Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi, 1100l2.
* Present address: Depanment of Agricultural Chemistry and Soil Science, Gujarat Agricultural University, Sardar Krushinagar, Gujarat, 585506.
Microbial immobilization of nitrogen was determined after the application of 15N labelled urea15N @ 100 and 200 mg N kg−1 in three different soils mixed with wheat straw15N @ 10 g kg−1 soil. Maximum immobilization 15N (95 per cent) of fertilizer N was found after 15N 7 days of incubation (DOI) but net immobilization remained 15N 89 per cent even after 60 DOI. Application of urea15N @ 200 mg N kg−1 maintained much higher level of 2M KCl extractable inorganic N in soil than that observed at 100 mg N kg−1 level. Remineralization of immobilized fertilizer N in sandy loam soil was higher than those in clay loam or silt loam soils. The share of soil N in the inorganic N pool was much higher in comparison to that of fertilizer N. This is attributed to turnover effect leading to loss of tagged N by immobilization and gain of nontagged N by mineralization.
Microbial immobilization, mineralization, 15N, straw
