Effects of sorbed orthophosphate on zinc status in three soils of eastern Canada

Abstract

SUMMARYP‐Zn interactions can affect fertilizer use and produce Zn deficiencies with certain crops. Phosphorus‐Zn sorption‐desorption reactions were studied in topsoil and subsoil samples from three Quebec soils. Soils were equilibrated with P solutions, then with Zn solutions, and finally with solutions containing no P or Zn. The first equilibration evaluated P sorption (Ps), the second evaluated Zn sorption (Zns) after P sorption (Ps), and the third evaluated Zn desorption (ZnD) as related to added P. Subsequently, Zn fractions were extracted sequentially with KNO3 (Znkno3), NaOH (ZnNaOH) solutions and concentrated HN03+ H202(ZnHNO,).One mmole sorbed P resulted in increases of 0.5 to 1.0 meq (mean = 0.72) increases in cation exchange capacity (CEC). Increased Zns with added P was equivalent to 4 to 5% of the increase in CEC induced by Ps in the Uplands (sand) and St. Bernard (loam) soils, and 0.4 to 0.9% in the Dalhousie (clay) soils, while one meq increase in CEC resulted in 1.5‐3.5% decrease in ZnD. There existed positive correlations between Ps and extractable soil Fe materials. Phosphate sorption enhanced associations between Zns, ZnD or Zn fractions and soil organic or crystalline Fe contents, confirming that P addition increased specific sorption of Zn on Fe components. Other mechanisms including precipitation, P‐induced negative charge and ‘bridge’ effects are also discussed.