Straw Return Plus Zinc Fertilization Increased the Accumulations and Changed the Chemical Compositions of Mineral-Associated Soil Organic Carbon

Abstract

Application of zinc (Zn) fertilization (e.g. ZnSO4) to increase soil Zn availability is a global strategy that biofortifies crops with Zn and thus helps improve human Zn nutrition, as Zn fertilizer promote the formation of soluble Zn-organic complexes, especially combined with returned straw. However, how soil organic carbon (SOC) conversion respond to Zn and/or straw plus Zn, has received little attention. Here, we explored the SOC, particulate organic carbon (POC), mineral-associated organic carbon (MAOC), and OC chemical composition’s responses to a field experiment site created in 2016 with the following treatments: control (CK, no straw return or Zn fertilizer), straw return (St), Zn fertilization (Zn), and straw return with Zn fertilization (St+Zn). The MAOC content under St+Zn increased by 4.39%–6.41%, which led to a slight SOC accumulation (3.72%–7.44%) compared to that of St alone. With straw return, the increase of ZnPOM (Zn content in particulate organic matter fraction) and ZnMAOM (Zn content in mineral-associated organic matter fraction) with Zn fertilization helped MAOC formation. The chemical compositions of POC and MAOC was affected mainly by straw return and Zn fertilization, respectively. In MAOC, both Zn and St+Zn increased the relative content of hydroxyl C (3400 cm–1) and reduced that of O-alkyl C (1030 cm–1) compared to CK and St, and the ZnMAOM content best explains the changes. In both the POC and MAOC fractions, the ratio of aromatic C to aliphatic C (1640/2922 ratio) decreased in Zn treatments compared to CK. Altogether, Zn’s positive effects on SOC and its fractions was closely linked to straw return, and Zn aid in MAOC and SOC accumulations when applied with straw.

Keywords: Straw return, zinc, calcareous soil, SOC fraction, FTIR spectroscopy