The Fate of Zn in Agricultural Soils: A Stable Isotope Approach to Anthropogenic Impact, Soil Formation, and Soil–Plant Cycling

Abstract

The supplementation of Zn to farm animal feed and the excretion via manure leads to an unintended Zn input to agricultural systems, which might compromise the long-term soil fertility. The Zn fluxes at three grassland sites in Switzerland were determined by a detailed analysis of relevant inputs (atmospheric deposition, manure, weathering) and outputs (seepage water, biomass harvest) during one hydrological year. The most important Zn input occurred through animal manure (1,076 to 1,857 g ha-1 yr-1) and Zn mass balances revealed net Zn accumulations (456 to 1,478 g ha-1 yr-1). We used Zn stable isotopes to assess the importance of anthropogenic impacts and natural long-term processes on the Zn distribution in soils. Soil-plant cycling and parent material weathering were identified as the most important processes, over the entire period of soil formation (13,700 years), while the soil pH strongly affected the direction of Zn isotopic fractionation. Recent anthropogenic inputs of Zn only had a smaller influence compared to the natural processes of the past 13,700 years. However, this will probably change in the future, as Zn stocks in the 0-20 cm layer will increase by 22% to 68% in the next 100 years, if Zn inputs remain on the same level as today.

Modelling of long term Zn, Cu, Cd, Pb dynamics from soils fertilized with organic amendments

“…This additional TE term, being a calibrated variable, was attributed to mineral weathering, although the site history also suggests that there is likely to be a contribution from inputs of fungicides to the labile Cu concentrations at the beginning of the measurement period. Estimates of TE weathering rates of 0.001-0.86 mg m -2 yr -1 for Zn and 0.0-0.039 mg m -2 yr -1 for Cd in Swiss agricultural soils have been reported (Imseng et al, 2018;Imseng et al, 2019), which were consistent with the fitted values. However, there is a need for more research on topsoil metal weathering rates and their contribution to determining labile metal concentrations in order to reduce the overall uncertainty on historic TEs inputs.…”

The Use of Q-ICPMS to Apply Enriched Zinc Stable Isotope Source Tracing for Organic Fertilizers

“…To this end, a multicollector ICPMS (MC-ICPMS) is used that achieves a precision of 0.01% relative standard deviation (RSD) for isotope ratio measurements which is adequate to study natural biogeochemical fractionation processes (Cloquet et al, 2008; Caldelas and Weiss, 2017). Analysis of such natural variations has allowed source tracing of metals on field or catchment scales (Borrok et al, 2009; Bigalke et al, 2010; Imseng et al, 2019; Yang et al, 2019). However, this approach requires that the isotope ratios of sources and sinks are distinguishable, which is not always the case (Wiggenhauser et al, 2018).…”

The Use of Stable Zinc Isotope Soil Labeling to Assess the Contribution of Complex Organic Fertilizers to the Zinc Nutrition of Ryegrass

“…These results suggest that soil Zn had a minor impact on Zn plant uptake, since soil Zn was about two times as high in the Strickhof compared with the Heitenried soil ( Table 1 ). The higher soil pH, and likely the higher carbonate concentration, in the Strickhof soil may have reduced the solubility of Zn derived from the fertilizer and soil due to a stronger adsorption of Zn on negatively charged binding sites of the soil (Diesing et al, 2008 ; Imseng et al, 2019 ). The lower solubility of fertilizer Zn and soil Zn in the alkaline Strickhof soil may have further lowered the concentration and uptake of Zn in the ryegrass shoots.…”

“…Complex organic fertilizers such as sewage sludge, animal manure, and compost are known sources of heavy metals such as zinc (Zn) in agroecosystems (Nicholson et al, 2003 ; Imseng et al, 2019 ). Bolan et al ( 2004 ) reported that the concentration of Zn in animal manure and sewage sludge ranged from 1.8 to 6480 mg kg −1 (median 378 mg kg −1 ).…”