Productivity and Profitability Assessment of Stem Amaranth and Changes in Soil Chemical Properties under Aonla-Based Multistoried Agroforestry

Aonla based multistoried agroforestry system could be a suitable model in improving agricultural productivity and profitability, particularly for the resource-poor country like Bangladesh. However, the adoption of multistoried agroforestry is still limited and most of the fruit orchards remain underutilized throughout the year. Therefore, a field experiment was carried out to evaluate the performance of stem amaranth as a lower storey crop and assess the changes in soil chemical properties under aonla based multistoried agroforestry system (MAFs). The experiment was performed at the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur, Bangladesh throughout the time from April 2021 to June 2021, following a randomized complete block design (RCBD) with three replications. There were four treatments as follows: T₁ = Aonla + carambola + lemon + stem amaranth, T₂ = Aonla + lemon + stem amaranth, T₃ = Aonla + stem amaranth, and T₄ = Sole stem amaranth. Results demonstrated that agroforestry systems have a significant effect on the yield of stem amaranth, where sole cropping of stem amaranth (T₄) and aonla + stem amaranth (T₃) provided the maximum yields. In spite of yield reduction in stem amaranth by 6.8%, 31.2%, and 41.1% under T₃, T₂, and T₁ systems, respectively, compared to the sole cropping; agroforestry systems have proven their superiority in terms of net return and benefit-cost ratio (BCR) over the sole cropping of stem amaranth. Moreover, soil fertility parameters like organic carbon, total nitrogen, available phosphorus, and exchangeable potassium were changed in a positive direction under agroforestry practices. The aforementioned findings indicate that stem amaranth cultivation with aonla based MAFs is a promising approach to enhance system’s productivity, profitability and soil fertility.

Introduction

A huge number of population of about 169.83 million [1] with a cultivable land of 8.09 million hectares [2] are concurrently threatening Bangladesh in serving its inhabitants with ample supply of food and nutrition. The ever-growing population, with a tremendous growth rate of 1.22% [3], is exerting immense pressure on the limited area of cultivable land. According to the UN [4], the population of Bangladesh will be augmented to 192.6 million by the year 2050, and it becomes evident that to feed this ever-growing population, it will be a must in the near future to double the crop production at least. Although Bangladesh has achieved a significant improvement in the agricultural sector, still 24.2 million people are suffering from food insecurity [5], [6]. In Bangladesh, agriculture is the mainstream profession for most people, where sustainable livelihood entirely depends on agriculture, but unfortunately, it has been troubled by both climatic and anthropogenic hazards in recent times [7], [8]. In addition, agricultural land is shrinking at the rate of 69,000 ha year⁻¹ due to a collective approach of industrialization, urbanization, housing, and new developmental projects, etc. [9], [10]. Moreover, almost 50% of total arable land contains less than 1.5% organic matter, where an ideal soil composition necessitates a minimum of 2.5% [11], [12]. Hence, to deal with the difficulties in agricultural production, nutrient sensitive, demand oriented and climate smart sustainable production systems should be looked for.

Under these circumstances, vertical expansion of agricultural land bases with the provision of producing food, fuel wood, poles, and multiple products from the same piece of land is insistent. Undoubtedly, it will be economically beneficial and ecologically sound for Bangladesh as there is neither scope for expanding forest areas nor sole cropping, but rather to combine both production systems [7]. Agroforestry, a collective approach of growing annual crops in association with woody perennials (trees, shrubs) on the same piece of land, could be a suitable candidate to address the issue of sustainable production and in overcoming future challenges. Agroforestry is a form of mixed cropping system where annual herbaceous crops are deliberately grown in combination with woody perennials in some sorts of spatial and temporal arrangement [8], [9]. The system utilizes growth resources, viz. light, H₂O, and nutrients, in a more efficient manner, which is not possible in mono-cropping systems [13]. Likewise, agroforestry improves soil fertility, water quality, biodiversity conservation, and especially sequestrate carbon to reduce global warming [14].

Among the different new and traditional agroforestry practices, fruit-tree based agroforestry is most popular in Bangladesh due to early return, maximum price of produces, dietary and nutritional security, and wider adaptability; and fascinatingly, farmers are currently practicing numerous fruit tree-based MAFs integrating mango, guava, jackfruit, litchi, aonla, etc. on their farming landscape [15], [16]. Among these practices, aonla (Phyllanthus emblica L.) dominated MAFs and is gaining popularity due to its deciduous nature, resulting in very minimum competitive impacts on lower crops, wider adaptability, and low input production system, which ultimately makes it a highly profitable and sustainable system among the farmers [8], [17]. Aonla, popularly known as ‘wonder fruit for health,’ is the richest source of vitamin C, having antioxidant, antimicrobial, and anti-inflammatory properties [18]. It carries ascorbic acid (300 mg–900 mg/ 100 g), amino acids, and different important phytochemicals including polyphenol, tannin linoleic acid, etc. [19].

Another component for MAFs could be Lemon, which is well-accepted for having anti-carcinogenic properties and raw materials for ethnic herbal medicine production [20]. Lemon is also an abundant source of vitamin C, which is adaptable to a wide range of environments; however, it is normally found under trees in homestead situations [21]. Therefore, it could be a potential candidate to grow as a middle storey crop. According to structural arrangement, there should be a lower storey component in multistoried agroforestry system. In Bangladesh, vegetables are normally cultivated as sole crop and are seldom found to grow as an inter-crop with trees in agroforestry system. Stem amaranth (Amaranthus viridis) is a member of the family Amaranthaceae could be a suitable option to grow as a lower storey crop having a good source of vitamins, minerals, dietary fibre, protein, essential amino acids like methionine and lysine [22]–[24]. Considering the potentialities and benefits of multistoried agroforestry systems, it would be of immense value if an economically and ecologically acceptable model is explored, giving consideration to aonla (as medicinal plants), carambola, lemon (as fruit trees), and stem amaranth (as summer vegetable). Therefore, rigorous scientific investigation is required and considering the above mentioned facts, the present study was conducted to evaluate the performance of stem amaranth in aonla based MAFs, and to examine the changes in soil chemical properties under aforesaid systems. The findings of the study might help us to get insights into better management strategies in the future to boost agricultural yields.

Materials and Methods

Description of Experimental Location

The experiment was performed in an established multistoried agroforestry research farm at Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur, Bangladesh, spanning from April 2021 to June 2021. The experimental soil was classified as shallow red-brown terrace soil according to the United States Department of Agriculture (USDA) system [25]. The area has a subtropical climate with three distinct seasons, namely, the monsoon or rainy season (May to October), the winter or dry season (November to February), and the pre-monsoon or hot season (March to April). The initial soil properties under different treatments are presented in Table I.

Table I. Initial Soil Properties

Characteristics	T1	T2	T3	T4
Soil pH	5.61	5.50	5.35	5.24
Organic carbon (%)	1.48	1.43	1.38	1.29
Total nitrogen (%)	0.106	0.09	0.07	0.064
Available phosphorus(mg P kg−1)	11.08	10.11	11.15	8.67
Exchangeable potassium (c-mol (+) kg−1)	0.19	0.18	0.21	0.18

Multistoried Orchard Establishment

In the year 2000, the orchard was established by planting aonla trees in a spacing 8 m × 8 m which formed the upper storey. After that, middle storied components carambola and lemon were planted in between aonla tree in 2008. Carambola plant was placed between two aonla trees, while each lemon plant was planted directly between an aonla tree and a carambola plant. The used varieties were local race, BARI Kamranga-1, and BARI Lebu-1 for aonla, carambola, and lemon, respectively. Carambola and lemon seedlings were purchased from On-Farm Research Division (OFRD) of the Bangladesh Agricultural Research Institute (BARI), Gazipur. BARI Danta-1, a popular variety of stem amaranth was sown in the alley between tree rows as a test crop. Therefore, in the present experiment, aonla tree was served as upper storey, carambola and lemon were served as middle storey, whereas stem amaranth was treated as lower storey crop.

Experimental Design and Treatments

The experiment was laid out in a randomized complete block design (RCBD) with three replications. Stem amaranth was cultivated in different agroforestry systems in association with the Aonla tree, Aonla + lemon tree, Aonla + carambola + lemon tree, and in open field conditions. Therefore, there were four treatments as follows-T₁: Aonla + carambola + lemon + stem amaranth, T₂: Aonla + lemon + stem amaranth, T₃: Aonla + stem amaranth, and T₄: Sole stem amaranth.

Field Preparation, Seed Sowing, Fertilizer Application and Intercultural Operations

The land was well prepared by using a disk rotavator followed by harrowing and laddering to get an optimum tilth for sowing of stem amaranth seeds. After completion of land preparation, seeds were sown in the assigned plots on April 04, 2021, maintaining a spacing of 30 cm × 10 cm. The size of the individual plot was 7 m × 1 m separated by 50 cm between two unit plots. Immediately after sowing, the plots were lightly irrigated to ensure proper germination. Fertilizers were applied as per recommended doses where cowdung, urea, TSP, MoP and gypsum were applied at the rates of 10 t ha⁻¹, 250 kg ha^–1, 150 kg ha^–1, 150 kg ha^–1, and 75 kg ha^–1, respectively [26]. Entire amount of cowdung, TSP, gypsum, half MoP and one-third of urea were applied during final land preparation. Remaining urea and MoP were applied in two installments at 15 and 35 days after sowing (DAS). Intercultural operations, viz., weeding, irrigation, and pest management, were performed as per the requirement to ensure better growth and development of the crops.

Crop Sampling, Data Collection and Harvesting

Randomly selected 10 plants from each replication were sampled for collecting data. Plant height (cm), number of leaves plant⁻¹ and stem diameter (mm) were recorded at 15 day’s interval at 40 DAS and 55 DAS. Leaf fresh weight plant⁻¹ (g), stem fresh weight plant^–1 (g), and total fresh weight plant^–1 (g) were recorded from the sampled plants during harvesting, which was done at 55 DAS on 28 May 2021. Accordingly, stem yield and total fresh yield of stem amaranth were recorded in both Kg plot^–1 and t ha^–1.

Light Measurement

Availability of light was measured above the canopy of stem amaranth in the abovementioned treatments by using a Sunfleck ceptometer (ACCUPAR LP-80) to quantify the percent transmission of Photosynthetically active radiation (PAR) by different agroforestry systems and expressed as µmolm^–2s^–1. PAR reading was recorded at 9:00 am, 12:00 pm, and 3:00 pm in a single day following a one-week interval, which started from 15 DAS and continued up to harvesting.

Soil Sample Collection, Preparation and Analyses

Initial and post-harvest soil samples were taken from 0 cm–15 cm soil depth from each unit plot. Collected soil samples were then air-dried, ground, and sieved through a 2 mm (10 mesh) sieve. Then, the processed soil samples were mixed together according to different treatments to make working samples and stored in clean plastic bags. Soil pH, organic carbon (C), total nitrogen (N), available phosphorus (P), and exchangeable potassium (K) were measured from the stored samples using the following protocols:

• Soil pH: Using a glass electrode pH meter, soil pH was determined, maintaining a soil water suspension ratio of 1:5 [27].
• Organic C: Walkley and Black’s wet oxidation method was used to determine organic C content in soil as described by [28].
• Total N: Total N in soil was quantified by using micro-Kjeldahl method [29].
• Available P: Available P in soil was determined by using the methodology of [30].
• Exchangeable K: Exchangeable K in soil was determined by using atomic absorption spectrophotometer (AAS) following standard laboratory protocol [31].

Economic Analysis

Total cost of production ha⁻¹ was calculated on the basis of initial planting cost, human labor, mechanical power costs, material cost (seed, fertilizers, manures, pesticide, etc.), land use cost, management cost, and interest on utilized capital.

• Gross return: Gross return ha^–1 from aonla, carambola, lemon, and stem amaranth were calculated by multiplying the total amount of production by their respective market prices.
• Net return: Net return was calculated by deducting the total cost of production from the gross return.
• Benefit cost ratio (BCR): BCR is the ratio of gross return to the total cost of production. It was calculated by using the following formula [16].

$$\begin{array}{rcl}BCR& =& Grossreturn\left(Tkh{a}^{-1}\right)÷Totalcostof\\ & & production\left(Tkh{a}^{-1}\right).\end{array}$$

Data Analysis

The recorded data were statistically analyzed by using Statistix 10 computer software and MS Excel following Analysis of Variance (ANOVA) technique to determine the significant variations of the results caused by different treatments. The significance of the differences among the treatment means was evaluated by the least significant difference (LSD) test at a 5% level of probability for the interpretation of results. Bar plot and boxplot were made by using the “ggplot2” package, and correlation heatmap was made by using “corrplot” package in RStudio.

Results and Discussion

Availability of Photosynthetically Active Radiation (PAR) in Different Agroforestry Systems

The mean Photosynthetically active radiation (PAR) throughout the stem amaranth growing season was significantly varied among different treatments (Figs. 1A, 1B). The highest PAR (1409.8 μmol m^–2 s^–1) was recorded in T₄ (Sole stem amaranth) treatment, which was considered as 100% light incidence on stem amaranth, while the lowest PAR (653.5 μmol m^–2 s^–1) was recorded in T₁ (Aonla + carambola + lemon + stem amaranth) treatment which was 46.4% of T₄ treatment. Accordingly, 81.3% and 77.8% PAR compared with T₄ treatment were recorded in T₃ (Aonla + stem amaranth) and T₂ (Aonla + lemon + stem amaranth) treatments, respectively. The incident radiation above the sole stem amaranth was 100%, but gradually, it reduced in other treatments with increasing canopy cover. Due to the presence of multiple components with extensive canopy coverage, agroforestry always resulted in the reduction of PAR received by lower storey crops compared to open field condition. Similar findings were also reported by Ferdous et al. [8], Pingki et al. [10], Riyadh et al. [32], and Pingki et al. [33], where they described light as the most limiting factor for the growth and development of associated under-storey crops.

Fig. 1. Availability of Photosynthetically active radiation (PAR) (A) and %PAR of Open Light (B) in different aonla based multistoried agroforestry systems. Different alphabetical letters showed the significant differences (P < 0.05) among the treatments.

Plant Height

Plant height of stem amaranth was significantly assorted by different agroforestry systems at 40 DAS; however, it was found insignificant at 55 DAS (Figs. 2A, 2B). At 40 DAS, the maximum plant height (41.7 cm) was recorded in T₁ (Aonla + carambola + lemon + stem amaranth) treatment, followed by T₂ (38.9 cm) and T₃ (37.6 cm) treatments. The lowest plant height (34.9 cm) was found in T₄ (Sole stem amaranth) treatment. At 55 DAS, the maximum plant height (77.5 cm) was found in T₁ treatment, which was insignificant to other treatments. Results revealed that plant height of stem amaranth was negatively associated with PAR, which might be attributed to variations of light availability under different systems. It was observed that crops cultivated under low light conditions showed apical dominance as a result of accumulation of high auxin [34]. The findings of the present study were endorsed by several researchers [7], [32], [33], [35], [36] in spices, aroid, cauliflower, and medicinal plants under multistoried agroforestry practices.

Fig. 2. Plant height of stem amaranth at different growth stages, (A) 40 DAS and (B) 55 DAS, under different aonla based multistoried agroforestry systems. Different alphabetical letters showed the significant differences (P < 0.05) among the treatments. [DAS–Day’s after sowing].

Number of Leaves Plant–1

Studied agroforestry systems showed significant impact on number of leaves plant^–1 of stem amaranth at both 40 DAS and 55 DAS (Figs. 3A, 3B). At 40 DAS, the maximum leaves plant^–1 (14) was found in T₁ (Aonla + carambola + lemon + stem amaranth) treatment, followed by T₂ (13) and T₃ (12) treatments, while T₄ (Sole stem amaranth) treatment gave the lowest number of leaves plant^–1 (10). Similar trend was observed at 55 DAS, where T₁ treatment exhibited the highest leaves plant^–1 (18) followed by T₂ (16) and T₃ (16) treatments. The lowest value (12) was recorded in T₄. A significant negative correlation was found between number of leaves plant^–1 and PAR. Compared to sole cropping, agroforestry systems resulted in higher leaves plant^–1, which might be due to the initiation and stimulation of leaf growth by lower light levels. Similar findings were reported by Bari and Rahim [35], Khatun et al. [37] in Aloe vera [10], [38] in cabbage, and in carrot [39].

Fig. 3. Number of leaves plant^–1 of stem amaranth at different growth stages, (A) 40 DAS and (B) 55 DAS, under different aonla based multistoried agroforestry systems. Different alphabetical letters showed the significant differences (P < 0.05) among the treatments. [DAS–Day’s after sowing].

Stem Diameter

The effect of agroforestry systems on stem diameter of stem amaranth was found significant at both 40 DAS and 55 DAS (Figs. 4A, 4B). At 40 DAS, the highest stem diameter (10 mm) was found in T₄ treatment which was followed by T₃ (8.3 mm) treatment, while the lowest diameter (5.6 mm) was recorded in T₁ treatment. Similar trend was also found at 55 DAS, where the highest diameter (15.2 mm) was recorded in T₄ treatment followed by T₃ (13.2 mm) treatment. The lowest stem diameter (8.4 mm) was recorded in T₁. The results demonstrated that stem amaranth attained its highest diameter under sole cropping; nevertheless, it gradually declined under agroforestry systems. Interaction between stem amaranth and other tree components for light, water, and nutrients might have reduced the photosynthetic activity and ultimately affected stem diameter under agroforestry practices. Similar results were also being reported [39]–[42] in carrot, tomato, ginger, turmeric, and papaya.

Fig. 4. Stem diameter of stem amaranth at different growth stages, (A) 40 DAS and (B) 55 DAS, under different aonla based multistoried agroforestry systems. Different alphabetical letters showed the significant differences (P < 0.05) among the treatments. [DAS–Day’s after sowing].

Leaf Fresh Weight Plant–1, Stem Fresh Weight Plant–1, and Total Fresh Weight Plant–1

The studied agroforestry systems showed a significant impact on leaf fresh weight, stem fresh weight, and total fresh weight plant^–1 of stem amaranth (Figs. 5A–5C). The highest fresh weight of leaves plant^–1 (42 g) was recorded in T₃ (Aonla + stem amaranth) treatment, which was statistically similar with T₄ (Sole stem amaranth), while the highest fresh weight of stem (116 g) and total fresh weight (157.7 g) were recorded in T₄ (Sole stem amaranth) treatment which was statistically insignificant with the values observed in T₃ (Aonla + stem amaranth) treatment. The lowest fresh weight of leaves (28 g), stem (65 g), and total fresh weight (93 g) were recorded in T₁ (Aonla + carambola + lemon + stem amaranth) treatment. Results showed a remarkable variation in individual plant growth. Growth of individual plants was suppressed under agroforestry systems, which might be due to competition for growth resources (light, water, and nutrients) between stem amaranth and perennial trees [32], [43]. It is obvious that, root system of perennial tree is well developed compared to annual crops, and tree showed dominant competition with associated crops in the root zone areas [41], [44]. The findings of the present study endorsed [35], [40], [42], [45], and [46] in other crops like aloe vera, asparagus, tomato, papaya, and eggplant associated agroforestry practices.

Fig. 5. Fresh weight of leaves (A), stem (B) and total fresh weight (C) plant^–1 of stem amaranth under different aonla based multistoried agroforestry systems. Different alphabetical letters showed the significant differences (P < 0.05) among the treatments. [TRE–Treatment; LFW_g–Leaf fresh weight (g plant^–1); SFW_g–stem fresh weight (g plant^–1); TFW_g–total fresh weight (g plant^–1)].

Stem Yield and Total Fresh Yield of Stem Amaranth

Stem yield and total fresh yield of stem amaranth were significantly varied under studied agroforestry systems (Figs. 6A–6D). Among the systems, T₄ (Sole stem amaranth) provided the maximum stem yield (27.1 kg plot^–1) and total fresh yield (36.8 kg plot^–1) of stem amaranth, which were statistically similar to the yields observed in Aonla + stem amaranth (T₃) system. In contrast, the lowest yield of stem (15.2 kg plot^–1) and total fresh yield (21.7 kg plot^–1) were found in Aonla + carambola + lemon + stem amaranth (T₁) system. Considering the yield in t ha^–1, the highest stem yield (38.7 t ha^–1) and total fresh yield (52.6 t ha^–1) were also recorded in T₄ (Sole stem amaranth) treatment, which were statistically similar with the stem yield (35 t ha^–1) and total fresh yield (49 t ha^–1) respectively, observed in Aonla + stem amaranth (T₃) system. Similarly, the lowest yield of stem (21.7 t ha^–1) and total fresh yield (31 t ha^–1) were documented in Aonla + carambola + lemon + stem amaranth (T₁) system. Our findings revealed remarkable improvement in stem amaranth yield under sole cropping and aonla + stem amaranth system; however, significant yield reduction occurred in other agroforestry treatments compared to sole cropping.

Fig. 6. Stem yield and total fresh yield of stem amaranth under different aonla based multistoried agroforestry systems. Different alphabetical letters showed the significant differences (P < 0.05) among the treatments. [TRE–(A)Treatment; SY_kg–Stem yield (kg plot^–1); (B) TFY_kg–total fresh yield (kg plot^–1); (C) SY_T–stem yield (t ha^–1); (D) TFY_T–total fresh yield (t ha^–1)].

The yield reduction under agroforestry systems occurred might be due to competition for light, water, and nutrients between trees and crops [47], [48]. In the present investigation, water and nutrients were not limiting factors because these were applied in sufficient amounts; nonetheless, root distribution and belowground interaction were not addressed in this experiment, which might have affected the yield of stem amaranth. Furthermore, Photosynthetically active radiation is considered as the most limiting factor in agroforestry [49], [50] and reasonably, we found a significant positive correlation between PAR and yield and yield contributing attributes of stem amaranth (Fig. 7). In the present study, stem amaranth received 46%–81% PAR in different agroforestry treatments compared to sole cropping; which might have impeded the photosynthetic activity, reduced the accumulation of photosynthates, and ultimately resulted in yield reduction of stem amaranth under agroforestry practices [51]. Our findings are corroborated by [8], [32], [33], [46], [52] on radish, aroid, cauliflower, eggplant, and tomato under different agroforestry practices.

Fig. 7. Correlation heatmap between the Photosynthetically active radiation (PAR) and studied yield and yield contributing attributes of stem amaranth grown under aonla based multistoried agroforestry systems. Blue and red color indicates positive and negative correlations, respectively, while increasing color intensity reflects a higher association. The level of significance is indicated by ^*, ^**, and ^*** at p < 0.05, p < 0.01, and p < 0.001. [PH_cm–Plant height (cm); NoL–number of leaves plant⁻¹; SD_mm–stem diameter (mm); LFW_g–leaf fresh weight (g plant^–1); SFW_g–stem fresh weight (g plant^–1); TFW_g–total fresh weight (g plant^–1); SY_kg–stem yield (kg plot^–1); TFY_kg–total fresh yield (kg plot^–1); SY_T–stem yield (t ha^–1); TFY_T–total fresh yield (t ha^–1)].

Correlation between PAR and Different Yield and Yield Contributing Attributes of Stem Amaranth

The degree of association among the variables was determined by using the correlation heatmap. Correlation heatmap reflected significant correlation between PAR and other yield and yield contributing attributes of stem amaranth using a color coded matrix and their level of significance (Fig. 7). Most of the variables under studied maintained a significant positive correlation with PAR except plant height and number of leaves plant^–1. It was observed that, plant height and number of leaves plant^–1 of stem amaranth showed a significant negative correlation with Photosynthetically active radiation. The findings of the present study suggesting that any change in PAR will correspondingly change the yield and yield contributing attributes of stem amaranth.

Economic Performances

To estimate the economic performance of stem amaranth under different aonla based MAFs and sole cropping, net return and BCR had been calculated and presented (Table II). Among the different production systems, Aonla + stem amaranth (T₃) system provided the highest net return (382,636 Tk ha^–1) and BCR (3.37) compared to others. Fascinatingly, all of the agroforestry systems provided higher net return and BCR compared to the calculated net return (245,357 Tk ha^–1) and BCR (2.64) under sole cropping of stem amaranth. Our study revealed that agroforestry practices provided higher economic benefits compared to sole cropping, which might be due to the combined yield from multiple components and effective utilization of resources. The findings indicating that, it is possible to increase farm income to a greater extent under agroforestry practices over the traditional single cropping system. Similar findings were reported under agroforestry practices by several authors [7], [10], [16], [42], [44], [46].

Table II. Economic Performance of Stem Amaranth Associated Different Agroforestry Systems

Systems	Gross return (Tk ha−1)	The total cost of production (Tk ha−1)	Net return (Tk ha−1)	BCR
T1 = Aonla + carambola + lemon + stem amaranth	491,698	174,456	317,242	2.82
T2 = Aonla + lemon + stem amaranth	464,000	168,357	295,643	2.76
T3 = Aonla + stem amaranth	543,900	161,264	382,636	3.37
T4 = Sole stem amaranth	394,500	149,143	245,357	2.64

Changes in Soil Chemical Properties

Both the initial and final chemical properties of top soil (0–15 cm) from different agroforestry systems and open field condition were analyzed and compared. The changes in soil pH, organic C, total N, available P and exchangeable K have been presented in Fig. 8. Initially, the highest soil pH (5.61) was recorded in Aonla + carambola + lemon + stem amaranth (T₁) system followed by Aonla + lemon + stem amaranth (T₂) and Aonla + stem amaranth (T₃) system; while the lowest pH (5.22) was found in T₄ (Sole stem amaranth) system (Table I). In post-harvest soil, the pH was slightly increased by 0.71% (from 5.61 to 5.65) in T₁ treatment but decreased by 1.27%, 0.56%, and 0.38% in T₂, T₃, and T₄ treatments, respectively compared to their respective initial soil pH (Fig. 8A). Likewise, the highest initial organic C (1.48), total N (0.106%) and available P (11.08 mg P kg⁻¹) was found in T₁ treatment followed by T₂ and T₃ treatments; however, the lowest organic C (1.26), total N (0.064%) and available P (8.67 mg P kg⁻¹) were recorded in T₄ treatment (Table I).

Fig. 8. Soil pH (A), organic C (B), total N (C), available P (D) and exchangeable K (E) in soil both before and after harvesting of stem amaranth under different aonla based multistoried agroforestry systems.

After harvesting of stem amaranth, total N and available P were increased in post-harvest soil. The rates of increment for total N were 24.5%, 6.7%, 5.7%, and 4.7%, while the available P was increased by 43.4%, 33.7%, 20.4%, and 2.3% in T₁, T₂, T₃, and T₄ treatments, respectively (Figs. 8C, 8D). Similarly, organic C was augmented by 8.8%, 3.5%, and 4.3% in T₁, T₂, and T₃ treatments, respectively; nonetheless, there had a reduction of 2.3% organic C in T₄ (Sole stem amaranth) treatment compared to their respective initial values (Fig. 8B). Exchangeable K responded irregularly under different agroforestry systems and open field condition; however, the highest initial exchangeable K (0.21 c-mol (+) kg⁻¹) was found in Aonla + stem amaranth (T₃) system (Table I). Interestingly, exchangeable K showed a zigzag fashion (both increasing and decreasing) in post-harvest soil, where it increased by 10.5% and 9.5% in T₁ and T₃ treatments but decreased by 11.1% and 16.7% in T₂ and T₄ treatments, respectively (Fig. 8E). Remarkable changes in soil chemical properties were observed after harvesting of stem amaranth under agroforestry and sole cropping. In post-harvest soil, most of the chemical properties were enhanced compared to their initial level, and fascinatingly, the dominant effect in enhancing soil chemical properties was exerted by agroforestry practices compared to sole cropping.

Soil pH was increased in Aonla + carambola + lemon + stem amaranth (T₁) system only but decreased in all other treatments. Leaf litter decomposition from multistoried agroforestry might have increased pH in T₁ system, while application of nitrogenous fertilizer in greater amount might be responsible for reducing the soil pH in other treatments. Organic C, total N, and available P were increased in greater amounts under agroforestry practices, which might be due to the accumulation of greater amounts of organic materials in soil from triple-tiered trees, leaf litter decomposition, and mineralization of organic residues. The findings are also endorsed by [14], [53]–[58] under different tree based agroforestry practices. Exchangeable K responded irregularly, which might be due to the uneven recycling of K, but still, this is unknown and needs to be assessed repeatedly.

Conclusion

The findings revealed that both the sole cropping and aonla + stem amaranth system provided the highest yields of stem amaranth. In the present investigation, significant positive correlations between Photosynthetically active radiation and different yield and yield contributing attributes of stem amaranth were found except for plant height and number of leaves plant^–1. Considering the net return and BCR, it was evident that all of the stem amaranth associated aonla based multistoried agroforestry systems were profitable compared to the sole cropping of stem amaranth. Among the studied systems, aonla + stem amaranth was superior in terms of economic performances and followed the order as aonla + stem amaranth > aonla + carambola + lemon + stem amaranth > Aonla + lemon + stem amaranth > sole stem amaranth. Our findings also revealed that soil chemical properties like organic C, total N, available P, and exchangeable K were improved under agroforestry practices which might help in maintaining the sustainability of production. Based on the above findings, it may be stated that stem amaranth cultivation under aonla based multistoried agroforestry systems might be productive and profitable. However, the wider dissemination of such technology in farmer’s field requires repeated and comprehensive analysis.