Do glucosinolate hydrolysis products reduce nitrous oxide emissions from urine affected soil?

New Zealand agriculture is predominantly comprised of pastoral grazing systems and deposition of animal excreta during grazing has been identified as a major source of nitrous oxide (N₂O) emissions. Nitrification inhibitors have been shown to significantly reduce nitrous oxide emissions from grazing pastoral systems, and some plants have been identified as having nitrification inhibiting properties. Brassica crops are one such example as they contain the secondary metabolite glucosinolate (GLS) whose hydrolysis products are thought to slow soil nitrogen cycling. Forage brassicas have been increasingly used to supplement the diet of grazing animals. The aim of this study was to determine if GLS hydrolysis products (phenylethyl isothiocyanate, 4-pent-1-yl isothiocyanate, 2-propenyl nitrile, 2 propenyl isothiocyanate, 4-pentene nitrile) produced in brassica crops reduced N₂O emissions from soil amended with urea or animal urine. In the laboratory, some GLS hydrolysis products added with urea to soil were found to decrease N₂O emissions and the most effective product (phenylethyl isothiocyante) reduced N₂O emissions by 51% during the study. There was some evidence that the reduction in N₂O emissions found in the lab could be attributed to inhibition of nitrification. Results suggest that the inhibition by GLS hydrolysis products was short-lived and, if considered for use, multiple applications may be necessary to achieve effective inhibition of N₂O emissions. This reduction, however, was not observed under field conditions. Further investigation is required to test more GLS hydrolysis products to fully understand their impact on N₂O emissions from urine affected soil.