A stable-isotope methodology for measurement of soil-applied zinc-fertilizer recovery in durum wheat (Triticum durum)

Abstract

A growth‐chamber study was used to develop a zinc stable‐isotope (⁶⁷Zn) tracing technique to directly measure the amount of soil‐applied zinc (Zn) granular fertilizer taken up by durum wheat (Triticum durum L.) in four different soil types. The ⁶⁷Zn‐tracer technique was then applied under field conditions at one site to test the ability of the method to measure the crop recovery of soil‐applied Zn granular fertilizer (⁶⁷Zn). The technique was developed by comparing plants treated with nil Zn fertilizer to natural‐abundance‐Zn‐coated fertilizer and ⁶⁷Zn‐coated fertilizer with plant parts analyzed for Zn isotopic composition using inductively coupled plasma–mass spectrometry. Zinc‐fertilizer recovery under growth‐chamber conditions was inversely related to the concentration of labile Zn in soils, with the plants on the most Zn‐deficient soils having the greatest amount of Zn derived from the added fertilizer. Zinc derived from fertilizer ranged from 0.3% (Luvisol) to 0.6% (Solonetz) to 13% (Calcisol) and 18% (Lixisol) for soils with DTPA‐extractable Zn of 3.5–0.21 mg kg–¹. Across the experiments, fertilizer recovery was measurable but very low (< 1% of added fertilizer being recovered by durum wheat). The recovery of Zn added to the Luvisol was slightly higher in the field than in the glasshouse (but all < 0.1%). Using this stable‐isotope technique, it was possible to directly assess the supply of soil‐applied Zn fertilizers to crop plants.