The study was carried out during the winter seasons of 2019–20 and 2020–21 at the Horticulture Research Centre (HRC), Bangladesh Agricultural Research Institute (BARI), Joydebpur, Gazipur 1701, Bangladesh. The study site was located in agro-ecological zone 28 (Madhupur tract) (23°98´N latitude and 90°41´E longitude and is 8.4 m above sea level). The soil type of the experimental region was a grey terrace that was chemically acidic and belonged to the Chhiata soil series (Texonomy: Aeric Haplaquepts) [35]. Texturally, the soil was clay loam (30.38% sand, 35.20% silt, and 34.42% clay) with a pH of 6.2%, 1.29% organic matter, 0.073% total N, 12.0 ppm P, 0.14 meq./100 g soil K, 15.0 ppm S, 0.78 ppm Zn, and 0.14 ppm B. The particle density, bulk density, and porosity of the soil were 2.55 g/cc, 1.38 g/cc, and 46.0%, respectively. The field capacity (FC) was 26.8% of the gravimetric water content, and the cation exchange capacity (CEC) was 7.4 Cmol kg⁻¹ soil. The physicochemical properties of the presowing and postharvest soils were analyzed by standard methods [36].

The climate conditions of the study site are characterized as subtropical and humid. The monthly average temperatures during the study period ranged from 13.0°C to 36.1°C, and the monthly rainfall ranged from 0 to 218 mm. The maximum and minimum monthly average temperature, humidity, and rainfall during the experimental periods (2019–20 and 2020–21) were recorded and are presented in Figs. 1a and 1b.

The experimental soils were opened by a tractor-driven plough with 4 passes, and a tractor-driven rotavator was also used for uniform tilling and levelling. The soil was manually cleaned to remove weeds and stubbles. The treatments were T₁ = Control (no Zn, B, Mo or Rhizobium inoculant), T₂ = Rhizobium inoculation (50 g kg⁻¹ seed), T₃ = Zn₃Mo₁ + Rhizobium inoculant as applied in T₂, T₄ = B₂Mo₁ + Rhizobium inoculant as applied in T₂, T₅ = Zn₃B₂ + Rhizobium inoculant as applied in T₂, T₆ = Zn₃B₂Mo₁ + Rhizobium inoculant as applied in T₂ and T₇ = Zn₃B₂Mo₁. All treatments were arranged in a randomized complete block design and repeated three times.

The other common fertilizers were applied in all plots in elemental form (i.e., N, P, K and S at 40, 24, 50 and 10 kg ha⁻¹, respectively) along with 5 t ha⁻¹ decomposed cow dung. The sources of N, P, K, S, Zn, B and Mo were urea, TSP, MoP, gypsum, zinc sulphate (monohydrate), boric acid, and ammonium molybdate fertilizers, respectively. The peat-based Rhizobium inoculum (rhizobium strain BARI RPs 504) was used at a rate of 50 g kg⁻¹ seed, which was prepared and supplied by the Soil Science Division of BARI. The experimental plots were divided into three equal blocks consisting of seven-unit plots in each block. The size of each unit plot was 3 m × 2 m. The unit plots were separated by 50 cm gaps, and the replicated blocks were separated from each other by a distance of 1 m.

The Rhizobium inoculum (strain) was isolated from clean and freshly collected healthy root nodules of Garden pea. The selected root nodules were cleaned with distilled water and sterilized several times with sodium hypochlorite (NaOCl) solution. The sterilized nodules were transferred to Petri dishes and then crushed with the help of a sterilized glass rod to obtain a milky suspension, which was subsequently streaked on a yeast extract mannitol agar (YEMA) plate. The isolate was subcultured on a series of YEMA plates for pure cultures of the Rhizobium strain. The pure culture was maintained on YEMA slants and incubated at 28 ± 2°C for 48 h. The slants were preserved in a refrigerator at 4°C after sufficient growth [37] for further investigation.

The identified isolate (Rhizobium) was confirmed by several tests, including Gram staining and growth on YEMA with congo red. Nodulation ability was also tested on homologous hosts by plant infection tests according to the technique of Somasegaran et al. [38]. A sterilized inoculation loop was used for the entire test. The isolate was inoculated into broth media and kept for 3–5 days in a rotary shaker for good growth. The growth culture (20 ml suspension) was inoculated into 100 g of sterilized peat soil made of poly pack, which was subsequently incubated for 5–7 days at 28 ± 2°C before field application.

Seeds of garden pea (BARI Motorshuti-3) were obtained from the Olericulture Division of HRC, BARI, Gazipur 1701, Bangladesh. Cowdung at 5 t ha⁻¹ and other common fertilizers, including half of the urea and half of the MoP, were applied basally during the final plot preparation. Full amounts of zinc sulphate, boric acid and ammonium molybdate were applied plotwise as per prescribed treatments. The applied fertilizers were mixed thoroughly into the soil. The peat soil carrier-based Rhizobium inoculant was coated gently with healthy dry seeds at a rate of 50 g kg⁻¹ seed, and the seeds were placed under shade for a few minutes for air drying before sowing. The plots with uninoculated seeds were sown first to avoid contamination, and then, the plots with inoculated seeds were sown at 120 kg ha⁻¹ with a spacing of 20 cm × 10 cm on 09 December 2019 and 10 December 2020. The remaining half of the urea and MoP was applied between the rows as banding at 25 days after sowing (DAS), and it was mixed properly with the soil.

As the soil was dry, postsowing irrigation was performed immediately after seed sowing to facilitate proper germination. Each plot was irrigated with a hosepipe starting at 7 DAS at regular intervals of 7–10 days based on the soil moisture. The crop was manually weeded twice, at 25 and 40 DAS. The fungicides Provax 200 wp and distance M-45 were sprayed with 2 g/L water at 35 and 45 DAS to control root rot and brown spot disease, respectively. The infestation of insects such as pod borers and aphids was minimized by spraying 0.5 ml/L water with Imitaf 20 SL at 35 and 45 DAS. The test crop was harvested plotwise on two dates at two stages. The first half was harvested at the green pod stage, and the second half was harvested at the dry seed stage. Green pods were harvested at the tender stage on 04 February 2020 and 05 February 2021 from four rows in each plot. The remaining crop in the plot was allowed to grow until maturity, and mature pods were harvested for dry seed yield. The perfect maturity of the garden peas indicated that when the plants and pods turned brown, the seeds became hard.

Active modulation data were calculated from five randomly selected plants in each plot at 50 DAS. Five plants were uprooted smoothly from each plot with the help of a hand hoe and were carefully washed and dried under normal conditions. The lengths of the roots of five plants were measured, and the number of root nodules on each plant was counted and averaged. Ten nodules were randomly selected from five plants of each treatment to measure the individual nodule length, diameter, and individual nodule weight, and the values were averaged. The detached pods of four rows in each plot were weighed by an electric balance to determine the yield of the green pods, which was converted to kg ha⁻¹. The green seeds were separated from the composite pods of four rows to measure the weight of the 100-green seeds. Fresh green pod samples (250 g) from each treatment were collected and preserved in a refrigerator at −30°C in the postharvest laboratory of the HRC of BARI for quality analysis. Total soluble solids (TSSs), titratable acidity, and vitamin C content were recorded following standard methods. The total soluble solid content was assessed by taking a drop of green seed juice on a hand refractometer glass lens (Atago Ltd., PAL-1, Tokyo, Japan), and the results are expressed in ⁰Brix as described by Anonymous [39]. The titratable acidity was determined according to the accepted method of Ranganna [40]. The level of vitamin C (ascorbic acid) was estimated from a standard method [39]. After the maturity of the remaining crop in each treatment plot, the growth and yield contributing characteristics, viz., plant height, number of branches plant⁻¹, number of pods plant⁻¹, pod length, number of seeds pod⁻¹, and 100-seed weight, were recorded for five randomly selected plants. Data on the dry seed and straw yields were recorded from the remaining mature test crops and converted to kg ha⁻¹.

Treatment basis straw and seed samples were oven-dried at 70°C for 48 h and ground with a Cyclotec^TM 1093 sample mill (Made in Sweden). The ground straw and seed samples were digested by a diacid mixture (HNO₃-HClO₄) (5:1) according to the method described by Piper (1966) [41]. The digested mixtures (straw and seed) were utilized to determine the N content following the Micro-Kjeldahl method [42], the P content via the spectrophotometer method, the K content via the atomic absorption spectrophotometer method and the S content via the turbidity method via BaCl₂ via the spectrophotometer. The Zn content of the digest was directly measured by atomic absorption spectroscopy (VARIAN SpectrAA 55B, Australia). The B content in the digest was determined by a spectrophotometer through the azomethine-H method [36]. The Mo concentration data are not shown due to a lack of laboratory facilities.

The seed protein content of garden peas was measured after multiplying the N content by the constant food factor of 6.25 [43].

Dry crop yields and nutrient contents in seeds and dry plants (straw) were used to determine nutrient (N, P, K, S, Zn and B) uptake according to the following formula [44]:(1) Nutrient uptake (kg/ha)=Nutrient content (%)×Dry matter yield (kg/ha.)100

Postharvest soil samples were collected by standard procedures at a soil depth of 0–15 cm. Total Rhizobium, free-living bacteria, phosphate-solubilizing bacteria (PSB), actinomycetes and fungal colonies were grown in different prepared media. After serial dilution, one drop of solution was poured into a Petri dish with different types of media. The Petri plates were incubated for three days to count total bacteria, Rhizobium, free-living bacteria, PSB, actinomycetes and fungal colonies. Bacterial media were prepared as nutrient agar media containing 28 g/L distilled water up to 1.00 L. The ingredients of the media were mixed in a normal glass flask with the required amount of distilled water. The initial pH of the medium was adjusted to 7.0. The medium was dissolved by boiling and autoclaved at 1210°C for 15 min. YEMA (yeast mannitol agar) medium contained the following ingredients: 0.5 g of K₂HPO₄, 0.2 g of MgSO₄·7H₂O, 0.1 g of NaCl, 0.2 g of CaCl₂·6H₂O, 0.01 g of FeCl₃·6H₂O, 10 g of mannitol, 0.5 g of yeast extract, 15.00 g of agar powder, and 1 L of distilled water. The initial pH of the medium was adjusted to 7.0 by adding 0.1 N HCl solution. The agar used in this medium was dissolved by boiling, and the medium was autoclaved at 1210°C for 15 min. PSB media plates were prepared with Pikovaskya’s medium. Composition of 1 l of Pikovskaya media: 10 g of glucose, 5 g of Ca₃(PO₄)₂, 0.5 g of (NH₄)₂SO₄, 0.2 g of NaCl, 0.1 g of MgSO₄·7H₂O, 0.2 g of KCl, 0.5 g of yeast extract, and 0.5 g of MnSO₄. H₂O (0.002 g), FeSO₄.7H₂O (0.002 g) and agar (15 g) were used [45].

Actinomycete agar media: Plates were prepared with Actinomycete agar media. The composition of the Actinomycetes agar medium in 1 l was 21.7 g of Actinomycetes agar with 5 ml of glycerol. The initial pH of the medium was adjusted to 7.0 by adding 0.1 N HCl solution.

PDA (potato dextrose agar) media: The plates were prepared with PDA media. The amount of PDA medium in 1 litre was 39 g. The initial pH of the medium was adjusted to 7.0 by adding 0.1 N HCl solution. The agar used in this medium was dissolved by boiling, and the medium was autoclaved at 1210°C for 15 min. After autoclaving, 10 ml of lactic acid was mixed per litre of media. Nitrogen-free bacteria (NFB) media: Plates were prepared with nitrogen-free bacterial media. The nitrogen-free bacterial media included 5 g of malic acid, 0.5 g of K₂HPO₄, 0.1 g of NaCl, 0.2 g of MgSO₄.7H₂O, 0.02 g of CaCl₂, 5% BTB in 2 ml of 0.02 N KOH, 8 ml of 1.64% FE-EDTA and 20 g of agar. The initial pH of the media was adjusted to 7.0 by adding 1 N KOH solution. The agar used in this medium was dissolved by boiling, and the medium was autoclaved at 12°C for 15 min.

The green pod and dry seed yield of garden peas were used to compute the gross return per hectare of land. The gross return was calculated after multiplying the yield by the farmgate unit price of the green pod and dry seed.(2) Gross return (USD ha−1) = Yield (kg ha−1) ×Unit price of green pod or dry seed

The gross margin was calculated by subtracting the total variable cost from the gross return according to the following formula:(3) Gross margin (USD ha−1) = Gross return (USD ha−1)−total variable cost (USD ha−1) 

Treatment total variable cost was measured by adding the cost incurred for labourers, ploughing and inputs of each treatment. The shadow prices (land rent, straw cost, etc.) were not considered.

The benefit-cost ratio (BCR) was calculated from the gross return divided by the total variable cost of cultivation. The BCR formula is as follows:(4) Benefit−costatio=Gross return (USD per ha.)Total variable cost (USD per ha.)

Data on growth, yield and yield attributes, quality characteristics, nutrient content and nutrient uptake were subjected to two-way ANOVA by using SAS software (version 9.4). The microbial population data in postharvest soil were analysed by analysis of variance (ANOVA) using SAS software (version 9.4). The mean separation test for all the data were was performed by using Tukey’s HSD test at the 0.05 (p ≤ 0.05) level of probability.

The year 2020–21 was found to be more favourable for the growth and development of garden peas, resulting in significantly greater green pod and seed yields from 2019–20 (Table 1). The use of a single Rhizobium inoculant or combined with Zn, B and Mo fertilizers had a positive influence on the green pod, seed, and straw yields of garden peas (Table 1). An increase in the green pod yield (8691 kg ha⁻¹) was recorded in the T₆ treatment group, which was significantly greater than that in the other treatment groups. Similarly, the T₆ treatment resulted in greater seed yield (1869 kg ha⁻¹) than did the T₇, T₅ and T₃ treatments. Both the green pod and seed yields were lowest in the control (T₁) treatment (Table 1). The highest straw yield (1770 kg ha⁻¹) was achieved in the T₆ treatment, followed by the T₇, T₅ and T₃ treatments (Table 1). However, compared with the control treatment, the combined application of the rhizobium inoculant and micronutrients (Zn, B and Mo) resulted in a 44.8% greater percentage of green pods and a 29.7% greater seed yield (Table 1).

The year of cultivation affected the plant height, number of branches per plant and number of pods per garden pea plant (Table 2). The experimental results indicated that the tallest plant (40.4 cm), the greatest number of branches per plant (5.54) and the greatest number of pods per plant (8.05) were recorded in 2020–21, while the lowest values were recorded in 2019–20. The application of Zn, B and Mo with Rhizobium inoculation had a significant influence on the growth and yield of garden peas (Table 2). The tallest plant (42.1 cm) was found in the T₆ treatment, which was comparable to the T₇, T₃ and T₄ treatments, while the greatest number of branches per plant (5.69) was also found in the T₆ treatment, followed by the T₇, T₅, T₄ and T₃ treatments. The lowest values of both parameters were detected in the control treatment (T₁) (Table 2). The increase in pod length (6.39 cm) in the T₆ treatment was comparable to that in the T₅ and T₇ treatments, although the greatest number of pods per plant (8.80) was also recorded after the application of 3 kg Zn, 2 kg B and 1 kg Mo ha⁻¹ with Rhizobium inoculation (50 g kg⁻¹ seed) (T₆), which was significantly equal to that in the T₇ treatment_, and the lowest values of both parameters were observed in the control T₁ treatment. Significantly, the maximum number of seeds per pod (6.11) was obtained in T_6, while the minimum value (4.85) was obtained in the control treatment. The 100 g green seed and dry seed weights reached a maximum of 55.6 and 27.1 g, respectively, in the T₆ treatment, both of which were significantly different from those in the other treatments. However, the performance of T₆ was statistically identical to that of T₇ for 100-green seed weights and that of T₇, T₅, and T₃ for dry seed weights. Both the green pod and dry seed weights were minimal in the control treatment (Table 2).

The year of cultivation affected only the length of the roots of the garden pea plants. The greatest root length (12.4 cm) was observed in 2020–21, and the lowest (11.7 cm) was in 2019–20 (Table 3). The root length, active nodulation, nodule length and diameter and nodule weight of garden peas significantly responded to the application of Zn, B and Mo combined with Rhizobium inoculation (Table 3). The longest root (12.7 cm) was noted in T6, which was comparable to most of the treatments, while the lowest value was observed in the control plot. In the present study, 50 days after sowing, more active nodules per plant (25.3) were recorded in the T₆ treatment than in the other treatments_, which was statistically similar to most of the treatments except for the control. However, the nodule length was greater (3.74 mm) in the same T₆ treatment group than in the T₇, T₅ and T₃ treatment groups. The greatest nodule diameter (2.67 mm) was found in the T₆ treatment group. In terms of nodule weight, the heaviest nodule (0.0076 g) was noted in the T₆ treatment group, which was comparable to that in the T₇ and T₅ treatment groups, but the control treatment group had the lightest (0.004 g) nodule (Table 3).

The vitamin C and protein contents were significantly different between the two years. The highest content of vitamin C (42.7 mg 100 g⁻¹) and maximum protein content (21.7%) of garden peas were attained in 2020−21, and both were lower in 2019−20 (data not shown). The quality traits, viz., TSS, titratable acidity, vitamin C content and protein content, of garden peas, responded positively to the application of Zn, B and Mo combined with Rhizobium inoculation (Fig. 2).

The highest total soluble solid content (⁰Brix 14.3) was detected in T_{6, which was} comparable to most of the treatments, and the minimum value (⁰Brix 12.3) was detected in the control treatment (Fig. 2). The value of titratable acidity was highest (1.31%) in the treatments with 3 kg Zn and 2 kg B ha⁻¹ Rhizobium inoculation (T₅), which was statistically similar to that in the T₆, T₄ and T₂ treatments (Fig. 2). The highest amount of vitamin C (43.5 mg 100 g⁻¹) was found in the T₆ treatment, which was statistically similar to most of the treatments, and the lowest amount (39.7 mg 100 g⁻¹) was found in the T₁ treatment (Fig. 2). The same T₆ treatment resulted in greater protein content (22.2%), which was statistically identical to that of all other treatments except the control (Fig. 2).

The year of cultivation affected the nitrogen (N), potassium (K), sulphur (S), zinc (Zn) and boron (B) contents in the seeds of garden peas but not the phosphorus (P) content (Table 4). In the second year (2020-21), relatively high N (34.7 g kg⁻¹), K (11.2 g kg⁻¹), S (3.90 g kg⁻¹), Zn (0.038 g kg⁻¹) and B (0.041 g kg⁻¹) levels were detected in the seeds, while all of these values decreased in the first year (2019–20) (Table 4). The application of Zn, B and Mo combined with Rhizobium inoculation affected the nitrogen, phosphorus, potassium, sulphur, zinc and boron contents in the seeds of the garden peas (Table 4). A significant increase in the nitrogen content (35.5 g kg⁻¹) was detected in T₆, similar to most of the treatments, although the minimum nitrogen content was detected in the T₁ (control) treatment. The maximum phosphorus content (8.86 g kg⁻¹) was comparable between the T6 treatment and the T₅ and T₇ treatments. The highest potassium content (13.3 g kg⁻¹) was in the T₆ treatment, while the lowest potassium content (6.91 g kg⁻¹) was in the control treatment. The sulphur content measured at the highest level (6.63 g kg⁻¹) in the same T6 treatment was statistically similar to that in the T₇ and T₅ treatments, whereas it was lower (2.61 g kg⁻¹) in the T₁ treatment (control). The maximum zinc content in the seeds (0.042 g kg⁻¹) was noted in T_6, which was statistically similar to that in the T₇ and T₅ treatments. The same T₆ treatment exhibited an increase in the content of boron (0.045 g kg⁻¹), which was statistically similar to that in the T₇ treatment. Both the Zn and B contents were minimal in the T₁ (control) treatment (Table 4).

The year of cultivation affected the nitrogen, potassium, sulphur and boron contents but not the phosphorus and zinc contents in the straw of garden peas (Table 5). Increased contents of nitrogen (14.3 g kg⁻¹), potassium (15.3 g kg⁻¹) and sulphur (3.04 g kg⁻¹) were detected in 2020–21, while the contents of all nutrients decreased in 2019–20 (Table 5).

Table 5 shows that the increased nitrogen content in straw (14.8 g kg⁻¹) in T6 was comparable to that in most of the treatments, although a lower nitrogen content (12.7 g kg⁻¹) was detected in the control treatment. The T₆ treatment resulted in a higher phosphorus content (5.42 g kg⁻¹) that was statistically identical to that of the T₇, T₅ and T₄ treatments, while the control treatment was responsible for the minimum phosphorus content (3.81 g kg⁻¹). The maximum potassium content (16.6 g kg⁻¹) was recorded in the T6 treatment, which was comparable to that in the T₇, T₅ and T₄ treatments, although the minimum potassium content (11.6 g kg⁻¹) was recorded in the T₁ treatment. An increase in the sulphur content (3.52 g kg⁻¹) was also detected in the T6 treatment group, followed by the T₇, T₅ and T₄ treatments, while a decrease in the sulphur content (1.81 g kg⁻¹) was detected in the control group (T₁). Significantly, the maximum zinc (0.0427 g kg⁻¹) and boron (0.0387 g kg⁻¹) contents were detected in T_6, while both were minimal in the control treatment (Table 5).

Figs. 3a and 3b show the effect of micronutrients (Zn, B & Mo) combined with rhizobium inoculation on the total uptake of different nutrient elements by garden peas. The cultivation year affected the total uptake of N, P, K, S, Zn and B by garden pea (seed + straw). The second year (2020–21) favored the maximum total uptake of N (86.6.0 kg ha⁻¹), P (22.2 kg ha⁻¹), K (45.9 kg ha⁻¹), S (12.2 kg ha⁻¹), Zn (0.132 kg ha⁻¹) and B (0.131 kg ha⁻¹), although the minimum uptake of all nutrients occurred from 2019–20 (data not shown).

The highest total uptake of nitrogen (92.5 kg ha⁻¹) was detected in the treatments involving the application of 3 kg Zn, 2 kg B and 1 kg Mo with Rhizobium inoculation (50 g kg⁻¹ seed) (T₆), which was statistically similar to the T₇ treatment, while the lowest total uptake value (62.7 kg ha⁻¹) was detected in the control treatment. Compared with the T7 treatment, the T₆ treatment was more effective at attaining the greatest phosphorus uptake (26.2 kg ha⁻¹) in garden peas, although the control treatment (T₁) had the lowest P uptake (Fig. 3a). The highest total potassium uptake (54.3 kg ha⁻¹) was obtained from the T₆ treatment, while the lowest was from the T₁ treatment (control). The maximum sulphur uptake by garden pea (14.9 kg ha⁻¹) in the T₆ treatment was comparable to that in the T₇ treatment, while the minimum was in the T₁ (control) treatment (Fig. 3a). The greatest zinc (0.154 kg ha⁻¹) and boron uptake (0.153 kg ha⁻¹) were recorded in T₆, which were significantly greater than those in the other treatments but were statistically similar to those in T₇. Both Zn and B uptake were the lowest in the T₁ (control) treatment (Fig. 3b).

Zn, B and Mo combined with Rhizobium inoculation affected Rhizobia, total bacteria, fungi, actinomycetes, PSB and free-living bacteria in the postharvest soil of garden peas (Table 6). In the case of Rhizobia, a significantly increased population (600 × 10⁵ cfu/g soil) was found in T_6, while a decreased population was noted in the T₁ (control) treatment.

The greatest population of total bacteria (3300 × 10⁵ cfu/g soil) was detected in the T₄ treatment, and the lowest population (2.0 × 10⁵ cfu/g soil) was detected in the T₁ treatment (control). Significantly, the maximum fungal population (5400 × 10⁵ cfu/g soil) was detected in the T₆ treatment, while the minimum fungal population was detected in the T₇ and T₂ treatments. The population of actinomycetes reached a maximum (1000 × 10⁵ cfu/g soil) in T_6, which was significantly greater than that in the other treatments. However, the actinomycete population was least abundant in the T₂ treatment (Table 6). The largest population of phosphate-solubilizing bacteria (400 × 10⁵ cfu/g soil) was observed in the T₂ and T₆ treatments, which was comparable to that in the T₃ and T₇ treatments, and a smaller population was observed in the T₅ treatment. The highest population of free-living bacteria (4200 × 10⁵ cfu/g soil) was recorded in the T₆ treatment, followed by the T₃ treatment, and the lowest population (11 × 10⁵ cfu/g soil) was registered in the T₁ (control) treatment (Table 6).

The use of Zn, B, and Mo with Rhizobium inoculation had an encouraging effect on the cost and return analysis of garden pea production (Table 7). The maximum gross returns of USD 4240 ha⁻¹ for green pods and USD 1596 ha⁻¹ for dry seeds of garden peas were recorded for the T₆ (Zn₃B₂Mo₁ + Rhizobium) treatment, followed by the T₇ treatment. The lowest gross return was recorded in the control treatment group. However, the benefit-cost ratio (BCR) was 5.70 for the green pod treatment and 2.29 for the dry seed from the T₂ (only rhizobium inoculation) treatment. The lowest BCR of 3.61 for the green pods of garden peas occurred in the T₃ treatment, and the minimum BCR of 1.48 for dry seeds occurred in the T₄ treatment (Table 7). The decreasing trend of the benefit-cost ratio might be related to the higher market price of Mo-containing fertilizer.