Dynamics of zinc fractions in the soil plant system under conditions of intensive forage cropping

Abstract

A pot experiment was carried out to study intensive cropping of alfalfa in two calcareous soils from southern Spain. The overall evolution of plant Zn content in the two soils showed no clear‐cut trends throughout the ten harvest studied. Zn levels ranged from 15.65 to 32.56 ppm, which although adequate from the standpoint of plant nutrition, was insufficient to meet the nutritional requirements of ruminants.

Initial values of exchangeable Zn were low in both soils but rose steadily under the influence of sucessive cropping. Cultivation also led to significant short and medium term increases in Zn associated with the organic matter fraction, while in contrast showing a general tendency to reduce Zn associated with Fe oxides. In overall terms Zn content in the sand, silt, and clay fractions tended to fall as a result of alfalfa cropping.