QUANTIFICATION OF NITROGEN MINERALIZATION AND IMMOBILIZATION IN SOIL IN THE PRESENCE OF ORGANIC AMENDMENTS

Quantification of the processes of gross mineralization and immobilization is very important to make full nitrogen balances. These processes were quantified in a clay loam soil (S) after application of nitrogen K (NO3)-N-15 (N) and four organic amendments (two composts of domestic waste of different ages (C1 and C3), residual waste from a treatment plant (B) and farmyard manure (F) as a control). This study was carried out during a 1-2 mo incubation at a temperature of 25 degrees C and a moisture content of 2/3 of the field capacity. The mineralization and immobilization processes depended on the nature of the organic amendments, their degree of stability and their nitrogen content. N mineralization was correlated with C/N ratios (r = 0.936), N contents (r = 0.880), hemicellulose contents (NDF - ADF) (r = 0.869), (hemicellulose + cellulose + lignin)/N ratios (NDF/N) (r = 0.886) and (cellulose + lignin)/N ratios (ADF/N) (r = 0.869). The immobilization of N was correlated to (cellulose + lignin) contents (ADF) (r = 0.607). The amount of mineralized N (mg kg(-1)) during this month was in the following decreasing order: S + N + B (94.3) > S + N + F (14.3) > S + N + C3 (4.92) > S + N (-0.31) > S + N + C1 (-20.1). Organic amendments application favored the process of N immobilization which decreased with the degree of stability of organic materials. The amount of N immobilization (mg kg(-1)) was in the following decreasing order: S + N + B (53.3), S + N + C1 (49.1), S + N + F (36.72), S C N + C3 (35.6) and S + N (29.1). The loss of nitrogen (between 2 and 20%) was attributed to denitrification or volatilization.