Origin of the high sensitivity of Chinese red clay soils to drought: Significance of the clay characteristics

•We examine the water retention properties of Chinese red clays soils.•These soils were recognized as highly sensitive to drought.•This is related to the high proportion of poorly available water.•It results from the stiffness of the microstructure.

The red clay soils which are widespread in China are known to be highly sensitive to drought during the dry season but the origin of this high sensitivity to drought remains unclear. Several red clay soils were selected in the Hunan province for study. We studied their basic physico-chemical properties and clay mineralogy, their structure and shrinkage properties, as well as their water retention properties. Results show that the amount of water available between − 330 and  −15,000 hPa water potential is consistent with that recorded in many other clay soils from different parts of the world and thus cannot explain the high sensitivity of the red clay soils to drought. This high sensitivity to drought might be related to the high proportion of poorly available water which was characterized by the amount of available water between − 3,300 and  −15,000 hPa water potential. Comparison with clay soils located in different parts of the world and for which the sensitivity to drought was not identified showed that this proportion of poorly available water is indeed much higher in the red clay soils studied than in clay soils representing a large range of both clay content and mineralogy. This specific behavior of the red clay soils studied is thought to be related to the history of their parent materials: these materials are continental sediments which may have been submitted to great hydric stress, thus leading to strongly consolidated soils with consequences such as a high proportion of poorly available water, strong aggregation and weak shrinkage properties.