Field experimental site, climatic condition, soil, biochar and straw amendment:
The experiment was conducted from November 2018 to March 2019 in Soil Science Division, BARI experimental field (23º59´21.584´´ N, 90°24´34.999´´E). The soil at the site of the experiment is under chiata soil series, brown hill soil type classified as Inceptisols. The chemical characteristics of the top soil (0-15 cm) are shown. The cowdung was collected from village near experimental field. The straws of mustard, chickpea and groundnut were collected from BARI experimental plot. These straws were air-dried at room temperature and pyrolysis in a conventional kiln at 500°C to 700°C for 1 h. It was then ground and passed through a 2 mm sieve. There were three replicates for each crop straw during the biochar-generating process. Mustard, chickpea and groundnut were chopped into 5-10 cm lengths before use. The physicochemical characteristics of the cowdung, biochars and straws are examined.
Biochar preparation and analysis:
Mustard, chickpea and groundnut ware collected and air-dried at room temperature. Then they are chopped into small pieces. After that they are placed into biochar making device (made in Soil Science Division, BARI) and pyrolyzed under oxygen-limited conditions. The pyrolysis temperature was raised into 700°C at a rate of approximately 20°C per minute and held constant for 2 h. Then the biochar was allowed to cool to room temperature and ground to pass a 0.25 mm sieve. All biochar samples were examined to determine their main characteristics without further treatment, and their characteristics are shown. After being thoroughly mixed with deionized water at a ratio of 1:20 and equilibrated for 1 h, the pH of the biochars was measured by Metler Toledo S220 with a combine electrode. The CEC of the soil samples was measured by ammonium acetate compulsory displacement method. Exchangeable base cations were extracted with 1.0 M ammonium acetate (pH 7.0) (Pansu and Gautheyrou, 2006). Ca2+ and Mg2+ were measured with AAS, and K+ and Na+ with flame photometer. The phosphorus was determined colorimetrically after digesting the biochars with sulphuric acid and hydrogen peroxide.
Treatments, maize cultivation, and field management:
Each plot size was 3m x 2 m with the adjacent plots sharing a soil boundary of 30 cm in width and 20 cm in height. Eight treatments were arranged in a randomized complete block design with three replications. The treatments were: i) Chemical fertilizer (CF) alone (CF, no BC, no S); ii) Chemical fertilizer with cowdung (CD) 5 t ha-1; iii) Chemical fertilizer with groundnut straw (GS) 10 t ha-1, iv) Chemical fertilizer with chickpea straw (CS) 10 t ha-1; v) Chemical fertilizer with mustard straw (MS) 10 t ha-1; vi) Chemical fertilizer with groundnut straw biochar (GSB) 10 t ha-1; vii) Chemical fertilizer with chickpea straw biochar (CSB) 10 t ha-1; and viii) Chemical fertilizer with mustard straw biochar (MSB) 10 t ha-1. All plots, received RDCF (N255 P50 K120 S40 Zn5 B2 kg ha-1) as a basal fertilizer. Before commencing the experimental set up, the cowdung, crop straw and biochar were incorporated into the soil corresponding to 15 day (d) before sowing. Top dressing of urea as mentioned above was done at 22 and 46 d after sowing (DAS), include in the control. Yield and yield contributing character samples were collected inside a quadrant area of 1.0 m2 per plot.
Pop corn Yield and Yield Components:
Plant height was measured on five random plants per plot. Thousand grain weight was determined by counting a hundred maize grains and weighing. Grain yield (t ha−1) was corrected to 12% moisture level. Grains yield was recorded after opening of ears of two central rows from each plot and then dried and weight was converted into kg ha-1.
Grain yield (kg) X 100 R-R x R L x No. of Rows.
Soil and Plant analyses:
Soil samples were analyzed before and after termination of the experiment at the depth of 0–15 cm. Soil samples were air dried and partially ground and pass through the 0.3 mm sieve. Soil pH was determined using Metler Toledo S220 with a combine electrode in a soil water ratio of 1:2.5 (w/w) as described by Mehmood et al. (2018). Organic carbon was determined by wet oxidation method (Walkley and Black, 1934) Total N was determined by modified Kjeldhal method. The base cations (Ca2+, Mg2+ and K+) were extracted with 1 M ammonium acetate (pH 7.0) (Pansu and Gautheyrou, 2006). Cu, Fe, Mn, Zn were determined by DTPA extraction followed by atomic absorption spectrophotometer (AAS). Boron was determined by CaCl2 extraction method. Phosphorus was determined by Bray and Kurtz method while S by turbidimetric method with BaCl2. The clean plant samples were air-dried and placed in an electric oven, dried at 105ºC for 24 h, weighted for dry biomass. Again, place it in the oven at 105ºC for 2h. Cool it in a desiccator and weight it again. Repeat drying, cooling and weighing until the weight become constant. The dried plant samples were homogenized by grinding using willey mill and used for nutrient analysis. Then, the grains were ground and N, P, K, Ca, Mg, S, B and Zn contents were determined according to the method described by described by Jones and Case (2018). Atomic absorption spectrophotometer (Thermo Scientific - SOLAAR S Series AA spectrometer) was used for metal ion and spectrophotometer (Agiland Technologies, cary 60 UV-Vis) for anion analysis. The accumulation of nutrients in the grains was estimated by multiplying nutrient content by dry grain weight.
Statistical analyses:
SPSS 15.0 (SPSS, Inc., Chicago, IL, USA) was used for the statistical analysis of data. A one-way analysis of variance was undertaken for each time interval of the incubations to determine significant differences between treatments. The significant effects for various treatments were detected using a t- test.