw [16]. Studies have shown that urea treatment improves the crude protein content and digestibility in ruminants, also increasing rice straw’s nutritional value that is otherwise insufficient in livestock forage [17]. In Korea, also, attempts were made to develop cultivars considering the quantity and pest resistance [18,19], preference and nutritional value of livestock [20], and as a result, this led to the development of various cultivars such as ‘Mogwoo’ with high dry matter yield and good forage value, and japonica-type ‘Mogyang’ [21]. The initial growth of Mogwoo was average, but in the later stage, the rice straws got heavier and less lodging due to the higher development of stems and leaves rather than the grain of rice, thus resulting in higher rice straws yield [22]. In addition, since it is a late maturity variety, it is a suitable variety when producing two crops (rice and barley) per year. Mogyang also has a large amount of stem and leaf, excellent forage value, and high yield, but due to temperature sensitivity the later the rice transplanting, the more delayed the late-emerging tiller occurs, so timely rice transplanting is required [23].

The rice straw’s nutritional value depends on many factors such as soil environment conditions, climate conditions, and harvest timing [17]. Research on the comparison of the growth and forage value of the two cultivars in reclaimed land soil is lacking. Therefore, this study is aimed at investigating the soil environment and weather conditions that could be affecting to the growth characteristics and forage value of the two cultivars of Mogwoo and Mogyang in the reclaimed land for two years, and to find suitable cultivars and the best harvest time.

2. Materials and Methods

2.1. Experimental Design and Agronomy

This experiment was conducted for two years from June 2019 to October 2020 in the reclaimed land in Seokmun, Gagok-ri, Songsan-myeon, Dangjin-si, Chungcheongnam-do (36°59′24 N, 126°40′15 E). The rice varieties used in the present study were artificially crossbred by the National Institute of Food Science and fostered by the pedigree method of breeding, with the purpose of creating new forage rice varieties, and both Mogwoo and Mogyang cultivars are late variety (

Table 1. The cross combination and main characteristics of ‘Mogwoo’ and ‘Mogyang’ in forage rice.

Cultivar	Systemic Name	Cross Combination	Provider	Maturity Classification
Mogwoo	Suweon 519	SR14495-51-1-2-1-2-1//Suweon431/IR71190-45-2-1	Rural Development Administration, Korea	Late maturity variety
Mogyang	Suweon 525	SR24592-HB2319/IR73165-B-6-1-1

). ‘Mogwoo’ is a variety with high harvest and forage value as a result of the replicated yield trial by using Dasan rice as a mother plant and crossbreeding F1 with Suwon 431 and IR7110-45-2-1 [22]. To obtain ‘Mogyang’, mother plants SR24592-HB2319 and IR73165-B-6-1-1 were crossbreeding, and as a result of the replicated yield trial, the plant type is good, the stem and leaf quantity is high, and it has proven to be a suitable variety for forage [23].

Rice seed disinfection was performed by a hot water disinfection method in which seeds (10 kg) were immersed in 60 °C water (100 L) for 10 min and then immediately in cold water for 10 min. Mogwoo and Mogyang were sown on the seed bed on 14 May 2019 and 20 May 2020, respectively, and 30 days after sowing, 5 to 8 individual seedlings per hill were transplanted at 30 cm × 15 cm intervals on 13 June 2019 and 19 June 2020, respectively, and the experiment was conducted at a total of about 661 m² (Figure 1).

The amount of applied fertilizer was N–P₂O₅–K₂O = 200–80–80 kg/ha, with 50% nitrogen, and both potassium and phosphorus were all used as basal fertilizers, and subsequent cultivation management followed the general conventional practices. Additionally, no pesticides or herbicides were applied. The harvest time of each variety is shown in (

Table 2. The harvest time of ‘Mogwoo’ and ‘Mogyang’ according to the growth stage.

Year	Cultivar	Transplanting	Heading Stage	Milk Stage	Dough Stage
2019
	Mogwoo	13 June	4 September	18 September	28 September
	Mogyang		3 September	13 September	26 September
2020
	Mogwoo	19 June	15 September	29 September	9 October
	Mogyang		13 September	26 September	7 October

).

2.2. Soil Samples and Analysis

For soil samples, the surface soil (about 0–10 cm on the surface) was collected in three replicates each time the crop was harvested, dried naturally a week long, and then sifted through a 2 mm sieve, before analysis. Soil analysis has been carried on according to the Rural Development Administration’s soil physical and chemical analysis (NIAST, 2000). pH and electrical conductivity (EC) were measured by pH meter (CP-500L, iSTEK, Seoul, Korea) and EC meter (Beckman) with soil and distilled water in a ratio of 1:5. Available phosphate (AP) was analyzed by the Lancaster method and organic matter (OM) by the Tyurin method, and Exchangeable Cations Ca, K, Mg and Na were extracted with 1N-NH₄OAC (pH 7.0) and analyzed by ICP (Varian Vista-MPX, Varian, Palo Alto, CA, USA).

2.3. Measurement of Chlorophyll and LA

Using a portable chlorophyll meter (SPAD 502Plus, Konica Minolta Sensing Americas, Inc, Ramsey, NJ, USA), a non-destructive measuring instrument that measures chlorophyll content with the light absorption rate of red light, chlorophyll content was measured in the flag leaf and third leaf in three or more replicates. In addition, the leaf area (LA) was measured by collecting 5 plants per 1 m² in width and length, and this was repeated for three 1 m² lots, and the leaf area was measured using an LI-3100 Area Meter (Lincoln, NE, USA).

2.4. Chemical Analysis for Forage Quality

As for the sample for analysis, grain, stem, and leaf samples were collected according to the growth stage of each cultivar, and dried at 80 °C for 72 h in a forced convection oven (LDO-150F). The dry weight was measured, and then the sample pulverized by a grinder was used for analysis. The crude protein (CP) content was analyzed using the Kjeldahl method as a standard analysis method of AOAC (1995). Additionally, neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed by Goering & Van Soest (1970) method. Total digestible nutrient (TDN) was calculated using the calculation formula of (1) for forage value evaluation by Holland and Kezar (1992). The relative feed value (RFV) was calculated by the formula of (2). DDM is the abbreviation of the digestible dry matter and DMI is the abbreviation of the dry matter intake. The percentage of dry matter (PDM) for each variety was calculated by the formula of (3).

TDN (%) = 88.9 − (0.79 × ADF (%))

(1)

RFV = DDM (%) × DMI (%)/1.29 [DDM (%) = 88.9 − (ADF (%) × 0.779, DMI (%) = 120/NDF (%)]

(2)

PDM (%) = (dry weight/fresh weight) × 100

(3)

2.5. Statistical Analysis

For statistical analysis of the experimental data, a two-way ANOVA analysis was performed to confirm the interaction between cultivar and growth stage using the statistical program R Ver.4.1.2, and Duncan’s multiple range test was used for post hoc test. It was tested within the significance level of p < 0.05, and all experiments data were collected in three replications.

3. Results

3.1. Weather and Paddy Field Condition

The weather in the experimental paddy field was observed for two years by the Korea Meteorological Administration after collecting data on temperature and precipitation during the rice cultivation period (Korea Meteorological Administration is about 7 km away from the experimental field) (Figure 2).

The average temperature during the rice cultivation period was the highest in August, with 25.9 °C in 2019 and 26.2 °C in 2020, so in 2020 it was about 0.3 °C higher than in 2019. Precipitation in Korea in 2019 was generally concentrated between July and September, with 174.5 mm in July, 121.1 mm in August, and 181.1 mm in September. On the other hand, in 2020, precipitation was 329.4 mm in July, 400 mm in August, and 257.7 mm in September, and despite being in the same region, it was confirmed that there was highly difference in precipitation in the two years.

The rice paddy soil used in this study is highly saline, making it unsuitable for the cultivation of field crops, so rice has been cultivated through an irrigated cultivation since it was reclaimed (

Table 3. The results of soil analysis according to the growth stage in reclaimed land soil for two years.

Year	Growth Stage	pH	EC	AP	OM	Exchangeable Cation
						K	Ca	Mg	Na
		1:5; w/w	dS/m	mg/kg	%	cmol+/kg
2019
	HS	7.4	4.1	340	2.9	1.29	7.9	3.5	2.2
	MS	6.9	5.1	254	2.9	1.31	8.3	3.7	2.4
	DS	6.6	4.2	212	2.0	1.09	7.4	2.9	1.4
2020
	HS	5.8	1.8	273	1.3	1.11	4.1	2.6	0.7
	MS	5.7	4.3	311	1.7	1.65	4.9	3.4	3.1
	DS	5.7	2.6	240	1.5	1.19	4.6	2.9	1.7
ANOVA
Year (Y)		**	*	ns	***	ns	***	ns	ns
Growth stage (G)		ns	ns	ns	ns	ns	ns	ns	ns
Y × G		ns	ns	ns	ns	ns	ns	ns	ns
CV(%)		6.9	30.6	19.0	13.7	12.7	9.15	12.4	37.1

Growth stage (HS: heading stage, MS: milk stage, DS: dough stage), Abbreviation: electrical conductivity (EC); available phosphate (AP); organic matter (OM); ‘***’ p value < 0.001, ‘**’ p value < 0.01, ‘*’ p value < 0.05, ‘ns’ non-significant.

).

There was no interaction between 2019 and 2020′s year and growth stage, but there was a significant difference within p < 0.05 in the pH, EC, OM, and the exchangeable cation Ca of the soil. The pH and EC were relatively lower in 2020 than in 2019, and the pH was 5.7–7.4, which is a slightly acid soil, and in both years it gradually decreased with growth stage. EC determines that the salt amount is high if it is more than 2 dS/m: in 2019, it was about 4.1–5.1 dS/m, slightly higher than in 2020. AP data were similar in both years at about 212–340 mg/kg. OM was 2.0–2.9% in 2019 and 1.3–1.7% in 2020. Exchangeable cation K was 1.09–1.65 and Mg was 2.6–3.7, which were similar in both years. However, it can be seen that Ca and Na in 2020 are 4.1–4.9 and 0.7–3.1, respectively, which are lower than in 2019.

3.2. Growth and Development Characteristics

Data that measure the growth of Mogwoo and Mogyang for two years according to growth stage of two cultivars are shown in (

Table 4. The growth characteristics of ‘Mogwoo’ and ‘Mogyang’ in accordance with the growth stage for two years.

Year	Cultivar	Growth Stage	Tiller Number	Plant Height	Culm Length	LA	Chlorophyll		Dry Weight
							Flag Leaf	Third Leaf
			No./m2	cm	cm				g/m2
2019
	Mogwoo	HS	513	108.0	83.2	7.2	34.3	44.9	1935
		MS	315	116.1	87.4	3.0	36.1	41.6	1545
		DS	367	109.8	81.9	3.6	34.7	40.6	2090
	Mogyang
		HS	301	109.4	76.4	5.4	31.5	40.0	1573
		MS	257	113.6	83.8	3.2	32.3	36.4	1709
		DS	227	124.7	80.6	2.6	33.3	36.4	1538
	ANOVA
	Cultivar (C)		**	ns	ns	ns	ns	*	*
	Growth stage (G)		ns	ns	ns	***	ns	ns	ns
	C × G		ns	ns	ns	ns	ns	ns	*
	CV(%)		26.1	7.2	7.9	26.5	9.1	11.3	10.6
2020
	Mogwoo	HS	405	117.5	53.0	5.0	34.2	43.8	1247
		MS	330	121.1	57.7	3.9	34.9	38.3	1247
		DS	497	121.2	67.5	9.0	32.8	31.4	2752
	Mogyang
		HS	374	110.6	71.6	4.7	40.1	44.2	1303
		MS	330	81.7	62.4	3.8	31.5	35.3	1465
		DS	343	92.1	48.7	3.8	30.0	23.9	1815
	ANOVA
	Cultivar (C)		ns	***	ns	**	ns	**	ns
	Growth stage (G)		ns	**	ns	**	**	***	***
	C × G		ns	***	***	**	*	*	**
	CV(%)		24.2	7.2	14.7	32.1	11.0	8.1	23.1

Growth stage (HS: heading stage, MS: milk stage, DS: dough stage), Abbreviation: leaf area (LA); ‘***’ p value < 0.001, ‘**’ p value < 0.01, ‘*’ p value < 0.05, ‘ns’ non-significant.

). In 2019, there was no significant difference (p < 0.05) between the plant height, culm length, and the chlorophyll content of the flag leaf. However, the tiller number was significantly different, the chlorophyll content in the third leaf, and dry weight within p < 0.05 in cultivar, and LA also had a significant difference in growth stage, but there was no interaction between cultivar and growth stage. Tiller number showed a trend of gradually decreasing from the heading stage to the milk stage, and it was higher in Mogwoo than in Mogyang.

The plant height was similar in the two cultivars, and it was confirmed that Mogyang was 124.7 cm during the dough stage, 14.9 cm higher than Mogwoo. The culm length was 87.4 cm for Mogwoo and 83.8 cm for Mogyang during the milk stage, the highest in both cultivars. LA gradually decreased as the growth period passed, with 3.6 for Mogwoo during the dough stage, which was higher than that of Mogyang at 2.6. As for the chlorophyll content in Mogwoo the highest values were 36.1 in the flag leaf during the milk stage, and 44.9 in the third leaf in the heading stage. Mogyang showed the highest LA values at 33.3 in the flag leaf during the dough stage, and at 40.0 in the third leaf during the heading stage. Mogwoo’s dry weight was 2090 g/m² in the dough stage, while Mogyang had the highest weight of 1709 g/m² during the milk stage, but based on the dough stage, it was confirmed that Mogwoo’s dry weight was higher than that of Mogyang.

In 2020, the plant height of third leaves, LA, and chlorophyll content had a significant difference within p < 0.05, and there was an interaction between cultivar and growth stage. Dry weight also had a significant difference within p < 0.05 in the growth stage, and interactions were also shown. Tiller number was the highest at 497 in the dough stage in the case of Mogwoo, and 374 in the heading stage in the case of Mogyang, but neither of the cultivars showed a constant trend over the growth stage. Plant height showed a large difference between the two cultivars, and Mogwoo suddenly grew from the milk stage until reaching 121.2 cm during the dough stage. On the other hand, it was confirmed that Mogyang’s growth to 81.7 cm during the milk stage and 92.1 cm during the dough stage was not significant in both cultivars. In 2020, the culm length was shorter than in 2019, and in 2020, in Mogwoo it gradually increased to 67.5 cm during the dough stage, but in Mogyang it was 48.7 cm, which confirmed a non-significant growth compared to the heading stage.

In the case of LA, both cultivars were not consistent, but Mogwoo had the highest at 3.9 and 9.0, respectively, during the milk and the dough stage in 2019, and the highest in the heading stage in 2020. Whereas Mogyang showed no significant difference in both years, with highest LA at 5.4 and 4.7 in the heading stage, respectively, and tended to gradually decrease as the growth stage passed. The chlorophyll content of Mogwoo was the highest at 34.9 in the flag leaf during the milk stage, and at 43.8 in the third leaf during the heading stage. Mogyang had the highest at 40.1 and 44.2 in the heading stage in both flag leaf and third leaf, respectively. As for dry weight, in 2020 it tended to decrease significantly compared to 2019 in both cultivars, in the heading and milk stage, but the opposite happened in the dough stage. Mogwoo’s dry weight was 2752 g/m² and Mogyang’s was 1815 g/m², which is increased in both cultivars in 2020 compared to 2019.

3.3. Chemical Analysis

Table 5. The chemical composition according to the growth stage of ‘Mogwoo’ and ‘Mogyang’ during the two years’ measurement.

Year	Cultivar	Growth Stage	CP	NDF	ADF	TDN	RFV	PDM
			%	%	%	%		%
2019
	Mogwoo	HS	8.5	68.2	40.8	56.7	77.9	31.9
		MS	7.8	54.3	36.5	60.1	103.8	38.7
		DS	9.7	68.2	42.7	55.1	76.3	37.3
	Mogyang
		HS	9.1	71.5	38.4	58.6	76.7	33.1
		MS	8.5	65.7	41.9	55.8	79.8	35.4
		DS	4.8	59.3	37.4	59.4	94.0	44.1
	ANOVA
	Cultivar (C)		**	ns	ns	ns	ns	ns
	Growth stage (G)		**	***	ns	ns	**	ns
	C × G		***	***	***	***	***	ns
	CV(%)		7.7	5.2	4.7	2.5	6.5	19.9
2020
	Mogwoo	HS	11.1	60.8	32.5	63.2	97.3	18.9
		MS	9.6	55.7	26.2	68.2	114.4	27.8
		DS	8.6	59.9	29.5	65.6	102.5	28.9
	Mogyang
		HS	9.6	66.3	36.8	59.8	84.5	22.2
		MS	8.4	64.2	35.8	60.6	88.5	29.9
		DS	7.0	64.8	35.6	60.8	88.0	34.3
	ANOVA
	Cultivar (C)		***	***	***	***	***	***
	Growth stage (G)		***	*	*	*	***	***
	C × G		ns	ns	ns	ns	*	ns
	CV(%)		5.2	2.8	6.2	2.6	3.6	7.8

Growth stage (HS: heading stage, MS: milk stage, DS: dough stage), Abbreviation: crude protein (CP); neutral detergent fiber (NDF); acid detergent fiber (ADF); total digestible nutrient (TDN); relative feed value (RFV); percentage of dry matter (PDM); ‘***’ p value < 0.001, ‘**’ p value < 0.01, ‘*’ p value < 0.05, ‘ns’ non-significant.

shows data of forage value and percentage of dry matter (PDM) for two years according to growth stage of the two cultivars. In 2019, there was no significant difference between the two cultivars for NDF, ADF, TDN, and PDM according to cultivar and growth stage, but CP had a significant difference within p < 0.05, and all but PDM had interactions. As for CP, it was confirmed that in Mogwoo it gradually increased as the growth stage elapsed, accounting for 9.7% during the dough stage, while in Mogyang it gradually decreased to 4.8% during the dough stage. Mogwoo’s NDF and ADF were the lowest at 54.3% and 36.5%, respectively, during the milk stage, while Mogyang’s were the lowest at 59.3% and 37.4%, respectively, during the dough stage. In addition, the TDN and RFV of Mogwoo were the highest at 60.1% and 103.8, respectively, during the milk stage, and in Mogyang they were the highest at 59.4% and 94.0, respectively, during the dough stage. As for PDM, it was confirmed that both Mogwoo and Mogyang had their lowest at 31.9% and 33.1%, respectively, during the heading stage.

In 2020, there was a significant difference within p < 0.05 depending on cultivar and growth stage, but no interaction appeared except for RFV. In both cultivars, the CP gradually decreased as the growth stage elapsed, with 8.6% in Mogwoo and 7.0% in Mogyang during the dough stage. Mogwoo’s NDF and ADF were the lowest at 55.7% and 26.2%, respectively, during the milk stage, while in the case of Mogyang, NDF was the lowest at 64.2% during the milk stage and ADF was the lowest at 35.6% during the dough stage. In addition, the TDN and RFV of Mogwoo were the highest at 68.2% and 114.4, respectively, during the milk stage, and the TDN and RFV of Mogyang were the highest at 60.8% and 88.5, respectively, during the dough stage. It was confirmed that PDM was the lowest at 18.9% and 22.2%, respectively, during the heading stage for both Mogwoo and Mogyang.

4. Discussion

Salt stress is one of the main environmental problems affecting crop growth and production on a global level. In saline soils, Rice is among a variety of crops that can be grown, usually by irrigated cultivation, and which solves the salt problem most directly and effectively. Although this experiment was conducted on the same soil for two years but the soil conditions changed remarkably due to the precipitation. The accumulated precipitation in 2019 was 614 mm and 1144 mm in 2020, about 1.5 times higher than in 2019, resulting in a slight decrease in salt in 2020 (Figure 2, Table 3).

There are many studies found similar with our finding, which is [24] have shown that precipitation has a greater effect on determining soil salinity levels than tidal water in high salt marsh elevations. In addition, the electrical conductivity remained very high in the two months when there was not much rainfall, but there are studies showing that the leaching process proceeded at a faster pace at the beginning of the rainy season in June both years [25,26]. In other words, that means that in a tropical region with high annual precipitation, a significant amount of salinity is removed from the soil by rainwater for a certain period of time. A large amount of rainfall can lead to salinity leaching from the surface soil, but in drought conditions, salt accumulates, becoming an important factor influencing the salinity of the soil surface [25].

As mentioned above, this experiment suggests that a certain amount of salt in the soil was removed by precipitation, and it directly affected to the growth and development change of the two cultivars (Table 4). In addition, it was confirmed that culm length and chlorophyll content were high in 2019, while tiller number, plant height, LA, and dry weight were higher in 2020, with Mogwoo showing the best values in both years. Results of plant height measurement in the reclaimed land soil showed that Mogyang’s height was 119 cm and Mogwoo’s was 108 cm [27]; Mogyang’s height was relatively high, and our experiments showed a similar trend in 2019. However, in 2020, Mogwoo and Mogyang showed opposite results, with lower culm length but higher plant height. This phenomenon was caused by an insufficient amount of sunlight, which is judged to be the reason the overgrowth occurred. That is, it rained frequently for three months from July to September, the cultivation period of the crop, resulting in excessive moisture and lack of sunshine, which caused the rice stems to grow long and tender. There are research results reporting that less sunlight during the rainy season causes plants to grow taller, leads to severe lodging, and produces lower yields [28]. The amount of sunlight is involved in the photosynthesis of plants, the root and stem, and seed development, and this was partially confirmed through this experiment.

In the case of culm length and chlorophyll content, they were affected by weather or growth stage more than by soil salinity in both cultivars. There was no constant pattern according to the growth stage in the flag leaf, but in the third leaf it was confirmed that it gradually decreased from the heading stage to the dough stage. In addition, it was confirmed that overall the flag leaf was much lower than the third leaf. In particular, in the case of Mogyang, there was a rapid decrease from the milk stage in both the flag and third leaf in 2020. The chlorophyll content of leaves is relatively easy to measure and is used as an indicator of the metabolism condition. According to one study measuring chlorophyll content under salinity stress, the leaf tip had a lot lower content than the middle and lower parts of the leaf, suggesting that this may be due to the different degree of sensitivity of chlorophyll in the various leaf parts and uneven sodium accumulation in the leaf [29]. The findings of [30] confirmed that the decrease in leaf area, harvest, and yield components under saline conditions were caused by reduced growth as a result of lower water uptake, sodium toxicity and chloride in the shoot cell, and decrease in photosynthesis. Moreover, it was suggested that the decrease in chlorophyll concentration could be caused by ions accumulated in salt inhibiting the biosynthesis of the different chlorophyll fractions.

There is a statistically significant negative correlation between plant height and tiller number, and biomass production and grain yield are highly connected to heading date, plant height, and tiller number [31]. Our experiments also confirmed that from the milk stage salinity in the soil decreased, while tiller number and plant height were increased. It was also confirmed that the number of tiller per plant and the number of spikelet per panicle are the most sensitive yield components to salinity and showed a significant linear response to salinity, which is partially similar to the results of the study in [32]. According to a study by [28], plant height, tiller number, volume of roots and shoots, weight of roots and shoots showed better results in the rainy season rather than in the dry season. In addition, it is known that in reclaimed land soil the forage yield of Mogwoo is higher than that of other cultivars [27,33]. Our experiments also showed that Mogwoo had much higher dry weight than Mogyang and, as expected, it was greatly affected by salt. Both cultivars were found to have low dry weight during the heading and the milk stage in 2020, but it increased rapidly during the dough stage. This phenomenon was due to the fact that Korea’s precipitation was high in July and August in the past, but in recent years, the trend of increasing rainfall in August and September instead has led to unfavorable weather conditions in the early stages of rice heading and ripening [34]. According to a study by [35], salt stress resulted in a considerable reduction of 77% in harvest across genotypes. In addition, the yield components such as tiller number per unit area, grain weight, and harvest index were significantly reduced by salinity. Furthermore, a study by [32] reported the adverse effects of salinity on grain yields and rice yield components varieties at higher salt levels (i.e., 4.5 dSm⁻¹) than those of low salt levels (i.e.,1.9 and 3.4 dSm⁻¹). In other words, under salt stress, plants were shorter, with lower survival rate and decreased straw biomass production. However, some studies show that an increase in total precipitation has a negative effect on crop yields rather than a positive effect [36]. In addition, simulations were conducted to estimate the potential impact on U.S. crop yields, and predicted that increased precipitation could lead to an average loss of $3 billion per year by 2030 due to increased excessive soil moisture conditions [37].

Changes in the external environment, such as high salt content in the soil and weather, not only affected growth, but also directly affected forage value, and likewise, the forage value of Mogwoo was better than Mogyang (Table 5). Conventional forage quality analysis includes measurements of CP, NDF, and ADF, and as crops mature, these values generally change consistently and are used to determine the ranking of quality [38]. A higher CP level can result in a better rumen environment for microbial degradation [39], and in the present study, CP tended to gradually decrease over the growth stage in both years, with higher values found in Mogwoo rather than in Mogyang. A study by [40] also confirmed that CP tends to decrease as the harvest period is more delayed in all cultivars shown by cultivating five varieties in paddy soil, such as Mogwoo and Mogyang.

The cell walls components forming plant structures that make the livestock feel full and satisfied are NDF and ADF. They are important indicators for forage quality evaluation, as they are related to intake and digestibility, thus, the lower their content, the higher the quality of the coarse fodder [41]. In this study, the contents of NDF and ADF showed some differences in 2019 and 2020, but there was no clear difference between the two cultivars. In general, as for Mogyang the harvest period was the more delayed, the NDF content gradually decreased, while Mogwoo showed no consistent tendency, with Mogwoo also showing a lower content than Mogyang: thus, it can be evaluated that the forage value of Mogwoo is high. A study by [42] evaluating the rate of degradation of hemicellulose and NDF components showed that the degradation occurs in the early stage of ensilage, which might explain the rice straw high NDF and low ADF decomposition. In general, there are a number of studies showing that TDN content is more influenced by percentage of starch in the panicle than the leaf and the stem [43,44,45]. According to a study by [45], it is more important to maximize the nutritional value of the leaves and stems than that of the panicles. Interestingly, in this experiment, it was confirmed that both cultivars had higher TDN content in 2020 compared to 2019, and generally higher in the milk stage. In addition, when the plant height was exceptionally high in 2020′s Mogwoo, it was confirmed that the TDN content was also the highest. In other words, in both cultivars the tiller number was the highest in 2020, and the TDN content was high too, especially because Mogwoo’s plant height was high. The rice grain filling process was very sensitive to salinity stress, and it was proved that in these conditions the carbohydrate content of rice was remarkably reduced, thus, clearly indicating that salinity stress is affecting the grain yield and TDN content [7]. RFV is an indicator for ranking the feed according to intake as potential digestible energy, and it can be used to grade hay quality [46]. Usually, if it is more than 100, it is judged to be a good forage value, and in both years it was confirmed that Mogwoo showed the highest RFV during milk stage.

5. Conclusions

This study was a cultivation experiment of two cultivars in the same soil environment, which showed relevant differences in growth and forage value due to the relative effect of weather conditions and characteristics of each cultivar, which led to the following conclusions. First, the pH, EC, AP, and exchangeable cation Na amount in the soil showed remarkable decrease due to precipitation, and despite the saline soil, the growth of Mogwoo was relatively superior to that of Mogyang. In both cultivars, experiments confirmed that higher precipitation in 2020 was advantageous for plants’ growth but not for culm length and chlorophyll content, and also that the increase of salt content in the soil, can be disadvantageous for crop growth. Second, even for the same cultivar, the forage value can vary depending on the cultivation environment, and this too confirmed that Mogwoo is superior to Mogyang. Therefore, it was suggested that in high-salt soil, if the salt content is lowered through water management, Mogwoo can bring a higher yield than Mogyang under the same conditions. Hence, through the results of this experiment, Mogwoo proved to be relatively less affected than Mogyang in unfavorable weather and soil environments, and it showed higher adaptability. As a result, it is recommended to harvest it during the dough stage, which showed the highest forage yield, and if it is for the preference of livestock, it is recommended to harvest it during the milk stage due to higher forage quality.