Water content at permanent wilting point: An approach for rewetting air-dried soils, considering the effect of hysteresis

Bachelor Thesis of Matthias Lang, conducted at the University of Basel in collaboration with Agroscope. Summary Estimating plant-available water in soil at permanent wilting point is challenging. To advance the current state of knowledge, measurements traditionally taken with the pressure plate apparatus can be compared to new data obtained using modern dewpoint hygrometer techniques. Comparing the measurements aquired with the two methods requires rewetting of air-dried soil samples, which is however complicated by the lack of a standardised method that takes into account the hysteresis effect. This thesis addresses this lack by developing, testing, and evaluating four dierent rewetting methods. Using the WP4-T apparatus by Decagon Device (now Meter Group), ten soil samples covering a wide range of textures were examined. The data were analysed through a two-way ANOVA considering soil properties such as clay, silt, and sand content, soil organic compound, bulk density, and management practices (fertiliser application and tillage method) and the rewetting method. The results reveal that only one method was successful in rewetting more than a single sample. Soil properties played a signicant role for the eectiveness of rewetting: Soils with high silt content (>40%) achieved the best results, while sandy soils (>50% sand content) and soils from no tillage sites performed poorly. Further research should implement a novel rewetting method, considering the increased hysteresis effect caused by the presence of water-repellent compounds.