Fine Woody Debris of Mangifera indica, Alstonia macrophylla, and Calophyllum inophyllum Affected Soil Hydrophobicity

Abstract

Mangifera indica (MI), Alstonia macrophylla (AM), and Calophyllum inophyllum (Cl) are medicinal plants with specific chemical compositions in leaves, roots, stem, and fruits/nuts. Among these, MI is known to have astringent, acrid, and refrigerant roots ancf bark, whereas AM and Cl are been reported for the presence of Alkaloids and Flavonoids, respectively, in stem-bark. These chemicals have specific characteristics that might interfere with and thereby change some soil properties. The objective of this study was to examine the effects of woody debris on soil hydrophobicity and wetting behavior using fine woody dusts. Arable top soil (0 -10 cm) (Udults) used for the experiment was air dried and sieved through 2 mm sieve. Air dried and ground woody dusts were sieved through 1 mm sieve prior to mixing with sieved soil to obtain § and 50% contents. Samples were exposed to four temperature levels (27, 60, 100, and 200°C) for 6 h. Hydrophobicity of soils was determined, in three replicates, with sessile drop contact angle of a water drop on a monolayer of samples fixed to a glass slide using a double-sided adhesive tape. Microphotographs of the drops were taken within 1 s by digital microscopic camera. Samples mixed with 5% woody dusts did not show a measurable contact angle within 1 s due to lateral wetting of the monolayers. Contact angle in samples with 50% woody dusts was highest with Cl, followed by AM and MI. Presence of flavonoids might be the reason for Cl to show a high hydrophobicity. The hydrophobicity of all the samples increased with time after heating which was measured up to 7 d. Contact angles of samples with 50% woody dusts increased by 12-16° with increasing temperature from 27 to 100°C. This can be attributed to changes in organic compounds in the woody dusts with the increasing temperature. Upon exposure to 200°C, hydrophobicity disappeared in all the samples showing that the organic materials responsible for causing the hydrophobicity lost either by evaporation or removal as CO2 and H20 .