CHAPTER I INTRODUCTION
2. Effects of different inorganic fertilizers and organic manures on growth, yield and nutrient content of Aman rice
3.8 Collection of initial soil and analysis
The soil of the experimental site belongs to the general soil type, Deep Red Brown Terrace Soils under Tejgaon Series. Top soils were silty loam in texture, olive-gray with common fine to medium distinct dark yellowish brown mottles.
The experimental area was flat having available irrigation and drainage system and above flood level. Soil samples from 0-15 cm depths were collected from experimental field. Soil samples were analyzed for both physical and chemical properties in the laboratory of the Soil Resource and Development Institute (SRDI), Farmgate, Dhaka. The initial soil samples were collected for analysis included particle size distribution, textural classes, soil pH, organic matter, total N (%), available P (ppm), exchangeable K (meq/100 g soil), available S (ppm), exchangeable Ca (meq/100 g soil), exchangeable Mg (meq/100 g soil) and available Zn (μg /g). The soil was analyzed following standard methods.
Soil pH was measured with the help of a glass electrode pH meter using soil water suspension of 1:2.5. The morphological characteristics and initial physico- chemical properties of soils are presented in Table 2.
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3.8.1 Textural classes
Particle size analysis of soil was done by hydrometer method (Black, 1965) and textural class was determined by plotting the value of % sand, % silt, % clay to Marshall’s triangular coordinate following the USDA system.
3.8.2 Soil pH
The pH was measured with the help of glass electrod pH meter using soil water suspension of 1:25 as described by Jackson (1962). By using standard buffer solutions to standardize pH meter weighed 10 grams of soil into a 50 ml beaker. 10 ml of distilled water was added and stared thoroughly. Let stand for at least 30 minutes, stirred two or three times. A pH meter using a glass electrode was read.
3.8.3 Soil Organic Matter
Organic matter in soil was determined by methods of Walkley and Black’s (1934) Wet Oxidation method. The principle is to oxidize the organic carbon with an excess of 1N K2Cr2O7 in presence of conc. H2SO4 and to titrate the residual K2Cr2O7 solution with 1N FeSO4 solution. To obtain the organic matter content, the amount of organic carbon was multiplied by the Van Bemmelen factor, 1.73.
Calculate C (%) and organic matter (%) a. Easily Oxidizable Organic C (%)
C (%) = (B-S) x M of Fe2+ x 12 x 100 g of soil x 4000
where: B = ml of Fe2+ solution used to titrate blank S = ml of Fe2+ solution used to titrate sample 12/4000 = equivalent weight of C in g.
To convert easily oxidizable organic C to total C, divide by 0.77 (or multiply by 1.30) or other experimentally determined correction factor. To convert total organic C to organic matter use the following equation:
b. Organic Matter (%) OM (%) = Total C (%) x 1.73
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3.8.4 Total Nitrogen
One gram of oven dry ground soil sample was taken into micro kjeldahl flask to which 1.1 g catalyst mixture (K2SO4:CuSO4.5H20: Se=100: 10: 1), 2mL 30%H2O2 and 5 mL H2SO4 were added. The flasks were swirled and allowed to stand for some minutes (about 10 minutes). Then heating (380°C) was continued until the digest was turned into clear and colorless. When the mixture was cooling, then it was taken into 100 ml volumetric flask and the volume was made up to the mark with distilled water. A blank reagent was prepared in a similar way. These digest was used for nitrogen determination.
After completion of digestion, 40% NaOH was added with the digest for distillation. The evolved ammonia was trapped into 4% H3BO3 solution and 5 drops of mixed indicator of bromocressol green (C21H14O5Br4S) and methyl red (C10H10N3O3) solution. Finally the distillate was titrated with standard 0.01 N H2SO4until the color changed from green into pink. (Bremner and Mulvaney, 1982).
The amount of N was calculated using the following formula.
% N = (T-B)×N×0.014×100/S
Where, T= Sample titration value (mL) of standard H2SO4 B= Blank titration value (ml) of standard H2SO4
N = Strength of H2SO4 S= Sample weight (g)
N = Normality or strength of H2SO4, 1.4 = Conversion factor
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3.8.5 Available Phosphorus
Available phosphorus was extracted from the soil samples by shaking with 0.5 M NaHCO3 solution at pH 8.5 following Olsen method (Olsen et al. 1954). The extracted phosphorus was determined by developing blue color by SnCl2 reduction of phosphomolybdate complex and measuring the intensity of color spectrophotometrically at 660 nm wavelength and the readings were calibrated to the standard P curve.
3.8.6 Exchangeable Potassium
Exchangeable potassium was extracted from the soil samples with 1.0 N NH4OAc (pH 7) and K was determined from the extract by flame photometer (Black, 1965) and calibrated with a standard curve.
3.8.7 Available Sulphur
Available sulphur in the soil was determined by extracting the soil samples with CaCl2 (0.15%) solution (Page et al., 1982). The sulphur in the soil was determined by spectrophotometer at 420 nm wave length.
3.8.8 Exchangeable calcium
Exchangeable calcium of soil was determined from 1 N ammonium acetate (pH 7.0) extract of soil by using flam photometer.
3.8.9 Exchangeable magnesium
Exchangeable magnesium of soil was determined from 1 N ammonium acetate (pH 7.0) extract of soil by using flam photometer.
3.8.10 Available zinc
1.5 g scoop of soil was transferred to a 125 ml Phillips beaker. Then 15 ml of extracting solution was added. The samples were sharked for 15 minutes on an
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oscillating shaker. Then the extract was filtered through Whitman No. 2 or equivalent filter paper into 10 ml funnel tubes. Zn was determined in the filtered extract via Atomic Absorption Spectrophotometer, using a bulk Zn standard containing 1.6 ppm Zn, which was diluted by the Atomic Absorption to make as many standards as the user specifies.
Calculations:
ppm Zn in soil = ppm Zn in solution x 10
Table 2 : The initial morphological, physical and chemical properties of soil in Boro season
Soil properties Value (SAU farm Dhaka)
Value
(Shakhepur,Tangail)
Locality SAU farm Dhaka Shakhepur, Tangail
Agro-ecological zone (AEZ) Madhupur Tract (AEZ 28)
Old Brahmaputra Flood Plain (AEZ 9)
Topography Fairly leveled Fairly leveled
Drainage Well drained Well drained
Flood level Above flood level Above flood level
Mechanical fractions:
Sand (%) 29 32
Silt (%) 52 57
Clay (%) 19 11
Texural class Silty loam Silty loam
pH 5 5.7
Organic matter (%) 2.22 2.15
Total N (%) 0.11 0.09
Available P (ppm) 11.08 10.96
Exchangeable K (meq/100g soil) 0.12 0.14
Available S (ppm) 9.11 9.98
Exchangeable Ca (meq/100 g soil)
10.30 13.95
Exchangeable Mg (meq/100 g soil)
0.91 1.04
Available Zn (μg /g) 5.83 5.51
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