PRS™-Probes Functionally Measure the Soil Supply Rate of N and P In Cranberry Bogs.

Ammonium and phosphate are important nutrients for cranberry production; however, NH₄⁺ can be difficult to monitor in these systems due to fluctuating water table levels.  Low soil pH and high Fe oxides in the soil limit the availability of P and make the results of Bray-1 P soil tests difficult to interpret. The objective of the study was to use cation and anion exchange membranes, called PRS™-probes, to monitor soil nutrient supply rates throughout the growing season in cranberry. Controlled release fertilizer (Osmocote™, Scotts Company, Marysville, OH) was applied after budbreak at rates of 0, 112, 224, or 336 kg/ha. In-season soluble granular fertilizer was also applied to all plots as per normal growing practices. To measure the soil nutrient supply rates of N and P, PRS™-probes were buried in soil and exchanged every two weeks throughout the growing season. At the end of the growing season, the soil nutrient supply, measured using the PRS™-probes, was summed to represent the cumulative soil nutrient supply rate for the season. The biweekly NH₄⁺-N supply rate as measured by PRS™-probes  was positively correlated with the controlled-release fertilizer treatment, and cumulative NH₄⁺-N supply rate was positively correlated with cranberry leaf tissue NH₄⁺-N. Although the cumulative P supply rate was positively correlated with the controlled-release fertilizer treatment it was not correlated with the cranberry leaf tissue P.  In the low pH, high Fe soil, P availability was enhanced by controlled-release fertilizer. The PRS™-probes are a functional tool for measuring the supply rate of soil NH₄⁺-N and P in cranberry bogs.