Distribution and Plant Availability of Soil Zinc Fractions

Abstract

This laboratory and greenhouse investigation was under‐taken to study the distribution and plant availability of zinc in different soil fractions. Total Zn (TZn) in 19 soils, which varied widely in chemical and physical properties, was fractionated into water‐soluble plus exchangeable (CA‐Zn), specifically adsorbed (AC‐Zn), organically bound (PYRO‐Zn), Mn‐oxide bound (HAH‐Zn), Al‐ and Fe‐oxide bound (AMOX‐Zn), and residual (RES‐Zn) forms. There was a wide variation in the magnitude of these fractions among soils. Most of the TZn, on an average, was present in the AMOX‐Zn (∼25%) and RES‐Zn (∼70%) fractions. The CA‐Zn, AC‐Zn, PYRO‐Zn, and HAH‐Zn fractions averaged 0.4, 3.3, 2.5, and 2.0% of the TZn, respectively. The CA‐Zn in the 19 soils increased with a decrease in soil pH, whereas the AC‐Zn increased with an increase in soil pH. The PYRO‐Zn in the soils varied directly with organic C and soil pH, HAH‐Zn increased with an increase in both soil pH and free Mn, AMOX‐Zn correlated more closely with free Al than with free Fe, and RES‐Zn varied positively with soil clay. A seven‐variable regression model, which included the six Zn fractions and soil pH, accounted for 94% of the variability in Zn uptake by corn plants (Zea mays L.) from these soils. This model separated soils that supplied inadequate amounts of Zn from those that supplied adequate amounts.