Organic Amendment for Disinfecting Soil Alters the Metabolites in Spinacia oleracea

Solar radiation and the incorporation of compost into soil is a practice for disinfecting soil that could have some other effects on spinach cultivation. The quality of spinach leaves after two types of soil disinfection, non-amended soil (NAS) and compost-amended soil (CAS), was compared in order to find biomarkers of both types of disinfection. These practices did not show significant differences in nutrient composition (N-P-K) compared to the control soil (CS). However, the amount of harmful nutrients such as NO 2 − was significantly lower in CAS (65.74 mg kg −1 FW) and NAS (49.99 mg kg −1 FW) than in CS (114.39 mg kg −1 FW). In addition, NO 3 − levels did not exceed the EU-recommended limit (<3500 mg kg −1 FW). Both types of disinfected soils produced higher concentrations of total phenols and more individual flavonoids in spinach leaves than the control. Combined chemometric analysis of the HRAMS data showed different clustering depending on the type of disinfection (NAS and CAS). Fifteen metabolite compounds could be identified, seven of which are beneficial for health and were more abundant in spinach grown in CAS compared to that grown in NAS or CS. Such beneficial metabolites measured with non-target analysis as markers of CAS-grown spinach. However, more studies are necessary in order to determine the differences between the metabolites of spinach grown in NAS or CAS.