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Quantifying Clay‐Fixed Ammonium in Paddy Soils and Determining Its Availability Using Alkaline Distillation
Author(s) -
Drescher Gerson L.,
Roberts Trenton L.,
Norman Richard J.,
Slaton Nathan A.,
Silva Leandro S.
Publication year - 2019
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2018.11.0436
Subject(s) - loam , chemistry , soil water , ammonium , silt , alkali soil , nitrogen , fertilizer , soil test , agronomy , environmental chemistry , soil science , environmental science , geology , organic chemistry , paleontology , biology
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 –1 NaOH), but no research has looked at the ability of N‐STaR to quantify clay‐fixed NH 4 (CF‐NH 4 ). This laboratory trial was initiated to determine the amount of CF‐NH 4 quantified via N‐STaR as well as the influence of soil drying conditions (oven dry vs. field moist) and alkali distillation method (NaOH vs. KOH) on the CF‐NH 4 recovered. Seven soils representing five clayey and two loamy soil textures were collected from various rice‐producing regions across Arkansas from the 0‐ to 15‐cm and 15‐ to 30‐cm soil depths. Total CF‐NH 4 and CF‐NH 4 recovered by N‐STaR varied greatly across soils and soil depths with a range of 35 to 299 mg N kg soil –1 and 6 to 21 mg N kg soil –1 , respectively. The N‐STaR recovered as much as 15% of total CF‐NH 4 and recovery was greatest for silt loam soils. Alkaline hydrolyzable‐N (AH‐N) concentrations were strongly influenced by soil drying conditions and the alkali used with a higher level (22%) of AH‐N recovered from oven‐dry than field‐moist soils and a higher (7%) recovery of AH‐N with NaOH than KOH. These results indicate that the N‐STaR method recovers a small, but significant percentage of total CF‐NH 4 and may capture the portion of CF‐NH 4 that may be plant available during the growing season.