Direct availability and geochemical reactivity of Zn in an agricultural soil amended with ZnO nanoparticles or ZnCl2

Zinc is an essential micronutrient for plants and it is often applied to zinc-deficient soils to increase crop yields. Recent studies suggest that nanoparticles (NPs) of ZnO have the potential for delivering Zn via soil in a... [ view full abstract ]

Zinc is an essential micronutrient for plants and it is often applied to zinc-deficient soils to increase crop yields. Recent studies suggest that nanoparticles (NPs) of ZnO have the potential for delivering Zn via soil in a more efficient manner than conventional fertilisers (containing e.g. ZnCl2 or ZnSO4.7H2O). However, the fate of ZnONPs in soil is not fully understood.
To compare the direct availability and geochemical reactivity of Zn from ZnONPs with that from ZnCl2, pots containing a sandy loam agricultural soil (pH=5.0; OC=1.1%; clay=3.1%) (500g of soil per pot) were amended with a suspension of ZnONPs or ZnCl2 solution (at 10 or 100 mg Zn kg-1) and kept for 120 days at constant moisture (70 % of WHC).
Each pot was equipped with two solution samplers to extract in-situ pore-water. The direct availability (expressed as total Zn concentration in pore-water) were characterised at day 1, 2, 3, 7, 15, 30, 60, 70 and 120 after amendment. After 120 days, soils were removed from pots, air-dried and analysed for pseudo-total Zn concentration (following aqua regia digestion). The geochemically available and reactive pools of Zn that remained in soil was characterised by soil extraction tests (with 0.01 M CaCl2, 0.43 M HNO3 or 0.4 M glycine (at pH 1.5) solutions).
In this presentation, the variation of the direct availability of Zn in amended pots along 120 days as well as the potential for subsequent release of Zn retained in soil will be presented. Implications for future fertilisation practices will be discussed.