Peer review

Open Access

Plant-derived denitrification inhibitors, such as procyanidins derived from grape seed extract (GSE), hold potential in mitigating nitrous oxide (N2O) emissions, a potent greenhouse gas and stratospheric ozone depleter. A deeper understanding of the effects of GSE – considering aspects like rate, source, application timing, storage, and interactions with soil properties and cropping histories – on denitrification inhibition remains elusive. We conducted a series of laboratory microcosm experiments to assess these effects using denitrification enzyme activity (DEA) and measurements of N2O and carbon dioxide (CO2) production rates under both anaerobic and aerobic conditions, soil inorganic nitrogen (N), and other major soil properties. Our results revealed that one commercial GSE brand (USP GSE) inhibited DEA, while another source was ineffective. Two non-procyanidin compounds in commercial GSE mixtures, tartaric acid and gallic acid, actually enhanced DEA. Inhibition efficiency of the USP GSE varied significantly across soils with differing crop histories and physical properties, exhibiting a positive dose-response in three out of the five soils examined. Greater efficiency was observed in sandy soils compared to silt loam soils and in soils with a history of continuous corn production as opposed to soybean. The GSE application timing relative to urea addition and a one-week room temperature storage had minor effects on denitrification inhibition. In corn-cultivated soil, co-application of GSE and urea reduced cumulative N2O production by 27 % compared to soils treated with urea alone. The CO2 production and nitrate levels remained largely unaffected by GSE application. These findings supported the potential of GSE as a soil amendment to reduce N2O emissions in corn-cultivated soils. However, challenges including purity of procyanidins, cost-effectiveness, and inconsistent performance under various systems warrant consideration for broader field applications.

Text in English