1. Introduction
Patchouli (Pogostemon cablin Benth) is a highly valued essential oil-producing plant in Indonesia, particularly in Aceh Province. Aceh patchouli is renowned globally for its distinctive characteristics, including a soft aroma and superior quality, with an oil content ranging from 2.5% to 5.0% and a patchouli alcohol content exceeding 30% [1]. The oil extracted from patchouli is extensively used as a binder in the fragrance industry, including in perfumes, cosmetics, soaps, and medicines. The demand for patchouli oil remains high and is increasing due to its essential role in various industries. Consequently, patchouli cultivation holds promising development prospects. For the people of Aceh, patchouli is one of the plantation crops that has very good prospects because it has high economic value. Although it has not been managed intensively because it is only an alternative crop, its contribution to community income is very high. The results of the research on the profits of patchouli farmers in Aceh can reach a B/C ratio of 3–4.0, which means that it provides a profit of three to four times the business capital spent on patchouli farming [2].
Despite its potential, Aceh’s patchouli production between 2018 and 2021 was inconsistent and unstable [3]. This fluctuation is attributed to several factors, including rudimentary cultivation technology, farmers’ limited knowledge of proper cultivation techniques, low soil quality, and inadequate soil fertility and fertilization management. Low soil quality and fertility levels are common problems in tropical climates in dryland agricultural systems [4]. The low level of soil fertility is indicated by the low content of soil organic matter [5], low CEC value and alkaline saturation [6], insufficient nutrient availability for plant integrity, and soil that is sensitive to erosion because it has some poor physical properties characterized by large bulk density, low soil porosity, and low aggregate stability index [7]. This condition is very common in drylands with the soil orders Inceptisols, Ultisols, and Oxisols [8]. These lands are generally widespread in Indonesia and include Aceh Besar Regency [9].
On the other hand, the low skill of farmers is also a factor that can affect patchouli production in Aceh, especially if it is associated with a cultivation system that is still not intensive and is still traditional. The cultivation of patchouli plants carried out by farmers in Aceh is a secondary business without serious intervention in soil and plant management. Farmers use local patchouli varieties with low yield potential and do not fertilize and maintain, so the yield achieved is still low.
Patchouli plants, like other crops, thrive under specific environmental conditions [10]. Optimal growth and production are supported by suitable soil conditions. Additionally, the plants’ varietal characteristics and genotypes significantly influence essential oil production, content, and quality [11]. Soil factors are particularly crucial for patchouli growth [12]. Research findings indicate that the distribution of patchouli planting areas in Aceh spans from the southwest region to the highlands of Aceh Province, resulting in varied production levels [13]. Although Aceh’s patchouli oil quality is among the best in Indonesia [14], the patchouli alcohol (PA) content remains relatively low. For instance, in Aceh Barat District, the PA content ranges between 26% and 28%, while the Indonesian standard requires a minimum of 30% [2]. The low yield and production of patchouli are partly due to varying climatic conditions and suboptimal soil fertility levels [15]. Patchouli plants are particularly nutrient-demanding; thus, if the soil’s physical and chemical properties are less than optimal, nutrient availability is affected, leading to plant deficiency symptoms [16].
A rapid evaluation using an omission experiment can provide valuable information on soil nutrient status [17]. This technique involves reducing one of the essential nutrients to determine its impact on plant growth [18]. The principle is that plant growth responds to the most limited nutrient, as plants extract nutrients from the soil, reflecting their relative growth [2]. This method is strategic because it yields faster and more accurate results in determining plant nutritional status [19], particularly in areas with limited soil nutrient information, such as Aceh.
In Aceh, patchouli plants are cultivated on marginal drylands, including Ultisols, Entisols, and Inceptisols soils. One significant patchouli development area in Aceh is in Inceptisols. Inceptisols [20], a common agricultural soil, have a wide distribution but generally exhibit low fertility and acidic reactions. Patchouli cultivation by Aceh farmers relies on the soil’s inherent nutrients and minerals, often through conventional shifting cultivation systems [1,21]. This system and the repeated use of land can deplete soil nutrients. Therefore, research is necessary to evaluate the response of patchouli plants to nutrient treatments, especially in Inceptisols. One quick method to assess nutrient adequacy in plants is to conduct omission trials [18,19]. Omission trials in fertilizers are experimental trials used in agriculture to determine the specific nutrient requirements of crops by systematically omitting one nutrient at a time. These trials help identify which nutrients are limiting crop growth and yield in a particular soil or region. This method has several advantages because (a) it can identify the most limiting nutrients in a given soil, (b) it helps in formulating site-specific fertilizer recommendations, (c) it optimizes fertilizer use efficiency, and (d) it reduces unnecessary fertilizer application, saving costs and minimizing environmental impact. By comparing the growth and yield of crops in each plot, farmers and researchers can determine which nutrients are deficient and need to be supplemented for optimal crop production.
This study aims to identify the nutrient-limiting factors for patchouli plants in Aceh’s Inceptisols using omission trials as a basis for the determination of temporary recommendations in the management of fertilizers on these plants, especially for patchouli farmers. In particular, the purpose of this study is to determine which macronutrients have the potential to be limiting factors for patchouli growth and to study nutrient stress based on leaf analysis in patchouli plants.
2. Methodology
2.1. Location
This research was conducted from February to August 2023 at the Experiment Station of the Faculty of Agriculture, Syiah Kuala University, Darussalam, Banda Aceh, Indonesia. Geographically, the site is located at 05°34′05.2″ N latitude and 95°22′36.1″ E longitude, with an altitude of 3 m above sea level. According to the Schmidt–Fergusson classification, the experimental location is in a tropical climate zone with climate type C. The area experiences an average annual rainfall of 2512 mm and daily temperatures ranging from 28 °C to 34 °C. The Inceptisols (typic Dystrudepts) soil used in the experiment was collected from patchouli planting areas in Lhoong Subdistrict, Aceh Besar Regency, Aceh Province. A map of the experimental site can be seen in Figure 1.
2.2. Materials
The materials used in the experiment included seeds of local patchouli varieties (Tapak Tuan), and the following fertilizers as sources of macronutrients: urea (46% N), SP-36 (36% P2O5), KCl (60% K2O), CaCO3 (84% CaO), MgO, and elemental sulfur (S). The main equipment used for analysis included a pH meter, an oven, analytical balances, an N digestion unit, a distillation unit, a Spectrophotometer UV-1800, and an atomic absorption spectrometer (AAS).
2.3. Treatments and the Experimental Design
The experiment was carried out with fertilizer nutrient treatments prepared based on the subtraction method (omission trials), consisting of eight fertilizer nutrient treatments. The experiment used a randomized block design (RBD) with three repetitions, resulting in 24 experimental units. The composition of fertilizer nutrient treatments is presented in Table 1. The experiment was conducted in a greenhouse using pots (approximately 5 kg capacity). Each pot was filled with 5 kg of soil and planted with one patchouli seedling.
Patchouli seedlings were obtained from stem cuttings, with each cutting measuring about 20 cm in length and containing five internodes. The cuttings were initially planted in polybags (approximately 500 g). Before planting, the soil in the polybags was watered to field capacity and left overnight. The next day, the cuttings were planted at a depth of about 10 cm. After planting, the cuttings were watered moderately (200 mL of water), covered with a plastic lid, and left for 10 days. After this period, the lid was removed, and the patchouli plants were grown until they were 45 days old. Seedlings that are 45 days old already have a developed root system and better physiological stability that allows the seedlings to be more resistant to environmental stresses and have better adaptability, so they can absorb nutrients and water more effectively.
The 45-day-old seedlings were then transferred to pots, and fertilizers were applied according to the treatments. The fertilizer doses were as follows: urea 142 kg ha−1 (0.36 g pot−1), SP-36 35 kg ha−1 (0.18 g pot−1), KCl 140 kg ha−1 (0.18 g pot−1), CaCO3 82 kg ha−1 (0.37 g pot−1), MgO 68 kg ha−1 (0.17 g pot−1), and S 30 kg ha−1 (0.08 g pot−1). Fertilizers were applied at the time of transplanting (seedling age 45 days). Urea was administered in two stages: half the dose (0.18 g pot−1) was administered immediately after transplanting, and the other half was administered 30 days after transplanting. Watering was carried out daily to maintain soil moisture. Soil moisture was kept at field capacity or 35–37.5% of soil water content. For watering, ion-free water obtained from the laboratory was used. The condition of the greenhouse where the experiment was conducted was open, which had a daily temperature varying between 24 and 32 °C, with humidity ranging from 72 to 94%.
2.4. Initial Soil Analysis
Soil analysis aims to determine the characteristics of the topsoil layer (0–20 cm) before being used in the experiment. The soil was collected from various patchouli cultivation areas on Inceptisols, which is the most extensively used soil order for patchouli crops. Before laboratory analysis, the soil was dried for two weeks. After air drying, the soil was sieved using a 0.5 mm sieve to prepare samples for analysis.
The soil characteristics analyzed included routine parameters such as soil texture, pH H2O, pH KCl, soil organic carbon (SOC) using the Walkley–Black method, total nitrogen (N) using the Kjeldahl method, available phosphorus (P) using the Bray 1 method, exchangeable cations (Ca, Mg, and K), and cation exchange capacity (CEC) using 1N ammonium acetate (pH 7). Additionally, exchangeable aluminum (Al) was extracted using 1M KCl solution, and electrical conductivity (EC) was measured with an electrical conductivity meter. The analysis procedures and assessment criteria followed the guidance of the Balai Pengujian Standar Instrumen Tanah dan Pupuk, Bogor [22]. Soil analysis was conducted at the Soil Chemistry Laboratory, Faculty of Agriculture, Syiah Kuala University, Banda Aceh.
Soils from the order Inceptisols Aceh Besar used in experiments as a medium for patchouli plants have several limiting factors, as presented in Table 2. These include a slightly acidic soil reaction, low exchangeable calcium (Ca) content, and a low base saturation percentage. The macronutrient status of carbon (C) and nitrogen (N) falls within the medium criteria, while the levels of available phosphorus (P), exchangeable potassium (K), and exchangeable magnesium (Mg) are categorized as high. Despite the moderate classification of nitrogen nutrient status, patchouli plants require high amounts of nitrogen [15]. The analysis results also show that the total P2O5 and K2O (25% HCl extract) are classified as medium and high, respectively.
2.5. Plant Nutrient Analysis
Analysis of patchouli plant nutrient concentrations was conducted 84 days after transplanting. The plant samples used for analysis were fully developed young leaves (3rd and 4th leaves). The selection of the 3rd and 4th leaves at the age of 84 HST was based on the optimization of essential oil content, physiological maturity, and data consistency in the study of patchouli plants [23]. The nutrient concentrations assessed were nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg).
Leaf analysis of patchouli was carried out using the wet destruction method. In this method, 1 g of dry leaf sample was digested using a mixture of sulfuric acid (H2SO4) and perchloric acid (HClO3), and then the volume was increased to 50 mL with distilled water [24]. Nitrogen concentration was determined by the Kjeldahl semi-micro method, which involves distillation and titration. Phosphorus was measured using a Spectrophotometer UV-1700, while potassium, calcium, and magnesium were measured using an atomic absorption spectrophotometer (AAS) (Shimadzu 7000 model). This is the standard method used for plant analysis in the laboratory at the Soil Research Institute in Indonesia [22]. The plant analysis was performed at the Soil and Plant Testing Laboratory of Syiah Kuala University, Banda Aceh. The details of the analysis method of each macronutrient of the patchouli plant are presented in Table 3.
2.6. Data Analysis
The data from the analysis were processed statistically using analysis of variance (ANOVA). If significant differences between treatments were found, Duncan’s multiple range test (DMRT) was performed at a 5% confidence level. The relationship between response variables was analyzed using regression and correlation. Correlation analysis between nutrient parameters in the patchouli leaves was carried out using the Spearman rank-order correlation coefficient, which was analyzed using the SPSS Statistics software, version 26.0 for Windows. All of the above analyses are based on statistical procedures according to Steel and Torrie [25].
3. Results and Discussion
3.1. Effect of Nutrient Treatment on Leaf Nutrient Content
The results of various analyses of patchouli leaf nutrient concentrations due to fertilizer nutrient treatments in Inceptisols are presented in Table 4. The table illustrates that fertilizer nutrient treatments significantly affected the concentration of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in the patchouli leaves.
3.1.1. Nitrogen (N) and Phosphorus (P) Content in Leaves
Figure 1 depicts the influence of fertilizer nutrient treatment on the concentration of N and P in the patchouli leaves at 84 days after planting (DAP). The lowest N concentration in the patchouli leaves was observed in treatments without nutrient application (no fertilizer = Co) and those that provided complete nutrition but lacked calcium (C-Ca). Similarly, low N concentrations were found in treatments without nitrogen (C-N) and in complete nutrient treatments (C1). Conversely, the highest N concentration was found in the complete nutrient treatment without sulfur. According to previous studies, the N concentration in patchouli leaves typically ranges from 2.5% to 3.5% of the dry weight of the plant, with deficiency occurring if the N content falls below 2.0% [26]. Therefore, N deficiency in patchouli plants in Inceptisols soil occurs when N and Ca nutrients are not provided. These two elements limit the growth of patchouli plants. Nitrogen is a very important macro element in plants because of its function in the photosynthesis process [27]. Symptoms of N deficiency include yellowing of leaves (chlorosis), starting from older leaves [24] (Figure 2).
Nitrogen is the largest component in the composition of the nutrient content of patchouli. The results of the analysis of nutrient content from patchouli stem and leaves show that the N level reached 5.58% [28]. The results of this experiment show that the N content in various fertilizer treatments ranged from 1.61 to 2.29%. The concentration of this N nutrient did not reach a sufficient level [24]. The difference is insignificant between no fertilizer and full fertilization at N uptake because the soil already has sufficient nitrogen reserves through natural processes, such as the mineralization of organic matter (medium). If the N-total content is sufficient (medium), the additional full fertilizer may not have a significant impact. In addition, plants may not utilize the extra N efficiently due to a lack of supporting nutrients. In fertilization without P, K, Mg, and S, the N content of plants is higher compared to C-N (without N) and Co (without fertilizer) and also C1 (fully fertilized) because in addition to receiving N fertilizer, plants receive a supply of other nutrients that can function for the nutrient absorption process, such as Ca, P, K, S, and Mg, which are involved in the nutrient absorption process [29].
Phosphorus helps healthy root development, thus increasing plant absorption of N, and phosphorus deficiency limits N uptake. Potassium is important in plant metabolism, including the synthesis of proteins that require N. A lack of K can hinder the efficiency of the use of N. Calcium is important in maintaining the structure and permeability of root cells, which allows roots to be more efficient in absorbing water and nutrients, including N. Magnesium, as the main component of chlorophyll, is needed for photosynthesis. The process of photosynthesis produces the energy needed for the absorption and metabolism of N. A lack of Mg can reduce photosynthetic activity, thereby limiting the use of N in protein synthesis. Even in fertilization without P, K, Mg, and N uptake is still higher because the nutrient content in the soil already has sufficient reserves. Ca deficiency interferes with root growth and reduces the plant’s ability to absorb N effectively. Sulfur is also required for the synthesis of proteins along with N, and S deficiency can reduce the ability of plants to utilize N effectively [27].
In the case of leaf P nutrients, the experimental results show that the lowest concentration was obtained in the treatment without P fertilizer, and the highest was obtained in the C-Ca treatment (without Ca) followed by C1 (complete nutrient application). Here it is shown that the nutrient balance suitable for P nutrient absorption was obtained if the plant received complete macronutrient fertilization from the fertilizer. The macronutrient content in the soil studied was relatively sufficient except for Ca, which was relatively low (Table 2).
Figure 2 also shows that the P content was higher in the fertilizer treatment without Ca (C-Ca) and exceeded the P content in a complete nutrient application (C1). This shows that the absorption of P by plants is also influenced by the Ca content of the soil. The relationship between phosphorus (P) concentrations in leaves and calcium (Ca) concentrations in plants is complex and often indicates antagonistic interactions, where an increase in one element can affect the availability or absorption of the other [30]. Phosphorus (P) uptake by plants is greatly influenced by the concentration of calcium (Ca) in the soil. This relationship can be positive or negative, depending on the levels of each element as well as on environmental conditions such as soil pH and water availability.
When Ca levels are low, the likelihood of the formation of insoluble calcium phosphate compounds is reduced. This increases the solubility of P in the soil solution, thus making it more easily absorbed by the roots of plants. Conversely, if soil Ca levels are high, especially in soils >7.5, P will react with Ca to form calcium phosphate compounds (Ca3(PO4)2) that are insoluble and cannot be utilized by plants, thus causing P deficiency, even though the total P in the soil is quite high [31].
The mechanism of high absorption of P in leaves occurs because, with sufficient macronutrients, P uptake will increase so that the concentration in the leaves also increases. The results of this experiment show that the P concentration due to fertilizer treatment increased from 0.07 to 0.13%, though this P concentration was still insufficient (still showing P deficiency in the patchouli leaves (Figure 2)). The results of the study indicate that high P absorption could increase the rate of photosynthesis, which produces high-energy compounds such as ATP and NADPH, which are used to reduce CO2 and form carbohydrates. These compounds are then translocated to all parts of the plant to support plant growth and development, such as leaf formation, leaf expansion, and stem and root development [27].
Figure 3 shows that the P levels in the patchouli leaves indicated unfulfilled nutrient adequacy status, with concentrations ranging from 0.07% to 0.13%. Although there was a response to fertilizer nutrient treatment, the P concentration in the patchouli leaves remained insufficient, resulting in deficiency symptoms such as reddish-purple interveinal lower leaves.
3.1.2. Calcium (Ca), Magnesium (Mg), and Potassium (K) in Leaves
Fertilizer nutrient treatment significantly affects the concentration of Ca in patchouli leaves. The concentration of Ca varied from 0.33% to 0.56%, falling below the nutrient adequacy range of 0.4% to 2.5% [24]. The lowest concentration was found in the C-Ca treatment, indicating that low leaf Ca concentration is related to soil Ca content. Similarly, low Ca concentrations were observed in treatments lacking phosphorus (C-P) (Figure 4). Without nutrient K, the concentration of leaf Ca is higher compared to other treatments [32]. This phenomenon is an indication of competition between the Ca++ and K+ cations. The ratio of calcium and potassium cations (Ca:K) in plants can vary depending on the type of plant, soil type, and growing conditions [24], and it ranges from 1:1 to 10:1, while in soils it ranges from 5:1 to 15:1 [33]. Healthy plants usually have more calcium than potassium, especially in old tissues such as the lower leaves, but in plants that require a high Ca:K ratio, can be more balanced or about 1:1 [24]. If the Ca:K ratio is too low (too much K or too little Ca), it can lead to calcium deficiency in plants, and if the Ca:K ratio is too high, then potassium uptake can be inhibited, which can lead to potassium deficiency in plants [34]. Fertile soils with good cation balance usually have more Ca than K or have an ideal ratio of about 3:1 [24].
Based on the results of this experiment, the Ca:K ratio of the patchouli plants was about 1:3 to 1:2 (very low), while in the soil it was 11:1 (low). These data show that the Ca:K ratio in these plants was so low that it could inhibit the absorption of Ca [24], leading to Ca deficiency in the plants, as shown in the leaf Ca deficiency in Figure 5. In the picture, it can be seen that the color of the patchouli leaves changed to brownish-yellow, accompanied by the appearance of brown spots. This symptom begins in the leaves of the shoots as immobile Ca in the plant [35]. The highest Mg concentration was found in the complete nutrient treatment without K (C-K), followed by the C-P treatment, while the lowest was observed in the control treatment (Co) (Figure 4). The concentration of Mg in the patchouli leaves ranged from 0.37% to 1.13%, indicating sufficiency. However, without Mg fertilization (C-Mg), the patchouli plants did not exhibit Mg deficiency symptoms.
Figure 5 shows that K concentration in the patchouli plants remained below the sufficient criteria, ranging from 0.98% to 1.14%. Complete fertilizer application without Mg and S increased K uptake, while treatments with complete nutrients (C1) and without calcium (C-Ca) maintained low leaf K concentration. These data show that even in the soil the content of exchangeable K was relatively high, i.e., 8 cmol(+) kg−1 (Table 1), but there was not yet a sufficient concentration of K in the patchouli leaves even though in some treatments KCl fertilizer containing K and other fertilizers containing N, P, Ca, Mg, and S were applied. This is related to the various properties of potassium in soil and plants [32]. The low K of leaves in the patchouli plants, even though the K content of the soil was high, is also suspected to be related to the very high Mg content of the soil. Mg is a valence cation (II) that, on the surface of colloids, can compete with the K cation [33]. The effectiveness of soil K solution for plant nutrients is influenced by the presence of other cations, especially calcium and magnesium. This can be explained via Mg++ and K+ cations, which are both essential cations that are absorbed by plant roots through an active transport mechanism. When the concentration of Mg++ in the soil is very high, these ions can compete with K+ for a place on cation transporters in the root membrane. As a result, it is harder for plants to absorb K+, even though K is available in high amounts in the soils.
The ratio between potassium (K) and magnesium (Mg) in soil and plants is essential for optimal nutrient balance and nutrient uptake. The K:Mg ratio in plant tissues usually ranges from 2:1 to 5:1 [24]. Plants typically need more potassium than magnesium, but if the K ratio is too high, it can lead to ionic antagonism, where magnesium becomes difficult to absorb. For example, in crops such as corn and wheat, a K:Mg ratio of about 3:1 is considered ideal, and if K is too high compared to Mg, symptoms of Mg deficiency such as chlorosis are shown between the leaf veins [35]. In patchouli plants, the K:Mg ratio is around 3:1 to 5:1 [24]. The ideal ratio of K:Mg in soil is usually in the range of 1:2 to 1:4. In balanced soil, the amount of Mg is usually higher than that of K because magnesium binds more easily to soil particles than potassium. If the K ratio is too high compared to Mg, the plant can experience Mg deficiency due to competition in absorption at the roots. If Mg is too high compared to K, then potassium uptake can be disrupted, causing symptoms of K deficiency such as yellowing of leaves at the edges and stunted growth [32].
The results of this experiment show that the K:Mg ratio of the patchouli plants ranged from 1:3 to 1:1, while in the soil it was 1:18. This comparison shows that the concentration of K and Mg cations in the leaves was not proportional, so the patchouli plant showed deficiency symptoms, as seen in Figure 5. Symptoms of K deficiency occurred, including chlorosis, which involves yellowish and pale leaves that start from the tips of the leaves and spread to the edges of the leaves to the entire plant except for the leaf veins. Based on the results of observations, the appearance of these leaf symptoms begins in old leaves because potassium is a mobile element in plants.
In Figure 6, the concentration of N nutrients in patchouli leaves was higher than that of other nutrients, with the order being N > K > Mg > Ca > P. The effect of fertilizer nutrient application indicates differences in nutrient uptake by the patchouli plants, suggesting dynamic interactions between nutrients in the soil affecting nutrient absorption. The concentration of N in the patchouli leaves at the age of 84 DAP varied from 1.61 to 1.73%. Without the application of fertilizer, the patchouli plants contained the lowest amount of N, but after the application of complete fertilizer, it increased, but the achievement of the highest N concentration was obtained by the omission treatment. P concentrations ranged from 0.07 to 0.11% and were relatively unchanged between the control treatment, complete nutrient administration, and omission treatment. The same results also occurred in K nutrients, with concentrations ranging from 1.02 to 1.04%. For the Ca element, the highest concentration was obtained in complete nutrient application in a range of 0.33–0.40%, while for Mg, the concentration in leaves varied greatly between the treatment without fertilizer, complete nutrient treatment, and omission treatment, with values of 0.37%, 0.6%, and 0.9%, respectively.
These data show that even though complete fertilizer inputs were administered, the concentration of macronutrients in the patchouli plants did not reach the optimum level. This is suspected to be related to low soil quality (Table 2), so this is a concern for farmers in the field in terms of managing a good nutrient cycle, especially in Inceptisols soil. In Aceh, Inceptisols is one of the orders whose distribution is almost evenly distributed in dryland agricultural areas and is widely used for annual agriculture and plantation crops [4]. The quality of this soil is generally low, so it is considered suboptimal land.
In summary, the results demonstrate the significant impact of fertilizer nutrient treatments on the nutrient concentrations of patchouli leaves in Inceptisols. These findings provide valuable insights into optimizing nutrient management practices to enhance patchouli growth and productivity in similar soil conditions.
3.1.3. Ratio Between N, P, K, Ca, and Mg in Leaves
The N:P ratio in the patchouli leaves turned out to be quite varied due to the treatment of fertilizer nutrients by omission (Table 5). In the control treatment without fertilizer (Co), the N:P ratio obtained was 1:23, while in the complete nutrient application (C1), the N:P ratio obtained was 1:15. The lowest N:P ratio was obtained in the C-P and C-K treatments, namely in the treatment with complete nutrients administered but without P and K. The largest N:P ratio was found in the treatment with complete nutrients administered but without Ca (C-Ca), with an N:P ratio of 1:12. The ideal N:P ratio in plants generally ranges from 1:8 to 1:12 [24,36]. The ideal ratio of N and P for patchouli plants is 3:1 or 5:1, but researchers have not reported much on this. However, based on the results of this study, the N:P ratio was below the normal limit, with the concentration of N in the leaves being far out of balance with the P concentration, so there was a tendency for these two elements to compete in the plant tissues. The difference in proportion between N and P could cause symptoms of N and P deficiency in the patchouli plants (Figure 3). These two nutrients are physiologically very important in plant metabolism and synergize with each other. Nitrogen functions as a constituent of chlorophyll in plants, while P acts as a constituent of energetic compounds (ATP, ADP, and AMP) that function as an energy source for metabolic processes [27], so if the status in the plant is insufficient, plant growth is disrupted.
Furthermore, as shown in Table 5, the N:K ratio between nutrient treatments did not vary, with a ratio of 1:2. In patchouli plants, a good ratio of N:K depends on the period or age of the plant. In the early phase of growth, a good N:K ratio is about 2:1 because a lot of nitrogen is needed for rapid leaf growth. In the active growth phase (3–6 months), the N:K is ideally in a 1:1 ratio, which is balanced between N and K to strengthen the stems and improve the quality of the leaves, while in the harvest phase, the N:K ratio ranges from 1:2 to 1:3 because the plant needs higher potassium for plant resistance and essential oil quality [37].
The ratio of C:K, K:Mg, and Ca:K in the leaves of patchouli plants also looked not too varied. In the Ca:K ratio, the proportion of Ca in the patchouli leaves was two to three times higher than that of K, while in the ratio of K:Mg, the proportion of Mg was more balanced the proportion of K. In the Ca:Mg ratio, the proportion of Ca was one to three times higher than that of Mg. From the values of the ratio between the cations K, Ca, and Mg, it can be said that the proportion between the three macronutrient cations was generally unbalanced, and this can interfere with the physiology of the patchouli plant, as previously described. The patchouli plant (Pogostemon cablin) needs a good balance of nutrients to support leaf growth, which is a major part in the production of essential oils. The ideal ratio of Ca:K is 2:1 or 3:1, while the ideal ratio of K:Mg is 3:1 or 4:1, and that of Ca:Mg is 3:1 or 5:1 [33]. However, the reality from the results of this experiment is that the balance between macronutrients in the patchouli plants was not balanced, so the plant showed symptoms of stress (deficiency) to some of these elements.
3.2. Correlation Matrix Analysis
Analysis of the correlation between nutrient concentrations of N, P, K, Ca, and Mg leaves of the patchouli plants is presented in Table 6.
The results of the analysis show that the concentration of N nutrients in the patchouli leaves was negatively correlated with the P content of the leaves but positively correlated with the K, Ca, and Mg content of the leaves. The P concentration in the patchouli leaves was negatively correlated with the K content but was not markedly correlated with the Ca and Mg content of the leaves. Likewise, between the concentrations of Ca and K, there was no significant correlation. The negative correlation between the N concentration and P concentration of the patchouli leaves shows that high N absorption could reduce P absorption, but this relationship was relatively weak because it had r = −0.449 *. In general, nitrogen and phosphorus are two essential macronutrients that usually synergize with each other in influencing plant growth. Nitrogen (N) plays a role in the formation of proteins, enzymes, and nucleic acids, and it is a major component of chlorophyll, which is important in photosynthesis, while phosphorus (P) plays a role in energy transfer through ATP (adenosine triphosphate), the formation of DNA and RNA, and the synthesis of phospholipids for cell membranes. However, at high concentrations, phosphorus uptake can be suppressed due to competition for absorption sites in plant roots [27]. The balance between the two is essential to ensure optimal growth, metabolic efficiency, and good yields.
The different effect between N and P is thought to occur because P is absorbed by plants in the negatively charged ions H2PO4− and HPO4=, which is the same as N absorbed in nitrate anion (NO3−) form. Nutrient uptake in the form of anions will increase the concentration of positive charges on the root surface to inhibit the absorption of nutrients in the form of anions [33], so fellow anion nutrients occur in competition. The concentration of nitrogen needed by plants (patchouli) will generally be ten times higher than the concentration of phosphorus nutrients needed, so if this ratio is not balanced, there will be competition. Furthermore, the synergistic effect between N nutrients with K, Ca, and Mg shows that an increase in one of the cation elements can increase the absorption of N nutrients because, with the absorption of positive nutrient ions in the soil solution, there will be an increase in the concentration of anions such as NO3−, SO4=, and PO43− [24]. For sulfate and phosphate anions, an increase in the concentration of positive ions can form compounds that become insoluble and inhibit P absorption.
3.3. Management of Nutrient Cycle
The results of this study indicate that the content of N, P, K, and Ca nutrients in the patchouli leaves was relatively low and is one of the obstacles to the growth of patchouli plants in Inceptisols because these nutrients do not meet the needs of patchouli plants. The low content of nitrogen, phosphorus, potassium, calcium, and magnesium in the patchouli leaves was also indicated by the appearance of deficiency symptoms, namely chlorosis and necrosis (Figure 3 and Figure 5). The ideal composition of macronutrient content in patchouli leaves is N 2.5–4.5%, P 0.2–0.4%, K 1.5–3.0%, Ca 0.5–1.5%, and Mg 0.3–0.8% [38]. The results of the leaf analysis before harvest were far from adequate (Figure 2 and Figure 4).
Based on the adequacy of macronutrients in the leaves of patchouli, with nutrient adequacy levels of N = 3.5%, P = 0.4%, K = 3%, and Ca = 1.0%, there was a nutrient deficit for N, P, K, and Ca of 49.4%, 20.0%, 34.7%, and 33.0%, respectively, but not for Mg. The most severe macro-nutrient deficiency occurred in element N, followed by K, Ca, and P. This is due to the function of this element, which is very important as a component of several biomolecules that regulate plant growth and development, such as chloroplasts, nucleic acids, proteins, and some secondary metabolites [39] Concrete suggestions in the management of nutrients due to nutrient deficiencies are to provide organic fertilizers and biological fertilizers, and to improve soil quality with organic amendments that can increase nutrient availability and improve the physical, chemical, and biological properties of the soil to maintain plant health [12,40].
Furthermore, the results of the preliminary soil analysis before the experiment show that not many problems were found in the Inceptisols soil because it had a rather acidic soil reaction (pH 6.03) with a medium content of soil organic matter, and total soil N, high available P (12.5 mg kg−1), medium exchangeable K (0.43 cmol(+) kg−1), high exchangeable Mg (8 cmol(+) kg−1), and high CEC (31.8 cmol(+) kg−1). The obstacles in terms of soil chemistry were the low exchangeable Ca content (4.8 cmol(+) kg−1) and low base saturation (33.7%). This indicates that what affects the low macronutrient content in patchouli leaves is not fully influenced by soil quality. In the field, farmers’ skills in applying cultivation techniques are also a determinant of the growth and yield of patchouli plants.
Therefore, to eliminate these limiting factors, adding fertilizer and providing amendments can increase nutrient availability and improve soil quality [41]. If we look at the quality of the Inceptisols soil studied, to improve the quality of the soil, complete fertilizer, organic amendments, and biological fertilizer can be applied. The use of organic fertilizer, apart from being a complete source of nutrients [42], can also increase the efficiency of N, P, and K fertilizers [43]. Organic amendments can improve the physical, chemical, and biological properties of soil, as has been widely studied [44]. The application of mycorrhiza as a bio-activator can also improve the yield and quality of patchouli [20]. Mycorrhiza combined with mineral fertilizers reduced by 50% of the full dose increases plant nutrients, especially phosphorus, nitrogen, and potassium [45].
In addition, the development of organic patchouli requires nutrient sources from organic fertilizers and biological fertilizers. Organic fertilizers that can be used include manure and compost from agricultural waste, while organic amendments can include biochar, green manure, and bio-compost or biofertilizer. Mycorrhizal biofertilizer combined with organic fertilizer is reported to increase nutrient availability, and Glomus sp. without being combined with organic fertilizer can increase the total N of Inceptisols [20]. The clay texture of Inceptisols soil also requires ameliorant materials such as biochar to create a crumbly structure so that root development is more optimal [46]. Further research is still necessary to obtain more information, especially to determine the optimal dose of N, P, K, and Ca fertilizers, which are factors limiting the growth of patchouli plants based on the results of this study. For the time being, farmers are advised to use complete nutrient fertilizers such as urea, superphosphate, and KCl to meet the main macronutrients, while secondary nutrients such as Ca can be provided through Ca-containing materials/fertilizers such as CaCO3, dolomite, and manure or compost.
4. Conclusions
Nutrient treatment of fertilizers N, P, K, Ca, Mg, and S through omission trials on Inceptisols soil affects nutrient concentration in patchouli leaves. Complete nutrient intake can increase P, Ca, and Mg absorption, but does not meet the criteria for sufficient P and Ca nutrient levels in patchouli plants. However, Mg absorption is high even without Mg nutrients, indicating that this element is not a limiting factor for patchouli plants. Complete fertilization is sufficient for the Ca nutrient needs of patchouli plants, but if Ca fertilizer is not applied, Ca absorption is reduced, making this element a limiting factor for patchouli. Nutrients that limit nutrient absorption by patchouli in the Inceptisols of Aceh are nitrogen, phosphorus, potassium, and calcium. At the same time, magnesium is a nutrient that meets the needs of patchouli, especially in cases in the study area, according to the results of data analysis. Further research is needed on the yield and quality of patchouli oil in the study area in terms of the nutrient status, including studying micronutrients and soil management to increase Aceh’s patchouli yield, including in other soil orders such as Ultisols and Oxisols, which dominate Aceh’s drylands.
Preparation, Z.Z.; conceptualization, Z.Z.; methodology, Z.Z.; writing original draft, Z.Z.; writing review and editing, S.S.; resources, S.S.; data curation, S.S.; formal analysis, S.S.; supervision, H.H.; visualization, H.H.; project administration, Y.J. All authors have read and agreed to the published version of the manuscript.
Not applicable.
The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.
The authors appreciate the Rector of Universitas Syiah Kuala for supporting this research. Thanks a lot to all the individuals included in this work.
The authors declare that they have no conflicts of interest.
Footnotes
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Enlarge this image.Figure 1. Map of the location of the research implementation of the experimental station of Syiah Kuala University, Banda Aceh, Indonesia.
Enlarge this image.Figure 2. The concentration of nitrogen and phosphorus in the patchouli leaves due to fertilizer nutrients treatments in Inceptisols. Note: the values with the same letter are not significantly different.
Enlarge this image.Figure 3. Symptoms of nitrogen and phosphorus nutrient deficiencies in patchouli leaves.
Enlarge this image.Figure 4. The concentrations of potassium, calcium, and magnesium in the patchouli leaves due to fertilizer nutrients treatments in Inceptisols. Note: the values with the same letter are not significantly different.
Enlarge this image.Figure 6. Differences in nutrient concentrations of N, P, K, Ca, and Mg in the patchouli leaves due to fertilizer nutrient treatments.
Fertilizer nutrient treatment on patchouli plants by omission trial method.
| No | Treatment Code | Treatment Description |
|---|---|---|
| 1 | Co | Without nutrients (not fertilized) |
| 2 | C1 | Complete nutrients of N, P, K, Ca, Mg, and S |
| 3 | C-N | Complete nutrients, without N |
| 4 | C-P | Complete nutrients, without P |
| 5 | C-K | Complete nutrients, without K |
| 6 | C-Ca | Complete nutrients, without Ca |
| 7 | C-Mg | Complete nutrients, without Mg |
| 8 | C-S | Complete nutrients, without S |
Soil characteristics of Inceptisols before fertilizer nutrient treatment experiments.
| Soil Parameters | Value | Criteria | Soil Parameters | Value | Criteria |
|---|---|---|---|---|---|
| Texture | - | Clay | Exch. Ca (cmol kg−1) | 4.80 | Low |
| Sand (%) | 8.70 | Low | Exch. Mg (cmol kg−1) | 8.00 | High |
| Silt (%) | 26.9 | Medium | Exch. K (cmol kg−1) | 0.43 | Medium |
| Clay (%) | 64.4 | High | Exch. Na (cmol kg−1) | 0.21 | Low |
| pHH2O (1:2.5) | 6.03 | Slightly acid | CEC (cmol kg−1) | 31.8 | High |
| pHKCl (1:2.5) | 5.90 | Slightly acid | BS (%) | 33.7 | Low |
| SOC (%) | 2.39 | Medium | Exch. Al (cmol kg−1) | 0.40 | Low |
| TN (%) | 0.25 | Medium | Total P2O5 (mg 100 g−1) | 56.1 | High |
| Available P (mg kg−1) | 12.5 | High | Total K2O (mg 100 g−1) | 37.9 | Medium |
| EC (mS m−1) | 0.40 | Low |
SOC = soil organic matter; TN = total nitrogen; EC = electrical conductivity; CEC = cation exchange capacity; BS = base saturation.
Macronutrients and analysis methods.
| Macronutrients | Analysis Methods | Equipment Used |
|---|---|---|
| Nitrogen (N) | Kjeldahl or Dumas method | Kjeldahl distillation, CHNS analyzer |
| Phosphorus (P) | Spectrophotometric, Asam molybdate (colorimetric) | UV-VIS spectrophotometer |
| Potassium (K) | Flame spectrophotometer | Flame photometer/AAS |
| Calcium (Ca) | Atomic absorption spectrophotometer | AAS (atomic spectrophotometer) |
| Magnesium (Mg) | Atomic absorption spectrophotometer | AAS (atomic spectrophotometer) |
| Sulfur (S) | Turbidimetry (formation of CaSO4) | UV-VIS spectrophotometer |
The variance analyses of nutrient concentrations of N, P, K, Ca, and Mg in the patchouli leaves due to fertilizer nutrient application.
| Sources of Variance | df | F Value | F Table | |||||
|---|---|---|---|---|---|---|---|---|
| N | P | K | Ca | Mg | 0.05 | 0.01 | ||
| Block | 2 | 0.86 | 0.09 | 0.12 | 3.77 | 0.13 | 3.74 | 6.51 |
| Treatments | 7 | 3.68 * | 28.04 ** | 42.6 ** | 3.66 * | 40.5 ** | 2.76 | 4.28 |
| Error | 14 | |||||||
| Total | 23 | |||||||
Note: **: Significant at p < 0.01; *: Significant at p < 0.05.
Ratios of nutrient concentrations of N, P, K, Ca, and Mg in the leaves of the patchouli plants in various fertilizer treatments at the age of 84 DAP in Inceptisols.
| Fertilizers Treatment Codes | N:P | N:K | Ca:K | K:Mg | Ca:Mg |
|---|---|---|---|---|---|
| Co | 1:23 | 1:2 | 3:1 | 1:3 | 1:1 |
| C1 | 1:15 | 1:2 | 3:1 | 1:1 | 2:1 |
| C-N | 1:18 | 1:2 | 3:1 | 1:1 | 2:1 |
| C-P | 1:27 | 1:2 | 3:1 | 1:1 | 3:1 |
| C-K | 1:27 | 1:2 | 2:1 | 1:1 | 2:1 |
| C-Ca | 1:12 | 1:2 | 3:1 | 1:2 | 2:1 |
| C-Mg | 1:26 | 1:2 | 2:1 | 1:2 | 1:1 |
| C-S | 1:26 | 1:2 | 3:1 | 1:2 | 1:1 |
DAP = days after seed planting.
Correlation matrix between nutrient content in soil and nutrient uptake of patchouli after 84 DAP.
| Leaf Nutrient Contents | N | P | K | Ca | Mg |
|---|---|---|---|---|---|
| (g kg−1) | |||||
| N (g kg−1) | 1 | ||||
| P (g kg−1) | −0.449 * | 1 | |||
| K (g kg−1) | 0.760 ** | −0.451 * | 1 | ||
| Ca g kg−1) | 0.415 * | −0.223 | 0.198 | 1 | |
| Mg (g kg−1) | 0.431 * | −0.075 | 0.101 | 0.308 | 1 |
**: Significant at p < 0.01; *: Significant at p < 0.05. Critical value: 0.409 (p < 0.05); 0.537 (<0.01); N = 24.
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Details
; Sufardi, Sufardi 2
; Helmi, Helmi 3
; Jufri, Yadi 3 1 Doctoral Program in Agricultural Science, Universitas Syiah Kuala, Jalan Tgk. Chik Pante Kulu 5, Darussalam, Banda Aceh 23111, Indonesia;
2 Department of Soil Science, Faculty of Agriculture, Universitas Syiah Kuala, Jalan Tgk. Hasan Krueng Kalee 03, Darussalam, Banda Aceh 23111, Indonesia;
3 Department of Soil Science, Faculty of Agriculture, Universitas Syiah Kuala, Jalan Tgk. Hasan Krueng Kalee 03, Darussalam, Banda Aceh 23111, Indonesia;