Nitrogen availability for flooded rice by the direct steam distillation method

Abstract

The objective of this work was to evaluate the ability of the direct steam distillation (DSD) method to extract alkaline hydrolyzable nitrogen fraction in the soil and to predict N availability in rice paddies. Twenty‑five soil samples were collected at the 0–20-cm soil depth, with contrasting texture and contents of soil organic matter. The mineralization of N by anaerobic incubation was determined in a laboratory, and leaf‑N content and N accumulation by rice plants were obtained in a greenhouse by simulating flooding conditions in pots. These variables correlated with N extracted by the DSD method. Soil‑N contents obtained with the method, as well as available N after 28‑day anaerobic incubation and N accumulated by rice plants after 45 days, showed high values. The evaluation of a more labile N fraction by the DSD method improves the estimation of N availability, in comparison to methods that only assess soil organic matter contents, which indicates that the DSD method has potential for evaluating N availability in rice paddies