Pasture Soils Research Articles

Mathematical Functions to Model the Depth Distribution of Soil Organic Carbon in a Range of Soils from New South Wales, Australia under Different Land Uses

The nature of depth distribution of soil organic carbon (SOC) was examined in 85 soils across New South Wales with the working hypothesis that the depth distribution of SOC is controlled by processes that vary with depth in the profile. Mathematical functions were fitted to 85 profiles of SOC with SOC values at depth intervals typically of 0–5, 5–10, 10–20, 20–30, 30–40, 40–50, 50–60, 60–70, 70–80, 80–90 and 90–100 cm. The functions fitted included exponential functions of the form SOC = A exp (Bz); SOC = A + B exp (Cz) as well as two phase exponential functions of the form SOC = A + B exp (Cz) + D exp (Ez). Other functions fitted included functions where the depth was a power exponent or an inverse term in a function. The universally best-fitting function was the exponential function SOC = A + B exp (Cz). When fitted, the most successful function was the two-phase exponential, but in several cases this function could not be fitted because of the large number of terms in the function. Semi-log plots of log values of the SOC against soil depth were also fitted to detect changes in the mathematical relationships between SOC and soil depth. These were hypothesized to represent changes in dominant soil processes at various depths. The success of the exponential function with an added constant, the two-phase exponential functions, and the demonstration of different phases within the semi-log plots confirmed our hypothesis that different processes were operating at different depths to control the depth distributions of SOC, there being a surface component, and deeper soil component. Several SOC profiles demonstrated specific features that are potentially important for the management of SOC profiles in soils. Woodland and to lesser extent pasture soils had a definite near surface zone within the SOC profile, indicating the addition of surface materials and high rates of fine root turnover. This zone was much less evident under cropping.

The potential for potassium chloride fertiliser applications to leach cadmium from a grazed pasture soil

Cadmium (Cd) is a biotoxic element that can enter the human food chain via plants grown in Cd-enriched soil. Chloride (Cl) can solubilise Cd in soil. Although fertilisers containing Cl are not recommended as they may increase plant uptake of Cd, potassium chloride (KCl) is regularly applied to replenish and maintain K in the soil of grazed pastures. A trial was conducted to see if an autumn application of low (0.02 mol L−1, equivalent to 30 kg K ha yr−1) or high (0.04 mol L−1) KCl and the same molar rates of CaCl2 (used as a check to other studies) would leach Cd over 4-months of normal (300-mm) or high (600-mm) autumn-winter rainfall without enriching Cd in plant shoots. Leaching losses of Cd were greater from the high KCl and CaCl2 treatments (1.80 and 1.70 g ha−1, respectively) than the low KCl treatment (1.27 g ha−1). All loads lost from the Cl treatments were greater than from the control treatment (0.53 g ha−1). Losses from Cl treatments represented 29–41% of the Cd applied in an annual application of 250 kg superphosphate ha−1. Pasture shoot Cd concentrations were not different to the control (mean = 0.088 mg kg−1). Applying Cl (e.g. as KCl) in autumn may be a simple strategy to help slow the enrichment of soil Cd and does not increase the uptake of Cd by pasture shoots.

Soil‐Gas Diffusivity and Soil‐Moisture effects on N2O Emissions from Intact Pasture Soils

Grazed pastures are recognized as a dominant source of nitrous oxide (N2O), a highly potent greenhouse gas. Studies have examined soil physical controls on N2O emissions, including soil moisture status. Limited attempts to link N2O emissions with soil‐diffusivity (Dp/Do), using repacked soil cores, have shown peak N2O emissions to align with a relatively narrow window ofDp/Do, despite a relatively wide range in water‐filled pore space (WFPS), across a range of soil bulk densities. Such detailed studies have not been performed withintactsoil cores. We investigated the effects of soil‐water characteristic (SWC) andDp/Doon N2O emissions from intact soil samples, retrieved at three depths (0–5, 5–10, 10–15 cm) from three perennial pasture sites that received a KNO3solution (1800 mg, N mL−1). We observed distinct fingerprints of SWC andDp/Do, which showed clear effects of soil structure on diffusion‐controlled gas emissions. Depth‐wise variation in soil moisture diminished as the soil was subjected to higher matric potential (> ∼ ‐100 kPa). Variation inDp/Do, was more pronounced in the dry soil (> ∼ ‐1000 kPa), being largely constrained by soil moisture in wet soil (∼ ‐100 kPa) with little depth‐wise variation. Measured N2O fluxes peaked within narrow ranges of WFPS andDp/Do, 0.90–0.95 and 0.005–0.01, respectively. The value ofDp/Docan be determined using parametric models and presents a pasture management (e.g., irrigation, soil physical disturbance such as pasture renovation and animal treading)) tool to minimize N2O emissions: soilDp/Doshould be maintained above a range of 0.005–0.01 to minimize N2O emissions.Core IdeasPeak N2O fluxes fromintactsoil cores occurred when diffusivity ranged from 0.005–0.01This peak N2O flux diffusivity range was 0.005–0.01 regardless of soil or depth (0–15 cm)The diffusivity range for peak N2O flux equalled that observed inrepackedsoil coresDiffusivity values are readily determined and add to the suite of soil management tools

Improved Pastures Support Early Indicators of Soil Restoration in Low-input Agroecosystems of Nicaragua.

Pasture degradation hinders livestock production and ecosystem services that support rural smallholder communities throughout Latin America. Silvopastoral systems, with improved pasture cultivars (especially Brachiaria spp.) and multipurpose trees, offer a promising strategy to restore soils and improve livelihoods in the region. However, studies evaluating the impact of such systems on pasture productivity and soil health under realistic smallholder constraints are lacking. We evaluated the impact of improved pasture grass and tree establishment on a suite of soil health indicators in actively grazed, low-input, farmer-managed silvopastoral systems. In August 2013, paired pasture treatments (improved grass with trees vs. traditional pastures) were established on nine farms with similar land-use histories near Matagalpa, Nicaragua. On each farm, one treatment was left as traditional pasture with naturalized grass (Hyparrhenia rufa), while the adjacent treatment was sown with the improved grass (Brachiaria brizantha cv. Marandu) and planted with tree saplings without fertilizer. In August 2015, we measured standing biomass and a suite of chemical, biological, and physical soil health variables. Improved silvopastoral systems with B. brizantha produced more standing grass biomass and supported higher levels of earthworm populations and permanganate oxidizable carbon (POXC) compared to the traditional control. Correlations suggest that earthworms and POXC were associated with incipient improvements to soil aggregate stability and water holding capacity. We report measurable improvements to soil health just two years following the establishment of improved pasture systems under common smallholder management practices and suggest that these systems, even with minimal fertility inputs, have the potential to enhance regional sustainability.

Use of a urease inhibitor to mitigate ammonia emissions from urine patches

ABSTRACT Urine deposition by grazing livestock is the single largest source of ammonia (NH3) volatilisation losses in New Zealand. Urease inhibitors (UI) have been used to mitigate NH3 losses from fertiliser urea and animal urine. In previous trials, the UI effect in reducing NH3 emissions from urine has been measured by applying urine mixed with the UI to the pasture soil thus increasing the chances of better interaction of the UI in inhibiting the urease enzyme. However, these trials do not represent a realistic grazing scenario where only urine is deposited onto the soil. This current research aimed to identify the best time to spray nBTPT (a UI containing 0.025% N-(n-butyl) thiophosphoric triamide) onto pasture soil to reduce NH3 losses from urine patches. The treatments were: a control (without urine and nBTPT), urine alone at 530 kg N ha–1 and urine plus nBTPT. The UI was applied to the chambers and soil plots 5 and 3 days prior to urine deposition, on the same day and 1, 3 and 5 after urine deposition in autumn. Ammonia losses were measured using the dynamic chamber method. The application of the inhibitor prior to urine deposition reduced NH3 losses with reductions of 27.6% and 17.5% achieved for UAgr-5 and UAgr-3, respectively. However, reductions in NH3 emission were 0.6–2.9% for inhibitor applied post urine deposition. There was also a reduction in both soil NH4 +–N concentration and soil pH in comparison with urine alone or with the treatments where nBTPT was applied after urine deposition.

Spatio Temporal Soil Moisture Dynamics and Runoff under Different Soil Cover Conditions in a Semiarid Representative Basin in Brazil

Abstract. Hydrological studies in small basins are essential for investigating the role of distinct processes on water resources conservation and to assess the impact of the natural ecosystems on improving water security especially in semiarid environments. In Brazil, the cooperative hydrological Network REHISA (“REde de HIdrologia do SemiÁrido”) comprises hydrologists from several universities of Brazil, focusing on field measurements, monitoring and modeling activities in well instrumented experimental rural catchments located at different regions and biomes in Semiarid environment. Water scarcity is a common aspect among the catchments, as well as risks of soil and water degradation. The objective of this work is to present assessments of near surface soil moisture spatial-temporal distribution, and to evaluate the impact of soil conservation techniques in reducing runoff, using small-scale experimental plots in a representative catchment of the Pernambuco State, Brazil. The study catchment is located in Alto Ipanema River Basin (AIRB) (with an area of 150 km2), which is located at the semiarid region of the São Francisco River (area of 641 000 km2). Soil and water monitoring was performed in experimental plots with different soil cover conditions (Bare soil plots; Plots with natural cover – Caatinga Biome vegetation; Plots with cactus Palma barriers; and Plots with mulch cover – Dry grass mulch at 4 t ha−1), where probes were installed for high resolution soil moisture assessment. In addition, regular soil moisture monitoring campaigns were conducted at 7 different locations, using a capacitance probe, with arboreal and shrub Caatinga vegetation, pasture and bare soil, predominantly Brachiaria decumbens. Mulch cover runs close to the Caatinga cover, but still with higher runoff generation, and presenting lower soil moisture temporal mean values. Caatinga was highly effective in terms of soil and water conservation at the small basin scale for both the dry and the wet season, resulting in a positive nexus between vegetation and water availability at the region.

Human disturbance affects enzyme activity, microbial biomass and organic carbon in tropical dry sub-humid pasture and forest soils

ABSTRACTThe Brazilian dry forest occupies an area of about 1 million km2 approximately 46% of which has been deforested. Many studies have been done on the effects of this on productivity and soil chemical attributes. However, little is known about soil enzymatic activity, which is sensitive to environmental changes. The objective of this study was to evaluate the effects of deforestation using different levels of human disturbance on soil enzyme activities, organic carbon content, microbial biomass, and microbial community. We studied areas covered with forest (TDF), old grass (OG), or new grass (NG). Soils from NG had increased microorganisms, which restored important processes related to carbon, sulfur, and nitrogen cycling, so that they resembled those in the forested area. The results of this study showed that the conversion of forest to pasture with a high level of human disturbance could decrease the activities of β-glucosidase, urease, alkaline phosphatase, and fluorescein diacetate in the soil by up to 87%, 66%, 62%, and 58%, respectively. These findings suggest that human disturbance can cause substantial changes in the enzymatic activity and microbial community in the soil. We suggest that maintaining grass pasture with low human disturbance should have fewer impacts on soil quality.

Reduction of viable Mycobacterium avium ssp. paratuberculosis in slurry subjected to anaerobic digestion in biogas plants

Cattle infected with Mycobacterium avium ssp. paratuberculosis (MAP) shed the bacterium in their feces. This may lead to considerable concentrations of MAP in slurry, which has been postulated to contribute to MAP transmission when this slurry is used as fertilizer. For other bacterial species, anaerobic digestion has been shown to reduce bacterial load and to increase the safety of organic waste. Therefore, the objective of this study was to investigate the effects of anaerobic digestion in biogas plants on MAP survival in slurry from 16 dairy farms with a history of MAP infection. Presence of MAP was determined using MAP culture and a commercial MAP IS900 quantitative PCR (qPCR) applied on untreated slurry samples, slurry samples after primary fermentation, and digestate. Unfermented slurry samples from most enrolled farms tested positive for MAP, via both culture and qPCR. After the fermentation process, MAP could no longer be cultured in most samples, with the exception of 2 samples from farms where high numbers of MAP-shedding cows were kept at the time of sampling. A Bayesian binomial model predicted a probability of 93% for a MAP-negative culture result after fermentation. In most samples, MAP DNA was still detectable when using the IS900 qPCR. The probability of a negative result in qPCR was estimated to be 27%. Results of this study indicate that subjecting MAP-positive slurry to anaerobic digestion in biogas plants leads to a reduction of viable MAP below the detection limit; however, MAP DNA remained detectable. It remains undetermined whether MAP DNA detected in fermentation products is a residue of MAP degradation or belongs to viable MAP below the detection limit or in a dormant state. In conclusion, subjecting MAP-positive slurry to anaerobic mesophilic digestion reduces viable MAP concentration below the detection limit. The use of digestion products as fertilizer on pasture and agricultural soils instead of untreated slurry may therefore reduce the risk of MAP transmission.

Dietary Nutritive Value, Dung Quality, Decomposition, and Nutrient Movement into Soil in Smooth Bromegrass Pastures

Legumes increase forage nutritive value in pastures; however, literature addressing the impacts on dietary nutritive value, dung quality, decomposition, and nutrient movement into soil remains scarce. Cattle grazing legume‐interseeded smooth bromegrass (Bromus inermis Leyss.) pastures may select diets with greater nutritive value and consequently produce dung that decomposes faster and increases nutrient movement into soil relative to cattle grazing N‐fertilized and unfertilized smooth bromegrass pastures. In 2014 and 2015, we collected rumen and dung samples from replicated experiments to evaluate effects of season (June and August), pasture type (legume‐interseeded, N‐fertilized, and unfertilized pastures), and harvest time (3, 7, and 30 d after deposition) on dietary nutritive value, dung quality, dung decomposition, and nutrient movement into soil. Cattle grazing legume‐interseeded pastures had similar dietary crude protein concentrations but 11% less dietary neutral detergent fiber concentrations than cattle grazing N‐fertilized pastures. Dung from cattle grazing legume‐interseeded pastures, meanwhile, had 5 to 12% greater N concentrations than dung from cattle grazing N‐fertilized and unfertilized pastures. From 3 to 30 d after deposition, dung C/N ratio decreased from 20.0 to 16.5; whereas, dry matter remaining diminished to 77.5%. Dung C/N ratio and dry matter remaining did not vary with season or pasture type. At Day 7, soil below dung from cattle grazing legume‐interseeded pastures had 20 and 42% greater inorganic N than soil below dung from N‐fertilized and unfertilized pastures. This research showed that pastures with legumes increases dietary nutritive value, resulting in greater dung quality and increased N movement into soil.

Native soil microorganisms hinder the soil enrichment with antibiotic resistance genes following manure applications

Bacterial genes responsible for resistance to antibiotic agents (ARG) are spread from livestock to soil through application of manure, threatening environmental and human health. We investigated the mechanisms of ARG dissemination and persistence to disentangle i) the influence of nutrients and microorganisms on the soil tetracycline (TET) resistome, and ii) the role of indigenous soil microbiota in preventing ARG spread. We analysed short-term (7 days) and persistent (84 days) effects of manure on the resistome of three antibiotic-free pasture soils. Four microcosm treatments were evaluated: control, mineral nutrient fertilization, and deposition of a layer of fresh manure onto soil or γ-irradiated soil. We quantified five TET-resistance genes, isolated 135 TET-resistant bacteria and sequenced both culturable TET-resistant and whole bacterial communities. Manure amendments, but not nutrient addition, increased the abundance of TET-r genes such as tet(Y). Such changes persisted with time, in contrast with the TET-resistant bacterial composition, which partially recovered after manure amendments. Manured γ-irradiated soils showed significantly lower nutrient content and higher TET-r gene abundance than non-irradiated soils, suggesting that native soil bacteria are essential for the fertilization effect of manure on soil as well as control the dissemination of potentially risky TET-r genes.

Strategic grazing management and nitrous oxide fluxes from pasture soils in tropical dairy systems

Greenhouse gases emissions are considered one of the most important environmental issues of dairy farming systems. Nitrous oxide (N2O) has particular importance owing to its global warming potential and stratospheric ozone depletion. The objective of this study was to investigate the influence of two rotational grazing strategies characterized by two pre-grazing targets (95% and maximum canopy light interception; LI95% and LIMax, respectively) on milk production efficiency and N2O fluxes from soil in a tropical dairy farming system based on elephant grass (Pennisetum purpureum Schum. cv. Cameroon). Results indicated that LI95% pre-grazing target provided more frequent defoliations than LIMax. Water-filled pore space, soil and chamber temperatures were affected by sampling periods (P1 and P2). There was a significant pre-grazing target treatment × sampling period interaction effect on soil NH4+ concentration, which was most likely associated with urinary-N discharge. During P1, there was a greater urinary-N discharge for LI95% than LIMax (26.3 vs. 20.9 kg of urinary-N/paddock) caused by higher stocking rate, which resulted in greater N2O fluxes for LI95%. Inversely, during P2, the soil NH4+ and N2O fluxes were greater for LIMax than LI95%. During this period, the greater urinary-N discharge (46.8 vs. 44.8 kg of urinary-N/paddock) was likely associated with longer stocking period for LIMax relative to LI95%, since both treatments had similar stocking rate. Converting hourly N2O fluxes to daily basis and relating to milk production efficiency, LI95% was 40% more efficient than LIMax (0.34 vs. 0.57 g N˗N2O/kg milk·ha). In addition, LI95% pre-grazing target decreased urea-N loading per milk production by 34%. Strategic grazing management represented by the LI95% pre-grazing target allows for intensification of tropical pasture-based dairy systems, enhanced milk production efficiency and decreased N-N2O emission intensity.

Identification of macrolide- and rifampicin-resistant Rhodococcus equi in environmental samples from equine breeding farms in central Kentucky during 2018

Rhodococcus equi causes severe pneumonia in foals and is most often recognized in people as an opportunistic pathogen. Longitudinal studies examining antimicrobial-resistant R. equi from environmental samples are lacking. We hypothesized that antimicrobial-resistant R. equi would be detectable in the ground (pasture soil or stall bedding) and air at breeding farms with previous documentation of foals infected with resistant isolates, and that concentrations of resistant isolates would increase over time during the foaling season. In this prospective cohort study, ground and air samples were collected from stalls and paddocks in January, March, May and July of 2018 at 10 horse-breeding farms with history of foal pneumonia attributed to macrolide- or Rifampicin-resistant R. equi. Environmental samples were cultured in the presence and absence of macrolides and Rifampicin to select for resistant organisms. Data were analyzed with linear mixed-effects and Hurdle models. Concentrations of total R. equi in bedding or air of stalls were significantly (P < 0.05) higher in January than other months. The proportion of resistant R. equi in soil samples from paddocks was significantly (P < 0.05) higher than stall bedding during all months. For each month, air samples from paddocks had a significantly (P < 0.05) higher proportion of resistant isolates than those from stalls. Fifty-five percent of resistant soil isolates and 34% of resistant air isolates were considered virulent by identification of the vapA gene. Concentrations of resistant R. equi isolates did not increase over time during the foaling season. Antimicrobial-resistant R. equi can persist in the environment at farms with a history of pneumonia caused by resistant R. equi infections, and exposure to resistant isolates in paddocks and stalls appears stable during the foaling season. Resistant isolates in the environment not only pose a risk for disease but also can serve as a repository for dissemination of resistance genes.

Management of a &lt;i&gt;Coxiella&lt;/i&gt; &lt;i&gt;burnetii&lt;/i&gt;-infected sheep flock after an outbreak of Q fever in humans

Following an outbreak of Q fever in a group of students who contracted the infection during a training course on a sheep farm, a detailed investigation of the sheep flock involved was conducted. Of 478 flock animals, 60 Coxiella burnetii ELISA-positive and 60 ELISA-negative ewes were selected for the trial and divided into four groups. A month after the initial ELISA screening, all ewes in the flock (except the control group) were vaccinated. Sequentially collected blood samples were tested with ELISA and PCR; feces, milk, manure, bedding, and soil were tested with PCR. The immune response to the vaccination was 92.7%, while the overall C. burnetii seroprevalence in the flock after the human outbreak was 64.9%. PCR was positive for 0.2% of milk samples and 34.4% of fecal samples of animals from all four trial groups. C. burnetii DNA was not detected in any of the blood samples. Manure was PCR-positive for about 35 months; bedding from the stable was also positive while samples of pasture soil were negative. It appears that extensive cleaning and disinfection combined with vaccination could be regarded as an appropriate approach to control/prevent Q fever in farm settings even in the short term.

Effect of Increasing Species Diversity and Grazing Management on Pasture Productivity, Animal Performance, and Soil Carbon Sequestration of Re-Established Pasture in Canadian Prairie.

Simple SummaryCanadian grasslands are recognized for providing high quality forage for grazing livestock and wildlife. The study was conducted on a re-established pasture in a Western Canadian semi-arid climate to investigate the effect of pasture species mixture and grazing management on pasture productivity, animal performance, and soil carbon sequestration. Pasture productivity and animal response were independent of pasture mixture but affected by grazing management. Average pasture dry matter productivity was greater with deferred-rotational grazing while pasture quality and animal gain were higher with continuous grazing. Soil carbon change varied with pasture seed mixture and grazing management interaction where pasture with 7-species mixture under continuous grazing had the lowest soil carbon gain. The objective of the study was to determine the effect of type of pasture mix and grazing management on pasture productivity, animal response and soil organic carbon (SOC) level. Pasture was established in 2001 on 16 paddocks of 2.1 ha that had been primarily in wheat and summer fallow. Treatments consisted of a completely randomized experimental design with two replicates: two pasture mixes (7-species (7-mix) and 12-species (12-mix)) and two grazing systems (continuous grazing (CG) and deferred-rotational grazing (DRG)). Pasture was stocked with commercial yearling Angus steers (Bos Taurus, 354 ± 13 kg) between 2005 and 2014. All pastures were grazed to an average utilization rate of 50% (40% to 60%). Average peak and pre-grazing pasture dry matter (DM) yield and animal response were independent of pasture seed mixture but varied with grazing management and production year. Average peak DM yield was 26.4% higher (p = 0.0003) for pasture under DRG relative to CG (1301 kg ha−1). However, total digestible nutrient for pasture under DRG was 4% lower (p < 0.0001) as compared to CG (60.2%). Average daily weight gain was 18% higher (p = 0.017) for CG than DRG (0.81 kg d−1), likely related to higher pasture quality under CG. Soil carbon sequestration was affected by seed mixture × grazing system interaction (p ≤ 0.004). Over the fourteen years of production, pasture with 7-mix under CG had the lowest (p < 0.01) average SOC stock at 15 cm (24.5 Mg ha−1) and 30 cm depth (42.3 Mg ha−1). Overall, the results from our study implied that increasing species diversity for pasture managed under CG may increase SOC gain while improving animal productivity.

Low-quality dwarf-shrub litter negatively affects the fitness of Alpine earthworms (Lumbricus rubellus Hoffmeister, 1843; Oligochaeta: Lumbricidae)

Alpine pastureland is increasingly abandoned, leading to shrub encroachment and to the accumulation of low-quality litter. Alpine key decomposers such as earthworms were found to feed on both low- and high-quality litter, but little is known how this might affect their life history traits.To fill this gap of knowledge, we conducted a laboratory experiment with the widespread earthworm species Lumbricus rubellus Hoffmeister, 1843. Hatchlings were provided with either of three aged litter types: grass and forb leaf litter as high-quality food sources and dwarf shrub leaves as low-quality food source. A control group was fed with aged cow dung. Biomass, days until (pre-)maturity, mortality, and reproduction rate were measured regularly to assess the impacts of food quality on earthworm development.We found pronounced impacts of food source quality on the fitness of L. rubellus. The low-quality litter led to significantly delayed development of up to 53 days, the lowest mean biomass (720 mg after 32 weeks) as well as a 50% drop of produced cocoons compared with the high-quality litter. However, the F2 generation showed the highest hatchling success in the shrub treatment.We conclude that the increased consumption of low-quality dwarf shrub litter led to negative effects on the development and reproduction of L. rubellus. Overall, this might be the main reason for declining earthworm densities in abandoned Alpine pasture soils, even though the biomass of the second generation was not significantly affected possibly due to a phenotypic variability in reproduction strategy. However, the decrease of such important decomposers and ecosystem engineers can have far reaching consequences for ecosystem processes such as litter accumulation and bioturbation and thus for the stability of Alpine soil ecosystems.

Microbial community structure in pasture and hayfield soils of the Helderberg region of New York State: a comparison of management strategies

ABSTRACTMicrobial communities in pasture and hayfield soils in upstate New York were studied to ascertain how land and livestock management practices influence microbial community structure. Three management approaches were compared: conventional pasture management (CM; low livestock density, low rotation frequency), multi-paddock management (MP; high livestock density, high rotation frequency) and mowing for hay (no livestock). Microbial functional groups were quantified by PLFA analysis. Soil attributes were measured, and management details were obtained by interviewing landowners. Microbial biomass in MP soils was higher, more diverse and contained proportionately more fungal (F) than bacterial (B) biomass than did CM and hayfield soils. Microbial biomass, diversity and F:B ratios in CM and hayfield soils were not different. Multivariate analyses suggest that different variables control microbial community structure in MP and CM soils.

Impacts of long term copper exposure on abundance of nitrogen cycling genes and denitrification activity in pasture soils

Soils are the main source of nitrous oxide (N2O) emissions, with 60–70% of global N2O production due to the enhanced denitrification activity with elevated nitrogen (N) availability associated with agricultural intensification. The amendment of agricultural soils with biosolids, the residual product of wastewater treatment, has been used for several decades as an inexpensive source of organic matter and N. Biosolids also contain elevated levels of trace elements such as copper (Cu), which influence the activity of the bacterial enzyme nitrous oxide reductase (N2OR). We extracted DNA from a pasture soil 20 years after application of biosolid and Cu salts and used an environmental genomics approach (GeoChip) to evaluate broad changes in the abundance and structure of families of N-cycling genes. We then focussed on abundances of individual bacterial genes involved in sequential N-reduction (nirS, nirK, and nosZ). There was no relationship between total soil Cu concentrations and the different N-cycling gene families (GeoChip; P > 0.1). However, increasing Zn was associated with decreased nitrification (amoA) and dissimilatory N-reduction (napA and nrfA) gene-family abundances (P < 0.1). When focused on individual bacterial denification pathway genes (qPCR), nosZ (nitrous oxide reductase) was found to be sensitive to Cu concentrations. Moreover, the activity of the Cu-dependent enzyme N2OR is potentially affected by historical Cu concentrations found in these pasture soils. The results highlight the sensitivity of a few key functional taxa (nosZ type denitrifying bacteria) to long-term Cu exposure in soil, and how these effects can translate into alteration of wider N-cycling processes such as those affecting net N2O emissions.

Hydrological trade-offs due to different land covers and land uses in the Brazilian Cerrado

Abstract. Farmland expansion in the Brazilian Cerrado, considered one of the largest agricultural frontiers in the world, has the potential to alter water fluxes on different spatial scales. Despite some large-scale studies being developed, there are still few investigations in experimental sites in this region. Here, we investigate the water balance components in experimental plots and the groundwater table fluctuation in different land covers: wooded Cerrado, sugarcane, pasture and bare soil. Furthermore, we identify possible water balance trade-offs due to the different land covers. This study was developed between 2012 and 2016 in the central region of the state of São Paulo in southern Brazil. Hydrometeorological variables, groundwater table, surface runoff and other water balance components were monitored inside experimental plots containing different land covers; the datasets were analyzed using statistical parameters; and the water balance components uncertainties were computed. Replacing wooded Cerrado by pastureland and sugarcane shifts the overland flow (up to 42 mm yr−1) and the water balance residual (up to 504 mm yr−1) and may affect groundwater table behavior. This fact suggests significant changes in the water partitioning in a transient land cover and land use (LCLU) system, as the evapotranspiration is lower (up to 719 mm yr−1) in agricultural land covers than in the undisturbed Cerrado. We recommend long-term observations for continuing the evaluations initiated in this study, mainly because there are few basic studies on tropical environments at the hillslope scale and more assessments are needed for a better understanding of the real field conditions. Such efforts should be made to reduce uncertainties, validate the water balance hypothesis and catch the variability of hydrological processes.

Antibiotic resistance genes and bacterial communities in cornfield and pasture soils receiving swine and dairy manures

Land application of animal manure could change the profiles of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and bacterial communities in receiving soils. Using high-throughput real-time quantitative PCR and 16S rRNA amplicon sequencing techniques, this study investigated the ARGs and bacterial communities in field soils under various crop (corn and pasture) and manure (swine and dairy) managements, which were compared with those of two non-manured reference soils from adjacent golf course and grassland. In total 89 unique ARG subtypes were found in the soil samples and they conferred resistance via efflux pump, cellular protection and antibiotic deactivation. Compared to the ARGs in the golf course and grassland soils (28 and 34 subtypes respectively), manured soils generally had greater ARG diversity (36–55 subtypes). Cornfield soil frequently receiving raw swine manure had the greatest ARG abundance. The short-term (one week) application of composted and liquid swine manures increased the diversity and total abundance of ARGs in cornfield soils. Intriguingly the composted swine manure only marginally increased the total abundance of ARGs, but substantially increased the number of ARG subtypes in the cornfield soils. The network analysis revealed three major network modules in the co-occurrence patterns of ARG subtypes, and the hubs of these major modules (intl1-1, vanC, and pncA) may be candidates for selecting indicator genes for surveillance of ARGs in manured soils. The network analyses between ARGs and bacteria taxa revealed the potential host bacteria for the detected ARGs (e.g., aminoglycoside resistance gene aacC4 may be mainly carried by Acidobacteriaceae). Overall, this study highlighted the potentially varying impact of various manure management on antibiotic resistome and microbiome in cornfield and pasture soils.

Land‐use changes influence the sporulation and survival of Phytophthora agathidicida, a lethal pathogen of New Zealand kauri (Agathis australis)

AbstractPhytophthora agathidicida is the accepted causal agent of dieback in remnant stands of long‐lived indigenous New Zealand kauri (Agathis australis) and poses a significant threat to the long‐term survival of this species. Little is known about the effect of key soil physicochemical characteristics on the growth of P. agathidicida. In this study, we investigated the growth of P. agathidicida in soils collected from adjacent areas under original kauri forest, short rotation pine (Pinus radiata) plantation forest and grazed pastures. A growth response assay was used to quantify asexual (sporangia) and sexual (oospore) spore counts over 8 days in soils sampled from each land‐use. Significantly higher numbers of sporangia (p &lt; 0.001) and oospores (p &lt; 0.01) were found in pasture and pine forest soil within 2 days of the growth assay trials, suggesting these soils may favour asexual/sexual reproduction in the early stages of P. agathidicida establishment compared to kauri forest soils. Additionally, oospore production significantly increased over 8 days in pine forest soil, suggesting that with an increase in inoculum loads, these soils potentially act as pathogen reservoirs. The soil physicochemical properties (e.g., pH, C and N, phosphorus content and electrical conductivity) investigated in this study did not significantly correspond to spore count data between land‐uses, suggesting that differences in growth response are driven by other edaphic factors not explored in the present study.