Nitrogen Fertilization Effects on Grassland Soil Acidification: Consequences on Diffusive Phosphorus Ions
- Ciprian Stroiaa,
- Christian Morelb and
- Claire Jouany *c
- a Faculty of Agriculture, Banat Univ. of Agricultural Sciences and, Veterinary Medicine, Calea Aradului 119, 300645 Timisoara, Romania
b INRA Transfert Sol-Plante et Cycle des Éléments Minéraux dans les Écosystèmes Cultivés, 71 Ave. Edouard Bourlaux, 33883 Villenave d'Ornon, France
c INRA UMR Agrosystèmes et Développement Territorial, BP 52627, 31326 Castanet–Tolosan, France
Soil acidification due to N supplied from fertilizer or aerial deposition in grasslands is well recognized and documented; however, little is known about its consequences on soil P availability. This question was addressed on a long-term field experiment done on grassland in Ercé (Central Pyrenees, France), where plots were treated for 6 yr with a factorial combination of mineral N added as NH4NO3 (0 and 190 kg ha−1 yr−1) and P (0 and 50 kg ha−1 yr−1) and managed with a frequent defoliation regime (3 cuts yr−1). Diffusive PO4 ion dynamics at the soil–solution interface was determined by coupling sorption studies with 32P labeling of PO4 ions (Pi) and dilution analysis. Results showed that the soil pH did not change in zero-N treatments (5.9 ± 0.1) in comparison with the initial soil (5.9 ± 0.1), whereas it decreased to 5.3 ± 0.1 on N-treated soils. Meanwhile the cation exchange capacity and exchangeable Ca2+ and Mg2+ contents decreased significantly and the saturation percentage of the adsorption complex by Al3+ increased from 2 to 15; no changes were observed for untreated soils. Furthermore, the gross amount of diffusive Pi (Pr) was accurately described as a function of the concentration of PO4 ions in the solution (Cp) and time (t) by a Freundlich kinetic equation; these dynamics were significantly modified by N supply but not by P.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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