Hydrological Connectivity in Sandy Loam Soil Mixed with Zeolite: Insights from FFC-NMR Relaxometry Applied to Laboratory and Field Samples

Using both laboratory and field samples, this paper investigates how zeolite concentration affects the hydrological connectivity of sandy-loam soil through Fast Field-Cycling Nuclear Magnetic Resonance relaxometry. Laboratory samples (LP) were prepared using four zeolite concentrations (0, 5, 10, and 15%), while field samples (FS) were collected in plots amended with the same concentrations to investigate the differences occurring during incubation time between LP and FS. For each zeolite concentration ZC, the results demonstrated that the F(T1) distribution of the FS systematically shifts towards the right compared to LP. This “scaling” effect between LP and FS was addressed using a dimensionless variable T1/σ(T1), where σ(T1) is the standard deviation of T1 considering the effects of pore size variability. The developed analysis demonstrated that the highest values of the structural connectivity index SCI correspond to ZC = 10% for LP, while ZC = 15% is necessary for FS, even if similar performance corresponds to ZC = 10%. Differences in the functional connectivity index (FCI) of LP and FS, which can be explained by environmental effects, were recognized. In conclusion, for sandy-loam soil, ZC = 10% is sufficient to improve the physical soil characteristics (highest values of structural connectivity) for both samples, while for FS, a ZC = 10% assures the minimum FCI values (the highest water-holding capacity).