Soil Clay Mineralogies in Relation to Fertility Management: Effect of Clay Mineral Types on Ammonium Fixation under Conditions of Wetland Rice Culture1

To assess the influence of soil clay mineralogy on the efficiency of normally used nitrogeneous fertilizers on soils under wetland rice (Oryza sativa L.) culture, ammonium fixation studies were carried out under hydromorphic conditions on 14 soil clays with a range of mineralogical compositions. Beidellitic and vermiculitic clays fixed more than 90% of the applied ammonium, while montmorillonitic clay fixed about 50%. Clays of all other mineralogical compositions, containing chlorite, hydrous mica, halloysite, kaolinite, and amorphous material did not fix significant amounts of ammonium. There is a need to develop management practices for soils of beidellitic and vermiculitic clay mineralogies to increase efficiency of ammonium (or ammonium‐forming) fertilizers on them through minimizing fixation.