Milani Narges, Hettiarachchi Ganga M, Kirby Jason K, Beak Douglas G, Stacey Samuel P, McLaughlin Mike J
Soil Science, School of Agriculture, Food & Wine, University of Adelaide, Glen Osmond, Australia.
Department of Agronomy, Throckmorton Plant Sciences Centre, Kansas State University, Manhattan, Kansas, United States of America.
PLoS One. 2015 May 12;10(5):e0126275. doi: 10.1371/journal.pone.0126275. eCollection 2015.
Zinc oxide (ZnO) nanoparticles may provide a more soluble and plant available source of Zn in Zn fertilizers due to their greater reactivity compared to equivalent micron- or millimetre-sized (bulk) particles. However, the effect of soil on solubility, spatial distribution and speciation of ZnO nanoparticles has not yet been investigated. In this study, we examined the diffusion and solid phase speciation of Zn in an alkaline calcareous soil following application of nanoparticulate and bulk ZnO coated fertilizer products (monoammonium phosphate (MAP) and urea) using laboratory-based x-ray techniques and synchrotron-based μ-x-ray fluorescence (μ-XRF) mapping and absorption fine structure spectroscopy (μ-XAFS). Mapping of the soil-fertilizer reaction zones revealed that most of the applied Zn for all treatments remained on the coated fertilizer granule or close to the point of application after five weeks of incubation in soil. Zinc precipitated mainly as scholzite (CaZn2(PO4)2.2H2O) and zinc ammonium phosphate (Zn(NH4)PO4) species at the surface of MAP granules. These reactions reduced dissolution and diffusion of Zn from the MAP granules. Although Zn remained as zincite (ZnO) at the surface of urea granules, limited diffusion of Zn from ZnO-coated urea granules was also observed for both bulk and nanoparticulate ZnO treatments. This might be due to either the high pH of urea granules, which reduced solubility of Zn, or aggregation (due to high ionic strength) of released ZnO nanoparticles around the granule/point of application. The relative proportion of Zn(OH)2 and ZnCO3 species increased for all Zn treatments with increasing distance from coated MAP and urea granules in the calcareous soil. When coated on macronutrient fertilizers, Zn from ZnO nanoparticles (without surface modifiers) was not more mobile or diffusible compared to bulk forms of ZnO. The results also suggest that risk associated with the presence of ZnO NPs in calcareous soils would be the same as bulk sources of ZnO.
由于与同等微米或毫米尺寸（块状）颗粒相比，氧化锌（ZnO）纳米颗粒具有更高的反应活性，因此在锌肥中它可能提供一种更易溶解且植物可利用的锌源。然而，土壤对ZnO纳米颗粒的溶解性、空间分布和形态的影响尚未得到研究。在本研究中，我们使用基于实验室的X射线技术以及基于同步加速器的μ-X射线荧光（μ-XRF）映射和吸收精细结构光谱（μ-XAFS），研究了在施用纳米颗粒状和块状ZnO包膜肥料产品（磷酸一铵（MAP）和尿素）后，锌在碱性石灰性土壤中的扩散和固相形态。土壤-肥料反应区的映射显示，在土壤中培养五周后，所有处理中施用的大部分锌仍保留在包膜肥料颗粒上或靠近施用点。锌主要以磷锌矿（CaZn2(PO4)2·2H2O）和磷酸锌铵（Zn(NH4)PO4）的形式沉淀在MAP颗粒表面。这些反应减少了锌从MAP颗粒中的溶解和扩散。尽管锌在尿素颗粒表面仍以氧化锌（ZnO）的形式存在，但对于块状和纳米颗粒状ZnO处理，也观察到锌从ZnO包膜尿素颗粒中的有限扩散。这可能是由于尿素颗粒的高pH值降低了锌的溶解度，或者是由于释放的ZnO纳米颗粒在颗粒/施用点周围聚集（由于高离子强度）。在石灰性土壤中，随着与包膜MAP和尿素颗粒距离的增加，所有锌处理中Zn(OH)2和ZnCO3形态的相对比例都增加。当包覆在大量营养素肥料上时，与块状ZnO相比，来自ZnO纳米颗粒（无表面改性剂）的锌的迁移性或扩散性并不更高。结果还表明，石灰性土壤中ZnO纳米颗粒存在的相关风险与块状ZnO源相同。
