Evolution of physical properties of a cultivated organic soil drained by drainage trench

Organic soils used for agriculture may undergo the formation of a Moorsh layer, restricting drainage and thus limiting their productivity. Drainage trenches filled with high-permeable materials are a potential solution to improve drainage in cultivated organic soils, but they also tend to evolve. The objective of this study was to compare the physical properties in and outside of the trench over time. An accelerated aging of a drainage trench was performed in a rectangular box (3×1 m) filled with layers of a reconstituted organic soil profile incubated for six months (equivalent to 1.5 years in the field) at room temperature with variable water applications to induce drainage. The evolution of the hydraulic properties of the soil, such as total porosity (TP) and air-filled porosity (AFP), was determined using the instantaneous profile method at the beginning and at the end of the experiment. For this purpose, tensiometers and water content sensors were installed at four different depths in and outside the trench. No significant changes in TP were observed either in or outside the trench at the different depths over time. AFP decreased significantly with time in the three evaluated layers within the drainage trench and remained constant at each depth outside it. At the 20-30 cm and 30-60 cm layers in the trench position, AFP decreased from 0.26 to 0.11 cm³ cm^‑3 and from 0.35 to 0.29 cm³ cm^‑3, respectively. The results indicated that the positive effect of drainage trenches on the physical properties of cultivated organic soils could be maintained for at least 1.5 years at depths greater than 30 cm.