Effect of doses fertilizer and harvest interval on the intensity of leaf spot diseases, production and quality of citronella grass (Cymbopogon nardus L.) essential oils in ultisols soil

Abstract

Until now, Indonesia is still a world exporter of essential oils, including citronella oil. So that the role of farming communities in the development of Indonesia's essential oil industry is very helpful. For this reason, a study was carried out on response of fertilization and harvest interval on the intensity of leaf spot diseases of citronella grass, and productivity in ultisols soil which was carried out from October 2020 to September 2022. The experiment was arranged in a randomized block design in factorial with 9 treatments, as the first factor is 3 levels of an organic fertilizer (NPK); P1 = 25 g clumps ⁻¹, P2 = 37.5 g clumps ⁻¹ and P3 = 50 g clumps ⁻¹. The second factor is the harvest interval with three levels which is 4 = harvest interval once every 4 months, 3 = harvest interval every 3 months and 2 = harvest interval once every 2 months, repeated three times. Each treatment plot consisted of 24 clumps with a plant spacing of 1 × 1 × 1 m. Varieties used is Serai wangi 1. Parameters observed were intensity of leaf spot diseases, vegetative growth, livestock production, oil production, quality analysis and R/C ratio. The results showed that there was an effect of fertilizer doses and harvest intervals on the development of leaf spot disease. It was seen that at the application of fertilizer doses of 37.5 g clumps ⁻¹ with harvest intervals once every three months showed the lowest disease attacks, namely on Cuvularia sp and Pestalotia sp (5.98%, 5.42% and 7.98 %, 7.44 %). In addition, the development of vegetative growth is also influenced by the application of fertilizer doses and harvest intervals on the parameters of canopy width, plant height, leaf length, leaf width and number of tillers. The best fertilizer dose is 37.50 g clump ⁻¹ successively (175.40 cm, 172.29 cm, 113.62 cm, 2.36 cm and 119.59 stems), with harvest intervals every 3 months (179.40 cm, 187.29 cm, 119.44 cm, 2.45 cm and 120.00 stems), as well as fresh leaves production tons/ha/year and oil production kg/ha/year the best is the application of fertilizer doses of 37.50 g clumps⁻¹ with harvest intervals once every 3 months (67.81 tons^−ha-year and 578.61 kg^{−ha- year},with, 67.40 tons^–ha-th and 517.60 kg^–ha-th). For oil quality, numerically, the application of fertilizer at a dose of 37.50 g of clump ⁻¹ with harvest intervals every 3 months is still high. The proper R/C ratio for farming occurs in the 2 nd year by administering a fertilizer dose of 37.50 g clump⁻¹ and harvesting intervals once every 3 months with an increase of 116.67%. So, the citronella grass variety Serai wangi 1 can be developed on ultisol soil types by applying an organic fertilizer (NPK).

1. Introductions

Indonesia is a major exporter of essential oils, including citronella essential oil. Through the Ministry of Agriculture's program, the development of essential oil-producing agriculture is always being improved, in line with the increasing income of Indonesian farmers with the opening of even wider employment opportunities [1].

In line with that the development of citronella grass continues to be improved because this commodity has many uses and can grow well from the lowlands to the highlands even on ultisol soils it can grow well as has been done by Ref. [2] In rural areas the development and processing of citronella oil properly is one of the strategic steps to spur the economy of rural communities and can open up employment opportunities thereby increasing competitiveness and added value [3].

In the world of exporters of citronella essential oil, there are conditions that must be met, namely having a high citronellal and geraniol content. The use of citronella essential oil, although its main components or derivatives have been used in the cosmetics, perfume, soap and pharmaceutical industries, is also used for botanical pesticide in controlling plant pests and disease-causing organisms in humans. 25% citronella oil can cause 86% mortality against the Musca domestica house fly [4]. In addition, citronella oil and cinnamic acid through enzymatic esterification have toxicity against Artemia salina (LC50 5.29 μg mL⁻¹) and as larvicides on Aedes aegypti (LC50 4.36 μg mL⁻¹) [5]. Furthermore, citronella essential oil with a concentration of 15% has an effective repellency against Culex sp mosquitoes [6]. Another benefit of citronella essential oil as an additive can increase the Piper aduncum botanical fungicide against the pathogens Sclerotium rolfsii, Pestalotia sp, and Fusarium oxysporum [7]. Not only citronella oil can be utilized, but the liquid waste from citronella oil distillation can also be used as a botanical pesticide, namely in controlling A. aegypti instar III mosquito larvae for 24 h with an LC 50 of 8.763% [8].

The distribution area of ultisols in Indonesia reaches 25% of the land area, which has the characteristics of accumulation of clay in the horizon below the surface so that water absorption is reduced as a result of increased surface runoff and soil erosion occurs. This is one of the obstacles in the fertility of ultisols, because ultisols are only determined by the organic content of the top layer. For this reason, it is necessary to add soil nutrients by applying inorganic fertilizers [9].

According to Mohr and Van Baren in Ref. [10], that ultisol soil type has low to moderate organic matter, with a Cation Exchange Capacity (CEC) < 24 me or 100 g clay. Such ultisol conditions can be overcome by various improvement efforts, such as applying lime, fertilizing and applying organic matter. Lime aims to increase soil pH, so as to increase the availability of some nutrients. While fertilization aims to increase the source of nutrients in the soil. The addition of organic fertilizer aims to improve the physical, chemical, and biological soil properties of the soil.

In the development of citronella grass, there are obstacles that are often encountered, namely leaf spot attack by Curvularia sp, Pestalotia sp, and Fusarium sp because what is used for the essential oil of citronella is the leaves, so pathogen attack on the leaves can reduce fresh leaves production from citronella as shown. found by Ref. [11] of 18.01–43.65%.

From the results of research [2] in the development of citronella on ultisols soil the best variety is Serai wangi 1 with harvest intervals once every 3 months. According to field surveys, most citronella grass farmers in Solok Regency, West Sumatra, still harvest it early due to the needs of life. In addition, disease attack on leaves harvested early will reduce the source of inoculum for the disease. For this reason, further research was carried out to know the response of fertilization and harvest interval on the intensity of leaf spot diseases on citronella grass, production, and quality of essential oils in ultisols soil, as described below.

2. Materials and method

This research was carried out from October 2020 to September 2022 at the IPPTP Laing Solok Experimental Garden, West Sumatra. The soil type used is ultisols which is located at an altitude of 468 m above sea level and has a climate of type. The research began with land clearing and plowing, followed by making planting holes with a size of 30 × 30 × 30 cm and spacing with 1 × 1 × 1 m. The distance between plots is 2 m. Each hole is added with cattle manure at the rate of 5 tons ha-1, agricultural lime 1 ton ha-1. The materials and soil were mixed to homogenize it and left for one week. 2 6-month-old citronella stalks (30 cm long) were planted in each hole. The variety used in this study is serai wangi 1. Fifteen days after planting, inorganics fertilizer was applied by making a 20 cm circular array, then the fertilizer was distributed to the array roundly, and array was covered with soil. The first harvest is carried out after the plants are 6 months old, for the next harvest based on the harvest interval treatment.

The experiment was arranged in a randomized block design in factorial with 9 treatments with three replications, the first factor being 3 levels of inorganic fertilizer (NPK Mutiara 16-16-16) P1 = 25 g clump −1, P2 = 37.5 g clump −1 and P3 = 50 g clump −1, as the second factor, namely the harvest interval with three levels consisting of 4 = harvest interval every 4 months, 3 = harvest interval once every 3 months and 2 = harvest interval once every 2 months, repeated three times. Each treatment plot consisted of 24 clumps with a plant spacing of 1 × 1 × 1 m. The variety used was Serai Wangi 1. The total number of leaf samples observed is 12.5% of the plants in a population. The parameters observed were disease intensity measured after 2 months, due to the fastest interval of harvesting being once every 2 months.

The disease intensity index of Pestalotia sp. infestation is 0 = symptomless/no spot, 1 = small than <3 % of infected leaves, 2 = 3–10% of leaves are infected, 3 = 11–25 % of leaves are infected, 4 = 26–50% of the leaves are infected 5= >50 infected leaves. Then, the score described for Curvularia sp onset was described in scores, namely score 0 = symptomless/no spot, 1 = spotting in one leaf sheet with 1–3 dots (<3%), 2 = spotting in one leaf sheet with 4–10 dots (3–10%), 3 = spotting in one leaf sheet with 11–25 dots (11–25%), 4 = spotting in one leaf sheet with 26–50 dots (26–50%), and 5 = spotting in one leaf sheet >50 dots (>50%). Conversion of [12] (Fig. 1).

$$I=\frac{\sum nv}{NV}\times 100\%$$ (1)

Fig. 1.

Scoring of leaf spot diseases symptoms caused by Curvularia sp. and Pestalotia sp.

I is the disease intensity index, ∑ is the sum, n is the frequency of leaf with v score, v is the scale of the symptom, N is the total number of leaves observed, and V is the maximal disease index.; Then vegetative growth (canopy width, plant height, longest leaf length, leaf width and number of tillers), herb production, oil production, quality analysis using the Gas Chromatography Mess Spectrum method, and R/C ratio. Followed by an analysis of the Revenue Cost Ratio (R/C Ratio). The statistical analysis used the Sirichai program version 6.2, if there is a significant difference it is continued with the Duncan's Multiple Range Test.

3. Results and discussion

The mean of disease intensity indicates that application of three doses of NPK fertilizer and intervals of harvest affect the disease intensity of citronella leaf spot disease however there is no interaction found between the application of fertilizer and interval of harvest. Morphological and microscopical characterization [13) of two pathogens found to affect citronella plant are Pestalotia sp. and Curvularia sp. Based on previous research [11] leaf spot diseases that often affect citronella plants are Pestalotia sp., Curvularia sp. and Fusarium sp. At 2 months old plants, it can be seen that the higher the dose of fertilizer, the higher the plant's resistance to leaf spot diseases. Application of 37.5 g of clump⁻¹ fertilizer did not differ significantly from the dose of 50 g of clump⁻¹ fertilizer against the disease intensity (7.98 and 7.91) % for Pestalotia sp., whereas for Curvularia sp., there was a difference in the response to fertilizer application. Fertilizer applied 37.5 and 50 g clump⁻¹ (5.98 and 5.61) % as well as the harvest interval once in 3 months and once in 4 months did not differ significantly. At the harvest interval determined as the second factor, the disease intensity produced by the Pestalotia sp. were 7.44 and 6.99 % and produced by Curvularia sp. which also showed the difference where the lowest is at the harvest interval once every 3 months namely 5.42 %. There is different response of the two pathogens on fertilizers application where the effect of Pestalotia sp. is higher than the Curvularia sp. (Fig. 2). In accordance with what was stated by Ref. [13] that NPK and POC fertilizers can reduce the intensity of disease caused by Fusarium oxysporum in tomato plants by 23.08% and 13.32% respectively. In addition, 250 kg/ha NPK fertilizer +20 t/ha manure +10 t/ha patchouli compost was able to reduce the intensity of budok disease on patchouli plants by around 48.49% [14]. Based on the estimation that the addition of potassium in plants can increase the thickness of the cell wall and this type of fertilizer acts as an activator for the formation of chitinase. Chitinase itself is an enzyme that can induce plant defense against pathogenic fungi [15]. Fig. 2 presented disease intensity index of the citronella grass affected by Pestalotia sp. and Curvularia sp.

Fig. 2.

Disease intensity index of the citronella grass affected by Pestalotia sp. and Curvularia sp. after fertilizer application and at different interval harvesting.

Vegetative growth affects the citronella grass production because the expected production is the leaves of the citronella. The application of various doses of fertilizer and harvest intervals affects the vegetative growth of citronella grass. The higher the dose of fertilizer and the slower the harvest, the better the vegetative development, as shown in Table 1. Furthermore, there is an effect of the treatment of harvest intervals and fertilization on the vegetative growth of citronella grass fragrance. Harvest intervals carried out once every 2 months with 25 g of fertilizer clump⁻¹ showed significantly different vegetative development compared to the treatment of once every 3 months and once 4 months with a combination of 37.5 g of fertilizer clump⁻¹ and 50 g of clump⁻¹, as shown in Table 2. Here it can be seen that increasing the dose of fertilizer on ultisols soil greatly affected the development of citronella grass, even though the application of 37.5 g of fertilizer clump⁻¹ showed no significant difference with a dose of 50 g clump⁻¹. In accordance with what was stated by Refs. [16,17] applying fertilizer to ultisols soil can increase the yield of corn plants due to improvements in the physical and chemical properties of the soil. Applying the right dose of fertilizer will be able to improve the physical, chemical, and biological properties of the soil so that the soil structure becomes loose as a result the roots will develop and more easily absorb nutrients to increase plant productivity in ultisols soils [18]. Because what is expected from the production of citronella is the leaves that will be processed into essential oils, the width of the plant crown, the length of the leaves and the number of tillers greatly affect the yield. Table 1 shows that the harvest interval once every 4 months and once every 3 months does not show a significant difference.

Table 1.

Vegetative growth of citronella grass (C. nardus L.) cv. Serai wangi 1 applied with three doses of fertilizer at different intervals of harvest.

Treatment	Vegetative Growth
	CW/cm	PH/cm	LL/cm	LW/cm	NT/Stem
Fertilizer Dosage
25 g clump−1	165.91 b	162.47 b	100.28 b	2.41 b	105.05 b
37.5 g clump−1	175.40 a	172.29 a	113.62 a	2.36 c	119.59 a
50 g clump−1	176.18 a	165.67 ab	112.68 a	2.46 a	115.47 a
Harvest Intervals
4 months	178.25 a	156.95 b	118.17 a	2.44 a	117.55 a
3 months	179.40 a	187.29 a	119.44 a	2.45 a	120.00 a
2 months	159.85 b	156.19 b	88.97 b	2.35 b	102.56
CV/%	12.49	14.62	13.36	11.10	14.47

Note: Numbers followed by the same lowercase letter were not significantly different at the 5% DMNRT test level. CW is canopy width, PH is plant height, LL is leaf length, LW is leaf width and NT is number of tillers.

Table 2.

Production of fresh leaves and citronella oil from citronella grass applied by three doses of fertilizers and harvested at 2, 3, and 4 month-intervals.

	Production
Treatment	Leaf production/ton/ha/year	Oil production/kg/ha/year
Fertilizer Dosage
25 g clump−1	53.74 a	391.07 c
37.5 g clump−1	67.81 c	578.61 a
50 g clump−1	61.4 b	493.89 b
Harvest Intervals
4 months	66.67 a	494.75 b
3 months	67.40 b	517.60 a
2 months	48.89 c	451.23 c
CV/%	8.62	7.26

Note: Numbers followed by the same lowercase letter were not significantly different at the 5% DMNRT test level.

With the attack of leaf spot disease and the vegetative development of citronella grass which has been fertilized and harvested at different intervals, the effect on leaf production will be seen. In Table 3 it can be seen that the production of citronella grass and essential oil in the application of 37.5 g of clump⁻¹ fertilizer with the treatment of harvest intervals once every 3 months showed the highest fresh leaves production, (67.81 tons ^−ha-year, 578.61 kg ^{−ha – year}) and (67.40 tons ^−ha-year, 517.60 kg ^{−ha – year}), followed in the application of 50 g of clump⁻¹ with harvest once every 4 months with fresh leaves production (61.40 tons ^−ha-yea, 493.89 kg ^−ha-year), the lowest production of fresh leaves and essential oils was obtained in the application of 25 g of clump⁻¹ with treatment of harvest intervals once every 2 months with fresh leaves production (53.74 tons ^−ha-year, 391.07 kg ^{–ha −year}) and (48.89 tons ^−ha-year, 451.23 kg ^{–ha −year}). When viewed from the application of fertilizers statistically there is a significant difference between the dose of 37.5 g of clump⁻¹ and the application of a dose of 50 g of clump⁻¹, (67.81 tons ^−ha-year, 578.61 kg ^−ha-year and 61.40 tons ^−ha-year, 493.89 kg ^−ha-year), with the treatment of harvest intervals once every 3 months and once every 4 months and (67.40 tons ^−ha-year, 517.60 kg ^−ha-year and 66.67 tons ^−ha-year, 494.75 kg ^−ha-year (Table 2).

Table 3.

The feasibility of citronella grass (C. nardus L) cv. Serai wangi at 1st year and 2nd year harvesting time.

	R/C Harvest Interval Ratio						Increase R/C (%)
Treatment	1st years Harvest Interval			2nd Harvest Interval
	4	3	2	4	3	2	4	3	2
25 g clump−1	0.48	0.52	0.19	1.02	0.93	0.61	112.25	78.84	221.05
37.5 g clump−1	0.51	0.54	0.38	1.04	1.17	0.62	103.92	116.67	63.16
50 g clump−1	0.52	0.54	0.39	0.98	0.93	0.62	88.46	98.15	58.97

The higher production of fresh leaves and essential oils in the 3-months harvest interval treatment, compared to the 4-month harvest interval, is estimated because leaf growth at the 3-month harvest interval is maximal while the leaf spot disease attack is still low. While the leaves are directly harvested immediately, at harvest intervals once every 4 months of course the incidence of leaf spot diseases will be higher. In accordance with what was reported by [11] leaf spot disease attacks will affect leaf production and oil production as shown in Table 3. This is in accordance with what was stated by Ref. [19], that the application of NPK fertilizer can increase vegetative growth which can increase plant production. Due to availability of nutrients N, P and K in the soil increases, so that what can be absorbed by plants for various metabolic processes needed for growth and production is sufficient.

The results of oil analysis carried out using the Gas Chromatography Mess Spectrum (GCMS) method showed that the quality of the oil was in accordance with what was reported by [19], especially the main contents such as citral, citronella, citronellol and geraniol. Apparently, all treatments showed quality with contents that meet export quality standards. The highest essential contents produced were citral, and citronella which resulted from the application of 37.5 g of fertilizer and harvest interval of every 3 months. The results of oil analysis carried out using the Gas Chromatography Mess Spectrum (GCMS) method revealed that the quality of the oil is in accordance with what was reported by Ref. [20], especially the main ingredients such as citral, citronella, citronellol and geraniol it turns out that all treatments showed quality with ingredients that met export quality standards, namely the essential content in numerical terms was the highest in the application of 37.5 g clump⁻¹ fertilizer with harvest intervals once every 3- months, namely on citral content, highest citronella. The export quality standard is a minimum citronellal content of 35%, while all treatments from the results of the GCMS analysis obtained citronellal levels above 40.96% as presented in Fig. 3.

Fig. 3.

The quality of citronella oil from citronella grass (C. nardus L.) applied by three doses of fertilizer on harvested intervals at 2, 3 and 4 month. Note: Analysis results using GCMS.

After conducting a feasibility analysis from this study, it turned out that in the second year, new plantings showed R/C > 1 at harvest every 3 months and every 4 months (Table 3). With an increase for harvest once every 4 months 88.46% and harvest once 3 months 116.67%, this is a decrease from that produced [2], this is assumed to be due to the influence of the weather and the influence of the intensity of the disease.

According to Ref. [21], farm revenue is calculated by multiplying the amount of production by the price per kilogram. Meanwhile, income is calculated by subtracting the total receipts from the total costs during the production process. The study shows that fertilizer doses and harvest intervals can affect oil production produced on Ultisol soil types. Nutrition as much as 37.5 g of clump ⁻¹ with harvest intervals every 3 months has business feasibility in the second year of planting with an R/C of 1.17% and an oil price of Rp.160,000 per kg, while providing inorganic nutrition of 50 g of clump ⁻¹ does not differ significantly significant because it is only the addition of financing that is not proportional to the resulting oil production.

In assessing whether a business is feasible or not, according to Ref. [22], apart from the variety used, it is also inseparable from its resistance to pests and diseases because this will be directly proportional to the maintenance costs. In the study, the response of Serai wangi 1 to attacks from leaf spot disease and harvest intervals, where the harvest which is done once every 3- months is more resistant to leaf spot disease attacks. However, based on what was stated by Ref. [23] business feasibility criteria in the R/C Ratio analysis, if the results of the R/C Ratio calculation >1 the business is feasible to continue, meaning that the revenue is greater than the costs incurred, if the results R/C Ratio <1 then the business is not feasible to run. If the R/C Ratio = 1, the business is said to be profitable.

4. Conclusions

It can be concluded that the fertilization and harvest intervals can suppress the intensity of leaf spot disease attacks on the Serai wangi 1 on ultisols soil, the best is the treatment with a fertilizer dose of 37.5 g clumps⁻¹ with harvest intervals once every 3 months. This can be seen in the development of leaf spot diseases caused by Curvularia sp and it turns out that fertilizer doses of 37.5 g clumps ^{– 1} with interval harvest once every 3 months, the intensity of the disease attack by Curvularia sp and Pestalotia sp (5.98%, 5.42% and 7.98%, 7.44 %). For the best vegetative growth, it was also the application 37.5 g clump⁻¹ fertilizer with harvest intervals once every 3-months, as well as fresh leaves production (67.81 tons ^−ha-year, 67.40 tons ^−ha-year), oil production (578.61 kg^{-ha −th} 517.60 kg^-ha-year). The oil quality such as the content of Citronella and Graniol numerically it was also seen that it was higher when applying fertilizer dose 37.5 g clump ⁻¹ with harvest intervals once every 3 months. For the R/C ratio in the 2 nd year of planting, it has shown a feasibility in the farming business of applied fertilizer 37.5 g of clumps ⁻¹ at harvest intervals once every 3 months with an increase of 116.67%. So that ultisol soil can also be used for the development of Serai wangi 1 with the addition of NPK fertilizers at a dose of 37.5 g of clump ⁻¹ and harvesting intervals once every three months.

Additional information

No additional information is available for this paper.

CRediT authorship contribution statement

Herwita Idris: Writing – original draft, Supervision, Methodology, Conceptualization. Nurmansyah: Methodology, Investigation, Funding acquisition, Data curation, Methodology, Investigation, Funding acquisition, Data curation. Wiratno: Visualization, Software, Resources, Data curation, Visualization, Software, Resources, Data curation. Eliza Mayura: Validation, Software, Formal analysis, Data curation. Riska: Software, Resources, Project administration, Formal analysis, Software, Resources, Project administration, Formal analysis. Tri Budiyanti: Visualization, Validation, Software, Funding acquisition. Helfi Gustia: Resources, Project administration, Funding acquisition, Data curation. Anwar Ilmar Ramadhan: Writing – review & editing, Writing – original draft, Validation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.