Description
One strategy to reduce nitrogen losses from intensively grazed forage systems is to slow the first stage of soil nitrification, specifically inhibiting the microbial oxidation of ammonium to nitrite. Plantain (Plantago lanceolata) leaves and roots are known to contain several bioactive compounds (e.g., aucubin, catalpol and verbascoside) that may contribute to this inhibition. Recent laboratory studies indicate that this inhibition occurs via consumption by grazing animals of precursor bioactive compounds in aboveground biomass and their subsequent excretion as secondary metabolites in urine and/or via active exudation from the roots. Different cultivars of plantain have been shown to impart differing nitrification inhibition activity via both mechanisms. The urinary effect was assessed by determination of net soil nitrification in soil microcosms treated with urine from sheep fed a diet containing either perennial ryegrass or plantain. Analyses showed significant treatment effects on the rate of net nitrification and microbial community structure over time. A preliminary evaluation of the root exudate effect involved the collection of root exudates from six plantain cultivars grown in a hydroponic system. The assay of the root exudates against a pure culture of an ammonium-oxidising bacterium indicated differences in the amount of inhibition imparted by the exudates of each cultivar. The exact means of soil nitrification inhibition by either mechanism is as yet unconfirmed. However, it is likely that these compounds (or derivatives thereof) inhibit the first enzymatic step of nitrification directly, without harm to the soil microbiome as a whole.
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Soil Nitrification Inhibition with Plantain (Plantago lanceolata)
One strategy to reduce nitrogen losses from intensively grazed forage systems is to slow the first stage of soil nitrification, specifically inhibiting the microbial oxidation of ammonium to nitrite. Plantain (Plantago lanceolata) leaves and roots are known to contain several bioactive compounds (e.g., aucubin, catalpol and verbascoside) that may contribute to this inhibition. Recent laboratory studies indicate that this inhibition occurs via consumption by grazing animals of precursor bioactive compounds in aboveground biomass and their subsequent excretion as secondary metabolites in urine and/or via active exudation from the roots. Different cultivars of plantain have been shown to impart differing nitrification inhibition activity via both mechanisms. The urinary effect was assessed by determination of net soil nitrification in soil microcosms treated with urine from sheep fed a diet containing either perennial ryegrass or plantain. Analyses showed significant treatment effects on the rate of net nitrification and microbial community structure over time. A preliminary evaluation of the root exudate effect involved the collection of root exudates from six plantain cultivars grown in a hydroponic system. The assay of the root exudates against a pure culture of an ammonium-oxidising bacterium indicated differences in the amount of inhibition imparted by the exudates of each cultivar. The exact means of soil nitrification inhibition by either mechanism is as yet unconfirmed. However, it is likely that these compounds (or derivatives thereof) inhibit the first enzymatic step of nitrification directly, without harm to the soil microbiome as a whole.
