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Quantity‐Intensity Relationships of Soil Ammonia in Long‐Term Rotation Plots
Author(s) -
Thompson T. L.,
Blackmer A. M.
Publication year - 1992
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/sssaj1992.03615995005600020025x
Subject(s) - loam , soil water , chemistry , fertilizer , crop rotation , ammonia , cation exchange capacity , potassium , environmental chemistry , soil science , agronomy , crop , environmental science , biology , biochemistry , organic chemistry
Reports of release of nonexchangeable NH + 4 from soils under some conditions and reports that management practices can change the affinity of the exchange complex for NH + 4 indicate a need to reevaluate the commonly accepted practice of determining exchangeable NH + 4 to assess the availability of NH + 4 to plants. To address this need, quantity‐intensity (Q/I) relationships were studied in soil samples from two Iowa soils, a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) and a Galva silty clay loam (fine‐silty, mixed, mesic Typic Hapludoll) in long‐term experiments having various crop‐rotation and N‐fertilizer treatments. The observed Q/I relationships gave no evidence for release of nonexchangeable NH + 4 . Potassium‐exchangeable NH + 4 concentrations were well correlated with measurements of labile NH + 4 ( r = 0.91, P < 0.01) and equilibrium activity ratios for NH + 4 ( r = 0.89, P < 0.01). No significant relationship was found between relative affinity of the exchange complex for NH + 4 and organic C within each soil. Soil management practices influenced NH + 4 availability as evaluated by KCl‐exchangeable NH + 4 and Q/I parameters, but did not change the relative affinity of the exchange complex for NH + 4 . Overall, indexes of NH + 4 availability based on determinations of K‐exchangeable NH + 4 were similar to those derived from studies of Q/I relationships.