Co

Passive soil C (1GGG yr)

L/N = Lignin to nitrogen ratio A = Lignin fraction

Source

Plant residue

Plant residue atmosphere fixation deposition

Sink leaching gaseous erosion crop

Sink leaching gaseous erosion crop

I = Immobilization M = Mineralization

Active soil P

Sources

fertilizer deposition

Labile P

fertilizer deposition

Labile P

Sink leaching erosion crop

Secondary P (M)

Primary P

mainly apatite

Passive soil P

Occluded P i_i

FIGURE 8.3. Flow diagram for the (a) carbon submodel, (b) nitrogen submodel, and (c) phosphorus submodel of Century (adapted from Parton et al., 1987, 1989b) (from Stewart etal., 1990).

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