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Abstract. Intensification of pastoral agriculture is occurring rapidly across New Zealand, including increasing use of irrigation and fertiliser application in some regions. While this enables greater gross primary production (GPP) and livestock grazing intensity, the consequences for the net ecosystem carbon budget (NECB) of the pastures are poorly known. Here, we determined the NECB over one year for an irrigated, fertilised and rotationally grazed dairy pasture and a neighbouring unirrigated, unfertilised, wintergrazed pasture. Primary terms in the NECB calculation were: net ecosystem production (NEP), biomass carbon removed by grazing cows and carbon (C) input from their excreta. Annual NEP was measured using the eddy-covariance method. Carbon removal was estimated with plate-meter measurements calibrated against biomass collections, preand post-grazing. Excreta deposition was calculated from animal feed intake. The intensively managed pasture gained C (NECB = 103 ± 42 g C m −2 yr −1 ) but would have been subject to a non-significant C loss if cattle excreta had not been returned to the pasture. The unirrigated pasture was C-neutral (NECB = −13 ± 23 g C m −2 yr −1 ). While annual GPP of the former was almost twice that of the latter (2679 vs. 1372 g C m −2 yr −1 ), ecosystem respiration differed by only 68 % between the two pastures (2271 vs. 1352 g C m −2 yr −1 ). The ratio of GPP to the total annual water input of the irrigated pasture was 37 % greater than that of the unirrigated pasture, i.e. the former used the water input more efficiently than the latter to produce biomass. The NECB results agree qualitatively with those from many other eddy-covariance studies of grazed grasslands, but they seem to be at odds with long-term carbon-stock studies of other New Zealand pastures.

Abstract. New Zealand's largest industrial sector is pastoral agriculture, giving rise to a large fraction of the country's emissions of methane (CH 4 ) and nitrous oxide (N 2 O). We designed a system to continuously measure CH 4 and N 2 O fluxes at the field scale on two adjacent pastures that differed with respect to management. At the core of this system was a closed-cell Fourier transform infrared (FTIR) spectrometer, which measured the mole fractions of CH 4 , N 2 O and carbon dioxide (CO 2 ) at two heights at each site. In parallel, CO 2 fluxes were measured using eddy-covariance instrumentation. We applied two different micrometeorological ratio methods to infer the CH 4 and N 2 O fluxes from their respective mole fractions and the CO 2 fluxes. The first is a variant of the flux-gradient method, where it is assumed that the turbulent diffusivities of CH 4 and N 2 O equal that of CO 2 . This method was reliable when the CO 2 molefraction difference between heights was at least 4 times greater than the FTIR's resolution of differences. For the second method, the temporal increases of mole fractions in the stable nocturnal boundary layer, which are correlated for concurrently emitted gases, are used to infer the unknown fluxes of CH 4 and N 2 O from the known flux of CO 2 . This method was sensitive to "contamination" from trace gas sources other than the pasture of interest and therefore required careful filtering. With both methods combined, estimates of mean daily CH 4 and N 2 O fluxes were obtained for 56 % of days at one site and 73 % at the other. Both methods indicated both sites as net sources of CH 4 and N 2 O. Mean emission rates for 1 year at the unfertilised, winter-grazed site were 8.9 (±0.79) nmol CH 4 m −2 s −1 and 0.38 (±0.018) nmol N 2 O m −2 s −1 . During the same year, mean emission rates at the irrigated, fertilised and rotationally grazed site were 8.9 (±0.79) nmol CH 4 m −2 s −1 and 0.58 (±0.020) nmol N 2 O m −2 s −1 . At this site, the N 2 O emissions amounted to 1.21 (±0.15) % of the nitrogen inputs from animal excreta and fertiliser application.

The concentration of selenium (Se) in liver, whole blood, erythrocytes and plasma, and the activity of glutathione peroxidase (GSH-px) in erythrocytes and plasma were monitored in calves transferred between low Se and high Se pastures to determine how each test responded to changes in dietary selenium concentration.Liver and plasma Se concentration and plasma GSH-px activity responded more rapidly than Se concentration in blood or erythrocytes and GSH-px activity in erythrocytes to changes in dietary Se intake. Erythrocyte GSH-px activity showed the greatest relative change in value.There was a close relationship (r = 0.97) between blood Se concentration and erythrocyte GSH-px activity in samples tested from SO mixed aged cattle.It was concluded that Se concentrations in plasma and liver provide the best indication of current dietary Se intake in cattle, but that erythrocyte GSH.px activity provides a suitable alternative test for the diagnosis of Se deficiency and might help to define more precisely which animals are likely to respond to Se supplementation.

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