Distribution of Selected Soil Nutrients in Aggregate Sizes of Soils Under Different Geologic Formations in Southeast Nigeria

Soil nutrients which are major factors to crop yield and food security could be loss to erosion as a result of structural break down leading to water pollution and low crop yield. Soils of southeast Nigeria like others in the humid tropical area are prone to degradation and are low in nutrient status. Therefore the study was conducted in other to investigate the distribution of selected soil nutrients in aggregate sizes under different geologic formations namely Asu River Group (ARG), Coastal Plain Sand (CPS), Falsebedded Sand Stone (FBS) and Bende Ameki Group (BAG) in Southeast Nigeria. At a depth of 0-15 cm, three replicate soil samples were taken from each formation. Collected samples were air dried, crushed and sieved using 2 mm mesh, properly labelled and analysed using standard methods. Samples for aggregate stability were not crushed after air drying. Core samplers were also used to collect samples for bulk density determination. Wet sieving method was used in separating samples into different sieve sizes of 2, 1, 0.5, and <0.25 mm respectively. The experiment which was analysed using ANOVA was laid in Randomised complete block design. Significant means were separated using LSD at 5 % probability. Result indicated significant (P < 0.05) variations in soil nutrients with sieve sizes. Soil organic carbon ranged from 10.30 % in aggregate diameter of 2 mm to 13.90 % in 0.5 mm in Asu River Group, 5.30% in 2 mm diameter to 12.30 % in < 0.25 mm in Coastal Plain Sand, 8.80% in 2mm sieve to 13.50 % in < 0.25 mm and in Falsebedded Sand and from 8.40 % in sieve of 0.5 mm to 15.8% in < 0.25 mm sieve size in Bende Ameki Group. Higher values of total nitrogen were noted in 0.5 and in < 0.25 mm sieve sizes. Available phosphorus was significantly (P<0.05) found more in aggregates size of 1mm in all studied soils except in Uzuakoli. The stability of aggregates using percentage water stable aggregates greater 0.25 mm (WSA > 0.25) was significantly higher in soils of Umuna (59.18%) under False bedded Sand Stone and least at soils of Obinze (26.27%) under Coastal Plain Sand and followed the order: FBS >ARG > BAG > CPS. Result also showed that soil organic carbon had significant (P < 0.05) positive relation with water stable aggregates WSA (r= 0.50), pH water (r= 0.53),total nitrogen (r=0.79), effective cation exchange capacity (r = 0.51) of the studied soils.