Aggregate Stability Indices of a Typic Hapludult under Different Land-Use Types and Varying Depths at Umuahia.

Abstract:

Stability of soil aggregates is among the soil conditions influencing the fertility and quality of soils. This study was conducted to access the implications of different land-use practices and depths of soil on aggregate stability indices. The trial was a split plot experiment in Randomized Complete Block Design (RCBD) involving two factors which were land-use practices (main plot factor) and soil depths (subplot factor). The land-use practices were of four levels {continuously cultivated land (CC), forest land (FL), grassland (GL), and oil palm plantation (OP)}; while the soil depths were of five levels (0 – 20, 20 – 40, 40 – 60, 60 – 80, 80 – 100 cm). Twenty treatments combination were obtained and replicated nine (9) times to give a total of one hundred and eighty (180) observational points. Nine (9) mini-pits of 100 cm each were randomly dug in the respective land-use, then disturbed and undisturbed soil samples were collected from the specified depths. The samples were prepared and analysed in a laboratory. Data generated were subjected to analysis of variance (ANOVA) using GenStat version 15. Results showed that there was significant (P ≤ 5%) difference in aggregate stability indices among the land-use practices and across the depths; also there was significant (P ≤ 5%) interaction between land-use practices and depths. The highest dispersion index of 29.48 % was observed under the FL at 0 – 20 cm depth, while the highest clay dispersion index of 42.31 % was observed under GL at 0 – 20 cm depth. Aggregated silt + clay increased with increase in depth with GL having the highest value of 29.98 % at the 80 – 100 cm depth. Highest and lowest clay flocculation index were observed at the CC and GL across the depths, respectively. The highest mean weight diameter across the depths was observed at the OP while CC had the lowest across depths. Therefore, aggregate stability indices vary across soils of different land-use practices and depths such that land-use practices that promote accumulation of organic carbon weaken the stability of micro aggregates but promoted macro aggregation and its stability.