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Universiteit Gent (2007)

EFFECT OF CLAY MINERALOGY ON WATER RETENTION OF SOILS IN EASTERN AND NORTHERN TANZANIA

Mpulila Thadeo

Titre : EFFECT OF CLAY MINERALOGY ON WATER RETENTION OF SOILS IN EASTERN AND NORTHERN TANZANIA

Auteur : Mpulila Thadeo

Université de soutenance : Universiteit Gent

Grade : Master of Science (MS) Physical Land Resources 2007

Résumé
In this study, the effect of clay mineralogy on water retention properties of the soils of Tanzania was evaluated. The A horizons and B horizons of nine soil profiles representing different soil orders (USDA Soil Taxonomy) were sampled using Kopecky rings. Within each horizon, three subsamples were taken for which soil water retention curves were developed. Physico-chemical soil properties and clay mineralogy were determined on composite soil samples for each horizon. The water retained at –10 kPa, –33 kPa and –1500 kPa and the available water capacity of the different soil profiles proved to be significantly different. The Andisol showed the highest water content at saturation attaining 0.708 m3 m-3 , as well as the highest available water capacity of 0.16 m3 m-3 , while the Entisol (sandy soil) had the lowest water content at saturation of 0.325 m3 m-3 and the lowest available water capacity of 0.027 m3 m-3 . The Oxisol retained relatively more water at saturation averaging to 0.609 m³ m- ³, but showed a relatively lower available water capacity of 0.073 m3 m-3 . Of the high water retention noted in the Vertisol profile, only a limited fraction is available to the plant. Evaluation of different parametric and point PTFs showed that the PTFs developed for specific soil types are restricted to predict the water content of these soils up to an acceptable level of accuracy. Apparently, the validity of these PTFs is only assured for soils taken from the calibration dataset. The soil water content at –10 kPa, -33 kPa and –1500 kPa was strongly positively correlated with the cation exchange capacity (r = 0.88, 0.87 and 0.78, respectively) and clay content (r = 0.65, 0.69 and 0.76, respectively) and strongly negatively correlated with sand content (r = -0.72, -0.77, and -0.86, respectively), and is somewhat less correlated with the silt content (r = 0.44, 0.51 and 0.59, respectively). These soil properties are the major predictors of the water content at a specified matric potential and of the van Genuchten (1980) model parameters. The influence of clay mineralogy on water retention seems to be significant and needs to be included when developing PTFs for tropical soils such as those of Tanzania.

Source : Pedon 19 - Physical Land Resources - Universiteit Gent

Page publiée le 24 décembre 2015, mise à jour le 25 janvier 2018