Integrating Indian Spinach (Basella alba) as a Lower Storey Crop in Multistoried Fruit Orchard: A Management Intervention for Improved Productivity and Economic Profitability

In Bangladesh, multistoried agroforestry is needed to address the challenges of declining cultivable land and recurring climatic threats, while also providing farmers with a sizable financial gain. Therefore, a field investigation was performed at the Gazipur Agricultural University in Bangladesh, with the goal of examining Indian spinach productivity in an aonla-established multi-storied agroforestry system. The experiment was designed as a two-factor randomized complete block design (RCBD) with three replications of factor A (T₁: Aonla + lemon + Indian spinach; T₂: Aonla + Indian spinach; T₃: Sole Indian spinach) and factor B (V₁: BARI Puishak-1; V₂: BARI Puishak-2; V₃: Genotype-10450; V₄: Genotype- 10451; V₅: Genotype-10452). The findings showed that different growth and yield-related attributes were affected by variations in Photosynthetically active radiation (PAR). Consequently, the yield declined in T₁ (aonla + lemon + Indian spinach) and T₂ (aonla + Indian spinach) compared to that in T₃ (sole Indian spinach), which could be explained by the competition of the components for above- and below-ground resources. Fascinatingly, the T₁ system provided the overall highest output compared to the others, as the agroforestry system’s multiple products contributed to the total output and confirmed its superiority over a single crop. Among the varieties, BARI Puishak 2 outperformed the other four. With a benefit-cost ratio (BCR) of 3.68 and a land equivalent ratio (LER) of 3.56, BARI Puishak 2, in conjunction with the T₁ agroforestry system (T₁V₂), exceeded the other treatment combinations. In summary, it can be concluded that using Indian spinach in multistoried agroforestry systems could be a magnificent approach to guarantee greater financial gain and support food and nutritional security in the economically insolvent farming communities of Bangladesh. 

Introduction

A vast population of over 169.83 million people and 8.09 million hectares of arable land pose a simultaneous threat to Bangladesh’s ability to provide its citizens with a sufficient supply of food and nutrition [1], [2]. In addition, with a phenomenal growth rate of 1.2%, the population is constantly expanding, placing a significant strain on limited land resources, and is expected to grow to 192.6 million by the end of 2050 [3], [4]. Therefore, it is necessary to increase crop production by at least double to feed this persistently enlarging population in the near future. Recently, Bangladesh has improved agricultural production but 24.2 million people are still fighting food shortages [5], [6]. Most people are directly or indirectly involved in agriculture, which is the most conventional profession; however, it has recently been plagued by anthropogenic and climatic hazards [7], [8]. Moreover, the combined effects of rapid urbanization, industrialization, and the construction of new homes for a rapidly expanding population and new development projects are shrinking agricultural land at a rate of 69,000 hectares annually [9], [10]. Furthermore, most arable land in Bangladesh encompasses less than 1.5% organic matter, although a minimum of 2.5% is required for optimum soil composition [11], [12]. Therefore, research should be conducted on climate-smart, demand-driven, and nutrient-sensitive sustainable agricultural methods to address these challenges in agricultural production.

In such conditions, it is imperative to expand agricultural land bases vertically so that they can produce poles, food, fuelwood, and other items from the same piece of ground. Bangladesh would undoubtedly benefit economically and environmentally by combining both production strategies, as there is a limited scope to expand forest areas separately. Agroforestry, a combined cultivation method for agricultural crops and woody perennials (trees and shrubs) on the same land, may be a suitable approach to solve the problem of sustainable production and overcome obstacles in the future. Agroforestry is a mixed cropping system in which woody perennials and annual herbaceous crops are planted together in a certain spatial and temporal arrangement [13], [14]. According to Patle et al. [15], the system makes better use of natural resources, including light, water, and nutrients, both above and below ground, which is not feasible in monocropping systems. Agroforestry also enhances soil fertility, water quality, biodiversity conservation, and most importantly, sequestrates carbon to mitigate global warming [16]. There are many new and traditional agroforestry systems practiced in Bangladesh, of which fruit-tree-based agroforestry is the most common, and aonla (Phyllanthus emblica L.)-based multistory fruit orchards are becoming popular as a lucrative and highly profitable system.

Aonla, popularly known as ‘wonder fruit for health’ exerts little negative effects on understory crops because of its deciduous nature, which is capable of producing yield under hostile environments and demands little inputs and management [17], [18]. Aonla fruit contains a tremendous amount of vitamin C, which also has anti-inflammatory, antibacterial, and antioxidant properties [19]. In addition to amino acids and other healthy phytochemicals such as rutin, emblicol, corilagin, linoleic acid, tannin, and polyphenol, aonla also contains ascorbic acid (300–900 mg/100 g) [20]. Lemons, which are widely recognized for their numerous health benefits, including their ability to prevent cancer, and their usage as a source of raw materials for the creation of ethnic herbal medicines [21], could be another suitable component of multistoried agroforestry systems. Lemon is also the richest source of vitamin C, which can grow under diverse environmental conditions including partial shade; hence, it has the potential to form the middle story of a multistoried fruit orchard. Finally, multistoried agroforestry should have a lower-story component based on the structural layout. Indian spinach (Basella alba), a popular leafy vegetable rich in vitamins A, C, and B₉ could be a wonderful choice for cultivation as a lower-story crop. It also contains dietary fiber, phenols, antioxidants, different bioactive chemicals, important amino acids, and minerals including calcium, magnesium, and iron [22], [23]. Given the potential and advantages of multistoried agroforestry systems, it would be extremely beneficial to investigate an economically and environmentally viable model that considers Indian spinach (as a summer vegetable), carambola, lemon (as a fruit tree), and aonla (as a medicinal plant). Considering the above-mentioned facts, the authors conducted the present study to assess Indian spinach productivity in an aonla-established multistoried agroforestry and evaluate the economic profitability along with land use performance compared to sole cropping. The findings of this study might assist in choosing compatible species to increase agricultural output and inform future management plans.

Materials and Methods

General Description of the Study Area

This research was conducted in the departmental research field under the Department of Agroforestry and Environment, Gazipur Agricultural University, Bangladesh, which is geologically relevant to the agro-ecological zone 28, specifically the Madhupur tract (Fig. 1). The study area is located at 24° 9ʹ N latitude and 90° 26ʹ E longitude, with an elevation of 8.2 meters above sea level. According to the United States Department of Agriculture’s (USDA) soil taxonomy, the study site's soil is categorized as shallow red-brown terrace soil under the order Inceptisols [24]. Throughout this experiment, the study area experienced a maximum and minimum temperature of 34°C and 11.9°C, respectively, with 243 mm annual rainfall.

Fig. 1. Location of the study area.

Establishment of the Farm

A multistoried fruit orchard was established in 2000 with a spacing of 8 m × 8 m, where aonla trees formed the upper-story, lemon trees were positioned between aonla trees as a middle story, and Indian spinach was grown as a lower story crop. The aonla plant’s average height was from 5.56 m to 5.64 m, its base diameter was between 20.02 cm and 20.06 cm, its breast height diameter was between 14.7 cm and 15.6 cm, and its canopy diameter was between 3.36 m and 3.44 m. Lemon plants range in height from 83.2 cm to 83.4 cm, base diameter from 15.1 mm to 15.2 mm, canopy diameter from 47.4 cm to 48.2 cm (North-South), and canopy diameter from 49.2 cm to 49.8 cm (East-West). The lemon was BARI Lebu-4, and the aonla race was local. The Plant Genetic Resources Centre (PGRC), BARI, Joydebpur, Gazipur, provided five Indian spinach genotypes (BARI Puishak 1, BARI Puishak 2, Genotype-10450, Genotype-10451, and Genotype-10452), which were then assessed in the aonla orchard’s vacant areas.

Experimental Design and Treatments

The experimental design was a two-factor randomized complete block design (RCBD) with three replicates. Factor A: agroforestry systems, that is, T₁, Aonla + lemon + Indian spinach; T₂, Aonla + Indian spinach; T₃, Sole Indian spinach (control). Factor B: Indian spinach varieties (V₁, BARI Puishak-1; V₂, BARI Puishak-2; V₃, Genotype-10450; V₄, Genotype-10451; V₅, Genotype-10452. Therefore, the present experiment consisted with a total of 15 different treatment combinations.

Land Preparation, Crop Sowing, and Intercultural Management

Soil was prepared by plowing and laddering to obtain a quality tilt prior to planting Indian spinach seeds. Plowing, leveling, weeding, stubble removal, and other land preparation tasks were appropriately completed. Seeds of Indian spinach were sown in well-prepared land with 30 × 20 cm spacing. The recommended doses of fertilizers were applied at a rate of 10 t ha⁻¹ cowdung, 165 kg ha⁻¹ urea, 110 kg ha⁻¹ TSP, 110 kg ha⁻¹ MOP, and 40 kg ha⁻¹ gypsum to ensure proper growth and establishment of Indian spinach [25]. Irrigation, weeding, and thinning were performed according to the requirements. Dithane M-45 at a rate of 2 g/L water was sprayed as needed to control the infestation of leaf spot disease.

Data Recording

Indian spinach was harvested three times at 20-day intervals: 45, 65, and 85 days after sowing (DAS). Vine samples were collected for data collection following harvest. Vine length, base girth, leaf per vine, leaf fresh weight, leaf dry weight, stalk weight, leaf/stem ratio, and yield of Indian spinach were measured at every harvest time. To calculate leaf dry weight, 50 g of leaf was oven-dried for 12 hours at 70°C. The leaf dry weight was calculated using the following formula:

$$\begin{array}{rl}Leafdryweight& =\frac{Subsampleovendriedweight}{Subsamplefreshweight}\\ & \times Totalfreshweightofleaves\end{array}$$

Light Measurements

To measure shade over understory crops, photosynthetically active radiation (PAR) was estimated every two weeks using a Sunfleck Ceptometer (LP-80 AccuPAR).

Economic and Land Use Performances

The benefit–cost ratio (BCR) is used in agroforestry to determine a system’s relative profitability in comparison to other traditional systems. BCR was estimated using the following formula [26]:

$$\begin{array}{r}BenefitCostRatio\left(BCR\right)=\frac{Grossreturn}{Totalcostofproduction}\end{array}$$

Land equivalent ratio (LER) shows how much land an intercrop needs compared to a species’ monocrop:

$$\begin{array}{r}LandEquivalentRatio\left(LER\right)=\frac{Ci}{Cs}+\frac{Ti}{Ts}\end{array}$$

where Ci is the yield of crops as an intercrop, Cs is the yield of crops as the sole crop, Ti is the yield of trees in the intercrop, and Ts is the yield of trees from sole trees [27].

Statistical Analysis

The “Analysis of Variance” (ANOVA) approach was used to statistically examine the experimental data in order to see how different treatments affected the outcomes. The significance of the differences between treatment means was assessed at a 5% level of probability using the least significant difference (LSD) test to interpret the data.

Results and Discussion

Availability of Photosynthetically Active Radiation

Undoubtedly, one of the most significant resources contributing to yield is light. The various strata of multistory agroforestry have varying PAR accessibility. Compared to the PAR above the aonla tree, the PAR above the lower-story Indian spinach and lemon was 48.91% and 50.17%, respectively, in an agroforestry system based on aonla + lemon + Indian spinach (Figs. 2a and 2b). Accordingly, the lower-storied Indian spinach received 73.07% PAR compared to aonla in an aonla + Indian spinach-based system throughout the Indian spinach growing season (Figs. 3a and 3b). Aonla, as an upper-storied component, might exert some negative effects on the understory crop as well as reduce the most important yield-supporting attributes, such as PAR. The upper canopy coverage limited the PAR over the lower-storied crops; hence, the lower-storied crops received less intensity of PAR because of partial shading, which might have minimized photosynthesis, dry matter production, and crop yield. Similar results were reported by Ferdous et al. [8] and Pingki et al. [10], who reported that light is the most important factor for the growth and yield of crops.

Fig. 2. Availability of Photosynthetically active radiation (PAR) at different strata of aonla + lemon + Indian spinach-based agroforestry system during Indian spinach growing season: (a) month wise and (b) average.

Fig. 3. Availability of Photosynthetically active radiation (PAR) at different strata of aonla + Indian spinach-based agroforestry system during Indian spinach growing season: (a) month wise and (b) average.

Crop Productivity

Effect of Agroforestry Systems

The vine length, base girth, leaf per vine, and SPAD values were significantly associated with the studied agroforestry systems (Fig. 4). The highest vine length (47.2 cm) and SPAD value (39) were recorded in the T₁ (aonla + lemon + Indian spinach) treatment, while the lowest vine length (37.2 cm) and SPAD value (35.5) were found in the T₃ (sole Indian spinach) treatment (Figs. 4a and 4d). The highest base girth (2.5 cm) and leaf per vine (78) were recorded in the T₃ treatment, whereas T₁ provided the lowest base girth and leaf per vine of Indian spinach (Figs. 4b, 4c). Similarly, the agroforestry practices studied had a significant impact on leaf fresh weight, leaf dry weight, stalk weight, leaf-stem ratio, and yield of Indian spinach (Figs. 5 and 6). Significantly the highest leaf fresh weight (220 gm), leaf dry weight (14.5 gm), stalk weight (158 gm), leaf-stem ratio (1.45), and yield (21.27 ton hac⁻¹) were found in T₃ treatment (sole Indian spinach), while T₁ treatment provided their lowest values (Figs. 5 and 6). In comparison to the sole Indian spinach (T₃), T₁ and T₂ treatments resulted in a reduction in base girth (by 13.73% and 12%), leaf per vine (by 23% and 15%), leaf fresh weight (by 17.6% and 10%), leaf dry weight (by 22% and 13%), stalk weight (by 8.65% and 4%), leaf stem ratio (by 12.57% and 7%), and yield (by 13.88% and 7.48%), respectively (Figs. 4–6). In contrast, vine length increased by 27% and 11.25%, whereas the SPAD value increased by 2.5% and 0.43%, respectively. Competition between two or more elements for scarce resources, particularly nutrients, water, and light, might have affected the productivity of Indian spinach and reduced the yield in agroforestry practices [28]. A decrease in PAR is closely related to a decrease in yield; however, Indian spinach in the T₁ treatment received less PAR than in T₂, and consequently, the yield reduction was larger in the T₁ treatment than in T₂. T₃ (sole Indian spinach) treatment under full sunlight may ensure maximum photosynthesis and growth indicators, resulting in maximum yield. In contrast, shading reduced % PAR in T₁ and T₂ treatments, resulting in lower carbon fixation and less leaf per vine, lower leaf fresh weight, and lower stalk weight, which finally decreased the yield. Moreover, the root system of perennial trees might have suppressed the lower storied annual crops from obtaining water and nutrients, which ultimately resulted in lower crop yields. Our findings are corroborated by Rita et al. [18] and other researchers [29]–[31], who also observed that crop yields were reduced owing to the presence of trees in agroforestry systems.

Fig. 4. Vine length (a), base girth (b), leaf per vine (c), and SPAD (d) value of Indian spinach grown under different agroforestry systems. Different alphabetical letters of the bar showed the significant differences (P < 0.05) among the treatments.

Fig. 5. Leaf fresh weight (a), leaf dry weight (b), stalk weight (c), and leaf-stem (c) ratio of Indian spinach grown under different agroforestry systems. Different alphabetical letters of the bar showed the significant differences (P < 0.05) among the treatments.

Fig. 6. Yield of Indian spinach grown under different agroforestry systems. Different alphabetical letters of the bar showed the significant differences (P < 0.05) among the treatments.

Effect of Varieties

Base girth, leaf per vine, and SPAD values varied significantly among the different varieties of Indian spinach, whereas vine length was insignificant (Fig. 7). V₅ produced the longest vine length (45 cm) of the Indian spinach (Fig. 7a). The highest base girth (2.52 cm) was found in V₂ which was statistically identical to V₁ and V₃, whereas V₂ produced the highest (86) leaf per vine. In contrast, V₅ had the lowest base girth (2.06 cm) and leaf per vine (41) (Figs. 7b and 7c). The highest SPAD value (39.07), which was not significant for V₂ (38.28), V₃ (38.12), and V₄ (38.3), was recorded in V₁ whereas V₅ produced the lowest (33.9) SPAD value (Fig. 7d). The studied varieties of Indian spinach showed significant variation in terms of leaf fresh weight, leaf dry weight, stalk weight, and leaf-stem ratio. The variety V₂ (BARI Puishak 2) produced the significantly highest leaf fresh weight (299 g plant⁻¹), leaf dry weight (19.2 g plant⁻¹), stalk weight (191 g plant⁻¹), and leaf-stem ratio of 1.55 (Figs. 8a–8d). In contrast, the lowest leaf fresh weight (103.7 g plant⁻¹), leaf dry weight (6.64 g plant⁻¹), and leaf-stem ratio (0.6) were produced by V₅, while V₄ provided the significantly lowest stalk weight (96 g plant⁻¹) of Indian spinach. The yield of Indian spinach varied significantly among the varieties. The highest yield (27.6 ton hac⁻¹) was obtained from variety V₂ (BARI Puishak 2), while V4 (Genotype-10451) provided the lowest yield (14.07 ton hac⁻¹) of Indian spinach (Fig. 9).

Fig. 7. Response of (a) vine length, (b) base girth, (c) leaf per vine, and (d) SPAD value to the different varieties of Indian spinach. Different alphabetical letters of the bar showed the significant differences (P < 0.05) among the treatments.

Fig. 8. Response of (a) leaf fresh weight, (b) leaf dry weight, (c) stalk weight, and (d) leaf-stem ratio to the different varieties of Indian spinach. Different alphabetical letters of the bar showed the significant differences (P < 0.05) among the treatments.

Fig. 9. Response of yield to the different varieties of Indian spinach. Different alphabetical letters of the bar showed the significant differences (P < 0.05) among the treatments.

The findings demonstrated that different genotypes of Indian spinach had significant differences among themselves and performed differently under shaded conditions. Variety V₅ had more apical dominance, so vine length was the highest, but base girth and leaf per vine were much less than the other varieties. However, V₂ proved superior in leaf vine⁻¹, girth of base, leaf fresh weight, leaf dry weight, stalk weight, and yield over the other varieties, which might be due to its genetic potential to grow under partial shade conditions.

Interaction between Agroforestry Systems and Indian Spinach Varieties

The interactions of agroforestry systems and Indian spinach cultivars with various growth- and yield-contributing traits showed notable variation across different treatment combinations (Table I). The results demonstrated that, the variety V₂ (BARI Puishak 2) produced the highest base girth (2.69 cm), leaf per vine (97), leaf fresh weight (328 gm), leaf dry weight (22 gm), and highest yield (29.3 ton hac⁻¹) in sole Indian spinach system (T₃V₂), while V₅ (Genotype-10452) produced the lowest base girth (1.8 cm), leaf per vine (33), leaf fresh weight (86.1 gm) and leaf dry weight (5.35 gm) in aonla + lemon + Indian spinach (T₁V₅) system. The lowest yield (12.83 ton hac⁻¹) of Indian spinach was produced by the variety V₄ (Genotype-10451) under the aonla + lemon + Indian spinach (T₁V₄) system (Table I). It was also observed that, the highest vine length (50.9 cm), SPAD value (41.9), stalk weight (201.7 gm), and leaf-stem ratio (1.71) were recorded in T₁V₅, T₁V₁, T₃V₅, and T₃V₄ treatment combinations, respectively; while, the lowest vine length (34.9 cm), SPAD value (32.9), stalk weight (92.25 gm), and leaf-stem ratio (0.62) were recorded in T₃V₄, T₁V₅, T₂V₄, and T₁V₅ treatment combinations, respectively (Table I).

Table I. Interaction between Agroforestry Systems and Varieties and their Combined Effects on Indian Spinach Yield and Yield-Contributing Characteristics

Treatment combinations	Vine length (cm)	Base girth (cm)	Leaf per vine	SPAD value	Leaf fresh weight. (gm)	Leaf dry weight. (gm)	Stalk weight.(gm)	Leaf stem ratio	Yield (ton hac−1)
T1V1	47.25 ± 0.71ab	2.38 ± 0.03cde	70.86 ± 0.74e	41.94 ± 0.4a	255.42 ± 0.6e	15.96 ± 0.04e	179.44 ± 3.91cd	1.41 ± 0.01e	24.46 ± 0.08d
T1V2	47.16 ± 0.61b	2.41 ± 0.03bcd	76.77 ± 1.14cd	40.52 ± 0.74ab	275.45 ± 0.53d	17.12 ± 0.03d	189.49 ± 2.26b	1.45 ± 0.01de	26.15 ± 0.05c
T1V3	45.18 ± 0.53bc	2.31 ± 0.05cdef	58.71 ± 0.6f	39.14 ± 0.62b	155.84 ± 0.58i	9.67 ± 0.04i	109.76 ± 1.83fg	1.43 ± 0.02de	14.94 ± 0.05h
T1V4	45.54 ± 0.36b	2.05 ± 0.05fgh	60.25 ± 0.48f	40.89 ± 0.88ab	134.45 ± 1.3j	8.37 ± 0.08j	93.66 ± 4.7hi	1.43 ± 0.02de	12.83 ± 0.13i
T1V5	50.89 ± 0.35a	1.81 ± 0.06h	33.40 ± 0.48i	32.92 ± 0.14e	86.11 ± 0.89m	5.35 ± 0.06l	148.58 ± 12.3e	0.62 ± 0.09f	13.2 ± 0.14i
T2V1	41.71 ± 0.87cd	2.49 ± 0.04abc	76.11 ± 0.97cd	39.68 ± 0.3ab	279.86 ± 1.19cd	17.77 ± 0.08c	188.64 ± 4.9bc	1.48 ± 0.03cd	26.35 ± 0.12c
T2V2	40.43 ± 0.53de	2.45 ± 0.03abc	85.80 ± 0.85b	38.67 ± 0.3b	295.11 ± 1.02b	18.72 ± 0.06b	190.26 ± 7.52b	1.54 ± 0.06c	27.3 ± 0.12b
T2V3	41.36 ± 0.66d	2.17 ± 0.03defg	69.36 ± 0.28e	39.07 ± 0.33b	165.33 ± 0.82h	10.51 ± 0.05h	108.55 ± 4.98fg	1.53 ± 0.03c	15.41 ± 0.1gh
T2V4	37.60 ± 0.45ef	2.13 ± 0.05efg	59.77 ± 0.2f	38.49 ± 0.41bc	148.59 ± 1.41i	9.47 ± 0.09i	92.25 ± 4.52i	1.61 ± 0.03b	13.55 ± 0.13i
T2V5	45.76 ± 0.19b	1.93 ± 0.07gh	40.28 ± 0.68h	33.97 ± 0.3de	102.31 ± 1.47l	6.51 ± 0.09k	178.36 ± 14.1d	0.59 ± 0.05f	15.79 ± 0.2gh
T3V1	39.95 ± 0.72de	2.5 ± 0.01abc	92.58 ± 1.28a	35.58 ± 0.24d	287.02 ± 0.93c	18.77 ± 0.06b	176.08 ± 6.7d	1.62 ± 0.04b	26.05 ± 0.13c
T3V2	37.03 ± 0.7ef	2.69 ± 0.02a	96.52 ± 1.25a	35.64 ± 0.13d	327.62 ± 0.58a	21.71 ± 0.04a	193.94 ± 1.59ab	1.66 ± 0.02ab	29.34 ± 0.04a
T3V3	35.50 ± 0.42f	2.65 ± 0.02ab	78.69 ± 0.92c	36.13 ± 0.31cd	186.07 ± 1.56f	12.25 ± 0.1f	114.14 ± 6.17f	1.62 ± 0.03b	16.89 ± 0.17f
T3V4	34.91 ± 0.77f	2.44 ± 0.03abc	71.97 ± 0.76de	35.49 ± 0.21d	178.18 ± 1.43g	11.66 ± 0.09g	103.4 ± 5.14gh	1.71 ± 0.04a	15.84 ± 0.14g
T3V5	38.57 ± 0.31def	2.44 ± 0.03abc	49.99 ± 0.63g	34.81 ± 0.24de	122.61 ± 2.1k	8.06 ± 0.14j	201.71 ± 8.02a	0.63 ± 0.02f	18.24 ± 0.2e

In comparison to sole cropping (T₃), different Indian spinach varieties V₁, V_2, V_3, V₄ and V₅ cultivated in agroforestry systems showed an increase in vine length at T₁ by 31.94% highest in V₅ and by 18.27% lowest in V₁ and also in T₂ treatment by 18.64% highest in V₅ and 4.41% lowest in V₁ (Table I). This type of highest and lowest increment was also found for stalk weight and leaf to stem ratio parameters. In the case of leaf per vine, abatement in the T₁ treatment by 33.19% in V₅ was the highest and 16.28% in V₄ was the lowest among all other varieties, whereas in the T₂ treatment, the highest was also noted in V₅ by 19.42%, but the lowest was in V₂ by 11.11%. This trend of decline was also noted for the base girth, leaf fresh weight, leaf dry weight, stalk weight, and yield of Indian spinach (Table I). The yield of Indian spinach was reduced as a result of the strong effects of middle-story lemons and upper-story aonla on the growth characteristics of lower-story Indian spinach. This result may be due to lower photosynthesis under partially shaded conditions and competition with perennial trees. It is evident that perennial trees have more developed root systems than annual crops, and in the root zone locations, the tree outcompeted Indian spinach, ultimately resulting in lower base girth, leaf weight, stalk weight, and lower yields. However, higher apical dominance under shaded conditions influenced vine length. Our findings also corroborated the outcomes of other studies [8], [18], [32], [33] on radish, stem amaranth, and aroid under fruit tree-based agroforestry systems.

Economic and Land Use Performances

Several tools are used to determine the economic and land use performance, and we used the benefit cost ratio (BCR) and land equivalent ratio (LER) in our study. The economic and land use performances demonstrated that agroforestry practices provided higher economic returns and profitable land use than sole cropping of Indian spinach (Table II). Compared to T₃ (single cropping), the gross return of Indian spinach was higher in both T₁ and T₂ agroforestry systems, while it was highest in T₁V₂ (222,768 Tk ha⁻¹) and lowest in T₃V₄ (95,034 Tk ha⁻¹). Similarly, net return was highest in T₁V₂ (162,268 Tk ha⁻¹) and lowest in T₃V₄ (34,534 Tk ha⁻¹). In compare to T₃ (sole cropping), higher BCR was exhibited by T₁ (aonla + lemon + Indian spinach) system followed by T₂ (aonla + Indian spinach) system. The highest BCR (3.68) was found in the T₁V₂ treatment combination and the lowest (1.57) in the T₃V₄ treatment combination. The T₁ agroforestry system was later discovered to have a greater LER than the T₂ agroforestry system. Surprisingly, the T₁V₂ system had the highest LER (3.56), while the lowest (2.17) was in the T₂V₄ treatment combination (Table II). In terms of land use, the benefit of intercropping over a single crop is indicated by a land equivalent ratio (LER) value greater than 1 [34]. According to our experiment, the T₁V₂ treatment combination had the greatest LER value (3.56), indicating that intercropping has a 3.56-fold greater advantage than solitary cropping and that a 3.56 times in area would be required to provide a comparable yield under the sole crop.

Table II. Economic and Land Use Performances of Indian Spinach Associated Different Treatment Combinations

Treatment combinations	Gross return (Tk ha−1)	Net return(Tk ha−1)	BCR	LER
T1V1	204766	144266	3.38	3.51
T1V2	222768	162268	3.68	3.56
T1V3	172840	112340	2.86	3.51
T1V4	165992	105492	2.74	3.43
T1V5	170712	110212	2.82	3.35
T2V1	189218	128718	3.13	2.32
T2V2	186412	125912	3.08	2.24
T2V3	129936	69436	2.15	2.22
T2V4	116622	56122	1.93	2.17
T2V5	127028	66528	2.10	2.18
T3V1	156294	95794	2.58	–
T3V2	176028	115528	2.91	–
T3V3	101322	40822	1.67	–
T3V4	95034	34534	1.57	–
T3V5	109458	48958	1.81	–

Agroforestry systems can yield higher economic returns for several reasons. For example, middle-storied lemons and upper-storied aonla produced better yields without any additional inputs (water and fertilizer) than their sole farming. Moreover, crop production benefits from trees in fields, including the addition of mulch, organic matter, and nutrient-rich soils [35]. The income table is further enhanced by additional tree resources, including fruit, firewood, timber, and non-timber products. Aonla and lemon, two fruits with greater market demand, and Indian spinach, a leafy vegetable that is popular in Bangladesh year-round, were the primary contributors to the better economic return (BCR) in the agroforestry system (T₁) over T₂ (aonla with Indian spinach) and T₃ (aonla only). These findings are best endorsed by Al Riyadh et al. [7], Rita et al. [18], Riyadh et al. [32], and Das et al. [36] under different agroforestry practices.

Conclusions

Considering the economic and land use performances, it can be stated that Indian spinach cultivation in underutilized spaces in association with fruit trees has the potential to uplift the system’s overall productivity and economic profitability. Although the accessibility of Photosynthetically active radiation (PAR) decreased which ultimately declined the yield of Indian spinach in agroforestry systems compared to sole cropping; however, the overall output remained the highest because of the combined output of the agroforestry systems. The results showed that incorporating Indian spinach into the underused spaces of this aonla-based multistory agroforestry can increase its economic turnover. In particular, BARI Puishak 2 has demonstrated superiority over other varieties in terms of yield, BCR, and LER. Therefore, cultivating Indian spinach in aonla-based multistoried agroforestry systems might be a suitable productive and profitable option to help resource-limited farmers. However, multilocation field trials should be conducted to improve the practicality of the system.

Acknowledgment

The authors greatly appreciate the Department of Agroforestry and Environment at Gazipur Agricultural University in Bangladesh for providing the facilities and resources required to successfully complete this research project.

Conflict of Interest

No conflicts of interest are disclosed by the authors.