Search

Biochar application has been recognised as an effective way to improve soil functions. In this study, we investigated how adding biochar as an amendment affects soil biological and physico-chemical properties in grazed pastures in a one-year field-based mesocosm experiment conducted on two contrasting soils – a sil-andic Andosol and a dystric Cambisol. Each site had two pastures managed under different nutrient and livestock practices: with and without effluent under dairy cow grazing on the Andosol, and with either nil or high phosphorus (P) fertiliser input under sheep grazing on the Cambisol. The soil amendment treatments were: (i) willow biochar produced at 350 °C (1% w/w); (ii) lime, added at the liming equivalence of the biochar application (positive control); (iii) no amendments (negative control). With few exceptions, after 12 months and compared with initial values and controls, biochar caused (i) an increase in soil total nitrogen (N) and Olsen P content (all P

The lace bug, Gargaphia decoris Drake (Hemiptera: Tingidae) is a biological control agent of the South American invasive tree Solanum mauritianum Scopoli (Solanaceae). Gargaphia decoris has been established with some success in New Zealand and South Africa. In this study, we used the climatic modelling software CLIMEX (Hearne Scientific Software Pty Ltd, Australia) to assess how current and future climatic conditions might influence the geographic distribution of the biocontrol agent in these countries and worldwide. CLIMEX parameters were based on experimental data and calibrated with distribution records from the insect’s native and non-native range. In its native range, our model predicts that G. decoris could expand its distribution into northern coastal regions of Brazil, with tropical dry summer or monsoon climate. It could also expand beyond its native range into other countries with temperate and subtropical climates, as well as several regions with tropical savanna, equatorial and monsoon climate in coastal regions. In New Zealand the greatest potential for further expansion is within the North Island, and in South Africa the expansion is limited to mostly coastal areas. In a future climate change scenario (A1B, CSIRO Mk3 2090), there is a predicted reduced distribution globally, especially for Asia, Africa, and the Americas. In Europe the climatic suitability for G. decoris will increase, with an expanded potential distribution. In South Africa the potential distribution is predicted to slightly reduce, while an expansion is predicted into the colder regions of New Zealand. These models provide a useful tool to inform future releases of G. decoris and to guide monitoring efforts within and beyond release areas.

A six-month mesocosm experiment was conducted to investigate the joined effect of biochar and earthworms on soil properties and plant (white clover) growth in two contrasting soils – a dystric Cambisol and a sil-andic Andosol, both soils with pH-H2O

Mating and oviposition complement each other in parasitoid reproduction; delay in either of these activities has disparate consequences for the fitness of the parasitoid. We investigated the effects of mating and oviposition delay on parasitism rate and progeny sex ratio in a parasitic wasp Diaeretiella rapae. Egg dynamics in the ovaries of females of different ages, and females which completed different numbers of oviposition bouts were also examined. Delay in mating and oviposition adversely affected reproductive performance of both male and female D. rapae. Delayed oviposition resulted in reduced parasitism rates in both mated and unmated females. The progeny sex ratio was female-biased, but the proportion of female offspring decreased towards the end of D. rapae life. Although females emerged with developed eggs, the egg load in the ovaries of unmated and naive females initially increased then continuously decreased with age, suggesting partial resorption of eggs towards the end of a females life. Oviposition rate of unmated females was low before mating. The extent of mating delay experienced by females affected the sex ratio of their progeny, causing overproduction of males. Delayed mating did not affect the courting capacity of males, but reduced the number of their offspring and proportion of female offspring. The duration of copulation was longer in older males. The results of this study clearly indicate the importance of parasitoid age in biological control programmes, and suggests the use of 1–2 days old D. rapae for best results.

Host age-dependent fitness of Diaeretiella rapae was studied on cabbage aphid Brevicoryne brassicae. When given a choice of nymphs of four different ages (1, 3, 5 and 7 days), females showed a strong preference for oviposition in older nymphs, which were also the largest in the body size, and left the majority of younger nymphs unparasitised. More than 70% of offspring emerged from 5-day and 7-day old parasitised nymphs. Parasitoids develop faster in older hosts than in younger hosts. Development time of males was shorter than females in older hosts, but the development time of males and females was similar in younger hosts. The body size of adult D. rapae was positively correlated with the age of the hosts in which they developed. The sex ratio of offspring was found to be female-biased. A higher proportion of females emerged from older hosts. D. rapae females emerged from older hosts lived significantly longer. The potential fecundity of the females emerged from older (larger in body size) hosts was significantly greater than of those emerged from younger hosts with smaller bodies. Results suggest that D. rapae preferred older hosts to maximise the reproductive fitness gain. The oviposition strategy of D. rapae is discussed in the context of efficiency of this parasitoid in biological control programmes.

Soil invertebrates are coming under increasing pressure as pastoral agriculture is intensified. Grazing livestock affects the soil invertebrate community by impacting on the physical habitat through treading, and on nutrient cycling through dung and urine return. In this study the sensitivity of soil invertebrates to livestock was examined by quantifying the abundance and diversity of invertebrates in the grazed pasture and comparing it with those under adjacent permanent fence lines on three different soil types at three locations. Resilience of the invertebrate communities was also explored by sampling mown, fertilised and irrigated plots within grazed pastures, where livestock had been excluded for the previous three years. Of the soil invertebrates the predatory and omnivorous nematodes, Oribatida and predatory macrofauna were the most sensitive to grazing livestock. In comparison, earthworms with their higher mobility and ability to burrow were more resistant to livestock. The combined effect of removing treading pressure and moisture stress in the fenced plots appeared to be the major factors influencing invertebrate recovery, rather than the quantity and quality of food entering the soil food-web as influenced by fertiliser application. Earthworms, exhibited the greatest resilience, doubling in abundance in the mown and irrigated plots. Nematodes were more resilient than the larger and longer-lived Oribatida. The oribatid community in the irrigated and mown plots were limited in both diversity and abundance in comparison to the community under the fence line. That the vulnerability of soil invertebrates to livestock treading was consistent at all three sites would suggest that organism characteristics (i.e., life-history and ability to move through the soil) and trophic interactions are important in structuring the biological community.

Earthworms play an important role as primary decomposers in the incorporation and initial mixing of plant litter. This study explored the response of earthworms to increasing fertiliser inputs, pasture production and livestock numbers (and their influence on food availability and soil physical condition) on six different managements in sheep-grazed and fifteen different managements in dairy-grazed pastures in a variety of New Zealand soils. Native earthworms were only found in some low-fertility pastures. Accidentally introduced peregrine earthworms, when present, dominate pasture soils. Of these, endogeic earthworms dominated the earthworm community and were positively associated with soil types with higher bulk densities. Peregrine anecic earthworms were absent from most hill-country sheep-grazed pastures, however in more fertile and productive dairy-grazed pastures they reached a biomass of up to 2370 kg ha−1. Only anecic earthworms showed a positive response to the increasing pressures associated with higher potential dry matter inputs and liveweight loadings of grazing livestock on soil, while epigeic earthworms declined. The positive response of anecic earthworms probably reflects the combined effect of the increase in food resources, including dung and plant litter, available on the soil surface, and their lower susceptibility to livestock treading pressure. Anecic species may be a suitable substitute for incorporation of surface litter in those soils where livestock treading limits epigeic earthworm populations. This study confirmed previous observations of limited distribution of the introduced Aporrectodea longa in pastoral hill-country soils in the North Island, and their near absolute absence from the South Island of New Zealand. This would suggest that large areas of New Zealand pastoral farmed soils could benefit from the introduction of anecic species from other parts of New Zealand which already contain A. longa.

Organic pasture management includes a focus on mixed livestock grazing, restrictions on nutrient inputs and livestock pest control. These are all factors which influence the environment of soil invertebrates. In this study, soil macrofauna, mesofauna and microfauna were collected from duplicate 11 and 20 year old organic and conventional legume-based sheep-grazed pasture systems. Pastures in both systems had received the same annual input of reactive phosphate rock and elemental sulphur and were stocked with the same numbers of sheep. The major difference between the two systems was absence of the chemical control of livestock pests on the organic system, resulting in lower sheep liveweights. Two ungrazed pastures which had not received any nutrient inputs for 20+ years were also sampled as part of the study to provide an additional contrast. No significant differences in either the diversity or abundance of the soil invertebrate community were found between the organic and conventional systems, despite the use of chemicals in the conventional system. The lack of difference suggests that many of the observed and reported responses to organic management reflect altered nutrient inputs and grazing management (which were the same in the current study), rather than the cessation of chemical controls in the organic system. In contrast, the invertebrate community in the unfertilised, ungrazed pasture was distinctly different from both the grazed systems. The ungrazed pasture had a higher diversity with more New Zealand endemic species than the grazed pasture. This included twice as many large Oribatida as soil pore size increased. The lower litter quality from the lack of nutrient inputs in the ungrazed pasture was reflected in both lower earthworm abundance and the Nematode Channel Ratio (indicative of a higher proportion of fungal- than bacterial-feeding nematodes), than the grazed pasture. We conclude that organic management when limited to a comparison of livestock pest control is not beneficial to soil invertebrates. Management practices such as stocking rates and fertiliser regime, by altering the soil physical environment and food resources, are more important in influencing invertebrate populations in this soil. Some would argue these altered management practices are an integral part of an organic production system.

The impact on soil invertebrates of changes in the physical environment and feed availability in intensive pastoral systems is difficult to predict given the number of interacting factors. This study explores the influence of a change in defoliation regimes (pastoral fallow, cut and carry, cow grazing), feed type and availability to ruminants (pasture and pasture supplemented with maize) and dairy cow stocking rates (3, 4 and 5 cows ha −1 ) on the abundance and diversity of soil invertebrates (macrofauna, mesofauna and microfauna). Samples were collected from two depths (0–7.5 and 7.5–15 cm) on a well-structured loamy Andosol soil in two seasons (autumn and winter). Treatments allowed an independent assessment of the influence of changes in food sources to the soil food-web from that of physical disturbance from livestock treading. There was a clear distinction in habitable pore space between the fallow and other treatments. The high porosity under fallow (28% under fallow vs. 11–13% under other treatments) appears to be an important factor, increasing faunal abundance and biomass, including macrofaunal predators and Oribatida. Large inputs of litter under fallow benefited epigeic earthworms and resulted in a dominance of bacterial-feeding nematodes (Nematode Channel Ratio 0.97), reflecting the still high quality litter from previous management. Grazed pastures had higher abundances of plant-feeding and plant-associated nematodes as they were stimulated by increased root growth (abundances up to 1.2 × 10 6 ind m −2 ). While there was little difference in total earthworm abundance between treatments, anecic A. longa became progressively more abundant under higher cow stocking rates as food availability and physical pressure increased (18 ind m −2 vs. 128 ind m −2 , under 3 and 5 cows ha −1 , respectively). Initial earthworm functional diversity is important and we suggest that anecic earthworms can substitute for epigeic earthworms in intensively managed pastoral systems by incorporating litter, as well as being important ecosystem engineers.

Surface energy balance and 24-h evapotranspiration were mapped on an agricultural landscape with SRF willows using a remote sensing-based model to provide information on the water use by different land cover types. The results demonstrate the influence of land cover and vegetation type on surface energy balance and water losses. The evapotranspiration from forests was much higher than for other land cover types, corresponding to the significant cooling of the land surface. The SRF willow plantings were on average 3.6 °C cooler than the surrounding grassy areas; the 24-hour evapotranspiration from willows was 1.6 times higher than the evapotranspiration from surrounding grass, but lower than evapotranspiration from the forests. The possibility of changes in evapotranspiration patterns, local climate, and regional water balance with increasing acreage in SRF crop are discussed.

This study examined the influence of superphosphate fertiliser application and sheep stocking rate on the density and diversity of soil macro- and mesofauna, particularly earthworms and oribatid mites in two sheep-grazed New Zealand hill pastures. The low-intensity (LI) long-term experimental farmlet is managed with no fertiliser and a low sheep stocking rate (9 stock units/ha); the high-intensity (HI) farmlet receives 34 kg P/ha/yr and has a high sheep stocking rate (16 stock units/ha). Soil mesofaunal samples were collected at two depths (0–7.5 cm and 7.5–15 cm). Earthworm species, major mesofaunal groups and oribatid species were identified, and the trophic groups, body size, biomass, mode of reproduction and global distribution of oribatid species established. Soil fertility, temperature, moisture, and pasture composition were also measured. The study tested the hypotheses that intensive pasture will have fewer native species, and among Oribatida, lower proportion of fungivores, higher proportion of asexuals, and higher proportion of smaller species with shorter life cycles. The results reflect the complex effect of intensive pasture management on soil organisms. Earthworm densities were higher in the intensive pasture system, with the exception of endemic Octochaetus multiporus. The low-intensity pasture system, where soil C:N ratio was wider, sheep stocking rate was lower and earthworm numbers were lower, supported higher density and diversity of soil mesofauna and Oribatida, which were concentrated in the topsoil (0–7.5 cm depth). In the high-intensity pasture system the zone of biological activity was expanded vertically—the mesofauna and Oribatida, although lower overall in density and diversity, were more evenly distributed between the 0–7.5 cm and 7.5–15 cm soil depths, suggesting reduced effect of livestock treading and greater food availability at depth. Pastoral intensification influenced oribatid trophic structure, with fungivorous species dominant in LI and herbofungivorous species in HI pasture, which probably reflected underlying differences in food resources, such as more fresh root biomass in HI. There was some evidence suggesting a shift to short-lived, cosmopolitan, and asexually reproducing Oribatida in HI at 0–7.5 cm soil depth. Oribatid density (which reflected mesofaunal densities), overall diversity, trophic groups, life-history characteristics and especially vertical distribution were more sensitive to soil management regime than their community structure.

This study explored the relationship between landscape-level factors (land use type) and the diversity of soil mites (Acari: Oribatida, Mesostigmata) at a within-site scale, using diversity measures including point diversity (local species diversity within a single sampling point), patterns of species turnover among the sampling points, and alpha diversity (total species richness in a habitat). The land use types included corn fields, intensive short-rotation forestry plantations, two types of abandoned agricultural fields, and hardwood forests. Land use type was identified as a significant factor influencing both small-scale (within individual soil cores) and site-scale diversity of Oribatida, which increased in the order “corn → willow → abandoned fields → forests”. There was no statistical relationship between land use type and abundance or diversity of Mesostigmata. Using a bootstrapping method to generate “random” communities, we found that all land use types had significantly more diverse patterns of species abundance than was expected by chance. On the other hand, the patterns of presence/absence of species were less diverse than expected by chance. Local site factors were significant in driving the patterns of diversity of soil mites at the site scale; land use type was less important. The overall structure of Oribatida and Mesostigmata assemblages was significantly related to land use type. We conclude that soil communities respond to land management on both local scales and habitat-wide scales.

To address the question of how production of woody biomass crops on retired agricultural land will affect soil biodiversity, we investigated the effects of site preparation techniques associated with production of willow (Salix sp.) on the abundance, species diversity and community structure of two groups of mites (Oribatida and Gamasida). The effects of tillage, herbicide application, cover crop and mode of planting were evaluated in a 4 year-long replicated field experiment. Twenty-eight species of Oribatida and 35 species of Gamasida were represented in willow plantings. The predaceous Gamasida had more pronounced changes in abundance and diversity in response to the site preparation treatments than saprophagous and mycophagous Oribatida. Results indicated that (1) soil cultivation had negative effects on the abundance and diversity of soil mites during the first year of the experiment, later superceded by other factors; (2) the use or lack of tillage contributed to differences in mite community structure; and (3) following the initial disturbances, the abundance and diversity of soil mites increased in all treatments up to the end of the experiment. The success or failure of the willow crop and the changes in soil environments created by the different plant communities could explain the differences in soil mite populations among treatments best, especially 2 and 3 years after the beginning of the experiment.