RELATING LOSS OF SOIL FERTILITY TO WATER AGGREGATE STABILITY AND NUTRIENT AVAILABILITY IN MOUNTAIN AGRICULTURAL CALCARIC SOILS

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.