EFFECT OF IMMOBILIZATION ON NITROGEN TRANSFORMATIONS AND TRANSPORT IN A FIELD 15N EXPERIMENT

Abstract

A microplot trial conducted between 31 May 1977 and 11 May 1978 containing straw alone and with ¹⁵NH₄⁺, glucose alone, with ¹⁵NH₄⁺ or with ¹⁵NO₃⁻, ¹⁵NH₄⁺ alone, and control treatments examined the interplay of N processes, particularly immobilization and clay fixation of ¹⁵NH₄⁺ under field conditions. The dynamics of the changes were examined by sampling the soil profiles 4 Oct. 1977 and 11 May 1978. In October 1977, total ¹⁵N recovery to 75 cm (avg 84%) was not affected by the treatments, but the distribution of inorganic ¹⁵N was affected by the treatments. The ¹⁵NH₄⁺-only treatment showed greater leaching than organic + ¹⁵N treatments. By May 1978, the organic + ¹⁵N amended treatments retained more ¹⁵N than the ¹⁵NH₄⁺-only treatment and the difference was attributed to less leaching in the organic amended treatments. All apparent immobilization and clay fixation of ¹⁵N occurred between May 1977 and October 1977. The type of organic amendment influenced the amount of immobilization and clay fixation of ¹⁵N. Addition of straw resulted in greater fixation of ¹⁵NH₄⁺ than in a treatment with ¹⁵NH₄⁺ only. There was more immobilization with glucose than with straw. Glucose amendment reduced the fixation of ¹⁵NH₄⁺ showing that immobilization can effectively compete against fixation for ¹⁵NH₄⁺ if adequate available carbon is present. The results showed that the type of amendment (straw vs. glucose or NH₄⁺ vs. NO₃⁻¹) added to a soil influences immobilization and clay fixation processes and thus changes the retention of N against leaching and denitrification.