A field experiment was carried out on 02 December 2015 and 30 November 2016 during rabi season at Central Farm, Regional Agricultural Research Station, Bangladesh Agricultural Research Institute (BARI), Rahmatpur, Barisal (22.42° N latitude, 90.23° E longitude and above 4 m elevation from sea level). Rahmatpur soil belongs to the Barisal series of non calcareous grey floodplain soil (AEZ-13). The experiment was laid out in Randomized Complete Block Design (RCBD) with four replications. There were nine treatments viz. T1: Control (non-inoculated and non-fertilized), T2: Vermicompost (VC) @ 2.5 t ha-1, T3: VC @ 5.0 t ha-1, T4: VC @ 2.5 t ha-1 + NPKSZnB, T5: VC @ 5.0 t ha-1 + NPKSZnB, T6: VC @ 2.5 t ha-1 + Rhizobium + PKSZnB, T7: VC @ 5.0 t ha-1 + Rhizobium + PKSZnB, T8: 100% NPKSZnB, T9: Rhizobium + 100% PKSZnB. The tested crop was gardenpea (cv. BARI Motorshuti-3). Peat based rhizobial inoculum (Rhizobium strain BARI RPs-501) was used containing 108 cells g-1 inoculum was used at the rate of 1.5 kg ha-1. Gardenpea seeds were mixed thoroughly with the inoculum before sowing. The unit plots measured 2 m × 3 m. Seeds were used at the rate of 75 kg ha-1. Nitrogen, phosphorus, potassium, sulphur, zinc and boron were used in the form of urea, TSP, MP, gypsum, zinc sulphate and boric acid, respectively. All P, K, S, Zn, B, vermicompost and 1/3rd N were applied at the time of final land preparation and the remaining 2/3 N was applied in two equal installments at 25 and 45 days of sowing. All the intercultural operations such as irrigation, weeding, insect control etc. were done as and when necessary. Vermicompost was prepared from kitchen waste of Gazipur municipality and used in the plot mixed with soil. Nodules were collected by carefully uprooting five sample plants selected randomly from each unit plot at the 50 percent flowering stage. Nodules were separated from the roots, counted and then oven-dried and weighed. Data on yield and yield components were recorded at maturity. The crop was harvested from 10 February to 15 March in 2016 and 05 February to 20 March in 2017. The initial soil samples at a depth of 0-15 cm from the experimental fields were collected and analyzed following standard methods. The vermicompost used in this experiment were also analyzed.
Data on yield and yield contributing characters were recorded and statistical analyses were conducted using standard statistical procedures (Gomez and Gomez 1984) implemented in Statistix 10. The data were examined by analysis of variance (ANOVA). Differences between the treatments were determined by ANOVA, and Fisher’s protected least significant difference (LSD) was calculated at the 0.05 probability level for treatment mean comparisons.
Methods of chemical analysis:
Soil pH was measured by a combined glass calomel electrode (Jackson, 1958). Organic carbon was determined by wet oxidation method (Walkley and Black, 1947). Total N was determined by modified Kjeldahl method. Calcium, K and Mg were determined by NH4OAc extraction method. Copper, Fe, Mn and Zn were determined by DTPA extraction followed by AAS reading. Boron was determined by CaCl2 extraction method. Phosphorus was determined by Bray and Kurtz method (Acid soils) and Modified Olsen method (Neutral + Calcareous soils). Sulphur was determined by CaH4(PO4)2.H2O extraction followed by turbidimetric turbidity method with BaCl2.