C. van Koten

Physicochemical properties of 50 New Zealand pasture soils: a starting point for assessing and managing soil microbial resources

New Zealands pastoral agriculture faces challenges associated with increasing on-farm productivity, while minimizing the environmental footprint of farming. Soil microorganisms mediate a wide range of processes that affect plant production and also have environmental consequences. However, there has been little attempt to manage these in a farming system context. This is primarily because of difficulties in determining what microbiological resources are present in soils, how they link with soil processes and function, and how variation in soil types, climate or farm management practices influence microbial function. We sampled 50 pasture soils from across 11 of New Zealands major soil groups, 10 geographical zones and under different grazing systems (high input dairy units to dry-stock grazing). The environmental and physicochemical properties of the soils were characterized and DNA extracted. The concentrations of elements primarily associated with fertilizer use (phosphorus, nitrogen and sulphur) were all significantly (P< 0.05) higher in dairy-based systems, yet soil carbon was unchanged. The concentration of many properties varied between the soil types, reflecting a combination of their pedogenesis and predominant land use. The amount of DNA in soils was closely related to anaerobically mineralizable nitrogen (P< 0.001), a measure of soil organic matter content, but did not vary with grazing system intensity. The extensive data set for each soil, coupled with DNA originating from the same samples, provides a unique opportunity for a number of ancillary studies to map biological resources in pastures and assess how these are regulated by edaphic and environmental properties.

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.

Soil aeration affects the degradation rate of the nitrification inhibitor dicyandiamide

Dicyandiamide (DCD) is a nitrification inhibitor of variable efficacy. In soils, DCD biodegradation rate is known to be a function of temperature; however, microbial activity can also be affected by soil aeration and substrate availability. Studies determining the effects of soil aeration on DCD degradation are few. We tested the null hypothesis that the rate of degradation of DCD in soil would be the same under aerobic and anaerobic conditions. Soils from two sites with different organic matter concentrations but the same parent material were sampled to the same depth, sieved, and repacked into tubes (‘soil cores’). These were saturated with a DCD solution (30 µg mL–1) and placed under controlled aeration conditions by imposing five levels of matric potential (0, –1, –3, –6, and –10 kPa) at a constant temperature (22°C). The relative O2 diffusivity (O2 diffusion coefficient in soil/O2 diffusion coefficient in air, Dp/Do) was measured, along with periodic destructive sampling of soil cores over 40 days, to assess the DCD concentrations. Fitting first-order exponential functions to plots of soil DCD concentration v. time showed that the DCD degradation rate was greater (P < 0.05) when the soil was aerobic (Dp/Do ≥ 0.01). Consequently, the null hypothesis was rejected. These results show that soil aeration determines the degradation rate of DCD.

Formulations for delivering Trichoderma atroviridae spores as seed coatings, effects of temperature and relative humidity on storage stability.

We aimed to evaluate different formulations for their ability to adhere Trichoderma atroviridae spores to wheat seeds, and promote survival during storage at a range of temperatures and relative humidities (RH).

Use of shallow samples to estimate the total carbon storage in pastoral soils

Abstract Using data from pastoral soils sampled by horizon at 56 locations across New Zealand, we conducted a meta-analysis. On average, the total depth sampled was 0.93±0.026 m (± SEM), and on a volumetric basis, the total C storage averaged 26.9±1.8, 13.9±0.6 and 9.2±1.4 kg C m−2 for allophanic (n=12), non-allophanic (n=40) and pumice soils (n=4), respectively. We estimated the total C storage, and quantified the uncertainty, using the data for samples taken from the uppermost A-horizon whose depth averaged 0.1±0.003 m. For A-horizon samples of the allophanic soils, the mean C content was 108±6 g C kg−1 and the bulk density was 772±29 kg m−3, for non-allophanic soils they were 51±4 g C kg−1 and 1055±29 kg m−3, and for pumice soils they were 68±9 g C kg−1 and 715±45 kg m−3. The C density—a product of the C content and bulk density—of the A-horizon samples was proportional to their air-dried water content, a proxy measure for the mineral surface area. By linear regression with C density of the A-horizon, the total C storage could be estimated with a standard error of 3.1 kg C m−2, 19% of the overall mean.

Increasing soil aeration reduces mitigation efficacy of dicyandiamide when targeted at ruminant urine-derived N2O emissions

Soil aeration effects on the efficacy of dicyandiamide (DCD) at reducing reactive nitrous oxide (N2O) fluxes from ruminant urine patches have not been assessed. We tested the null hypothesis that increasing soil aeration and dissolved organic carbon (DOC) levels, following ruminant urine deposition, would reduce DCD efficacy, as determined from measurements of N2O fluxes. Soil aeration was controlled (−1 or −10 kPa, the former being wetter and less aerated) within a factorial experiment that also included DCD and ruminant urine (700 kg N ha−1) treatments, destructively sampled over 40 days. Increased soil aeration corresponded with a decrease in DCD efficacy. However, contrary to the null hypothesis, increasing soil DOC concentrations following urine application did not correspond with greater DCD degradation rates. In fact, at −1 kPa applying urine increased the DCD half-life from 23.5 (±3.0) to 53.3 (±7.5) days, while at −10 kPa the DCD half-life was not affected by urine application (14.9 [±2.9] and 16.7 [±2.7] days, with or without urine, respectively). The efficacy of DCD at mitigating urine-induced cumulative N2O fluxes was 95% at −1 kPa and 57% at −10 kPa. This study confirms that the degradation of DCD is slower, and thus its efficacy is better, in wet soils compared with well-aerated soils.

The occurrence of ryegrass staggers and heat stress in sheep grazing ryegrass-endophyte associations with diverse alkaloid profiles

Abstract AIMS: To compare ryegrass pastures infected with endophytes producing diverse alkaloids for their ability to cause ryegrass staggers in grazing lambs; to compare respiration rates and rectal temperatures of these lambs after exposure to heat stress, and to compare liveweight gains during the study period. METHODS: Ryegrass pastures of cultivar Trojan infected with NEA endophytes, branded NEA2 (T-NEA2), endophyte-free Trojan (T-NIL), Samson infected with standard endophyte (S-STD), Samson infected with AR37 endophyte (S-AR37) and endophyte-free Samson (S-NIL), were grazed by lambs (n=30 per cultivar) for up to 48 days in February and March of 2012 and 2013. Pasture samples were analysed for alkaloid concentrations and lambs were scored for ryegrass staggers at intervals during the study period. Liveweight was recorded at the start (Day 0) and end of the study, and rectal temperatures and respiratory rates were measured in lambs exposed to heat stress on Days 23 and 26, in 2012 and 2013, respectively. RESULTS: Concentrations of alkaloids were lower in 2012 than 2013, associated with warmer and drier conditions in 2013, and the prevalence of ryegrass staggers was low in 2012. In 2013, concentrations of ergovaline were similar in T-NEA2 and S-STD, but concentrations of lolitrem B were lower in T-NEA2 than S-STD. S-AR37 produced epoxy-janthitrems but no lolitrem B or ergovaline. In 2013, by Day 20, 9/30 (30%) sheep grazing S-STD had severe staggers (score ≥4), and by Day 47 all sheep had been removed from this cultivar due to severe staggers. By Day 47, 18/30 (60%), 4/30 (13%) and 0/30 (0%) sheep grazing S-AR37, T-NEA2 and T-NIL pastures, respectively, had severe staggers. There were no differences in mean daily weight gain of lambs between cultivars in either year. In both years, mean rectal temperature and respiration rate following exposure to heat stress were highest in sheep grazing S-STD and T-NEA2, and lowest in sheep grazing T-NIL. CONCLUSIONS: In lambs grazing different ryegrass pastures infected with endophytes, ryegrass staggers was most severe on S-STD, less severe on S-AR37 and least on T-NEA2. When under heat stress, lambs grazing ergovaline-producing S-STD and T-NEA2 pastures had increased respiration rates and rectal temperatures compared with lambs grazing T-NIL. CLINICAL RELEVANCE: If ambient temperatures are suitable, NEA2-branded endophytes have the potential to express concentrations of ergovaline sufficient to induce heat stress in grazing sheep.

Nitrous oxide emissions from drained peat soil beneath pasture

ABSTRACT Nitrous oxide (N2O) emissions (EN2O) from drained peat soils used for pastoral agriculture have not been measured throughout the year in New Zealand. In response to this research gap, EN2O was measured fortnightly for 1 year in the Waikato region in a plot that was not grazed or nitrogen (N) fertilised. The time series was variable, the frequency distribution skewed and the fortnightly means correlated. To account for these factors, the data were loge transformed and an order 2 autoregressive model used to estimate a mean EN2O of 4.3 g N ha−1 d−1 and 95% confidence limits of 0.6–29.1 g N ha−1 d−1. There was a statistically significant, inverse relationship between EN2O and the depth to groundwater. In winter, when rainfall totalled 393 mm, EN2O and soil N content were significantly greater under a rain shelter designed to minimise N loss by leaching, than in an uncovered plot.

Ergovaline does not alter the severity of ryegrass staggers induced by lolitrem B

AIM: To investigate a possible interaction between lolitrem B and ergovaline by comparing the incidence and severity of ryegrass staggers in sheep grazing ryegrass (Lolium perenne) containing lolitrem B or ryegrass containing both lolitrem B and ergovaline. METHODS: Ninety lambs, aged approximately 6 months, were grazed on plots of perennial ryegrass infected with either AR98 endophyte (containing lolitrem B), standard endophyte (containing lolitrem B and ergovaline) or no endophyte, for up to 42 days from 2 February 2010. Ten lambs were grazed on three replicate plots per cultivar. Herbage samples were collected for alkaloid analysis and lambs were scored for ryegrass staggers (scores from 0–5) weekly during the study. Any animal which was scored ≥4 was removed from the study. RESULTS: Concentrations of lolitrem B did not differ between AR98 and standard endophyte-infected pastures during the study period (p=0.26), and ergovaline was present only in standard endophyte pastures. Ryegrass staggers was observed in sheep grazing both the AR98 and standard endophyte plots, with median scores increasing in the third week of the study. Prior to the end of the 42-day grazing period, 22 and 17 animals were removed from the standard endophyte and AR98 plots, respectively, because their staggers scores were ≥4. The cumulative probability of lambs having scores ≥4 did not differ between animals grazing the two pasture types (p=0.41). CONCLUSIONS AND CLINICAL RELEVANCE: There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated.