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.