Placement of ion-exchange membranes for monitoring nutrient release from flooded soils

Placement of Plant Root Simulator (PRS®) probes (ion-exchange membranes in a plastic support) may strongly influence nutrient supply measurements and their relationship to nutrient loss to overlying water due to gradients in ion activity and redox potential with depth. A laboratory study was conducted with two soils contrasting in potential nutrient loss (manured vs. unamended control) to determine the impact of probe placement (vertical, horizontal, and flat on the soil surface) on nutrient supply rate. The supply rates of the redox-sensitive nutrients Mn and Fe were generally 1–2 orders of magnitude lower for PRS probes placed on the soil surface than buried vertically. In contrast, the supply rate of P and K varied by 1–2 orders of magnitude between soils, but placement impacts were modest or absent. The ratio between manured and control soils in water P concentration was identical to that of soil P supply rate determined with PRS probes placed flat on the soil surface. All placements were effective in demonstrating the increased potential for loss of P and K from the manured soil, but only measurements from PRS probes placed on the soil surface were closely related to loss of the redox-sensitive nutrients Mn and Fe.

An assessment of nutrient dynamics in streambank soils of the Lower Little Bow River in southern Alberta using ion exchange membranes

Nutrient dynamics in streambanks may impact nutrient movement to water, and may be influenced by cattle activity, river water level fluctuations, and time. Our objective was to determine the influence of these factors on nutrient (NO3-N, P, S, Fe, Mn, Cu, Zn, Ca, Mg) dynamics in streambanks along the Lower Little Bow River in southern Alberta using Plant Root Simulator or PRS® probes. Three experiments were conducted from 2012 to 2015. In the first experiment, few significant (P ≤ 0.05) effects were found among three reaches varying in cattle impact except for Fe and Mn, which generally increased with increasing cattle impact. In the second experiment (probe placement), adsorption of P, Fe, Mn, S, Ca, and Mg was significantly greater for submerged than exposed streambanks, and the opposite trend occurred for Cu and Zn. In the third experiment on the influence of probe burial periods from 0.2 to 14 days, maximum nutrient adsorption generally occurred within 1 to 7 days, and S adsorption showed an exponential increase with time. Overall, few cattle impact effects were found on nutrient dynamics, certain nutrients were greater in submerged than exposed banks, and 7-day burial of PRS probes was sufficient to assess nutrient dynamics.