Using rainfall simulation, TDR, and tracer anions to determine effects of soil properties on nitrate leaching

Two experiments were performed to evaluate NO3-N leaching features using tracer anions combined with use of non-destructive time domain reflectometry (TDR) techniques. A laboratory experiment was conducted to study the effects of different soil bulk density (1.10, 1.33, 1.57, and 1.81 g/cm 3) in the zone of N application and antecedent soil moisture by mass (10 and 15%) on NO3-N leaching during rainfall simulation (6.5 cm/h for 70 min to runoff/drainage pans with 7.6 cm soil layer). Surface runoff, subsurface drainage, and soil extract samples were analyzed for NO3-N, Br (added with rainfall), and Cl (added uniformly to soil) concentrations. TDR probes were horizontally installed either beneath the zone of NO 3-N applied in a line sources for determination of resident solute transport from measured soil bulk electrical conductivity (ECb), or just 1 cm below the soil surface to estimate solute concentrations in the "mixing zone". It was found that the 15% soil moisture content treatment had a longer time to the beginning of drainage and less drainage volume compared to 10% soil moisture. Greater compaction caused lower concentrations and losses of NO3-N in subsurface drainage. A second experiment was outdoor rainfall simulation (5 cm/h for 60 min to lysimeters), using two tillage practices (no-till and tillage) and two methods of N-fertilizer applications (local soil compaction and no compaction as a line source). The results showed that local compaction in the zone of application reduced NO3-N leaching significantly; however, tillage did not have a significant effect. In both studies, soil ECb and volumetric water content, measured by TDR, beneath the fertilizer line sources provided "real-time" information; it was found that NO3-N in top soil has a curvilinear relationship to ECb beneath line sources that had the potential to simultaneously indicate solute leaching and water infiltration/movement in that zone. This study could provide new information for improving N fertilizer applicators.