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Assessing nitrogen mineralization from soil organic matter using anion exchange membranes

Qian, P. and J.J. Schoenau. 1995. Fert. Res. 40:143-148


A simple method to assess differences in potential contribution of organic nitrogen mineralization to plant available N among soils may be useful in fertility research as well as routine soil testing. We deployed a method to assess mineralizable soil organic N using anion exchange membrane (AEM) burial. The method is based on a simple closed incubation system in which strips of AEM are buried directly in soil to adsorb NO3- released from organic matter. An index of mineralization was obtained using the amount of NO3- adsorbed on an AEM strip removed at the end of each incubation. The same incubation system but using 0.001 M CaCl2 solution to extract NO3- N was used as the reference method. The mineralization indices obtained from both methods were compared with each other and with plant uptake. A total of 74 soils from across Saskatchewan were used in the study to provide a range of soil properties. Correlations between test values and N uptake by plants in two separate experiments showed the 2 week AEM incubation to be more closely correlated with plant N uptake (r2 = 0.86**** and 0.57****, respectively) than the reference method (r2 = 0.60**** and 0.48****, respectively). With this method, we were able to determine the influence of different tillage systems and landscape positions on mineralizable N. The results showed that the NO3- released from soil organic matter and accumulated on the AEM reflected the expected effect of three different tillage systems and two landscape positions on mineralizable N. Cropping systems with continuous alfalfa (Medicago sativa) showed higher N release from soil organic matter than a canola (Brassica napus)-lentil (Lens culinaris)-barley (Hordeum vulgare) rotation did. Higher N mineralization was found in the lower slope positions of the landscape where organic matter contents are highest. Direct burial of AEM appears to be a simple and effective method of including a measure of N mineralization in a soil test.

Key Words

anion exchange membrane, incubation, N mineralization, organic matter, slope, tillage