Effect of Phosphorus and Zinc Fertilization on the Solubility of Zn²⁺ in Two Alkaline Soils

Abstract

Concentrations of Zn2+ in equilibrium with two alkaline soils were calculated from the reactions of EDTA (ethylenediaminetetraacetic acid) chelates. The initial speciation of EDTA was varied to allow equilibrium with Zn2+ concentrations in the soil to be approached from above and below. Fertilizer Zn was added at 0 to 5 mg kg−1 as ZnSO4 and reacted thoroughly with the soil before additions of P or EDTA chelates. Phosphorus was added at 0 or 62 mg kg−1 as a mixture of KH2PO4 and K2HPO4. Concentrations of soluble Zn2+ in unfertilized soil were extremely low, approximately 5 × 10−10 M in the noncalcareous soil at pH 7.2 and 1 × 10−10 M in the calcareous soil at pH 7.6. These Zn2+ concentrations were raised 7‐ to 14‐fold by 5 mg kg−1 of added Zn, and the higher levels persisted for at least 11 weeks. Buffering of Zn2+ by the soils was substantial, ranging from about 15 to 45 (nmol g−1)/(nmol L−1). Additions of P caused small decreases in the concentrations of Zn2+ and other divalent cations in solution. Only in the Zn‐fertilized calcareous soil were the percent decreases in Zn2+ greater than those of the major divalent cations, Ca2+ and Mg2+. This effect of P in the calcareous soil is of special interest because of its apparent selectivity for Zn, but the effect was small as shown by reductions of only 12 to 19% in the [Zn2+]/[Ca2+ + Mg2+] concentration ratio.

Zinc-phosphorus interactions in two cultivars of tomato (Lycopersicon esculentum L.) grown in chelator-buffered nutrient solutions

“…These values are in accord with estimates of free Zn :+ concentrations in soil solutions of alkaline soils where Zn deficiencies are fairly common (Norvell et al, 1987). It remains to be determined whether this apparent critical free Zn activity is consistent across diverse plant species (and cultivars), and across different metal chelators, and future research in our laboratory will address these questions.…”

“…Decreased solubility of soil Zn may result from enhanced sorption of Zn by hydrous oxides (Loneragan et al, 1979;Norvell et al, 1987), but would not explain the frequent occurrence of this effect in solution-cultured plants. When the plant Zn concentration is reduced due to an increase in dry matter production stimulated by P, a dilution effect has been invoked (Loneragan et al, 1979;Takkar et al, 1976).…”

Zinc Deficiency in Selected Cultivars of Wheat and Barley as Tested in Solution Culture

“…In the case of Zn, the critical range of free ion activity for healthy plant growth in chelate-buffered nutrient solution is 10-160 pM for barley (Hordeum vulgar) (Norvell and Welch 1993), 10 -60 for wheat (Triticum aestivum) (Parker 1993), and more than 25 for rice (Oryza sativa) (Yang, Römheld, and Marschner 1994). These values correspond well with estimated activity of Zn 2þ in the soil solution of alkaline soils in which the crops commonly show Zn deficiency (Norvell, Dabkovska-Naskret, and Cary 1993), indicating that chelate-buffered nutrient solutions with low activity of Zn are useful in evaluating cultivars for differential Zn efficiency as shown in the field.…”

Soil fertility management in organic greenhouses in Europe

“…Several surveys indicate very high P levels in soil used for organic vegetable production both in open field (von Fragstein et al 2004;Zikeli et al 2014) and greenhouse conditions (Voogt, 1999;von Fragstein et al 2004;Voogt et al 2011;Zikeli et al 2014). Several publications (Boyle and Lindsay, 1986;Norvell et al 1987;Pérez-Novo et al 2009) indicate that high soil P levels can negatively affect the bioavailability of Manganese (Mn), Copper (Cu) and Zinc (Zn) among other negative effects like eutrophication.…”