Disentangling the effect of sheep urine patch size and nitrogen loading rate on cumulative N2O emissions

Abstract

Abstract. Ruminant urine nitrogen (N) concentration and volume are important parameters influencing the size and N loading rate of urine patches deposited to soil. Such parameters can influence N cycling and emissions of the greenhouse gas, nitrous oxide (N 2 O) from grazed grassland, yet, there is limited information on the effect of these parameters within typical ranges reported for sheep. We used an automated, high-frequency gas monitoring system to investigate N 2 O emissions from varying urine N application rates and patch sizes under field conditions. Using artificial sheep urine, we manipulated urine N concentration to provide two urine N application rates (4 and 16 g N/L; equivalent to 200 and 800 kg N/ha). We investigated the effect of urine patch size with equal N application rates (4 · 125 cm 2 vs 500 cm 2 , at 200 and 800 kg N/ha) and the effect of patch size with unequal N application rates, but the same total amount of N applied (62.5 mL over 125 cm 2 at 800 kg N/ha and 250 mL over 500 cm 2 at 200 kg N/ha). Cumulative emissions of N 2 O generally increased with N loading rate, whether applied as one large urine patch or four smaller ones. Cumulative N 2 O emissions increased when the N was applied in four smaller urine patches compared with one large patch; this difference was significant at 800 kg N/ha, but not at 200 kg N/ha. When the total amount of N applied was held constant (1 g of N), the amount of N 2 O released was similar when urine was applied as a high N concentration small patch (800 kg N/ha) compared with a low N concentration large patch (200 kg N/ha). Urine N 2 O emission factors in this study were, on average, 10 times lower than the IPCC default of 1% for sheep excreta. This research clearly demonstrates that the chemical and physical nature of the urine patch influences N 2 O emissions, yet further research is required to gather more data on typical sheep urine volumes (individual and daily), urination frequency, urine N concentrations and the typical volumes of soil influenced by urine deposition, to provide more accurate estimates of emissions from sheep grazed pastures.

Restoration management of cattle resting place in mountain grassland

“…Hence, dung deposition has a significant effect on the chemical status of the soil and thus presents a potential source of available nutrients for plants [ 56 , 57 ]. Furthermore, urine is another source of nutrient especially N, which occurs primarily as a hydrolyzed urea, and is easily plant-available after deposition [ 58 ] and enables increased plant biomass N uptake and biomass productivity [ 59 , 60 ].…”

The contribution of cattle urine and dung to nitrous oxide emissions: Quantification of country specific emission factors and implications for national inventories

“…We recognise that urine and dung patches are not normally this large, and have “edges”, but this method of application was deemed the most appropriate to simulate the urine patch and dung pat. It is possible that by applying the N source across the whole area of the chamber that N 2 O production and emission may have been affected, but there is no evidence to suggest that this would result in either an under- or over-estimate of the true emission ( Marsden et al, 2016 ). In addition to the urine and dung patches that were established for the N 2 O chamber measurements, larger areas of grassland (2 m × 2 m) on each plot (i.e.…”

Elucidating three-way interactions between soil, pasture and animals that regulate nitrous oxide emissions from temperate grazing systems

“…This position is strongly in agreement with a recent life cycle assessment (LCA) study at the study site (the NWFP), which found that amongst all sources of uncertainty surrounding carbon footprints of grazing enterprises, uncertainty associated with N 2 O EFs is the largest, and therefore hedging the risk through a mixed strategy would be a sensible approach ( Takahashi et al, 2019 ). In this context, other on-farm options that could contribute to the solution package include: light interception control through manipulation of sward structure ( Congio et al, 2019 ); fertiliser selection to enhance pasture growth and thus the stocking rate ( Louro et al, 2016 ); diet formulation to control N load and urination volume ( Marsden et al, 2016 ); and direct control of grazing intensity ( Tang et al, 2019 ).…”