224
Isabel Serrasolses, Victoria Diego and David Bonilla
N in the soil profIle was studied, particularly the total and mineral N, and the
major soil N fluxes such as net mineralization, nitrification and leaching
losses.
16.2 Total Nitrogen and C:N Ratio in the Soil Profile
Nitrogen concentration in holm oak leaf litterfall averaged 0.97% in Prades
(V. Diego, unpubl. data) and 0.94% in Montseny (Mayor and Roda 1992),
giving a C:N ratio of 53. This high C:N ratio decreases rapidly in the forest
floor through N immobilization in the Land F horizons. The F layer is the
richest horizon in N: 1.66-1.91% N in Prades and 1.56% in Montseny
(Fig. 16.1). In a litterbag decomposition study at Prades, 2.2 kg N ha- 1 year- 1
was immobilized during the initial phases of leaf litter decay when the C:N
was higher than 35 (Serrasolsas 1994). After this period of N immobilization
in the Land F horizons, the litter is no longer N-limited for microbes and net
N mineralization begins. Both organic carbon and N decrease at the same
2.5 T""ir==:::====,---------~
o Prades
•
Montseny
F layer
2.0
H layer
1.5
1.0
Leaf liuerfaJl Ii
0.5
0.0 - 1 - - - , - - - - , - - - - . , - - - - , - - - , - - - - 1
o
10
20
30
40
50
60
% C
Fig. 16.1. Relationship between organic carbon (% C) and total nitrogen (% N) in leaf litterfall,
forest floor and mineral soil at Prades and Montseny. (Data from Hereter 1990, 1992; Serrasolsas
1994)