Measuring the Water Potential of a Crimson Clover Cover Crop Residue Left on the Soil Surface.

The decomposition of cover crop residues on the soil surface depends on environmental conditions such as temperature and water potential. While measuring temperature is relatively easy, measuring the water potential of crop residues on the soil surface presents difficulties. This work was conducted to determine if a Campbell Scientific CS625 reflectomer could be used to measure the water potential of a crimson clover cover crop residue. For that purpose, a crimson clover residue was collected, applied on the soil surface, and a CS625 reflectometer was placed at the interface between soil and crop residue. The reflectometer was connected to a CR200 Campbell Scientific datalogger, which was programmed to record temperature and reflectometer period every 15 min. At different times throughout the growing season (June-Sep), residue samples were collected and their water potential measured with a Decagon Potentiameter. A good relationship was found between residue water potential and reflectometer period (MPa = (27.69 – 9.03 Ln(Period))/(1-0.38 Ln (Period)); R2=0.95). This equation was used to estimate water potential of the clover residue from June through October. The results indicate a strong diurnal variation in water potential in response to temperature. In summary, our data suggest that it is possible to estimate the water potential of a crimson clover cover crop residue with a CS615 reflectometer, and that the water potential of the surface residue experiences wide diurnal variations in response to temperature.