A Laboratory Exercise to Demonstrate Nitrogen Mineralization and Immobilization

Nitrogen mineralization and immobilization are important components of the IV cycle. A simple laboratory exercise was developed to illustrate the importance of the N content of crop residues on the level of nitrate–N in the soil. An Embden fine sandy loam (Pachic Udic Haploborolls) was treated with 50 mg nitrate–N kg–1 and incubated for 2, 4, and 6 wk with 10 g kg–1 of crop residues differing in N content from 8 to 41 g N kg–1. The students were required to prepare the experiment and analyze the soils for nitrate content. The students were also required to analyze the data graphically to determine the critical level of N in the plant material, below which net immobilization occurred and above which net mineralization occurred. These critical levels were found to be 24, 22, and 20 g N kg–1 for the 2‐, 4‐, and 6‐wk incubaton periods, respectively. The experiment was easily conducted and strengthened the students' understanding of the concepts of N mineralization and immobilization.