Effect of plantain on nitrous oxide emissions and soil nitrification rate in pasture soil under a simulated urine patch in Canterbury, New Zealand

Abstract

PURPOSE: The aim of this research was to quantify the effect of plantain (Plantago lanceolata L.) on soil nitrification rate, functional gene abundance of soil ammonia oxidisers, and the concomitant effect on nitrous oxide emissions from urine patches in a shallow, free-draining soil in Canterbury during late autumn/winter season. MATERIALS AND METHODS: Urine was collected from dairy cows grazing either ryegrass/white clover (RGWC), 30% plantain (P30) mixed in with RGWC or 100% plantain (P100) pasture, and applied at two rates (700 or 450 kg N ha⁻¹) to intact soil blocks growing either RGWC, P30 or P100 pasture. RESULTS AND DISCUSSION: Results showed that increased plantain content reduced N-concentration in urine from 7.2 in RGWC urine to 4.5 and 3.7 g N L⁻¹ in P30 and P100 urine, respectively. Total N₂O emissions and emission factors (EF₃) from urine-treated pastures were low, < 2 kg N ha⁻¹ and < 0.22%, respectively. Urine application at the lower urine N-loading rate of 450 kg N ha⁻¹ (i.e. representative of that in a P30 urine patch) resulted in 30% lower N₂O emissions (P < 0.01) and 35% lower soil nitrate concentrations (P < 0.001) compared to those at the higher urine loading rate of 700 kg N ha⁻¹ (i.e. representative of that in a RGWC urine patch). Increasing plantain content in the pasture sward from 0 to 30% and 100% with urine N applied at the same loading rate did not reduce N₂O emissions or nitrification compared to the standard ryegrass-white clover pasture. Cow urine derived from the different pasture diets had no effect on N₂O emissions, N transformation or ammonia-oxidiser abundance in soil compared to the RGWC urine applied at the same rate. CONCLUSIONS: The main effect of plantain in this study appears to be related to the reduction in urine N-loading rate, rather than factors related to urine properties or plantain-soil interactions.