Quantifying Clay-Fixed Ammonium in Paddy Soils and Determining Its Availability Using Alkaline Distillation

Core Ideas Alkaline hydrolyzable nitrogen recovery is influenced by soil drying. N‐STaR soil test quantifies a portion of clay‐fixed ammonium. NaOH recovered more clay‐fixed ammonium than KOH. The Nitrogen Soil Test for Rice (N‐STaR, Oryza sativa L.) has been calibrated and is being used to predict rice nitrogen (N) fertilizer rates. Research has identified the organic forms of N quantified via N‐STaR (NH 4 released by distillation with 10 mol L...