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

Quantification of the processes of gross mineralization and immobiliza tion 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 domesti c waste of different ages (C1 and C3), residual waste from a treatment plant (B) and farmyard manure (F) as a control). This study was carri ed 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 a nd immobilization processes depended on the nature of the organic amen dments, their degree of stability and their nitrogen content. N minera lization 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 + li gnin)/N ratios (ADF/N) (r = 0.869). The immobilization of N was correl ated to (cellulose + lignin) contents (ADF) (r = 0.607). The amount of mineralized N (mg kg(-1)) during this month was in the following decr easing 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 f avored 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 denitrifica tion or volatilization.