Zealand Pastures Research Articles

A conceptual model for the population dynamics of Cirsium arvense in a New Zealand pasture

Based on a critical review of published research we have developed a conceptual model for a pasture population of Cirsium arvense (Californian thistle) focusing on plausible mechanisms for the regulation of population size: 1) plants overwinter as creeping roots with adventitious buds and subterranean shoots; 2) a main spring cohort of shoots supported by mobilized carbohydrates is regulated numerically by overwintered root mass and apical dominance; 3) shoot death is promoted by interspecific competition, disease and weed control practices; 4) new creeping roots formed throughout the growing season support a low level of shoot recruitment; 5) overwintered root mass is a linear function of photosynthetic opportunity; 6) shoot growth predominates over root growth during the first half of the growing season; 7) root buds, elongating as apical dominance subsides with autumnal shoot senescence, produce the main spring cohort of shoots; 8) creeping root formation is reduced by intraspecific competition; and 9) shoot growth declines with interspecific competition. The validation of these mechanism models should be the focus of ongoing research.

Quantification of soil macro pore size and shape using resin impregnation

Subtle changes in soil pore size and shape as a consequence of changes in land use and management practices can have significant impacts on the movement of air, water, plant roots and soil biota. This paper describes a resin impregnation technique adapted for use in New Zealand pasture soils to quantify these soil pore attributes. Image analysis of the resin impregnated soil enables detailed assessment of soil pore shape and macro pore size distribution (>50 µm).

Varying atmospheric methane concentrations affect soil methane oxidation rates and methanotroph populations in pasture, an adjacent pine forest, and a landfill

We describe experiments to better understand how CH4 oxidation rates by different methanotroph communities respond to changing CH4 concentrations. We used a novel system of automatically monitored chambers to investigate the response of CH4 oxidation rates in a New Zealand pasture and adjacent pine forest soil exposed to varying atmospheric CH4 concentrations.Type II methanotrophs that dominate CH4 oxidation in the forest soil became progressively saturated as CH4 concentrations rose from ambient (1.8ppmv) to 570ppmv, as shown by a decrease in uptake efficiency from 20% to 2% removal. By contrast, CH4 oxidation in the pasture soil where Type I methanotrophs dominate increased in proportion to the increase in CH4 inlet concentration, oxidising about 2% of the inlet CH4 flux throughout. Modelling based on Michaelis-Menten kinetics revealed that low-affinity (Type I) methanotrophs were solely responsible for CH4 oxidation in pasture soils, whereas high affinity (Type II) methanotrophs only contributed about 10% of the CH4 oxidation in the forest soil. Increased aeration status using a soil–perlite (1:1) mixture doubled CH4 oxidation rates at both ambient (1.8ppmv) and 40ppmv atmospheric CH4. A similar volcanic soil previously exposed for 8 y to high CH4 fluxes from a landfill had removal efficiencies consistently above 95% for atmospheric CH4 concentrations up to 7500ppmv when the CH4 oxidation rate was7000μg CH4 kg−1soil h−1.

Economic values for evaluating pasture plant traits

Economic values (EVs) are an estimate of the change in farm system profit per unit of change in a defined plant trait. Cultivars within species such as perennial ryegrass differ in the major production traits of dry matter yield, nutritive value and persistence, but the impact of those differences on farm financial performance is seldom calculated and reported. This paper explains what EVs are, describes how they can be calculated, and discusses some of the associated methodological issues. EVs have been derived for seasonal dry matter yield in New Zealand dairy systems. Extra feed produced in late spring has consistently low economic value, while extra feed produced in early spring has consistently high value. There have been no systematic investigations into the EVs of nutritive value and persistence in New Zealand pastures; this is a clear opportunity for future research. The lack of data on cultivar differences in these traits will restrict the application of EVs to pasture cultivar evaluation. This gap is now being addressed by new industry initiatives. Keywords: pasture cultivars, evaluation, traits, economic values, performance values

Implications of albedo changes following afforestation on the benefits of forests as carbon sinks

Abstract. Increased carbon storage with afforestation leads to a decrease in atmospheric carbon dioxide concentration and thus decreases radiative forcing and cools the Earth. However, afforestation also changes the reflective properties of the surface vegetation from more reflective pasture to relatively less reflective forest cover. This increase in radiation absorption by the forest constitutes an increase in radiative forcing, with a warming effect. The net effect of decreased albedo and carbon storage on radiative forcing depends on the relative magnitude of these two opposing processes. We used data from an intensively studied site in New Zealand's Central North Island that has long-term, ground-based measurements of albedo over the full short-wave spectrum from a developing Pinus radiata forest. Data from this site were supplemented with satellite-derived albedo estimates from New Zealand pastures. The albedo of a well-established forest was measured as 13 % and pasture albedo as 20 %. We used these data to calculate the direct radiative forcing effect of changing albedo as the forest grew. We calculated the radiative forcing resulting from the removal of carbon from the atmosphere as a decrease in radiative forcing of −104 GJ tC−1 yr−1. We also showed that the observed change in albedo constituted a direct radiative forcing of 2759 GJ ha−1 yr−1. Thus, following afforestation, 26.5 tC ha−1 needs to be stored in a growing forest to balance the increase in radiative forcing resulting from the observed albedo change. Measurements of tree biomass and albedo were used to estimate the net change in radiative forcing as the newly planted forest grew. Albedo and carbon-storage effects were of similar magnitude for the first four to five years after tree planting, but as the stand grew older, the carbon storage effect increasingly dominated. Averaged over the whole length of the rotation, the changes in albedo negated the benefits from increased carbon storage by 17–24 %.

Incidence and diversity of phosphate-solubilising bacteria are linked to phosphorus status in grassland soils

The extent to which soil phosphorus (P) status affected the incidence of soil phosphate-solubilising bacteria (PSB) and their taxonomic abundance and diversity was examined at three long-term fertiliser trials (Whatawhata, Winchmore and Ballantrae) in New Zealand. Bacteria were isolated from rhizosphere (ryegrass and clover) and non-rhizosphere soils differing in P status. The P-solubilising phenotype was determined on agar supplemented with sparingly-soluble mineral phosphates (Ca2OH(PO4)3 and CaHPO4). The frequency of P-solubilisation in the bacterial population was significantly greater (P < 0.001) in soils of low-P status, demonstrating a selection pressure for this trait based on soil P availability. P-solubilising bacteria from high-P level soils and soils which had not received P fertiliser (nil-P soils) were identified based on 16S rRNA-gene sequence analysis. Across the samples, the P-solubilising community was very rich with 39 genera of PSB found, spanning 24 families and 4 phyla. At Ballantrae and Winchmore, the PSB composition differed (P < 0.05) across soil P status, which was associated with an alteration in abundance of Actinobacteria, Pseudomonadaceae and Moraxellaceae. The phylogenetic composition of PSB differed significantly (P < 0.05) between sites, however nearly half the families were common across all sites, constituting a ‘core community’ of P-solubilising bacteria for these New Zealand pasture soils. As the abundance and composition of P-solubilising bacteria are under strong selection pressure affected through farm management strategies, better understanding of their ecology provides the opportunity to increase the availability of soil P for plant-uptake.

Field release, establishment and initial dispersal of Irish Microctonus aethiopoides in Sitona lepidus populations in northern New Zealand pastures

The clover root weevil Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) became an economically important pasture pest in New Zealand shortly after it was discovered in the Waikato region in 1996. A classical biological programme was initiated and an Irish biotype of Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was released at four sites in the North Island in late summer 2006. These sites in Waikato, Hawke’s Bay and Manawatu (two sites) regions were monitored monthly and parasitoid establishment confirmed at all sites within four months. In the winter of 2007, parasitism exceeded 70%. A widespread North Island drought in summer 2008 had a severe impact on S. lepidus populations at the Waikato and the two Manawatu release sites, resulting in parasitism below detection levels in the following summer. However, populations recovered by autumn. Within three years at the Hawke’s Bay site, M. aethiopoides appears to be suppressing S. lepidus populations and has dispersed naturally over 60 km.

St. John’s wort beetles would not have been introduced to New Zealand now: A retrospective host range test of New Zealand’s most successful weed biocontrol agents

St. John’s wort, Hypericum perforatum, was a serious weed in New Zealand (NZ) pastures in the 1930s. Following successful biological control of the weed in Australia, two agents, the chrysomelid beetles Chrysolina hyperici and C. quadrigemina, were introduced to NZ in 1943 and 1965, respectively. At the time, the Australian host specificity testing, which had not included other Hypericum spp., was deemed sufficient for approval for release in NZ. We reviewed worldwide reports which suggest that St. John’s wort beetles will attack a range of Hypericum species in the field. A series of laboratory tests were conducted to simulate modern host-range-testing protocols. Larval feeding choice, larval development and female oviposition choice all suggested that at least two of NZ’s indigenous Hypericum species were suitable hosts for the two Chrysolina species, and a third indigenous Hypericum, while an unsuitable host, was not altogether avoided. We conclude that the two Chrysolina species would not have been approved for introduction to NZ under current risk assessment protocols. Had this happened, NZ would have missed out on one of its greatest biocontrol success stories, despite there being no evidence for subsequent impacts on the populations of indigenous congeners. This case stresses the need for better procedures to predict the realized host-range of an agent from the potential range in contained host-range testing, and raises issues surrounding risks and benefits to indigenous biodiversity.

The impact of invertebrate pests on pasture persistence and their interrelationship with biotic and abiotic factors

New Zealand pastures are host to a range of native and exotic invertebrates. Many of these are pests that feed on the sown plant species, often causing plant death and deterioration in the productivity and persistence of the sward. While most research has focused on pest biology and control, studies of plant productivity show dramatic acute (short-medium term) and chronic (longterm) effects. For example, grass grub has been reported to cause 50% losses to ryegrass swards and Argentine stem weevil can cause a 20% loss of productivity, but the long term effects through loss of the sown species and changes in composition can be even more severe. Insect damage can be exacerbated by other biotic (e.g. weed invasion, grazing animals, plant pathogens) or abiotic factors (e.g. climate, soil fertility) to further reduce plant persistence. Some biotic and abiotic factors may interact with insect pests to have positive effects on pasture persistence, e.g. biocontrol agents that reduce pest density or addition of fertiliser to enable plants to recover from insect damage. For many pasture pests, knowledge of their ecology is based on research from over 20 years ago that, while still valid, needs to be updated to account for modern intensive pasture management practices, such as intensive grazing with a lack of reseeding, and new cultivars. To improve pasture persistence, integrated research programmes are needed that examine the relative importance of all factors contributing to plant survival and develop strategies to mitigate their effects. Keywords: Argentine stem weevil, black beetle, clover root weevil, drought, grass grub, grazing pressure, manuka beetle, nematodes, pasture persistence, pasture quality, pasture yield, porina, soil fertility, striped chafer.

What factors lead to poor pasture persistence and weed ingress?

In an ideal pasture, sown species would persist indefinitely and there would be no weeds. 'Poor persistence' occurs when the desirable species are replaced by weedy, undesirable species. Unfortunately, poor persistence of sown pasture plants is the reality that most farmers experience. In this paper we review the literature on three key factors leading to poor persistence and weed ingress: 1) inter-specific competition; 2) sward disturbance; and 3) propagule pressure. We reveal that grazing and other management decisions, pasture insect pests, nutrients, climate and the composition of the sown species mix have a critical influence on these factors, and hence over the replacement of sown pasture plants by weeds. The key practical message from this review is that farm practices that improve the vigour of sown species, reduce pasture gaps and minimise weed propagule pressure will improve the persistence of sown species and minimise weed ingress. An outstanding deficiency is our lack of knowledge of the economic impacts, and hence weed status, of most of the ca 187 volunteer plant species that may invade and replace sown plants in New Zealand's pastures.

Argentine stem weevil (Listronotus bonariensis, Coleoptera: Curculionidae) population dynamics in Canterbury, New Zealand dryland pasture

The Argentine stem weevil (Listronotus bonariensis) was an economically important pest in New Zealand pastures until the release of the parasitoid Microctonus hyperodae. This contribution uses historical data to investigate the regulation of the pest populations prior to, and somewhat during, the establishment of this parasitoid in dryland Canterbury, New Zealand. Thus, a significant goal of this study is to provide an L. bonariensis population dynamics baseline for any future work that aims to analyse the full effects of M. hyperodae on the weevil, now that equilibrium with the weevil host has been reached.The population dynamics of L. bonariensis, based on a life-table approach, were investigated using data collected regularly for eight years from populations in Canterbury, New Zealand. The key factor affecting end-of-season L. bonariensis density was found to be variation in second generation fourth instar prepupal and pupal mortality. This may have been caused by arrested development and ongoing mortality resulting from the onset of cooler autumnal conditions.A compensatory response was found in recruitment to the second summer weevil generation, whereby the realised fecundity of the emergent first summer generation of weevils was found to be negatively related to the density of adult weevils per ryegrass tiller. This is the first time that this has been found via long-term population analysis of L. bonariensis, although indications of this have been found elsewhere in caging, pot and small plot experiments.In this study, the effect of the parasitoid biocontrol agent Microctonus hyperodae on L. bonariensis population dynamics was unclear, as the analysis covered a period when the parasitoid Microctonus hyperodae was introduced and still establishing. It does, however, raise important questions for future analysis in terms of the interaction between parasitism and unrealised fecundity.The results in this contribution also highlighted regional differences. Overwintering mortality of adult weevils in Canterbury was constant between years, whilst earlier studies in the North Island Waikato region indicated this mortality was density dependent. In addition, the availability of tillers in endophyte-free ryegrass pastures in Canterbury had no influence on egg and early-instar larval survival, which contrasts with the finding from endophytic Waikato pastures.

Gains and losses in C and N stocks of New Zealand pasture soils depend on land use

Previous re-sampling of 31 New Zealand pasture soil profiles to 1m depth found large and significant losses of C and N over 2–3 decades. These profiles were predominantly on intensively grazed flat land. We have extended re-sampling to 83 profiles, to investigate whether changes in soil C and N stocks were related to land use. Over an average of 27 years, soils (0–30cm) in flat dairy pastures lost 0.73±0.16MgCha−1y−1 and 57±16kgNha−1y−1 but we observed no significant change in soil C or N in flat pasture grazed by “dry stock” (e.g., sheep, beef), or in grazed tussock grasslands. Grazed hill country soils (0–30cm) gained 0.52±0.18MgCha−1y−1 and 66±18kgNha−1y−1. The losses of C and N were strongly correlated, and C:N declined significantly. Further, results reported to 60 and 90cm show that the pattern of losses and gains extend beyond the IPCC accounting depth of 30cm. Specific causes for the soil C and N changes are unknown, but appear to be related to land use. In general, the losses under dairying correspond to systems with greater stocking rates, fertiliser inputs and removal of C and N in exported products. Gains in hill country pastures may be due to long-term recovery from erosion and disturbance following land clearance. The unexpected and contrary changes of C and N in different pasture systems (initially thought to be at steady state) demonstrates the need for global and national-scale collection of robust data investigating soil biogeochemical changes, not only for grasslands but also for other land uses. Re-sampling of soils can constrain the directions and magnitude of soil C and N change associated with land use and management to underpin C and N inventories and correctly identify mitigation options.

Dissolved organic matter leaching in some contrasting New Zealand pasture soils

Leaching of dissolved organic matter (DOM) from pastoral soils is increasingly seen as an important but poorly understood process. This paper examined the relationship between soil chemical properties, microbial activity and the losses of dissolved organic carbon (DOC) and nitrogen (DON) through leaching from six pasture soils. These soils differed in carbon (C) (4.6–14.9%) and nitrogen (N) (0.4–1.4%) contents and in the amount of organic C and N that had accumulated or been lost in the preceding 20+ years (i.e. −5131 to +1624 kg C ha−1 year−1 and −263 to +220 kg N ha−1 year−1, respectively). The paper also examined whether between‐soil‐type differences in DOC and DON leaching was a major explanatory factor in the observed range of soil organic matter (SOM) changes in these soils. Between 280 and 1690 kg C ha−1 year−1 and 28–117 kg N ha−1 year−1 leached as DOC and DON, respectively, from the six soils in a lysimeter study, with losses being greater from two poorly drained gley soils. Losses of C and N of this magnitude, while at the upper end relative to published data, could not fully explain the losses at Rawerawe, Bruntwood and Lepperton sites reported by Schipper et al. (2007). The study highlights the leaching of DOM as a significant pathway of loss of C and N in pasture soils that is often ignored or given little attention in predictive models and nutrient budgeting. Leaching losses of DOC and DON alone, or in combination with slightly increased respiration losses of SOM given a 0.2°C increase in the mean annual soil temperature, do not fully explain long‐term changes in the SOM observed at these sites. When soils examined in the present study were separated on the basis of drainage class, the losses of DOC by leaching were correlated with both total and hot‐water extractable C (HWC), the latter being a measure of the labile SOM fraction. Basal microbial CO2 respiration rates, which varied between 1 and 3.5 µg CO2‐C g−1 soil hour−1 in surface soils (0–75‐mm depth), was also linked to HWC and the quantities of C lost as DOC. Adoption of the HWC method as an approach that could be used as a proxy for the direct measurement of the soil organic C lost by leaching as DOC or respired needs to be examined further with a greater number of soils. In comparison, a poor relationship was found between the hot‐water extractable N (HWN) and loss of DON by leaching, despite HWN previously being shown to be a measure of the mineralizable pool of N in soils, possibly reflecting the greater competition for N than C in these soils.

Observations on bee species visiting white clover in New Zealand pastures

Click to increase image sizeClick to decrease image sizeKeywords: ApoideaLasioglossum spp.Leioproctus spp.Bombus terrestrisApis melliffera

The responses of three C4 grasses to elevated temperature and CO2 in the field

A series of field experiments were carried out to assess the impact of two important global change factors (increased temperature and elevated atmospheric CO2) on the germination and growth of three C4 grass species found in New Zealand pastures: Digitaria sanguinalis (summer grass), Paspalum dilatatum (paspalum) and Pennisetum clandestinum (kikuyu).

The effect of DCD on nitrate leaching losses from a winter forage crop receiving applications of sheep or cattle urine

Dicyandiamide (DCD) is an effective mitigation option for decreasing nitrate-nitrogen (NO3-N) losses in drainage water from New Zealand pastures. This study determined the relative effect of DCD on decreasing NO3-N losses from simulated sheep or cattle urine patches applied to a winter forage crop. Lysimeters were collected from a site in North Otago (Mottled Fragic Pallic Timaru silt loam). Keywords: drainage, lysimeters, urine, nitrate, dicyandiamide, winter forage cropping

Isolation and identification of plant growth-promoting bacteria associated with tall fescue

Tall fescue (Festuca arundinacea) is a useful alternative to ryegrass in New Zealand pasture but it is slow to establish. Naturally occurring beneficial bacteria in the rhizosphere can improve plant growth and health through a variety of direct and indirect mechanisms. Keywords: rhizosphere, endorhiza, auxin, siderophore, P-solubilisation

Survival ofCampylobacterspp. in bovine faeces on pasture

To determine the survival on pasture of Campylobacter spp. naturally present in bovine faeces and compare this with a previously published study using laboratory-cultured Campylobacter spp. Ten freshly collected cow pats were deposited on pasture during summer, and Campylobacter spp. were enumerated by enrichment broth culture. The counts in three pats were below detection limits. Counts of Campylobacter spp. in the other seven pats fell below detection limits within 14 days. The geometric means of the counts up to 7 days produced a T(90) of 2.2 days. Characterization of Campylobacter spp. by PCR and pulsed field gel electrophoresis indicated the presence of at least six genotypes of Campylobacter jejuni, Campylobacter coli and Campylobacter lari. Campylobacter spp. naturally present in cow faeces exhibited a similar survival rate to that previously determined using laboratory-cultured strains. The highly variable counts of naturally occurring Campylobacter spp., and the predominance of lower counts, also support the earlier decision to use laboratory-cultured strains in survival experiments. This study reaffirms the short survival of Campylobacter spp. in cow faeces deposited on pasture. This information will be incorporated into a 'reservoir model' for Campylobacter spp. in cow pats on New Zealand pastures.

A survey of enteric bacteria and protozoans in fresh bovine faeces on New Zealand dairy farms

To determine the counts and/or prevalence in fresh bovine faeces of Escherichia coli, enterococci, Campylobacter, Salmonella, shiga toxin-producing E. coli (STEC), Giardia and Cryptosporidium, as inputs to numerical models designed to estimate microbial loadings on pasture grazed by cattle in New Zealand. In each season over one year, samples of freshly deposited bovine faeces were collected from four New Zealand dairy farms (n = 155), and enumerated for E. coli, enterococci, Campylobacter, Giardia and Cryptosporidium. They were also tested for the presence of Salmonella and STEC. The overall median bacterial counts (g(-1) wet weight) were E. coli- 5.9 x 10(6); enterococci - 1.3 x 10(4); Campylobacter- 3.9 x 10(5). All counts were highly variable within and between samplings, and few seasonal or regional patterns emerged. However, mean Campylobacter counts were consistently higher in spring. No Salmonella spp. was detected, and only two samples were positive for STEC. Cryptosporidium and Giardia were isolated from 5.2% and 4.5% of the samples, respectively, yielding low numbers of (oo)cysts (1-25 g(-1) and 1-17 g(-1), respectively). Fresh bovine faeces are a significant source of E. coli, enterococci and Campylobacter on New Zealand pastures, although numbers are likely to vary markedly between faecal samples. The study provides the first significant set of indicator and pathogen counts for one of the largest sources of faecal contamination of natural waters in New Zealand, and will be used to model these inputs.

Degradation and metabolite formation of 17 β-estradiol-3-sulphate in New Zealand pasture soils

Estrogens-sulphates such as 17 β-estradiol-3-sulphate and estrone-3-sulphate are excreted by livestock in the urine. These conjugates are precursors to the free counterparts 17 β-estradiol and estrone, which are endocrine disrupting chemicals. In this study microcosm laboratory experiments were conducted in three pasture soils from New Zealand to study the aerobic degradation and metabolite formation kinetics of 17 β-estradiol-3-sulphate at three different incubation temperatures. The degradation of 17 β-estradiol-3-sulphate followed a first-order kinetic and the temperature dependence of the rate constants was sufficiently described by the Arrhenius equation. Degradation was different between the three investigated soils and the rate constants across the soils were significantly correlated to the arylsulphatase activity at 7.5 and 15 °C. Estrone-3-sulphate and 17 β-estradiol were identified as primary metabolites and estrone as a secondary metabolite. Results suggest arylsulphatase activity originating from soil microbial biomass is the main driver for the degradation of 17 β-estradiol-3-sulphate.