The Effect of Moisture Adjustment Procedures on Substrate Hydration and Wettability

Similar to minerals soils, organic substrates have been shown to exhibit hysteretic behavior. Consequently, irrigation and drying cycles of substrate materials influence a given materials ability to capture and retain water. The purpose of this study was to determine the effect drying a substrate to a specific moisture content (starting at high moisture and drying down to specific lower moisture contents) vs hydrating (starting at low moisture contents and wetting up to specific higher moisture content) may have on the wettability of that material. Pine bark, peat moss and coconut coir materials attained a moisture content of 50% by weight through one of two technique, hydration or drying. Hydrated treatments were dried to 25% moisture content allowed to equilibrate for 24 h and hydrated up to 50%. Similarly, dry down treatments were initially hydrated to 66% moisture content allowed to equilibrate for 24h and dried to 50% moisture content.  Treatments were then tested for water capture and retention. Differences in the ability to capture water were noted between the two methods of attaining 50% moisture for all treatments.  After the initial hydration event bark that was dried down to 50% moisture content retained 36.5% moisture compared to 33.5% for the sample that was hydrated up to the same moisture.  At the last hydration event the dry down treatment retained 39.8% moisture compared to 35.1 % for the hydrated treatment. In a similar trend the peat which was dried to 50% moisture content held 29.5% water while the hydrated treatment retained 24.4%.  More interestingly, were the values attained for peat after the last hydration event in which the dry down treatment reached 54.4% and with the hydrated treatment only reaching 34%. This is consistent with previous research showing hysteresis to be more pronounced in peat than in pine bark.  Coir treatments comparing the two methods followed trends more similar to bark than peat, however retained the most water out of the three components which is expected since coir has been shown to be more hydrophilic.  At initial hydration, coir dried down to 50% retained/captured 58.9% of the applied water and the hydrated coir retained 52.7%. Again similar to the difference observed in bark, at the last hydration event coir which was dried down to 50% attained 70.2% compared to 65.9% of the applied water for the hydrated treatment.