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Zusammenfassung:
Phosphate release kinetics in soils are of global interest because sustainable
plant nutrition with phosphate will be a major concern in the future.
Dissolution of phosphate-containing minerals induced by a changing rhizosphere
equilibrium through proton input is one important mechanism that
releases phosphate into bioavailable forms. Our objectives were (i) to determine
phosphate release kinetics during H+ addition in calcareous soils of the
Schwäbische Alb, Germany, and to assess the influence of (ii) land-use type
(grassland vs. forest) and (iii) management intensity on reactive phosphate
pools and phosphate release rate constants during H+ addition. Phosphate
release kinetics were characterized by a large fast-reacting phosphatepool,
which could be attributed to poorly-crystalline calcium phosphates, and a
small slow-reacting phosphate pool probably originating from carbonate-bearing
hydroxylapatite. Both reactive phosphate pools—as well as total phosphate
concentrations (TP) in soil—were greater in grassland than in forest soils. In
organically fertilized grassland soils, concentrations of released phosphate
were higher than in unfertilized soils, likely because organic fertilizers contain
poorly-crystalline phosphate compounds which are further converted into sparingly
soluble phosphate forms. Because of an enriched slow-reacting phosphate
pool, mown pastures were characterized by a more continuous slow phosphate
release reaction in contrast to clear biphasic phosphate release patterns in
meadows. Consequently, managing phosphate release kinetics via management
measures is a valuable tool to evaluate longer-term P availability in soil in the
context of finite rock phosphate reserves on earth.
