Field evaluation of anion exchange membranes as a N soil testing method for grasslands

The in situ use of anion exchange membranes (AEMs) as a soil-testing procedure may provide a more precise evaluation of N availability to forages than standard methods. The main objective of this study was to evaluate the potential of AEMs to predict soil NO 3 –N availability for forage production in the western part of the province of Quebec, Canada. In 1995 and 1996, AEMs were buried (0–15 cm) in soils at four sites. The fertilizer treatments consisted of five NH 4 NO 3 rates (0, 60, 120, 180, and 240 kg N ha –1 ). At all sites, NO 3 − sorbed on the AEMs (NO 3AEMs ) increased with increasing N fertilizer rates. The NO 3AEMs fluxes were significantly related to water soluble NO 3 –N (NO 3w ) concentration in soil (R 2 varied from 0.35 to 0.98) in the two growing seasons. Forage N uptake was better related with NO 3AEMs fluxes (R 2 = 0.88 and 0.92 in spring 1996 and 1995, respectively) than with NO 3w concentration (R 2 = 0.39 and 0.97 in spring 1996 and 1995, respectively). Based on their simplicity, rapidity, and low cost, AEMs have many practical advantages over water NO 3 –N extraction for assessing grass forage soil N availability in cool continental climates.