Alterations in soil aggregate stability of a tropical Ultisol as mediated by changes in land use

Abstract

Aggregate stability is considered to be an appropriate indicator of the relative resistance of soils to detachment by the forces of wind or water. Structural weakness and high rates of erosion in red yellow podzolic (RYP) soils of Matara district are, in general, discussed as prominent problems in intermediate scale agricultural estates. The present study was conducted to ascertain the impacts incurred on the stability of soil aggregates by the alteration of natural forests to agricultural lands, using tea, rubber, and tea/rubber intercropping soils. Surface soils were taken to assess the wet and dry aggregate stabilities, bulk density (D_B), clay content, and soil organic carbon (SOC) content. The D_B of rubber (1.62 g cm⁻³) and tea/rubber intercropping (1.61 g cm⁻³) soils differed significantly (P < 0.05) from forest (1.33 g cm⁻³) and tea (1.48 g cm⁻³) soils. Rubber and tea/rubber intercropping soils had significantly high clay contents as well. Forest soil had the highest SOC content, whereas tea, tea/rubber, and rubber soils respectively showed 45, 50, and 70% decline. The aggregate size distribution did not differ noticeably in forest, tea, and tea/rubber intercropping soils. However, rubber soils with the least SOC content had a lower percentage of macro-aggregates (> 0.5 mm) and significantly low wet and dry mean weight diameters. Above results revealed that the changes in land use negatively influenced the SOC pool and the stability of aggregates. Significant and consistent relationship between the carbon stocks and the wet and dry stabilities of aggregates has not been noted. It was clear that the content of SOC would not be considered as the solitary factor that affects wet and dry stabilities of aggregates in the tested Rhodudults.