Sustainability Indicators of the Banana and Lemongrass Intercropping System in Different Harvest Seasons: Growth, Yield, Seasonality and Essential Oil Properties

Abstract

Lemongrass (Cymbopogon citratus) has potential for intercropping with banana (Musa spp.) plants, thus contributing to the sustainability of plantations. The study evaluated the growth and yield of ‘Prata Anã’ banana and seasonality, yield and essential oil properties of lemongrass grown in intercropping and the land equivalent ratio. A randomized block design in a split plot arrangement was used, evaluating two cropping systems (sole crop and intercropping) and three harvest seasons during the year for lemongrass and two harvest seasons for banana, separately. The banana can be intercropped with lemongrass without interfering with its growth and production. The biomass production and essential oil yield of lemongrass differed according to cropping system and seasonality. The chemical composition of the essential oil showed stability in the concentration of citral (mixture of neral and geranial), with an average of 94.43%. Seasonal variations were observed in the content of these compounds and other components of the essential oil, emphasizing the importance of the time of harvest in the overall value of the oil. The result demonstrates the viability of intercropping, which not only provides crop yields for both species and produces more per unit area than a sole crop but also optimizes the use of resources and promotes more sustainable farming practices.

1. Introduction

Lemongrass (Cymbopogon citratus) is a multicultural aromatic herb of great environmental and commercial value, belonging to the Poaceae family [1]. A native of southwest Asia, it has successfully adapted to the weather in several areas of the globe, particularly those with a warm climate, and has a long growing cycle [2].

Lemongrass has been the subject of a number of studies aimed at increasing its versatility and potential for use in different industrial sectors. This plant can be used as a fresh or dried raw material and is widely applied in gastronomy and the food, cosmetics, pharmaceutical and chemical industries [3]. Lemongrass is a plant rich in bioactive compounds with organoleptic, nutritional and functional properties. These compounds include phenolics, vitamins (thiamine, niacin, pantothenic acid, riboflavin, ascorbic acid, folic acid), minerals (Mg, P, K, Zn, Cu, Fe) and essential oils [4]. Essential oils are volatile compounds that produce the characteristic aroma of lemongrass and are produced in concentrations of between 1% and 2% of the dry mass. The main constituent of these oils is a mixture of geranial and neral geometric isomers that represents between 70% and 80% of the total [4,5]. They have great commercial value as precursors of ionones in perfumery and precursors of vitamin A in the chemical industry [6].

The yield and chemical composition of lemongrass essential oil depend on a number of variables, including the correct botanical identification of the species, the soil and climate conditions of the growing region, the time and method of harvesting, the genetic characteristics of the plant, the drying and storage conditions of the leaves and the method of extracting the essential oil [7].

Intercropping is a farming technique in which two or more crops are grown in proximity to each other in the same field and is a strategy for increasing biodiversity in an agroecosystem [8]. The agronomic compatibility of these crops results in favorable biological interactions, leading to optimized yields, as well as crop density and fertility [9]. The diversity of banana cropping systems is an important strategy for improving food and nutritional safety, enhancing the health of ecosystems and strengthening the resilience of smallholder farmers [10].

Bananas can be used in intercropping [10,11,12] and in diversified and sustainable agroforestry systems [13,14]. The banana plant provides fruit of great nutrient and economic potential and also contributes to improving the environment, conserving the soil, regulating the local climate and increasing biological diversity [13]. ‘Prata Anã’ (AAB–triploid) is the main banana of the Pome subgroup growing in Brazil, with great productivity and wide acceptability among both growers and buyers. The plant is vigorous, with a height of 2.0 to 3.5 m, tolerant to cold, but susceptible to sigatoka leaf spot, yellow sigatoka (Mycosphaerella musicola, Leach) and black leaf streak, black sigatoka (Mycosphaerella fijiensis, Morelet) [15] and moko (Ralstonia solanacearum), moderately susceptible to Fusarium wilt and moderately resistant to the nematodes Radopholus similis and Medoidogyne incognita [16].

Growing herbs in intercropping can generate additional revenue for farmers, contributing to the plant-sociological and entomofauna balance of crops, reducing the costs and environmental damage of excessive pesticide use [17,18,19]. In addition, intercropping can enable lemongrass to gain a foothold in consumption centers, capitalizing on the interest in more popular fruit crops, including bananas. The intercropping of bananas with lemongrass could an opportunity for sustainably managing plantations [20,21].

The aim of this study was to evaluate the feasibility of intercropping as a total or partial replacement of the traditional sole crop in banana plantations, especially for smallholders. To this end, the study sought to determine whether the combination of the two species could improve the yield of both component species without compromising the yield of lemongrass oil and without altering the properties of the oil. Different indicators were used to describe the intercropping system of banana and lemongrass, in successive harvest seasons, in a mesothermal climate in the subtropical region of the state of São Paulo, Brazil.

2. Materials and Methods

2.1. Study Location

A replicated field study was carried out at the São Manuel Farm, School of Agriculture, São Paulo State University, in the state of São Paulo, Brazil (22°44′28″ S, 48°34′37″ W), located at an altitude of 740 m above sea level. The region has a Cwa climate, i.e., warm temperate (mesothermal) and humid, according to the Köppen–Geiger classification [22]. The soil is classified as Latossolo Vermelho Distroférrico with a sandy texture [23] or Dystrophic Typic Hapludox [24]. Meteorological parameters such as daily rainfall (mm) and maximum, minimum and average temperatures (°C) during the experimental period were obtained from a meteorological station located 300 m from the experimental site (Figure 1).

2.2. Experimental Site Management

Before experimentation and during the harvest seasons, soil samples (0–20 cm depth) were collected from each experimental area (sole crop and intercropping) for chemical analysis. The sampling included 20 subsamples collected from the in-row and inter-row plots of the two cultivation areas. The chemical properties of the soil are presented in

Table 1. Soil analysis data from the experimental site.

Chemical Soil Properties	Planting	Sole Crop	Intercropping
pH (1:2.5 soil/CaCl2 suspension 0.01 mol L−1)	5.6	4.9	5.3
Soil organic matter (g kg−1)	11.8	13.9	16.1
Presin (mg kg−1)	9.2	15.0	13.2
S (mg kg−1)	5.4	9.3	8.9
H + Al (mmolc dm−3)	15.1	17.2	17.3
K (mmolc dm−3)	1.3	1.6	1.8
Ca (mmolc dm−3)	16.4	19.7	21.6
Mg (mmolc dm−3)	6.0	6.9	7.1
Sun of bases (mmolc dm−3)	23.7	28.2	30.5
Cation exchange capacity (mmolc dm−3)	38.0	42.0	49.0
Base saturation (%)	61.0	65.0	69.0
Fe (mg kg−1)	32.0	20.0	25.0
Cu (mg lg−1)	2.4	2.2	2.8
B (mg kg−1)	0.3	0.7	0.9
Mn (mg kg−1)	8.6	8.4	9.3
Zn (mg kg−1)	2.3	4.1	4.7

.

2.2.1. Banana Growing

The experimental site was previously prepared by plowing, sorting and liming, based on soil analysis and recommendations for banana plantations. Complementary nutrient treatment was carried out according to soil analysis and recommendations for banana plantations [25]. Sixty days before planting, 450 kg of dolomitic limestone was applied to the entire area. At planting, 150 g of thermophosphate and 2 kg of tanned cattle manure were applied per linear meter of furrow. Cover fertilization began 60 days after planting and was divided into 6 monthly applications, with rates of 114, 171, 171, 228, 228 and 228 g per plant of ammonium sulfate and 70, 105, 105, 140, 140 and 140 g per plant of potassium chloride.

The banana plants were micropropagated [26], grown in the greenhouse and planted in the field with 5–6 leaves and at 30 cm tall, in December 2020. The field had 3 m between rows and 2.5 m between plants (i.e., 1333 plants ha⁻¹). Weed control, tiller thinning, pest and disease control, removal of male inflorescences and pistils and bagging of bunches were carried out in agreement with standard cultivation techniques [27].

2.2.2. Lemongrass Growing

The lemongrass plants had been collected from the medicinal plant garden and grown in the nursery. The seedlings were planted at 15 cm high in January 2021, in 20 × 20 × 20 cm holes, predrilled and fertilized with 5 L of tanned cattle manure per hole. The lemongrass was spaced 60 cm apart in the row of banana plants, giving a total stand of two lemongrass plants between banana plants in the row [28] (Figure 2). In order to calculate the land equivalence ratio, two rows of lemongrass were planted as a sole crop. The crops were grown under a dryland system.

2.3. Cropping Systems and Harvesting Seasons

The treatments corresponded to the cultivar Prata Anã (AAB), grown as a sole crop and in intercropping with lemongrass, and the harvesting seasons for lemongrass and bananas.

A replicated trial was conducted during two consecutive harvesting seasons for banana cropping. The first harvest season was from December 2020 to April 2022 and the second from August 2022 to April 2023. The first harvesting season corresponded to the period between planting and harvesting, while the second season was from the emission of the inflorescence to harvesting.

The lemongrass was also harvested in replicated growing seasons throughout the year, with harvests every four months [28,29], in the first and second year of cultivation, as follows: 1st crop cycle (winter—June/2021 and 2022), 2nd crop cycle (spring—October/2021 and 2022) and 3rd crop cycle (summer—February/2022 and 2023).

2.4. Experimental Design

The experimental design was randomized blocks with four replicates in a split plot arrangement (2 × 3). The plots corresponded to the cropping systems (sole crop and intercropping) and the subplots to the three crop cycles of lemongrass in each year of cultivation. The banana plots corresponded to the cropping systems (sole crop and intercropping) and the subplots to the two harvesting seasons (2 × 2). Replicates consisted of four banana plants per experimental plot and guard plants outside the trial.

2.5. Harvesting

Banana plants were assessed at the end of each growing season, when the bunches were harvested. The banana bunches were harvested in the morning, when the fruit in the middle of the second hand had reached a minimum size of 34 mm in diameter [30].

Lemongrass was harvested by hand with a knife and the leaves were cut at 0.20 m from the ground level [28,29].

2.6. Growth and Yield Assessments

Banana growth evaluations consisted of measurements of plant height, pseudostem diameter and the number of leaves. These biometric indicators were measured at the harvesting time. Plant height was the distance between the soil level and inflorescence insertion, and pseudostem diameter was measured at 30 cm from the soil surface by measuring the circumference and calculated by Equation (1). The number of leaves was obtained by counting the number of leaves per plant in which more than half of the leaf area was green [21].

$$\mathrm{D}={\displaystyle \frac{\mathrm{C}}{\mathsf{\pi }}}$$

(1)

where:

D = diameter;

C = circumference.

The banana yield was estimated from the fresh mass of marketable bunches per plant divided by the number of days in the total cycle (planting to harvest) and multiplied by 365 days (kg⁻¹plant⁻¹year⁻¹) [31]. The cumulative yield corresponded to the sum of two harvesting seasons [21].

The yield of lemongrass was evaluated based on the indicators of fresh and dry mass of the clump. The lemongrass leaves were cut and immediately weighed using an analytical scale, model AG 200 (Gehaka, São Paulo, Brazil). A 100 g sample was then taken and placed in an oven (Prolab, São Paulo, Brazil) at 65 °C until it reached a constant mass to determine the dry matter, with the values presented as a percentage of dry matter. The yield was calculated by the product of the clump’s mass and the number of plants per hectare, according to the cropping density and in tons per hectare [7].

2.7. Determination of Land Equivalent Ratio

The land equivalent ratio was calculated according to Equations (2)–(4) [20]:

$${\mathrm{L}\mathrm{E}\mathrm{R}}_{\mathrm{b}}={\mathrm{Y}\mathrm{B}}_{\mathrm{i}}/{\mathrm{Y}\mathrm{b}}_{\mathrm{s}\mathrm{c}}$$

(2)

$${\mathrm{L}\mathrm{E}\mathrm{R}}_{\mathrm{l}}={\mathrm{Y}\mathrm{L}}_{\mathrm{i}}/{\mathrm{Y}\mathrm{l}}_{\mathrm{s}\mathrm{c}}$$

(3)

$${\mathrm{L}\mathrm{E}\mathrm{R}}_{\mathrm{t}}={\mathrm{L}\mathrm{E}\mathrm{R}}_{\mathrm{b}}+{\mathrm{L}\mathrm{E}\mathrm{R}}_{\mathrm{l}}$$

(4)

where:

LER_b = land equivalent ratio of banana; YB_i = yield of banana in intercropping; Yb_sc = yield of banana in sole crop; LER_l = yield of lemongrass in intercropping; Yl_sc = yield of lemongrass in sole crop; LER_t = total land equivalent ratio.

2.8. Lemongrass Essential Oil Extraction

Freshly harvested lemongrass leaves, cut transversely every 0.02 m, were subjected to steam distillation. A modified Clevenger-type apparatus (Sigma-Aldrich, São Paulo, Brazil) was used, consisting of a 2 L round-bottom flask equipped with a heating mantle. The 100 g of ground plant material was placed in 1 L of distilled water, and the essential oil was extracted for 120 min. After phase separation, the extracted essential oil was stored in an amber glass bottle at 4 °C until analysis [1].

2.9. Lemongrass Essential Oil Content and Yield

The essential oil content was determined based on the weight of 100 g of the dry matter of the plants. The content of oil recovered was multiplied with lemongrass yield to obtain oil yield in kg ha⁻¹ [1].

2.10. Essential Oil Analysis by Gas Chromatography Coupled with Mass Spectrometry (GC and GC-MS)

For qualitative analysis, a gas chromatograph coupled to a mass spectrometer (GC-MS, TRACE 1300, Thermo Scientific, Sigma-Aldrich, São Paulo, Brazil) with a TR-5 MS capillary column (30 m × 0.25 mm × 0.25 μm) and helium (99.9999% purity) as the carrier gas (flow rate of 1.0 mL min⁻¹) was used. The system operated in full scan mode with electron impact (70 eV) from 40 to 450 m/z. The injector temperature was maintained at 220 °C with a split flow ratio of 1:20, following a temperature program from 60 °C to 240 °C (3 °C min⁻¹). The interface temperature was held at 240 °C. Then, 1 µL of a solution obtained by diluting the essential oil samples in ethyl acetate (1 mg mL⁻¹) was injected.

Quantitative analysis of the essential oils was performed using a gas chromatograph with a flame ionization detector (GC-FID, TRACE 1300, Thermo Scientific, Sigma-Aldrich, São Paulo, Brazil), equipped with a TR-5 fused silica capillary column (30 m × 0.25 mm × 0.25 μm), and helium (99.9999% purity) as the carrier gas (flow rate of 1.0 mL min⁻¹). The injector and detector temperatures were maintained at 220 °C and 300 °C, respectively. The split flow ratio was 1:20, following the same temperature program as the GC-MS system [32,33].

The chemical constituents of lemongrass essential oil were identified by comparing the mass spectra with the libraries of the National Institute of Standards and Technology (NIST 14), Flavour & Fragrance Natural & Synthetic Compounds (FFNSC3) and the linear retention indices (LRIs) were calculated according to Adams [34]. The LRIs were obtained by injecting a series of n-alkanes (C9–C24, Sigma-Aldrich, 99%, São Paulo, Brazil) under the same chromatographic conditions as the samples, according to van den Dool and Kratz [35].

2.11. Statistical Analysis

Each harvesting season was analyzed separately. The composition of the essential oil was only evaluated in the second year of cultivation and the cumulative banana yield was only compared between the cropping systems. The growth and yield components were analyzed using the Shapiro–Wilk normality test and analysis of variance. Once the F-test was significant (p < 0.05), the means were compared using Tukey’s test for lemongrass data and a t-test (LSD) for banana data. Analyses were performed using the statistical program R v.4.3.1 [36] and software GraphPad Prism, v. 8.0.1. Principal component analysis (PCA) was carried out using XLSTAT version 2019.4.1 (Addinsoft, New York, NY, USA) to better visualize and explain the variability between the climate data and the lemongrass indicators assessed.

3. Results

3.1. Banana Growth and Yield

The growing and productivity indicators of the ‘Prata Anã’ banana plant showed no significant interaction between cropping systems and harvest seasons. There was a difference in the average height, with the plants in the intercropping system being taller (2.1 m) compared to the plants in the sole crop (2.0 m). The plants showed greater height, number of leaves and yield in the second harvest season. The cumulative yield assessment showed no difference between the intercropping (34.1 kg plant⁻¹) and sole crop (34.4 kg plant⁻¹) systems (

Table 2. Plant height, pseudostem diameter, number of leaves, yield and accumulative yield of the ‘Prata Anã’ banana plant as a sole crop and intercropped with lemongrass in two harvest seasons.

Cropping System	Plant Height (m)	Pseudostem Diameter (cm)	Number of Leaves	Yield (kg−1 Plant−1 Year−1)	Cumulative Yield (kg Plant−1)
Intercropping	2.1 ± 0.30 a	17.0 ± 1.36 a	7.7 ± 1.25 a	17.0 ± 5.71 a	34.1 ± 1.10 a
Sole crop	2.0 ± 0.18 b	16.9 ± 1.12 a	7.8 ± 0.96 a	17.2 ± 6.27 a	34.4 ± 1.30 a
Overall mean	2.1	17.0	7.8	17.1	34.3
CV (%)	3.3	5.3	6.2	6.8	4.8
1st crop cycle	1.9 ± 0.13 b	16.0 ± 0.60 b	7.0 ± 0.54 b	11.6 ± 0.64 b	-
2nd crop cycle	2.3 ± 0.21 a	17.9 ± 0.75 a	8.6 ± 0.83 a	22.7 ± 1.18 a	-
Overall mean	2.1	16.9	7.8	17.2	-
CV (%)	10.7	3.0	7.3	6.5	-

Means ± Standard Deviation followed by different letters in the column differ by the t-test (LSD) at 5% probability. CV = Coefficient of variation.

).

3.2. First Growing Season of Lemongrass

There was no significant interaction between the cropping systems and harvest seasons, nor between the cropping systems (p < 0.05), for lemongrass yield, dry mass, essential oil content and yield (

Table 3. Yield, dry mass, oil content and essential oil yield in lemongrass sole crop and intercropped with ‘Prata Anã’ banana plants in the first growing season.

Crop Cycles	Yieldlemongrass (t ha−1)	Dry Mass (%)	Oil Content (%)	Yieldoil (kg ha−1)
1st crop cycle	0.66 ± 0.05 b	32.00 ± 0.54 a	1.37 ± 0.18 a	3.08 ± 0.54 c
2nd crop cycle	1.27 ± 0.31 b	27.00 ± 0.91 b	1.47 ± 0.14 a	5.18 ± 1.47 b
3rd crop cycle	8.08 ± 0.99 a	31.00 ± 1.45 a	1.10 ± 0.02 b	15.2 ± 2.48 a
Source of variation	p-value
Cropping system (CS)	0.856 ns	0.055 ns	0.562 ns	0.606 ns
Crop cycle (CC)	<0.001 **	<0.001 **	<0.001 **	<0.001 **
CS X CC	0.951 ns	0.085 ns	0.152 ns	0.257 ns
CVCS (%)	15.5	5.5	11.1	5.81
CVCC (%)	18.9	8.2	9.3	9.2

ns = not significant; ** = significant at 1% by the F-test. Means ± Standard Deviation followed by different letters in the column within each factor differ by the Tukey test at 5% probability.

). Differences were observed between crop cycles, with a significant increase in dry mass production in the three crop cycles carried out in winter (first), spring (second) and summer (third crop cycle).

The average yield of dry mass was 0.66 t ha⁻¹ in the first crop cycle and 8.08 t ha⁻¹ in the third crop cycle, which represents an increase of 1143%. This increase in mass production directly influenced the yield of essential oil, which is proportional to the amount of raw material available. The average yield of essential oil was 3.08 kg ha⁻¹ in the first crop cycle and 15.2 kg ha⁻¹ in the third crop cycle. No differences in oil content were significant between the cropping systems, but there was a variation between crop cycles. The average essential oil content was 1.37% in the first crop cycle and 1.47% in the second, differing from the third crop cycle, which showed a content of 1.10% (Table 3).

3.3. Second Growing Season of Lemongrass

There was a significant interaction between cropping systems and crop cycles for essential oil yield, yield of lemongrass and essential oil content (

Table 4. Lemongrass yield, essential oil yield and essential oil content of lemongrass as a sole crop and intercropped with banana plants in the second growing season.

Productive Indicators	Cropping System	Crop Cycles			Average Cropping System
		1st	2nd	3rd
Yieldlemongrass (t ha−1)	Intercropped	10.0 ± 0.36 b	1.79 ± 0.24 a	12.7 ± 0.98 b	8.13 b
	Sole crop	15.8 ± 2.13 a	1.71 ± 0.30 a	14.9 ± 1.81 a	10.80 a
	Average crop cycles	12.90 b	1.75 c	13.80 a	*
Yieldoil (kg ha−1)	Intercropped	23.0 ± 1.08 b	3.25 ± 0.98 a	24.0 ± 0.55 b	16.75 b
	Sole crop	30.5 ± 0.91 a	2.16 ± 0.65 a	27.2 ± 0.99 a	19.95 a
	Average crop cycles	26.75 a	2.71 b	25.60 a	**
Essential oil content (%)	Intercropped	0.62 ± 0.02 a	0.70 ± 0.04 a	0.58 ± 0.04 a	0.63 a
	Sole crop	0.56 ± 0.03 a	0.52 ± 0.09 b	0.63 ± 0.04 a	0.57 b
	Average crop cycles	0.59 a	0.61 a	0.61 a	*

Means ± Standard Deviation followed by different letters indicate a significant difference (p ≤ 0.05) by Tukey’s test. * Significant interaction effect at 5% and ** = significant at 1% by the F-test.

). In the 1st crop cycle in winter and the 3rd crop cycle in summer, it was observed that lemongrass grown as a sole crop had the highest yields compared to that intercropped with banana plants, reaching 15.82 and 14.9 t ha⁻¹, respectively. This also had a positive effect on the yield of essential oil, which showed the highest averages, with 30.2 and 27.2 kg ha⁻¹, as well as the highest yields.

During the crop cycle in spring 2022 (2nd crop cycle), there was a significant decrease in lemongrass biomass production compared to the other crop cycles, with lemongrass production showing no difference between the cropping systems, averaging 1.75 t ha⁻¹.

Essential oil content in the second year of cropping was significantly correlated between cropping systems and crop cycles (Table 4). There was a difference in essential oil content between cropping systems only in the second crop cycle, which took place in the spring of 2022.

Lemongrass intercropped with banana plants had the highest value (0.63%) compared to the sole crop (0.57%). In the other crop cycles (first and third), there were no differences between the cropping systems in essential oil content, with an average of 0.58 and 0.60%, respectively (Table 4). In the second crop cycle of lemongrass, there was no interaction or differences between harvests for dry mass, with an average of 37%.

3.4. Principal Component Analysis

Principal component analysis (PC1 and PC2) represented 89.07 of the total variation of the data (Figure 3). PC1 explained 60.98% of the total variation and effectively separated minimum, maximum and average temperatures and accumulated rainfall from the crop cycles in the first and second growing seasons of lemongrass. The indicators that were most positively correlated with PC1 were lemongrass dry mass and yield and yield in the first and third crop cycles in the second growing season. The PC1 analysis indicated that the values of these indicators were higher in comparison with the second crop cycle on the opposite side of PC1. Lower temperatures and accumulated rainfall during the second crop cycle in the second growing season were positively correlated with the lowest lemongrass yield and essential oil yield.

PC2 was responsible for 28.09% of the total variation and was mainly correlated with the lemongrass oil content, which presented a negative correlation in the third crop cycle of the first growing season. PC2 scores and loads indicated that plants in this period produced the lowest oil content.

3.5. Land Equivalent Ratio

The banana showed LER = 1.03 in the first growing season and LER = 0.98 in the second growing season (Figure 4a). These data point to banana intercropped with lemongrass having values close to 1.0 in both growing seasons, representing the efficiency of the cropping system as a whole and indicating a positive effect on the yield of intercropping compared to the sole crop. This result suggests that the sole crop requires more area to produce the same quantity as the intercropping system.

Lemongrass presented the average LER = 0.77 in the first crop cycle, LER = 1.10 in the second and LER = 0.94 in the third crop cycle in the two growing seasons evaluated (Figure 4b). These data indicated a competitive advantage for the lemongrass sole crop in the first and third crop cycles. The total LER calculated by adding the LER of the banana and the LER of the lemongrass in all growing seasons and crop cycles showed values > 1.0, suggesting the advantage of the intercropping system over the sole crop.

3.6. Chemical Composition of Essential Oil

The chemical composition of lemongrass essential oil showed that a total of 25 components were detected and quantified, representing an average of 99% of the total components present in the oils, of which only 17 were identified. Citral, a compound formed by the combination of the isomers geranial and neral, was the major component found in all oil samples, followed by (E)-isocitral and geraniol, as well as a mixture of geraniol and geranyl acetate. These components represent on average 96.5% of the composition of lemongrass essential oil (

Table 5. Chemical composition (%) of lemongrass essential oil as a sole crop and intercropped with ‘Prata Anã’ banana plant in the second year of cropping.

N°	Substances			1st Crop Cycle		2nd Crop Cycle		3rd Crop Cycle
		IRLCal.	IRLlit.	Mon.	Interc.	Mon.	Interc.	Mon.	Interc.
1	6-metil-5-hepten-2-ona	993	981	0.25	0.25	0.23	0.28	0.46	0.41
2	n-Octanal	1011	998	0.05	0.05	0.06	0.08	0.10	0.08
2	o-Cymene	1031	1022	0.10	0.15	tr	tr	tr	Tr
3	Limonene	1034	1024	0.24	0.28	0.35	0.40	0.49	0.49
4	(Z)-β-Ocimene	1038	1032	0.05	tr	tr	tr	tr	tr
5	n.i.	1058		tr	tr	0.03	0.07	0.07	0.08
6	4-Nonanone	1077	1078 *	0.27	0.26	0.30	0.39	0.34	0.36
7	Linalool	1106	1095	0.41	0.39	0.45	0.49	0.58	0.54
8	n.i.	1117		0.09	tr	0.03	0.07	0.06	0.06
9	exo-Isocitral	1151	1140	0.10	0.10	0.16	0.16	0.16	0.16
10	n.i.	1159		0.16	0.13	0.13	0.16	0.15	0.13
11	n.i.	1169		0.16	0.16	0.62	0.65	0.66	0.64
12	Rosuferan epoxide	1178	1173	0.16	0.13	0.10	0.16	0.30	0.29
13	(E)-Isocitral (=Isogeranial)	1188	1177	1.09	1.09	1.17	1.27	1.31	1.26
14	(4Z)-Decennial	1200	1193	0.07	0.05	0.10	0.08	0.08	0.06
15	n.i.	1206		0.22	0.23	0.15	0.17	0.31	0.28
16	n-Decanal	1214	1201	0.09	0.07	0.09	0.09	0.13	0.10
17	n.i.	1230		0.06	0.06	0.05	0.09	0.06	0.07
18	n.i.	1241		0.10	0.10	0.11	0.14	0.10	0.11
19	Neral (=Z-citral)	1249	1235	34.25	34.12	35.75	36.35	37.05	37.32
20	Geraniol	1259	1249	0.60	0.56	tr	0.07	0.58	0.36
21	Geranial (=E-citral)	1280	1264	60.06	60.64	59.47	58.59	56.36	56.69
22	n.i.	1350		0.08	0.08	0.18	0.00	0.08	0.04
23	Geranyl acetate	1384	1379	1.01	0.95	0.20	0.15	0.25	0.20
24	γ-Cadinene	1520	1513	0.21	0.14	0.15	0.12	0.07	0.08
25	Cariophyllene oxide	1592	1582	0.30	0.22	0.21	0.18	0.25	0.25
	Total number of substances identified			99.41	99.47	98.78	99.47	98.49	98.65

TR: Retention time; IRLcal: calculated linear retention index; IRLlit: linear retention index from the literature [34]; tr: trace substance (tr ≤ 0.01); n.i.: unidentified substance; (*): linear retention index from NIST Webbook: https://webbook.nist.gov/chemistry/ (accessed 14 May 2024).

).

The essential oil components did not vary according to sole cropping or intercropping with banana plants. However, seasonal variations were observed in the content of the main components. The essential oil obtained from the first crop cycle had the highest content of geranial (60.35%), geranyl acetate (0.98%) and geraniol (0.58%) and the lowest content of neral (34.18%) and (E)-isocitral (1.09%). In subsequent crop cycles there was a decrease in geranial (56.52%), geranyl acetate (0.22%) and geraniol (0.47%) and an increase in neral (37.1%) and (E)-isocitral (1.28%) in the third and last crop cycles.

These results indicate that the time of the crop cycle can influence the quality and yield of essential oil constituents in lemongrass. With regard to the lemongrass harvest, there was stability in the citral concentration over the crop cycles, with an average of 94.43%, which demonstrates a high stability for the compound.

4. Discussion

The banana cultivar Prata Anã can be intercropped with lemongrass without interfering with its growth and production. These results are very advantageous, given that lemongrass could be grown in the banana rows, allowing machines to be used between the rows, and that the residual fertilizer from the banana plants in the first growing season was used for lemongrass, without the need for additional fertilization. There was also no need for weed control, which made it easier to manage the banana crop [21]. This shows that intercropping is more efficient in terms of land use and promotes the sustainability of the crop [11,37].

The analysis of the relative area required to grow the same quantity of both crop components in the intercropping if they were grown as sole crops rather than in consortium was carried out by the land equivalent ratio (LER). Values LER > 1 indicate intercropping’s advantage [20]. The LER is the most used indicator of the yield advantage of multicrop farming over monocrop farming and is generally measured through the production of plant biomass per unit area. Most of the time crop yields are compared between two systems using the same area [20]. The average total LER had values > 1.0, indicating higher yields in intercropping compared to sole cropping.

This metric is essential for understanding the relative performance of crops in an intercropping system, especially with regard to efficient utilization of available resources. Furthermore, values close to 1.0 for the partial LER indicate a good interaction between banana and lemongrass, suggesting that these crops are complementary in their use of natural resources. LER also reinforced the positive efficiency of the intercropping system as a whole, due to the quantity of inputs used directly and exclusively for banana production and, consequently, the intercropping produced more per unit area than the sole crop.

Banana yields in the second growing season were significantly higher than in the first. The yield of the second harvest is usually higher than that of the first because the plants are better established in the field. For the same reason, the second crop cycle is shorter than the first cycle. In addition, in this study, adverse weather conditions, such as less rainfall and lower temperatures, had a negative effect on the growth and yield of bananas in the first harvest season.

Intercropping can strengthen and stabilize agroecosystems in the context of climate change by improving resource use efficiency, increasing soil water retention capacity and increasing the diversity and quality of habitats for beneficial insects that ensure pollination and natural pest control [38].

Unfavorable weather is causing a decrease in soil fertility and an increase in the incidence of pests and diseases in banana plantations. As a result, banana yields decline [39]. This is why numerous farmers may consider using intercropping to boost their income from production and, consequently, their economic return [40]. In addition, growers are generally concerned about preserving environmental resources [41,42]. The preservation of biodiversity and the promotion of environmentally friendly agricultural practices are crucial to ensuring the continuity of ongoing human food supply in perpetuity [43,44].

Lemongrass biomass production varied throughout the year according to the crop cycles. These results are consistent with studies by Thakur et al. [45] and Mwithiga et al. [46], who reported a gradual increase in lemongrass production over the harvesting seasons. Yeshitila [47] attributes this increase in production to the growth triggers provided by cutting at harvest, which allows the plants to develop more tillers and therefore greater production. Furthermore, environmental conditions such as light, temperature and water availability have a significant impact on plant growth and development [14]. The results of the present study were positively correlated with climate data, showing and explaining the decrease in productivity and oil yield of lemongrass that occurred in the crop’s second cycle in 2022, when the winter was colder and there was less rainfall. The effect on lemongrass biomass and essential oil yields is one of the most striking effects of climate change on lemongrass growing seasons and crop cycles.

This study also showed differences in productivity between the lemongrass sole cropping and the intercropping with ‘Prata Anã’ bananas, varying according to the crop cycle assessed. In the second lemongrass growing season evaluated, this difference in production between the sole crop of lemongrass and the intercropping with ‘Prata Anã’ bananas may be due to the height of the banana plants, which can shade the lemongrass. The main risk of introducing intercropping in orchards is related to the influence of shade intensity on the growth, biomass allocation, yield and quality of fruit trees as the main crop in the system [48].

Banana production depends on light availability. The amount of light available depends on the spatial distribution of the banana plants and the density of the crop. As the fruit ripens, the canopy increases in size, reducing the amount of light available in this area. Therefore, to make good use of intercropping in banana plantations, a succession of short-cycle annual crops and more shade-tolerant species is recommended during the ripening stage [10].

Ntamwira et al. [10] reported that smallholder banana plantations in East and Central Africa were often intercropped with several annual crops to improve land use, a crop system limited by the availability of light under the banana canopy. Bananas produced by smallholders in the African Great Lakes region are commonly pruned to increase light for shorter intercrops. This reduces the overall profitability of the farm [49]. Similarly, Kumar et al. [50] reported a reduction in lemongrass production when intercropped with pomegranate (Punica granatum), due to shading. The wider geometry of the lemongrass plant provides a better intercropping advantage in the early growing stage [1].

In addition to shading, competition for nutrients may have favored the banana plants in the second growing season due to their better-distributed root system with a larger area of coverage, which caused a reduction in lemongrass production. The findings are in line with those of Yogendra et al. [1], investigating the intercropping of lemongrass with food crops in India and observing a decrease in the growth and production of lemongrass intercropped with millet (Panicum miliaceum) and beans (Phaseolu vulgaris), due to the shading and deeper rooting of these crops.

Lemongrass harvested in three different seasons of the year presented a range of essential oil yields and chemical compositions. The decrease in oil content in the first crop cycle may be related to environmental, physiological and genetic factors that affect the biosynthesis and accumulation of secondary metabolites in plants [1,18]. The composition of essential oil can vary according to climatic factors such as temperature, humidity, light and rainfall, which affect the secondary metabolism of plants and the biosynthesis of volatile compounds. These variations can occur between different seasons, which can lead to changes in the quantity and quality of essential oil components [51].

Madi et al. [52] observed differences in the content of essential oil extracted in summer and winter. Kumar et al. [50], evaluating the impact of harvests on the chemical composition of the essential oil of lemongrass species of the Cymbopogon genus in South India, noticed medium to high stability in the citral content over harvests for most of the species evaluated. Madi et al. [52] evaluated the chemical composition of essential oil extracted from lemongrass grown in Egypt and identified citral concentrations that were higher in summer and lower in winter. The differing yields of lemongrass essential oil between the cropping systems (sole crop and intercropping) can be explained by the higher concentration of secondary metabolites in the intercropped plants, in response to the stress caused by shading and other adverse climatic conditions, as reported by Madi et al. [52].

Lemongrass essential oil is extracted from the whole plant, excluding the roots, and has a light-yellow color and a lemony odor due to the presence of citral in its composition [53]. Lemongrass essential oil is a rich source of citral, a compound with multiple pharmacological properties that also serves as a chemical marker for the species [54]. The Brazilian Pharmacopoeia states that essential oil of lemongrass grown in Brazil must contain at least 60% citral (geranial + neral) and the concentration of essential oil should be between 0.5 and 2% [55]. All the lemongrass harvests in this study were within this range for oil content, with an average of 1.29% for the first year of cultivation and 0.60% for the second year. This study highlights the importance of a detailed analysis of growing conditions and harvest times to optimize the yield and quality of lemongrass.

Several studies have analyzed the beneficial effects of citral in different areas of application. In the medical field, citral has demonstrated anti-inflammatory, antibacterial, antifungal and antitumor properties [56,57], acting on different cellular and molecular targets [58].

In the agricultural field, citral has also been used as a natural agent to improve soil health, especially due to its antimicrobial and cytotoxic properties, and can help in bioremediation processes of environments contaminated by harmful substances and microorganisms, as well as promoting the physical health of farm workers by reducing exposure to pathogens and toxins [3]. Citral has also been used as a biopesticide and biofungicide, which can control pests and diseases that affect agricultural crops, reducing dependence on synthetic chemicals that can cause damage to the environment and human health [5]. In addition to fungal control, studies have shown that essential oils have insecticidal properties [11,59]. Essential oils can therefore be considered natural and safe alternatives for pest and disease control, contributing to sustainable agricultural production.

This study focused on the evaluation of banana and lemongrass intercropping, discussing some of the underlying questions and challenging issues faced when implementing sustainable banana and lemongrass growing management practices. However, there are still some issues that require further analysis, particularly in terms of assessments in consecutive harvest seasons, which can improve yield without compromising the component crops of intercropping. Further studies could also be carried out to assess the possibility of cutting more lemongrass throughout the growing season and increasing its stand grown in the banana rows. As a result, the outcomes are recommendable to a wide range of farmers, especially smallholders.

5. Conclusions

The banana and lemongrass intercropping system performed well in the harvest seasons studied and lemongrass did not affect the yield of the main banana crop. The total land equivalent ratio showed values >1.0 indicative of a positive effect on the yield of intercropping compared to the sole crop. The growth and production of banana plants, as well as the production, yield and chemical composition of lemongrass essential oil, did not differ in the first year of cropping, regardless of whether it was grown as a sole crop or intercropped with banana plants. In the second year, lemongrass grown in monoculture showed higher biomass production and yield of essential oil. The chemical composition of the essential oils was predominantly citral and a mixture of neral and geranial, representing about 94.4% of the total compounds identified.