Research Article

Effects of Multiple Harvests and Different Manure Fertilization levels on the Yield and Feed Value of Kenaf (Hibiscus Cannabinus L.)

Byamungu Mayange Tomple1*, Ik-Hwan Jo2, Rajaraman Bharanidharan1, Seun-Gun Won2 and Muhammad Mahboob Ali Hamid3*

1Department of Eco-friendly Livestock Science, Institutes of Green-Bio Science and Technology, Seoul National University, Pyeongchang, South Korea; 2Department of Animal Resources, College of Natural and Life Sciences, Daegu University, Gyeongsan, 38453, South Korea; 3Institute of Animal and Dairy Sciences, Faculty of Animal Husbandry, University of Agriculture Faisalabad, Punjab, Pakistan.

Received | October 10, 2023; Accepted | June 11, 2024; Published | August 01, 2024

*Correspondence | M. Mahboob Ali Hamid, Institute of Animal and Dairy Sciences, Faculty of Animal Husbandry, University of Agriculture Faisalabad, Punjab, Pakistan; Email: [email protected]

Citation | FTomple, B.M., I.H. Jo, R. Bharanidharan, S.G. Won and M.M.A. Hamid. 2024. Effects of multiple harvests and different manure fertilization levels on the yield and feed value of Kenaf (Hibiscus Cannabinus L.). Pakistan Journal of Agricultural Research, 37(3): 195-206.

DOI | https://dx.doi.org/10.17582/journal.pjar/2024/37.3.195.206

Keywords | Feed value, Forage yield, Harvesting periods, Kenaf, Manure application levels, Environment

Copyright: 2024 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

The Intergovernmental Panel on Climate Change (IPCC) estimated that the management of manure contributed approximately 6% to global anthropogenic methane emissions during the 26th Conference of Parties (COP26) in 2021. Subsequently, a global initiative, the Methane Pledge, was launched, with participation from over 100 countries, including Korea, all committing to a 30% reduction in methane emissions by the year 2030. To tackle this environmental challenge, the Food and Agriculture Organization of the United Nations (FAO, 2023) proposed several strategies to mitigate these emissions, focusing on enhancing manure management practices.

Manure is recognized for its well-balanced nutrient composition, which is essential for supporting plant growth (Xu et al., 2022). It has been reported that manure has highly advantageous in kenaf (Hibiscus cannabinus L.) cultivation, enhancing organic matter efficiency, promoting soil structure and fertility improvements, and optimizing the utilization of fertilizers. The global demand for kenaf has been gradually increasing (Mohd et al., 2013). Kenaf is considered as a warm-season crop with versatile applications and environmentally sustainable cellulose, establishing itself as a pivotal asset in both commercial and subsistence agriculture (Al-Mamun et al., 2023). The rapid growth cycle, robust plant characteristics, stress resistance, quality bast fiber, and high yield collectively render the crop an appealing and advantageous choice (An et al., 2017). Kenaf demands minimal inputs to attain maximum yield within a brief timeframe (Robynn et al., 2013), and the effective harvesting, typically conducted between 11 and 13 weeks after planting, results in appropriate CP content and plays a vital role in achieving a balance between forage quality and quantity (Nam et al., 2018). Harvesting periods significantly affect fresh biomass yield, dry matter yield, nutritional and mineral compositions, and forage quality parameters, with the soft dough stage identified as the optimal harvesting period (Poe et al., 2022).

The chemical composition and in vitro digestibility of kenaf position it as a valuable fodder plant, particularly in arid regions. It provides high nutritional value and serves as a protein supplement for ruminants, and all above-ground plant organs, including leaves, stems, flowers, and seeds, have the potential to contribute significantly to feed production (Hajer et al., 2020). According to Kujoana et al. (2023) the leaves of kenaf can be utilized as a source of roughage and protein for cattle and sheep due to their high digestibility. Additionally, because of their high palatability and significant crude protein content at an early stage of growth, kenaf stalks can serve as a potential protein supplement for animal feeding. Despite some farmers incorporating kenaf into fodder, there is insufficient information regarding its nutritional value and its potential as an animal feed resource. In Korea, realizing the suitability of kenaf as a forage crop and identifying optimal growth conditions is essential. This highlights the need for farmers to embrace scientific cultivation practices, fostering the expansion of local and international markets for kenaf fiber and products (Al-Mamun et al., 2023).

Moreover, comprehensive investigations into the application of livestock manure at different ratios can reduce the use of mineral fertilizers and improve crop yield and quality, as reported by Xu et al. (2022). Therefore, the primary objective of this two-year study is to ascertain the appropriate manure fertilization application level and identify the optimal harvesting period to maximize the nutritional benefits of kenaf for animal feed resources.

 

Table 1: Physicochemical properties of soils.

Year	pH (1:5)	OM (g/kg)	EC (dS/m)	T-N (%)	Available P2O5 (mg/kg)	Ca2+	K+	Mg2+
						(cmol+/kg)
2019	7.3	12.0	0.23	0.14	422.3	6.07	1.18	2.07
2020	7.8	18.0	0.38	0.17	491.7	4.10	0.46	0.93

 

pH: Potential of Hydrogen, OM: Organic Matter, EC: Electrical Conductivity, T-N: Total Nitrogen, Available phosphorus (P2O5).

 

Materials and Methods

Field experiment and soil physicochemical properties

Two growing seasons (2019 and 2020) experiment was conducted in Gyeongsan, South Korea, located at latitude 35° 54’ 11.12” N and longitude 128° 51’ 22.67” E. The soil’s physicochemical properties before the application of manure are detailed in Table 1. The soil primarily comprised a blend of sand and clay, exhibiting favorable physicochemical characteristics that did not significantly hinder plant growth. Laboratory assessments indicated higher levels of pH, organic matter (OM), electrical conductivity (EC), total nitrogen (T-N), and available phosphorus (P2O5) in 2020 compared to 2019. Conversely, concentrations of calcium, potassium, and magnesium ions slightly decreased from 2019 (6.07, 1.18, and 2.07 cmol+/kg, respectively) to 2020 (4.10, 0.48, and 0.93 cmol+/kg, respectively).

 

Table 2: Weather characteristics during the study periods.

Year	Items	Classification	May	June	July	August	September
2019	Temperature (℃)	Minimum	11.3	16.3	21.4	22.5	17.9
		Maximum	27.7	28.2	30.0	32.1	27.2
		Average	19.5	21.9	25.4	26.7	22.1
	Precipitation (mm)	Total (701.5)	23.0	242.1	105.7	174.4	157
2020	Temperature (℃)	Minimum	12.0	17.3	18.9	23.3	15.5
		Maximum	24.4	29.1	25.8	31.9	25.0
		Average	18.0	23.0	22.0	27.0	19.8
	Precipitation (mm)	Total (975.1)	46.4	142	338.5	246.6	201.6
30-year average (1989-2018)	Temperature (℃)	Minimum	10.7	16.3	21.0	21.1	15.4
		Maximum	24.8	27.5	30.0	30.4	26.2
		Average	17.7	21.6	25.1	25.3	20.3
	Precipitation (mm)	Total (803.4)	84.6	122.4	230.4	228.8	137.2

 

A-C: Different letters in the same column are significantly different (p<0.05), CP: Crude Protein, OM: Organic Matter, ADF: Acid Detergent Fiber, NDF: Neutral Detergent Fiber, TDN: Total Digestible Nutrients.

 

Table 3: Manure characteristics

Composition	MC (%)	TS (%)	VS (%)	TN (%)	TP (%)	NH4-N	Cu	Mg	Zn
						(mg/kg)
Mean	6.0	94.0	68.2	21.5	9.2	43.7±0.6	21.4±1.1	7,869±153	137±4

 

MC: Moisture Content, TS: Total Solids, VS: Volatile Solids, TN: Total Nitrogen, TP: Total Phosphorus, NH4-N: Ammonium. Data represent mean ± Standard deviation

 

 

Weather characteristics of the field experiment

Meteorological information, about temperature and precipitation, for the two-year experiment is presented in Table 2. The mean temperature exhibited a gradual rise from May to August in both years, aligning with the 30-year mean. Notably, the maximum temperature in 2019 surpassed that of 2020, potentially reflecting the impact of recent global warming. Furthermore, precipitation in 2020 notably exceeded the levels recorded in 2019, creating more favorable conditions for the growth of kenaf (Figure 1).

Experimental treatments and data collection

The two-year experimental setup employed a randomized complete block design, incorporating four main plot treatments (Treatment 1: 100 DAP, Treatment 2: 110 DAP, Treatment 3: 120 DAP, Treatment 4: 130 DAP), each replicated three times. The sub-plots received four manure fertilization levels (0 kg N/ha - control, 150, 200, and 250 kg N/ha), with each level replicated three times. Initial manure fertilization occurred post-planting, supplemented by additional fertilization during the growth period. Table 3 provides the characteristics of the manure materials. For the evaluation of forage productivity under various manure fertilization levels and harvesting periods, the kenaf variety “Hongma 74-3” was utilized. Standardized agricultural science and technology research surveys (RDA, 2012) were conducted to assess agricultural growth, traits, and forage yield, encompassing parameters such as plant height, leaf ratio, stem ratio, and dry matter yield.

Land preparation, planting methods, and harvesting periods

Each replication comprised a 5×1 m plot. Kenaf was planted under four distinct manure fertilization levels, initially applied post-planting, with supplementary organic fertilization during the growth phase. Seed broadcasting was carried out by hand, with a seeding level of 80 kilograms/ha onto dry soil, resulting in a planting density of 20×20 cm. The first experiment spanned from May 8th to September 15th, 2019, while the second experiment took place between May 16th and September 23rd, 2020. In 2019, the harvests took place on August 16th, August 26th, September 5th, and September 15th, while in 2020, they occurred on August 24th, September 3rd, September 13th, and September 23rd.

Chemical composition analysis

Samples were collected from each experimental section, subjected to a 3-day drying process in a dry oven, and subsequently weighed. Leaves and stems underwent separate drying, and their respective dry weights were determined. The analysis of forage chemical composition followed the scientific methodologies outlined by the Association of Official Analytical Chemists - AOAC (2012). Crude protein (CP) content was ascertained through the Kjeldahl digestion method, while fiber analysis, encompassing neutral detergent fiber (NDF) and acid detergent fiber (ADF), was conducted using the procedure outlined by Van Soest et al. (1991). Total digestible nutrients (TDN) were computed utilizing the formula by Moore and Undersander (2002): TDN = 88.9 - (0.79 × ADF).

Statistical Analysis

The statistical analysis of all experimental data, including agricultural growth, yield, and feed value under various manure fertilization application levels and harvesting periods, was conducted using SAS Statistical Package Program (version 9.1; SAS Institute Inc.; Cary, USA). The least significant difference (LSD) tests were employed to identify significant differences among treatment mean values. Differences were considered significant if the p-value was less than 0.05.

Results and Discussion

Agricultural growth, traits, and kenaf yield under varied harvesting periods

The impact of diverse harvesting periods (100, 110, 120, and 130 DAP) on kenaf’s plant height, DM ratio, leaf ratio, stem ratio, and DM yield is presented in Table 4. The most substantial kenaf growth was noted during the 130 DAP harvesting period for both 2019 and 2020, as well as the two-year mean. A noteworthy escalation in plant height (p<0.05) was observed as kenaf growth advanced. Remarkably, the plant height in 2019 and 2020 exhibited a significant difference between the control and other harvesting periods, with the mean plant height in 2020 slightly surpassing that of 2019. These variations in plant height were likely influenced by fluctuations in rainfall patterns during the growth period, resulting in a year-by-treatment interaction. Kenaf, being photosensitive, responds to the timing of planting, which can be affected by climate change (Adetumbi et al., 2022). The peak DM ratio for kenaf during the summer of 2019 and the two-year mean, impacted by varying harvesting periods, was identified during the earlier harvesting period of 100 DAP. Conversely, in the summer of 2020, the DM ratio of kenaf exhibited no statistically significant difference among all treatments (p>0.05). Similar findings were reported by Nam et al. (2018), indicating a lack of statistically significant difference in the DM ratio among various treatments. In the summer of 2019, the leaf ratio demonstrated a noteworthy increase during the harvesting period of 110 DAP, while the stem ratio exhibited a significant rise during the harvesting periods of 120 and 130 DAP compared to the earlier periods. In contrast, throughout the summer of 2020, the leaf ratio experienced a notable increase as kenaf growth advanced from 100 to 130 DAP, while the stem ratio exhibited a significant decrease (p<0.05). During the summer of 2019, the DM yield of kenaf, subject to various harvesting periods, peaked in the earlier harvesting period, with no significant difference observed between the harvesting periods of 120 and 130 DAP (p>0.05). Interestingly, in the summer of 2020, as kenaf matured, a substantial increase in DM yield was noted. Adetumbi et al. (2022) reported that global climate effects, characterized by variations in the seasonal amount, timing, distribution, and intensity of precipitation, have a significant impact on crop productivity. The two-year mean of the DM yield of kenaf under different harvesting periods indicated no significant difference among all treatments (p>0.05). Nevertheless, the DM yield of kenaf appeared to be higher in the harvesting periods of 100 and 130 DAP. Nam et al. (2018) suggested that late-maturing kenaf crops generally exhibit superior yields compared to early-maturing ones.

 

Table 4: Effects of multiple harvesting periods on the agriculture growth, traits and yield of kenaf.

Year	Days after planting	Plant height (cm)	DM ratio (%)	Shoot ratio (%)		DM yield (ton/ha)
				Leaves	Stem
2019	100	141.0±40D	25.3±4.0A	36.0±7.0AB	64.0±7.0AB	11.2±3.0A
	110	167.3±27C	21.0±3.0B	42.6±12A	57.4±12AB	8.5±3.0AB
	120	180.8±48B	16.7±1.0C	30.8±5.0B	69.2±5.0A	6.1±5.0B
	130	207.9±27A	18.6±2.0BC	31.6±5.0B	68.4±5.0A	5.7±1.0B
	p-value	<0.0001	<0.0001	0.0125	0.0125	0.0125
2020	100	148.2±38D	29.0±4.0	37.0±7.0B	63.0±7.0A	9.1±4.0B
	110	176.0±55B	22.9±6.0	36.7±9.0B	63.3±9.0A	9.9±5.0B
	120	161.8±44C	29.4±8.0	46.3±8.0A	53.7±8.0B	11.2±6.0B
	130	216.5±61A	25.6±8.0	48.6±3.0A	51.4±3.0B	22.7±17A
	p-value	<0.0001	0.2796	0.0014	0.0014	0.0206
2-year mean	100	144.6±42C	27.1±5.0A	36.5±8.0	63.5±8.0	10.2±4.0
	110	171.6±44B	22.0±4.0B	39.6±11	60.4±11	9.2±5.0
	120	171.3±48B	23.1±9.0AB	38.6±10	61.4±10	8.6±6.0
	130	212.2±51A	22.1±7.0B	40.1±10	59.9±10	14.2±9.0
	p-value	<0.0001	0.0081	0.6380	0.6380	0.2125

 

A-D Different letters in the same column are significantly different (p<0.05)

 

Table 5: Effects of different manure application levels on the agricultural growth, traits and yield of kenaf.

Year	Manure application levels (kg N/ha)	Plant height (cm)	DM ratio (%)	Shoot ratio (%)		DM yield (ton/ha)
				Leaf	Stem
2019	0	156.4±39C	20.8±2.0	35.2±5.0	64.8±5.0	6.6±3.0B
	150	168.8±27B	19.9±3.0	37.8±10	62.2±10	6.7±2.0B
	200	176.3±47B	20.7±4.0	30.5±5.0	69.5±5.0	8.3±2.0AB
	250	195.5±31A	20.2±3.0	37.6±9.0	62.5±9.0	9.9±4.0A
	p-value	<0.0001	0.8819	0.1922	0.1922	0.0040
2020	0	155.9±47B	28.1±7.0	40.7±7.0B	59.3±7.0A	9.7±5.0B
	150	182.4±46A	25.5±6.0	40.8±8.0B	59.2±8.0A	13.5±8.0AB
	200	179.8±59A	28.0±10	39.2±7.0B	60.8±7.0A	19.4±9.0A
	250	184.4±47A	25.2±4.0	47.9±5.0A	52.1±5.0B	10.5±4.0AB
	p-value	<0.0001	0.7810	0.0094	0.0094	0.0090
2-year mean	0	156.1±45C	24.5±6.0	37.9±8.0AB	62.1±8.0AB	8.1±4.0
	150	175.6±40B	22.7±5.0	37.9±12AB	60.7±12AB	10.1±6.0
	200	178.0±58B	24.3±9.0	34.9±9.0B	65.1±9.0A	13.8±7.0
	250	190.0±41A	22.7±5.0	42.7±10A	57.3±10B	10.2±5.0
	p-value	<0.0001	0.7593	0.0093	0.0093	0.2570

 

A-C Different letters in the same column are statistically different (p<0.05)

 

Agricultural growth, traits, and kenaf yield under various manure application levels

Table 5 outlines the influence of varied manure fertilization application levels (0, 150, 200, and 250 kg N/ha) on kenaf’s parameters such as plant height, DM ratio, leaf ratio, stem ratio, and DM yield. The kenaf plant height in 2019, 2020, and the two-year mean exhibited a discernible response to manure fertilization applications, with each successive increment in nitrogen dose significantly enhancing kenaf plant height. This observation is in accordance with the findings of Olanipekun et al. (2021), which emphasize the positive impact of increased livestock manure application and various other types of combined fertilizers on agronomic growth, including plant height. During the summer experiment of 2020, the leaf ratio displayed a tendency to be slightly higher compared to the previous year. The two-year mean leaf ratio of kenaf, influenced by various manure fertilization application levels, demonstrated no significant difference between the control and the manure fertilization application level of 150 kg N/ha (p>0.05). However, the highest leaf ratio of kenaf was observed at the nitrogen fertilization application level of 250 kg N/ha (p<0.05). Conversely, the stem ratio in the summer experiment of 2020 tended to be slightly lower than that of the previous year. In this study, the stem ratio of kenaf decreased significantly as the nitrogen content in the manure fertilization increased (p<0.05). Comparable trends were observed in the study by Nam et al. (2018), indicating a significant increase in the leaf ratio of kenaf with higher organic fertilization levels, accompanied by a significant decrease in stem ratio. The DM yield in 2020 slightly surpassed that of 2019 (Table 5, Figure 1), likely due to the significantly higher precipitation levels in 2020, which created more favorable conditions for the growth of kenaf (Table 2). The two-year mean of DM yield, influenced by various manure fertilization application levels, indicated that the highest DM productivity was observed at the manure fertilization application level of 200 kg N/ha. However, no significant difference was noted among all the manure fertilization treatments. This discovery is consistent with the findings of Danalatos and Archontoulis (2010), who reported no variance in kenaf fresh matter yield between nitrogen levels of 0, 50, 100, and 150 kg N/ha. They proposed that this lack of difference could be attributed to the plant’s low nitrogen requirements or the high initial available nitrogen in the soil.

Effects of varied harvesting periods on the nutritional value of kenaf leaves

The CP, OM, ADF, NDF, and TDN contents of kenaf leaves harvested at 100, 110, 120, and 130 DAP are displayed in Table 6. As the kenaf plants developed, the 2-year mean CP content of their leaves, which varied depending on the harvesting season, showed no significant difference (p>0.05) and varied between 12.9 and 16.2 percent. In a previous study, Kim et al. (2018) examined several kenaf crop types in Korea and found that the CP level in the leaves ranged from 22.1 to 26.2 percent, which is higher than the CP level of the present study. But according to the present study, the kenaf collected in the summer of 2019 had a little lower mean CP concentration than the kenaf gathered in 2020. Due to different harvesting periods in 2019, the OM content in kenaf leaves varied from 8 to 9, with the maximum concentration recorded at 120 DAP. Consistent with the results of this investigation, Kim et al. (2018) revealed that the OM concentration of kenaf leaves ranged from 5.2 to 6.6 percent, slightly greater than the OM level of kenaf stems. On the other hand, when the plants grew and the kenaf development advanced over the summer of 2020, the OM content of the kenaf leaves considerably reduced (p<0.05). When harvest intervals were extended from 3.5 to 10.5 weeks after planting, Hajer et al. (2020) observed a significant decrease in leaf OM content from 15.9 to 12.0 in research with almost similar parameters. ADF content in kenaf leaves during a two-year period, impacted by different harvesting periods, showed a substantial (p<0.05) decline when harvesting was postponed from 100 to 130 DAP. These results are consistent with those of Omenna et al. (2016), who found that harvesting kenaf near the start of the blooming phase yields the maximum fiber content. Under various harvesting conditions, the NDF content of kenaf leaves in 2019 had the greatest level at 120 DAP. According to the 2-year mean NDF content of kenaf leaves, the maximum amount was found during the early harvesting period and at 120 DAP. Due to varying harvesting periods, the TDN content of kenaf leaves in 2019 and 2020 as well as the 2-year mean revealed the highest level at 130 DAP. The TDN content of kenaf leaves considerably increased (p<0.05) as kenaf development progressed. This is not the case with the research by Nam et al. (2018), where the TDN content of kenaf increased dramatically with the growth of kenaf.

Effects of varied manure application levels on the nutritional value of kenaf leaves

The CP, OM, ADF, NDF, and TDN content of kenaf leaves at varying manure fertilization application levels of 0, 150, 200, and 250 kg N/ha are shown in Table 7. In 2019, the CP content of kenaf leaves was considerably increased (p<0.05) by an increase in nitrogen content from the manure fertilization but the mean CP concentration was slightly lower compared to the kenaf harvested in 2020 (Table 7 and Figure 2). The 2-year mean showed that, with the manure fertilization application level of 200 kg N/ha, the CP concentration in kenaf leaves was the highest among

 

Table 6: Effects of multiple harvesting periods on the feed value (chemical composition, %) of kenaf leaves.

Year	Days after planting	CP	OM	ADF	NDF	TDN
2019	100	12.9±0.80	8.3±0.10D	24.5±1.51A	37.1±1.27B	69.6±1.18B
	110	14.2±1.88	8.7±0.16C	21.0±0.74B	32.3±2.03C	72.3±0.59A
	120	14.1±0.51	9.8±0.12A	24.7±3.66A	41.9±4.47A	69.4±1.45B
	130	13.7±1.12	9.0±0.17B	21.9±0.78B	35.1±0.81BC	71.6±0.61A
	p-value	0.2061	<0.0001	<0.0001	0.0002	<0.0001
2020	100	13.0±0.69	9.9±0.30A	22.6±0.47A	34.8±0.53A	71.0±0.37D
	110	15.0±1.62	9.1±0.07B	20.4±1.84B	30.8±1.73C	72.8±1.45C
	120	14.2±2.29	8.5±0.04C	17.4±0.40C	31.3±0.78C	75.2±0.32B
	130	16.2±1.27	8.5±0.03C	15.9±0.38D	33.6±0.72B	76.4±0.30A
	p-value	0.2070	<0.0001	<0.0001	<0.0001	<0.0001
2-year mean	100	12.9±1.27	9.1±0.9	23.5±2.25A	35.9±2.29A	70.3±1.78C
	110	14.6±2.38	8.9±0.44	20.7±1.86BC	31.5±2.82B	72.6±1.47AB
	120	14.1±1.95	9.1±0.75	21.1±4.29B	36.6±7.14A	72.3±3.39B
	130	15.0±2.34	8.7±0.32	18.9±3.82C	34.3±3.07AB	74.0±3.02A
	p-value	0.2130	0.2784	0.0005	0.0028	0.0005

 

A-D Different letters in the same column are significantly different (p<0.05), CP: Crude Protein, OM: Organic Matter, ADF: Acid Detergent Fiber, NDF: Neutral Detergent Fiber, TDN: Total Digestible Nutrients

 

Table 7: Effects of different manure application levels on the feed value (chemical composition, %) of kenaf leaves.

Year	Manure application levels (kg N/ha)	CP	OM	ADF	NDF	TDN
2019	0	13.1±0.42B	9.1±0.11C	22.8±0.43AB	34.8±1.19	70.9±0.40AB
	150	12.9±2.08B	10.5±0.15A	23.9±1.04A	38.0±0.49	70.0±0.82B
	200	14.4±0.47A	10.1±0.18B	21.9±2.13B	35.4±0.88	71.6±1.68A
	250	14.5±1.05A	10.2±0.11B	23.4±1.24A	38.0±6.01	70.4±0.98B
	p-value	0.0197	<0.0001	0.0150	0.2153	0.0149
2020	0	14.0±1.52	9.3±0.11B	22.6±0.43A	34.9±1.0A	71.0±0.34C
	150	14.7±1.07	10.2±0.17A	18.4±0.62B	31.2±0.85B	74.3±0.51B
	200	15.3±0.91	10.2±0.13A	17.9±1.21BC	30.4±0.33B	74.8±0.13AB
	250	14.4±2.38	9.4±0.05B	17.4±0.81C	34.0±1.83A	75.2±0.64A
	p-value	0.4544	<0.0001	<0.0001	<0.0001	<0.0001
2-year mean	0	13.5±1.59B	9.2±0.82C	22.7±1.02A	34.9±1.85AB	71.0±0.81B
	150	13.8±2.53AB	10.3±0.56A	21.2±3.14AB	34.6±3.80AB	72.2±2.48AB
	200	14.9±1.87A	10.1±0.40AB	19.9±4.21B	32.6±4.08B	73.2±3.32A
	250	14.4±1.96AB	9.8±0.55B	20.4±3.86B	36.0±5.98A	72.8±3.08A
	p-value	0.0539	0.0525	0.0485	0.0185	0.0482

 

A-C Different letters in the same column are significantly different (p<0.05), CP: Crude Protein, OM: Organic Matter, ADF: Acid Detergent Fiber, NDF: Neutral Detergent Fiber, TDN: Total Digestible Nutrient

 

the treatments. This indicates a significant departure from the control group and confirms the findings of Byamungu and Jo (2021), which show that nitrogen fertilization is critical to increasing yields and increasing the CP content in kenaf leaves. In comparison to the summer of 2020, the ADF of kenaf leaves in 2019 was somewhat lower. The study found that when the nitrogen fertilizer was applied at several levels (from 0 to 250 kg N/ha), the 2-year mean ADF content of kenaf leaves decreased significantly (p<0.05). Similarly, there was no discernible difference in the NDF content between the control and manure fertilization application level of 150 kg N/ha, according to the 2-year mean of NDF content of kenaf leaves, which showed the maximum NDF content at the manure fertilization application level of 250 kg N/ha. The NDF concentration rose considerably (p<0.05) when the nitrogen component in the manure fertilization formulation increased from 0 to 250 kg N/ha. Nonetheless, in this investigation, the ADF and NDF of kenaf leaves were less than those of the kenaf stem. This is consistent with research by Byamungu and Jo (2021), who observed that kenaf cultivars varied in their cell wall composition and function, leading to increased ADF in the stem as opposed to the leaf. There was no significant difference in the TDN content of kenaf leaves in 2019 between the application levels of 150 and 250 kg N/ha of manure fertilization and the greatest TDN content recorded at the manure fertilization application level of 200 kg N/ha. Nonetheless, in 2020, the application level of 250 kg N/ha yielded the greatest TDN content among the treatments (p<0.05). Different levels of manure fertilization application had an impact on the 2-year mean TDN content of kenaf leaves, which was 71.0, 72.2, 73.2, and 72.8 percent, respectively. The fertilizer application levels of 200 and 250 kg N/ha showed the greatest TDN concentration.

Effects of varied harvesting periods on the nutritional value of kenaf stem

The concentration of CP, OM, ADF, NDF, and TDN in kenaf stems harvested at 100, 110, 120, and 130 DAP is shown in Table 8. Due to varying harvesting periods, the CP content of kenaf stem in 2019 and 2020 as well as the 2-year mean showed that the greatest CP concentration was at 120 DAP, reaching 3.7 percent. In a recent study, Kim et al. (2018) evaluated the nutritional properties of leaves, stem bark, flowers, and seeds from various kenaf cultivars, including Jangdae, Baekma, Jeokbong, Jinju, and C14. They reported that the CP concentration in the leaves of these kenaf varieties was 4.7, 5.8, 5.5, 4.6, and 4.8 percent, respectively. At 100 and 120 DAP, the O Mcontent of kenaf stem showed the highest values in 2019. Nonetheless, when kenaf growth advanced in 2020 and the 2-year mean, the OM content in the stem considerably dropped (p<0.05), falling from 7.5 percent

 

 

Table 8: Effects of multiple harvesting periods on the feed value (chemical composition, %) of kenaf stem.

Year	Days after planting	CP	OM	ADF	NDF	TDN
2019	100	3.5±0.79	7.4±0.15A	56.0±1.53B	69.0±1.57B	44.6±1.21A
	110	3.0±1.00	7.1±0.26B	57.9±2.08B	70.1±2.10AB	43.1±1.58A
	120	4.0±0.31	7.4±0.15A	60.9±1.24A	72.3±6.89AB	40.8±0.98B
	130	3.4±0.32	6.7±0.21C	61.2±2.20A	75.0±1.82A	40.5±1.83B
	p-value	0.2011	<0.0001	<0.0001	0.0454	<0.0001
2020	100	2.4±0.63	7.6±0.37A	57.1±0.49C	70.0±0.46B	43.8±0.39A
	110	2.9±0.25	7.0±0.21B	59.6±5.26BC	70.3±0.80B	41.8±4.17AB
	120	3.4±0.22	6.8±0.63BC	62.5±1.33B	75.4±0.40A	39.5±1.03B
	130	3.0±0.43	6.6±0.15C	69.8±0.81A	75.3±0.72A	33.8±0.64C
	p-value	0.2002	<0.0001	<0.0001	<0.0001	<0.0001
2-year mean	100	3.0±1.07	7.5±0.47A	56.6±1.66C	69.5±1.93B	44.2±1.31A
	110	3.0±2.97	7.1±0.65B	58.8±5.26C	70.2±3.69B	42.5±4.14A
	120	3.7±1.03	7.1±0.36B	61.7±3.08B	73.9±5.37A	40.1±2.50B
	130	3.2±0.41	6.7±0.45C	65.5±5.23A	75.1±2.21A	37.2±4.12C
	p-value	0.2267	<0.0001	<0.0001	<0.0001	<0.0001

 

A-C Different letters in the same column are significantly different (p<0.05), CP: Crude Protein, OM: Organic Matter, ADF: Acid Detergent Fiber, NDF: Neutral Detergent Fiber, TDN: Total Digestible Nutrients

 

Table 9: Effects of different manure application levels on the feed value (chemical composition, %) of kenaf stem.

Year	Manure application levels (kg N/ha)	CP	OM	ADF	NDF	TDN
2019	0	3.7±0.32AB	6.3±0.20C	58.2±1.67	70.2±0.98	42.9±1.32
	150	3.2±0.74BC	7.9±0.21A	60.0±0.86	74.6±1.44	41.5±0.68
	200	2.7±0.98C	7.2±0.16B	58.4±2.20	71.8±1.55	42.8±1.74
	250	4.3±0.36A	7.3±0.19B	59.4±2.24	70.0±8.40	42.0±1.77
	p-value	0.0004	<0.0001	0.3378	0.3124	0.3367
2020	0	2.1±0.48B	7.1±0.46A	60.3±1.16B	70.2±0.48B	41.2±0.92A
	150	3.2±0.30A	7.2±0.12A	60.9±0.81B	73.7±0.55A	40.8±0.64A
	200	3.1±0.38A	7.1±0.21A	62.6±3.07AB	73.3±0.54A	39.4±2.42AB
	250	3.3±0.28A	6.6±0.10B	65.1±2.85A	73.7±0.81A	37.4±2.25B
	p-value	<0.0001	0.0003	0.0120	<0.0001	0.0120
2-year mean	0	2.9±0.94B	6.7±0.66C	59.3±3.48B	70.2±3.23B	42.1±2.75A
	150	3.2±1.10AB	7.6±0.57A	60.5±2.55AB	74.2±1.73A	41.1±2.56AB
	200	2.9±1.30B	7.1±0.26B	60.5±4.52AB	72.5±2.13AB	40.1±3.57AB
	250	3.8±0.74A	6.9±0.44BC	62.3±4.65A	71.8±6.06AB	39.7±3.67B
	p-value	0.0428	<0.0001	0.0019	<0.0001	0.0019

 

A-C Different letters in the same column are significantly different (p<0.05), CP: Crude Protein, OM: Organic Matter, ADF: Acid Detergent Fiber, NDF: Neutral Detergent Fiber, TDN: Total Digestible Nutrients

 

 

to 6.7 percent. As kenaf maturity increased, the ADF content in the stem in 2019 and 2020, as well as the 2-year mean, showed a substantial rise (p<0.05). With increasing maturity, the NDF concentration of kenaf stem increased considerably (p<0.05) in 2019 and 2020 as well as the 2-year mean, which was impacted by varied harvesting seasons. This supports the research by Hajer et al. (2020), which demonstrates that the cell walls were more lignified in stems harvested at mature stages compared to those harvested at earlier stages. The 2-year mean, which showed the greatest TDN concentration in kenaf stem in 2020 and 2019, was noted in the earlier harvesting seasons. This suggests that TDN content significantly decreased (p<0.05) as kenaf growth advanced.

Effects of varied manure application levels on the nutritional value of kenaf stem

The CP, OM, ADF, NDF, and TDN content of kenaf stem with varying levels of manure fertilization application (0, 150, 200, and 250 kg N/ha) is presented in Table 9. The CP content of kenaf stems reached its highest values in 2019, 2020, and the 2-year mean when the highest manure fertilization application level was used. Xu et al. (2022) explained this increase, noting that applying livestock manure fertilization at various ratios can reduce the need for mineral fertilizers while enhancing crop yield and quality. Additionally, in this study, the CP content of kenaf stems in 2019 was slightly higher than that in 2020 (Table 9 and Figure 3). On the other hand, due to varying levels of manure fertilization application, the 2-year mean of the OM content in kenaf stem peaked at 150 kg N/ha. In 2019, there was no discernible variation in the ADF, NDF, and TDN content of kenaf stems under different levels of manure fertilization treatment. However, when the nitrogen content in the manure fertilization application levels increased from 0 to 250 kg N/ha in 2020, the ADF and NDF content of kenaf stem exhibited a considerable rise (p<0.05), whereas the TDN content dramatically reduced (p<0.05). As the nitrogen content of the manure fertilization rose, there was a substantial (p<0.05) drop in the 2-year mean of ADF concentration in kenaf stem, which was influenced by varied levels of manure fertilization application. Conversely, the kenaf stem’s 2-year mean of NDF content revealed the greatest NDF content at 150 kg N/ha, with no significant difference between the 200 and 250 kg N/ha manure fertilization application levels. According to Kujoana et al. (2023), the fiber levels observed in this study are deemed suitable for ruminant nutrition. The 2-year mean showed the greatest TDN concentration in the control group; there was no significant difference in the manure fertilization application levels of 150, 200, and 250 kg N/ha. It’s interesting to note that as the nitrogen concentration of the manure fertilization grew from 0 to 250 kg N/ha, the TDN content reduced dramatically (p<0.05).

Conclusions and Recommendation

Comparing the treatments used in this study to the control, the effects on agricultural growth, characteristics, forage production, and feed value of kenaf were substantial and favorable. While there were no discernible changes in the DM yield of kenaf across different levels of manure fertilization application, the level of 200 kg N/ha proved to be particularly significant when compared to other treatments. Kenaf growth was shown to be positively correlated with manure application; the tallest plants were correlated with the greatest manure level. At a manure fertilization application level of 200 kg N/ha, the mean CP content in kenaf leaves was significantly greater. Furthermore, the mean ADF content decreased as the nitrogen levels in manure rose. Additionally, at the 110, 120, and 130 DAP harvesting periods, the 2-year mean CP content of kenaf leaves was higher, but the ADF content considerably dropped as kenaf development advanced. The 120 DAP period and the early harvesting period had the greatest NDF levels. The stem’s 2-year mean NDF was greater during the 120 and 130 DAP periods, whereas the stem’s mean CP content was higher during the 120 DAP harvesting period. In summary, optimal growth and development of kenaf were achieved with a manure fertilization level of 200 kg N/ha and harvesting between 110 and 120 DAP. It is strongly suggested that farmers use these guidelines in view of the worldwide pledges made to lower methane emissions and enhance manure management methods. By doing this, kenaf is not only better cultivated and produced, but its potential as a priceless source of enhanced nutritious animal feed is also maximized.

Acknowledgements

The author and co-authors would like to express their sincere gratitude to their supervisor and mentor, Prof. Dr. Jo Ik-Hwan, for his invaluable advice and support throughout this study. They extend their best wishes to him as he embarks on his well-deserved retirement.

Novelty Statement

The research identifies that a manure rate of 200 kg N/ha and a harvest period between 110 and 120 days after planting optimize both yield and nutritional quality. This dual approach offers comprehensive insights into sustainable kenaf production and forage quality enhancement, aligning with global methane reduction initiatives through improved manure management.

Author’s Contribution

Byamungu Mayange Tomple: Conceptualized and designed the study, conducted field surveys, performed chemical analysis, wrote the abstract, introduction, methodology, collected data, entered data into SAS, conducted the statistical analysis, wrote the results and discussion, conclusion, and references.

Ik-Hwan Jo: Conceptualized, designed, and supervised the study.

Rajaraman Bharanidharan: Analyzed data, reviewed the manuscript, proofread, and conducted plagiarism checks.

Seun-Gun Won: Supervised the research, contributed to its design and provided intellectual content.

Muhammad Mahboob Ali Hamid: Supervised the study, reviewed the manuscript, performed proofreading, and revised the manuscript.

Conflict of interest

The authors have declared no conflict of interest.

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