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 proced ure may provide a more precise evaluation of N availability to forages than standard methods. The main objective of this study was to evaluate the pot ential of AEMs to predict soil NO3-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 con sisted of five NH4NO3 rates (0, 60, 120, 180, and 240 kg N ha(-1)). At all sites, NO3- sorbed on the AEMs (NO3AEMs) increased with increasing N fertil izer rates. The NO3AEMs fluxes were significantly related to water soluble NO3-N (NO3w) concentration in soil (R-2 varied from 0.35 to 0.98) in the tw o growing seasons. Forage N uptake was better related with NO3AEMs fluxes ( R-2 = 0.88 and 0.92 in spring 1996 and 1995, respectively) than with NO3w c oncentration (R-2 = 0.39 and 0.97 in spring 1996 and 1995, respectively). B ased on their simplicity, rapidity, and low cost, AEMs have many practical advantages over water NO3-N extraction for assessing grass forage soil N av ailability in cool continental climates.