A field experiment was carried out for onion during rabi season of 2015-2016 at Central Farm, Regional Spices Research Center, Magura. The experiment was laid out in Factorial Randomized Complete Block Design (RCBD) with four replications. There were six treatment combinations viz. T1P1U: 0% P ´ without AM, T2P2U: 50% P ´ without AM, T3P3U: 100% P ´ without AM, T4P1AM: 0% P ´ with AM, T5P2AM: 50% P ´ with AM, T6P3AM: 100% P ´ with AM. The tested crop was onion (cv. BARI Piaj-1). The unit plots measured 3 m × 2 m in size. Soil-based arbuscular mycorrhizal (AM) inoculum and infected root pieces of the host plant was used at the rate of 1 kg soil m-2 in the seedbed for producing onion seedlings. A layer of AM inoculum was firstly placed in each bed and was covered with a thin soil layer of 1 cm. Seeds were sown in the seedbed and transplanted after 30 days in the field. The physical and chemical properties of the soil of seedbed and initial soil samples at a depth of 0-15 cm from the experimental fields were collected and analyzed following standard methods and presented.
Soil pH was measured by a combined glass calomel electrode (Jackson, 1958). Organic carbon was determined by Wet Oxidation Method (Walkley and Black, 1934). Total N was determined by the modified Kjeldahl method (Jackson, 1962). Calcium, K and Mg were determined by NH4OAc extraction method (Black, 1965). 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 the Modified Olsen method (Neutral + Calcareous soils) according to Olsen et al. (1954). Sulphur was determined by CaH4(PO4)2.H2O extraction followed by turbidimetric turbidity method with BaCl2.
Nitrogen, phosphorus, potassium, sulphur, zinc and boron were used in the form of urea, TSP, MoP, gypsum, zinc sulphate and boric acid, respectively. Recommended fertilizer dose (BARC, 2012) for onion (120 kg N, 45 kg P, 120 kg K, 30 kg S, 3 kg Zn, 1 kg B kg ha-1) were used. Phosphorus was used in three levels (0%, 50% and 100%). All K, S, Zn, B and 1/3rd amount of urea-N were applied at the time of final land preparation and the remaining 2/3rd amount of urea N were applied in two equal installments at 25 and 45 days of transplanting. All the intercultural operations such as irrigation, sticking, weeding, insect control etc. were done as and when necessary. Data on yield and yield components were recorded at maturity.
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.