Phosphorus is usually the primary limitation to algal growth in fresh water bodies. Phosphorus is routinely applied to cranberry beds and cranberry production is intimately linked to surface waters. Our objective is to minimize phosphorus movement from cranberry beds to adjacent surface waters. As part of a project studying phosphorus dynamics in cranberry systems, we examined the suitability of anion exchange membranes (AEM) for estimating plant available phosphorus in cranberry soils. A time course in sand and peat soils showed a biphasic response with exchangeable phosphorus dropping by half after 7 days compared to initial values. Soil pH had no effect except in relation to soil solution aluminum and iron ions as a function of pH. AEM showed a linear response to phosphorus concentration. In 2004 we placed AEM in plots in a commercial cranberry bed fertilized with 0 to 33.7 kg P per hectare at weekly intervals. Exchangeable phosphorus was always proportional to rate of fertilizer. The week following fertilizer application exchangeable phosphorus tripled, but was back to ambient levels by 2 weeks. AEM appear to reflect plant available phosphorus in cranberry soils and may prove a suitable replacement for chemical soil testing.