The percentage organic matter was determined by the method described by FAO (1974). Soil samples were collected and ground to pass through 0.5 mm sieve. One gram of each soil sample was weighed into 250 ml Erlenmeyer flasks and 10 ml of K2Cr2O7 solution was dissolved into each flask and swirled gently to disperse soil. Twenty milliliters of concentrated H2SO4 was rapidly added using automatic pipette and swirled gently until the soil and reagents were mixed, then the mixture was swirled more vigorously for one minute, the flasks were then rotated and allowed to stand in a sheet of asbestos for about 30 min. One hundred milliliters of distilled water was added to each flask, then 3 - 4 drops of indicator (ferroin) was added and filterated with 0.5 N ferrous sulphate solution to the end point, from greenish or dark green to red (maroon colour) and in reflected light against a white background. The organic matter was calculated according to the following formula:
%Organic matter = (me K2SO4 – me FeSO4) x 0.003 x 100 x f x1.729 Weight of air-dried soil % Organic matter =
Where, correlation factor “ƒ” = 1.33, me = normality of solution × milliliter of solution used and 1.729 = conversion