RELATING LOSS OF SOIL FERTILITY TO WATER AGGREGATE STABILITY AND NUTRIENT AVAILABILITY IN MOUNTAIN AGRICULTURAL CALCARIC SOILS | RELATON ENTRE PERTE DE FERTILITÉ, STABILITÉ DANS L'EAU DES AGREGATS ET DISPONIBILITÉ DES ELEMENTS NUTRITIFS DES SOLS CALCAIRES MONTAGNEUX À USAGE AGRICOLE | RELAZIONE TRA PERDITA DI FERTILITÀ, STABILITÀ IN ACQUA DEGLI AGGREGATI E DISPONIBILITÀ DEGLI ELEMENTI IN SUOLI CALCAREI MONTANI AD USO AGRICOLO

English. We investigated the topsoil from some mountain Regosols for their nutrient status and loss of fertility due to aggregate breakdown, establishing also the relationship between the nutrient losses, the soil characteristics and the aggregates stability. The aggregate stability varied from 57 to 80%. The nutrient losses differed among elements and varied from 20 to 96%. The availability of nutrients directly influenced the quality of nutrient losses, but did not influence the quantity of nutrients lost. K, Mg and Ca were the most susceptible element to the water abrasion (>85% of their total loss was due to water abrasion). Instead for C, N, and partly P, important loss occurred because of the water saturation alone and their losses were related to the aggregates ruptures due to fast wetting (r=0.98, 0.99 and 0.81, respectively). These findings suggest a high vulnerability to soil fertility losses, and that a great depletion can occur even because of rainfall of low intensity, but sufficient to water saturated the topsoil.We investigated the topsoil from some mountain Regosols for their nutrient status and loss of fertility due to aggregate breakdown, establishing also the relationship between the nutrient losses, the soil characteristics and the aggregates stability. The aggregate stability varied from 57 to 80%. The nutrient losses differed among elements and varied from 20 to 96%. The availability of nutrients directly influenced the quality of nutrient losses, but did not influence the quantity of nutrients lost. K, Mg and Ca were the most susceptible element to the water abrasion (>85% of their total loss was due to water abrasion). Instead for C, N, and partly P, important loss occurred because of the water saturation alone and their losses were related to the aggregates ruptures due to fast wetting (r=0.98, 0.99 and 0.81, respectively). These findings suggest a high vulnerability to soil fertility losses, and that a great depletion can occur even because of rainfall of low intensity, but sufficient to water saturated the topsoil.

French. Les horizons superficiels des Regosols provenant d'une zone montagneuse ont étés analysés pour d'une part  déterminer leur statut nutritif et leur perte de fertilité du à la rupture des agrégats, et d'autre part établir les relations entre la perte des éléments nutritifs, les caracteristiques du sol et la stabilité des agrégats. La stabilité des agrégats varie de 57 à 80%. La perte des éléments nutritifs  est différent selon les éléments et varie de 20 à 96%. La disponibilité des éléments nutritifs influence directement la qualité des pertes, mais n'influence pas la quantité des éléments perdus. K, Mg et Ca sont les éléments les plus susceptibles à l'abrasion de l'eau (>85% des pertes totales sont dues à l'abrasion de l'eau). Au contraire, pour C, N, et en partie P, d'importantes pertes ont été déjà atteintes pendant la seule phase de saturation des agrégats à l'eau, et leurs pertes sont corrélées  à la rupture des agrégats pendant le fast wetting (r=0.98, 0.99 et 0.81, respectivement). Ces données montrent un'élevé vulnérabilité de ces sols à la perte de fertilité et indiquent qu'une importante perte d'éléments nutritifs pourrait intervenir aussi en cas de pluie faible mais dont la quantité d'eau tombée suffirait à saturer l'horizon superficiel.

Italian. In questo studio, i topsoil di alcuni Regosols di un'area montana sono stati investigati per il loro status nutritivo e le perdite di fertilità dovute alla rottura degli aggregati, e le relazioni tra perdita di nutrienti, caratteristiche del suolo e stabilità degli aggregati sono state definite. La stabilità degli aggregati varia da 57 a 80%. La perdita di nutrienti differisce tra gli elementi e varia da 20 a 96. La disponibilità di elementi influenza direttamente la qualità della perdita di elementi nutritivi, ma non la loro quantità. K, Mg e Ca sono i più vulnerabili all'azione abrasiva dell'acqua (>85% della loro perdita totale è dovuta all'abrasione). Invece, per  C, N, e parzialmente P, importanti perdite si verificano già a causa della saturazione in acqua degli aggregati e la loro perdita è correlata alla rottura degli aggregati dovuta al fast wetting (r=0.98, 0.99 e 0.81, rispettivamente). Questi risultati suggeriscono un'elevata vulnerabilità di questi suoli nei confronti della perdita di fertilità, e che un grande impoverimento può verificarsi anche a causa di piogge con bassa intensità, ma sufficienti a saturare il topsoil.