*2.4.2. Determination of soil organic matter*

About 0.70 g each of the air-dried and sieved soil samples were weighed and 10.0 ml of 1.0 N K2CrO7 solution and 20.0 ml concentrated H2SO4 were added immediately [69]. The solution was mixed for 1 minute by swirling until the soil and reagents were thoroughly mixed. The mixture was allowed to stand for 30 minutes after which 100 ml distilled water was added and then allowed to cool under running water. 3-4 drops of Ferroin indicator was added and then titrated with 0.5 N Ferrous Ammonium Sulphate. Near the end-point, the solution took a greenish colour and later changed to dark green. At this point, the 0.5 N Ferrous Ammonium Sulphate was added drop by drop until the colour changed from green to reddish-brown at the end point. The Ferrous Ammonium Sulphate solution was standardized using 1 N potassium dichromate before use. Blank titration was carried out in the same manner, but without the soil sample.

The % organic Carbon was determined as follows:

*% Organic Carbon* <sup>=</sup> (*meq*. *FAS for blank* <sup>−</sup> *meq FAS for sample*) (0.003 *<sup>x</sup>* <sup>100</sup> *<sup>f</sup>* ) *Weight in g of air* −*dried soil*

Where, f = 1.334

% Organic matter = 1.729 x % Total Organic Carbon

meq- Milligram equivalent = normality of solution x ml of solution used.

#### *2.4.3. Determination of soil particle size by the Bouyoucos hydrometer method*

This is a measure of the size distribution of individual particles in a soil sample. Particle size distribution analysis is often used in soil science to evaluate soil texture. The soil texture is based on different combination of sand, silt, and clay separately, that makes up the particle size distribution. The size range of sand is 2.0 mm-0.05 mm, silt is 0.05 mm-0.002 mm and clay is less than 0.002 mm (< 0.002 mm). Particle size distribution analysis result can be used to predict the water retention capacity and unsaturated hydraulic conductivity of soils [70]. About 50.0 g of air-dried soil sample sieved to < 2 mm was weighed into 250 ml beaker. 20 ml of 5.0 % Sodium Hexametaphosphate was added along with 350 ml distilled water. The mixture was stirred mechanically on an end-to-end shaker at 100 revolutions per minutes for 5 minutes. The water-soil slurry was transferred to a sedimentation cylinder and sufficient water was added to bring the level to the 1000 ml mark. The top of the cylinder was covered and inverted several times until all the soil particles are in suspension. The cylinder was placed on the flat surface and the time was recorded. The soil hydrometer was placed on the suspen‐ sion carefully and slided slowly into the suspension until the hydrometer was floating. The first reading was taken on the hydrometer at 60 s after the cylinder was set down. The hydrometer was removed and the temperature of the suspension was measured. After the first hydrometer reading, the suspension was left standing for 3 hours and the second reading was taken. The temperature of the suspension was also measured at this point. The first reading measured the percentage of silt and clay in suspension while the second reading indicated the percentage of clay in the suspension. When taking the hydrometer reading, the hydrometer was carefully lowered into the cylinder about 25 s before the reading was taken to ensure that it came to rest before the appointed reading time. The readings were taken at the top of the meniscus formed by the suspension around the stem of the hydrometer. As soon as the reading was taken, the hydrometer was carefully removed and rinsed with distilled water. The results were corrected to a temperature of 20 oC and 2.0 were subtracted to compensate for the added dispersing agent.

Correction factor for Temperature = 0.3 [Observed Temperature (T oC) – 20 o C]

% Clay + % Silt = [H1 + 0.3 (T1 - 20) – 2.0] 2 % Clay = [H2+ 0.3 (T2 - 20) – 2.0] 2 Sand = 100 – [H1 + 0.3 (T1 - 20) – 2.0] 2 Silt = 100.0 – (% Sand + % Clay) Where, H1 = Hydrometer reading at 60 s T1 = observed Temperature at 60 s (= 28 oC) H2 = Hydrometer reading at 3 hours

T2 = observed Temperature at 3 hours (= 28 oC)
