Potassium sorption in soils of Delta State of Nigeria

Potassium sorption of some soils derived from different parent materials in Delta State was studied being a major problem that affects the efficiency of K fertilizers use. Twelve composite soil samples were collected from three different parent materials: Basement complex, Coastal plain sand and Shales. Different amounts of potassium chloride (KCl) were added to 1 kg of each soil (oven dry basis); 50, 100, 400 and 600 mg in three replicates. The soils were incubated near field capacity at 20-25ºC room temperature for 1, 14, 28 and 42 days, respectively. The pH of soil ranged from 4.75 to 6.72, organic carbon ranged from 2.21-20.88 g/kg, the exchangeable cations are in the following order of abundance; Ca2+ > Mg2+ > K+ > Na+. Fractional recovery (FR) values for short incubation periods, 1 and 7 days, were higher than the values for long incubation periods (28 and 42 days), respectively. The amount of K required to increase the soil test value by a unit (mg/kg) was 2.58 mg/kg for all the soils. From the sorption study silt, H+ and Ca2+ were identified as agents of fixation because of the significant negative correlation between FR and those of soil properties. The FR values for all the soils were on the average low. The average amount of K required to increase 1.0 N NH4OAC (pH 7.0) extractable K by 1 mg/kg (K fertilizer factor) was found to be 2.58 mg/kg and, hence, recommended for soils of Delta State, Nigeria. The main Potassium fixing agents identified were silt, H+ and Ca2+.