Validation of a Simple, Inexpensive Ion Exchange Resin Technique to Monitor Soil Nitrate and Ammonium.

Because of the dynamic nature of nutrients in soil, especially nitrogen (N), it is desirable to have tests that integrate monitoring of nutrient status through the crop cycle.  Various ion exchange resins have been used for this purpose in the past, but most require construction of specialized containers, excavation for placement, or both.  We compared accuracy and exchange capacity of a sheet-based resin material attached to a wooden plot marker with standard colorimetic measures from bulk soil treatments.  Individual sheets, 2.5 cm by 15 cm were individually attached to a wooden garden marker and inserted to a depth of 15 cm into pots that had previously received N and phosphorus (P) fertilizer at rates necessary to achieve the equivalent of 40, 80, 120, and 160 kg N and P2O5 ha^-1.  Resin sheets were all installed at the initiation of the trial in one of two soils, a sandy loam or a silt loam, with one pair of anion/cation sheets removed at 7, 14, and 21 and 28 days after initiation.  We expect that the resin adsorption of ions will be highly correlated with bulk soil test estimates of nutrient availability and that this sampling process will allow accurate assessment of nutrient availability over time