Water retention characteristics of soils with contrasting clay mineral composition in semi-arid tropical regions

In semi-arid tropical regions, the availability of reliable data for water retention in relation to soil type, texture, and organic matter content is low. It would be therefore desirable to develop pedotransfer functions (PTF) in order to estimate water retention characteristics from easily available soil parameters. In the present study, a soil database containing water retention characteristics, particle size distribution, and total organic carbon content of 663 horizons from semi-arid regions in NE Brazil and SE Niger was used to investigate the effect of contrasting clay mineral composition on water retention and PTF characteristics for soils from semi-arid tropical regions. For soil water content at field capacity (- 33 kPa) and wilting point (-1500 kPa), PTFs were established and validated with disturbed samples from LAC soils (soils containing predominantly low activity clay; CEC < 24 cmol/kg clay) and non-LAC soils. The PTFs for the LAC soil group differed considerably from the PTFs for non-LAC soils with respect to the contribution of total organic carbon and silt content to the prediction of soil water content at field capacity and wilting point. For the particle size classes sand, loamy sand, sandy loam, and sandy clay loam, the mean measured soil water contents in LAC soils were significantly smaller than in non-LAC soils at a matric potential of -33 kPa. The results demonstrate the influence of clay mineral composition on soil water retention and its importance for the development of pedotransfer functions.