H. Clark

Photosynthetic responses of temperate species to free air CO2 enrichment (FACE) in a grazed New Zealand pasture

A New Zealand temperate pasture is currently exposed to either ambient air or air enriched to 475 µbar CO2 using free-air CO2 enrichment (FACE) technology. Sheep graze the site regularly, which results in heterogeneity in nutrient return. To investigate leaf photosynthetic responses, leaf gas exchange characteristics and nitrogen (N) content were measured in two consecutive years in spring under standard conditions on Lolium perenne L. and Trifolium subterraneum L. and on Trifolium repens L. and Paspalum dilatatum Poir. in the second year only. Leaves of the three C3 species growing under FACE conditions had lower (up to 37% in 1998 and 22% in 1999) photosynthetic rates than leaves growing under ambient conditions, when measured at the same standard conditions of high light and 360-380 µbar CO2. Differences in photosynthetic rates were correlated with leaf N content and stomatal conductance when measured under these conditions. There was no difference in photosynthetic capacities between ambient or FACE grown P. dilatatum, a C4 grass. Photosynthetic N use efficiency (A/N) differed among species. For the C3 species A/N was on average 25% greater under FACE conditions and L. perenne had the highest (240 µmol CO2 mol N -1 s -1 ) and T. repens the lowest A/N (142 µmol CO2 mol N -1 s -1 ) under ambient CO2 partial pressure (p(CO2)). A/N of L. perenne was similar to that of P. dilatatum measured under ambient p(CO2) but 21% greater under FACE conditions. In the second year, leaf stable carbon isotope compositions (δ 13 C) were determined for P. dilatatum, L. perenne and T. repens to assess long-term responses of leaf transpiration efficiency. Using the difference in δ 13 C between ambient and FACE-grown P. dilatatum as a reference to difference in δ 13 C in ambient and FACE air, we concluded that the ratio of leaf intercellular to ambient p(CO2) (Ci/Ca) was similar between FACE and ambient grown L. perenne and T. repens.

Methane emissions from beef cattle – a comparison of paddock- and animal-scale measurements

Methane (CH4) emissions from a herd of 58 grazing cattle were determined in a field experiment using paddock-scale (micrometeorological) methods. The emissions were also measured daily from each animal, using the sulfur hexafluoride tracer method. The paddock-scale methods exploit how the gas, once emitted from the cattle, is transported and dispersed by the wind. Hence, the emission rate may be calculated from measurements of windspeed, wind direction and turbulence statistics, as well as CH4 concentration upwind and downwind of the herd. The paddock-scale methods include a mass-budget approach, flux-gradient method and gas dispersion model. Accuracy can be assessed in unprecedented detail because the animal-scale (reference) method included all individuals in the herd, and the measurement site was ideal for micrometeorological methods (flat, usually windy and free of obstructions that alter the turbulent airflow). The cattle were hand-reared steers of average weight 325 ± 20 kg. Based on the animal-scale method, the average CH4 emission rate over 9 days was 161 ± 20 g/steer.day. The gas dispersion model, when utilising vertical concentration profiles, yielded on average 27% greater emissions. The other paddock-scale methods agreed with the animal-scale method, provided the cattle were at least 22 m away from the location of the downwind concentration measurements. When the cattle were allowed to graze as closely as 5 m from the instruments, the paddock-scale methods gave greater emissions than the animal-scale method; reasons for this are discussed.

Within- and between-animal variance in methane emissions in non-lactating dairy cows

Several studies on methane (CH4) emissions have focussed on selecting high and low CH4-emitting animals. One challenge faced by this work is the lack of consistency, or repeatability, in animal rankings over time. Repeatability for individual animals over time needs to be high to reliably detect high and low CH4-emitting animals. A possible explanation for the lack of repeatability is a relatively high within-animal variation in daily CH4 emissions, meaning that animals could then change their ranking when compared at different points in time. An experiment was undertaken with four non-lactating dairy cattle to assess the within- and between-animal variation in CH4 emissions over time when measured using the sulfur hexafluoride (SF6) tracer technique. Two contrasting diets were fed to the cattle at maintenance energy levels: lucerne silage (diet 1) and a cereal + lucerne + straw mixed ration diet (diet 2). Daily CH4 measurements were undertaken for 23 days on diet 1 and 30 days on diet 2. There was a significant (P < 0.001) difference between diet 1 and diet 2 in daily CH4 production, with mean (±s.e.) production of 124.3 (11.1) g CH4/day from diet 1 and 169.8 (±11.0) g CH4/day from diet 2. Lower CH4 yield (g CH4/kg dry matter intake) was recorded on diet 1 (22.8 ± 2.0) than diet 2 (32.0 ± 2.0). Cows differed significantly (P < 0.05) from one another in daily CH4 yield (diet 1: cow 1 = 19.4 ± 0.6, cow 2 = 22.2 ± 0.8, cow 3 = 23.2 ± 0.7, cow 4 = 25.4 ± 0.6; diet 2: cow 1 = 26.0 ± 0.7, cow 2 = 36.4 ± 0.7, cow 3 = 29.3 ± 0.7, cow 4 = 36.6 ± 0.7). Variances for daily CH4 yield were smaller for diet 1 (within animal = 6.91, between animals = 6.23) than for diet 2 (within animal = 10.09, between animals = 27.79). Estimates of repeatability (variation between animals/total variation) for daily CH4 yield were 47 and 73% in diet 1 and 2, respectively. Coefficients of variation in average daily CH4 emissions in this experiment ranged from 8 to 18% despite the fact that each animal received the same quantity and quality of feed each day. While further research is required, the high within-animal variability in CH4 emissions measured using the SF6 tracer technique may explain why there has been difficulty in obtaining consistent rankings in CH4 yields when animals are measured on multiple occasions. The results also suggest that the SF6 tracer technique may exaggerate apparent between animal differences in CH4 emissions.

The effect of level of intake and forage quality on methane production by sheep

In an experiment to determine the effect of level and quality of forage intake on methane (CH4) emissions, 16 wether lambs were allocated over two periods to two dietary treatments consisting of ryegrass at two stages of physiological maturity: an advanced stage of flowering and seeding (reproductive phase) and before flowering (vegetative phase). Additionally, in each period the lambs were divided into four groups and fed differing levels of food, from three-quarters maintenance to twice maintenance, to ensure a range of dry matter intakes amongst lambs. Apparent in vivo digestibility was measured and the mean values were 62.5% and 75.3% (s.e.d. = 0.84) for reproductive and vegetative ryegrass, respectively. Methane emissions were measured with the sulfur hexafluoride tracer technique. Daily methane emission was highly correlated with the amount of dry matter intake (DMI) (R2 = 0.83) and the regression was similar for both types of feed. Mean CH4 emissions per unit of DMI were 23.7 and 22.9 g/kg DMI (s.e.d. = 0.59) for reproductive and vegetative phases of ryegrass, respectively. The CH4 emissions per unit of DMI were not related to either level of DMI or diet quality.

Fumaric acid supplements have no effect on methane emissions per unit of feed intake in wether lambs

Recent reports suggest that supplementing the diet of ruminants with up to 10% fumaric acid (FA) can produce large reductions in methane (CH4) emissions, but the results have been equivocal. This trial evaluates the potential of FA to reduce enteric CH4 emissions from 18-month-old wethers fed lucerne. On two occasions, methane emissions were measured on 20 wethers fed a diet of dried ground lucerne with FA added to the diet at 0, 4, 6, 8 and 10 g FA/100 g dry matter (n = 4 wethers/treatment). Individual daily CH4 emissions were estimated using the sulfur hexafluoride (SF6) tracer gas technique together with measurements of daily dry matter intake (DMI) and total faecal output. Rumen samples were collected twice during the treatment periods in order to evaluate the effect of FA on rumen pH. There was a significant negative regression between FA% in the diet and CH4 emissions/day. However, the addition of FA did not affect CH4 emissions/kg DMI because high levels of FA supplementation reduced DMI. Rumen pH increased linearly with increasing level of FA supplementation. In conclusion, the effect of FA on CH4 emissions in this trial was associated with the resulting reduction in DMI and there were no decreases in CH4 emissions/kg DMI.

Monensin controlled-release capsules for methane mitigation in pasture-fed dairy cows

This experiment was undertaken to evaluate controlled-release capsules (CRC) that released monensin, for the mitigation of methane production from cows. The evaluation has been bought about by government policies to lower agricultural greenhouse gas (GHG) emissions, whilst maintaining profitability of dairy farms in New Zealand. The experiment used 60 Friesian–Holstein cows fed ryegrass (Lolium perenne L.)-dominant pasture, starting in week 7 of lactation. The CRC were placed in the rumen of 30 cows and effects of monensin on milk production were measured over 11 weeks by comparison with 30 control cows (Con). Cows were grazed as a single herd for the majority of the trial, but 32 (16 CRC, 16 Con) were fed indoors for 36 days (four 9-day periods) for measurement of intakes and methane. Monensin CRC did not affect methane production, which averaged 19.7 g/kg dry matter intake (DMI). There were also no significant treatment effects on DMI (16.5 kg DM/day) and milk production (21.3 kg/day) when measured indoors or on milk production over the whole experiment (21.7 kg/day). Ruminal metabolites measured from five rumen-fistulated cows in either group were not significantly different. At the conclusion of the experiment, monensin release rate from the CRC (10.8 mg/kg DMI) retrieved from five fistulated cows averaged 52% of anticipated values. Inadequate performance of the controlled delivery device prevented an unequivocal evaluation of the monensin CRC for methane mitigation in dairy cows fed pasture.

Carbon dioxide emissions from mineral springs in Northland and the potential of these sites for studying the effects of elevated carbon dioxide on pastures

Abstract Sites in Northland with mineral springs were examined for their potential as experimental areas to study the effects of elevated carbon dioxide (CO2) on grassland. A suitable site was defined as having: (1) grassland species; (2) cold springs; (3) high levels of gas flow; and (4) high concentrations of CO2. Two sites were selected for detailed study‐Hakanoa Springs near Kamo and Waiare Spring near Kaeo. At Hakanoa, the vegetation was scrubby but at least 10 grassland species were present. Two vents released large volumes of CO2 resulting in concentrations at 10 cm above ground level that ranged from 5000 μl/litre near the vent to 400 μl/ litre 10 m downwind. At Waiare, the spring was situated in a grazed grass paddock that contained 10 grass species as well as Trifolium repens and Lotus spp. There was little enrichment of CO2 above the canopy but high concentrations were measured at mid‐canopy height with a maximum value exceeding 2000 μl/litre. Because of the nature of the enrichment within, but...

Greenhouse gas emissions from New Zealand agriculture: issues, perspectives and industry response

The prosperity of New Zealand (NZ) rests to a large extent on agriculture. Although our total greenhouse gas (GHG) emissions are unusually small for a developed nation, agricultural emissions make up almost half of the total emissions from NZ. Emissions from NZ agriculture have been rising at close to 1% a year since 1990 and by 2010, the midpoint of the first commitment period of the Kyoto Protocol, they are projected to be 7.2 Mt per year higher than the 1990 baseline. This excess has a potential cost of over NZ

Emergence of the Global Research Alliance on Agricultural Greenhouse Gases

0.5 billion. Despite the continued rise in absolute emissions, emissions intensity, the amount of GHG produced per unit of food produced, has been dropping and the emissions intensity of NZ agriculture goods compares favourably with that of other developed nations. The NZ agricultural sector has actively engaged in the search for cost-effective mitigation solutions and, in partnership with the government, has funded research through the Pastoral Greenhouse Gas Research Consortium (PGGRC). The PGGRC has been in existence since 2002 and has invested NZ

Methane emissions from young and mature dairy cattle

16 million in research into reducing methane and nitrous oxide emissions from pastoral agriculture. The structure of this research funding body, its objectives, achievements and future challenges are briefly outlined.