Dairy Farm Soil Research Articles

Contrasting response of comammox Nitrospira, ammonia oxidising bacteria, and archaea to soil pH and nitrogen inputs

This study aimed to investigate the effect of soil pH change, and nitrogen amendment on ammonia oxidiser abundance and comammox Nitrospira community composition. The experimental design used soil mesocosms placed in a temperature-controlled incubator for 90 days. A Templeton silt loam was used as its physiochemical properties are typical of the region's dairy farms. The results showed that comammox Nitrospira clade B preferred the natural (pH 6.1–6.2) soil pH with no applied nitrogen. Furthermore, synthetic urine (N700) decreased the abundance of comammox Nitrospira clade B. This may have been because the large amounts of available ammonia in the N700 treatments inhibited the growth of comammox Nitrospira.These results suggest that while comammox Nitrospira clade B are present in New Zealand dairy farm soils, but their role in nitrification in the very high nitrogen environment under a urine patch in grazed pastures may be limited. Further research is needed to confirm this.In contrast to comammox, the AOB community (dominated by Nitrosospira) responded positively to the application of synthetic urine. The response was greatest in the high pH soil (7.1), followed by the natural and then the low pH (4.9) soils. This may be due to the difference in ammonia availability. At high pH, the ammonia/ammonium equilibrium favours ammonia production. Calculated ammonia availability in the N700 treatments accurately predicted the AOB amoA gene abundance.Interestingly, the AOA community abundance (which was predominantly made up of Thaumarchaeota group I.1b clade E) seemed to prefer the natural and high pH soils over the low pH. This may be due to the specific lineage of AOA present. AOA did not respond to the application of nitrogen.

Biological Control of Hyalomma Ticks in Cattle by Fungal Isolates.

Ticks pose a major threat to cattle health and production in Pakistan because they transmit pathogens of diseases like Babesiosis and Theileriosis. Hyalomma spp., found across Africa, Asia, and Europe, are especially problematic. This study explored biocontrol of Hyalomma spp. using spore-free fungal culture filtrates collected from dairy farm soil in Kohat, Pakistan. Three fungal species of the genera Alternaria, Aspergillus, and Penicillium were isolated, and their filtrates were tested against tick adults and larvae. Filtrate concentrations were prepared at different strengths. Data were taken after the exposure of adults and larvae ticks to various concentrations of the fungal filtrates. Results indicated that at 100% concentration, all fungal filtrates induced 100% mortality in adults and larvae. Decreasing filtrate concentration lowered tick mortality. The lowest concentration caused the least mortality. The effect was time- and dose-dependent. In conclusion, spore-free fungal culture filtrates can provide biocontrol of Hyalomma spp. in a time- and concentration-dependent manner. Further research should explore the active compounds causing mortality and optimal application methods. The process outlined here provides a natural biocontrol alternative to chemical pesticides to reduce tick infestations and associated cattle diseases in Pakistan.

Molecular characterization of chlorpyrifos degrading bacteria isolated from contaminated dairy farm soils in Nakuru County, Kenya

Chlorpyrifos (CP) is an organophosphate widely used as an insecticide and acaricide. Extensive application of CP contaminates ecosystems, polluting the environment and food products, creating health complications to humans due to its neurotoxicity. The study evaluated CP bioremediation by bacteria isolated from dairy farm soils in Nakuru County, Kenya, through enrichment culture technique. The growth response of the bacteria and degradation of chlorpyrifos was monitored every five days using UV-VIS Spectrophotometer (600nm). Enrichment culture technique led to the isolation of eighteen (MA1-MA18) potential CP degraders belonging to the genera Pseudomonas, Stenotrophomonas, Bacillus, Alicaligenes, and Achromobacter. The efficacy of four (4) strains was further investigated using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The results showed that all four strains significantly degraded chlorpyrifos in Minimum Salt Medium (MSM): Lysinibacillus sp.HBUM206408 (87.16 %), Stenotrophomonas maltophilia (82.04 %), Pseudomonas putida (89.52 %), and Achromobacter insuavis (91.08 %) within 16 days, producing 2-Hydroxy-3, 5, 6-trichloropyridine (TCP) as the main metabolite. Therefore, these strains can be used to degrade chlorpyrifos in contaminated soil. There is a need for further studies to determine the possible mechanisms and other metabolites of chlorpyrifos degradation by the isolates obtained in the study. Besides, future studies should explore the efficacy and survival of the organisms in the contaminated environment.

Antibiotic resistance and phylogenetic profiling of Escherichia coli from dairy farm soils; organic versus conventional systems.

The prevalence and spread of antimicrobial resistance (AMR) as a result of the persistent use and/or abuse of antimicrobials is a key health problem for health authorities and governments worldwide. A study of contrasting farming systems such as organic versus conventional dairy farming may help to authenticate some factors that may contribute to the prevalence and spread of AMR in their soils. A case study was conducted in organic and conventional dairy farms in the South Canterbury region of New Zealand. A total of 814 dairy farm soil E. coli (DfSEC) isolates recovered over two years were studied. Isolates were recovered from each of two farms practicing organic, and another two practicing conventional husbandries. The E. coli isolates were examined for their antimicrobial resistance (AMR) against cefoxitin, cefpodoxime, chloramphenicol, ciprofloxacin, gentamicin, meropenem, nalidixic acid, and tetracycline. Phylogenetic relationships were assessed using an established multiplex PCR method. The AMR results indicated 3.7% of the DfSEC isolates were resistant to at least one of the eight selected antimicrobials. Of the resistant isolates, DfSEC from the organic dairy farms showed a lower prevalence of resistance to the antimicrobials tested, compared to their counterparts from the conventional farms. Phylogenetic analysis placed the majority (73.7%) of isolates recovered in group B1, itself dominated by isolates of bovine origin. The tendency for higher rates of resistance among strains from conventional farming may be important for future decision-making around farming practices Current husbandry practices may contribute to the prevalence and spread of AMR in the industry.

Bioavailable Cu can influence nitrification rate in New Zealand dairy farm soils

Bioavailable Cu can influence nitrification rate in New Zealand dairy farm soils

Production, Optimization, and Characterization of an Acid Protease from a Filamentous Fungus by Solid-State Fermentation.

Acid proteases represent an important group of enzymes, extensively used in food and beverage industries. There is an increased demand for acid proteases adapting to the industrial extreme environment, especially lower pH. Thus, this necessitates the search for a better acid protease from fungi that best performs in industrial conditions. The fungal isolates were isolated from grape and dairy farm soil using potato dextrose agar and further screened for protease production based on the hydrolysis of clear zone on skim milk agar. The potential fungi were then subjected to secondary screening under solid-state fermentation (SSF). After the secondary screening, the potential fungus was identified to the genus level by the macroscopic and microscopic methods. The growth conditions and media composition for the potential fungus were further optimized under SSF. The crude enzyme produced by the potential isolate was characterized after partial purification by acetone and ammonium sulfate precipitation. A total of 9 fungal isolates showed protease production in primary and secondary screening; however, one potential isolate (Z1BL1) was selected for further study based on its protease activity. The isolate was identified to the genus Aspergillus based on their morphological features. The maximum acid protease from the isolate Z1BL1 was obtained using fermentation media containing wheat bran as a solid substrate, 1 mL of 3.2 × 106 inoculum size, 50% moisture content, and pH 4.5 upon 120-h incubation at 30°C. The acetone-precipitated enzyme exhibited the maximum activity at 50°C and pH 5 with stability at pH 4–6 and temperature 40–60°C. Thus, the acid protease produced from Aspergillus showed suitable enzyme characteristics required in the industry and could be a candidate for application in the food industry after further purification.

Molecular Characterization of Chlorpyrifos Degrading Bacteria Isolated from Contaminated Dairy Farm Soils in Nakuru County, Kenya

Chlorpyrifos [O, O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphonothioate] is an organophosphate widely used as an insecticide against a broad spectrum of pests, including as an acaricide against ticks and mites. Due to environmental persistence and toxicity, it should be eliminated quickly from contaminated sites through biodegradation. Microbial bioremediation is one of the most viable ways of removing Chlorpyrifos (CP) from the environment. However, few studies have been conducted on the bacterial diversity that degrades Chlorpyrifos. The enrichment culture technique conducted in this study isolated chlorpyrifos degrading bacteria in soils from dairy farms in Nakuru County, Kenya. The growth response of the bacteria and degradation of Chlorpyrifos was monitored every five days using UV-VIS Spectrophotometer (600nm). Sequential soil and liquid culture enrichments led to the isolation of eighteen (MA1-MA18) bacterial chlorpyrifos degraders with DNA sequences homologous to members of the genera Pseudomonas, Stenotrophomonas, Bacillus, Alicaligenes, and Achromobacter. The efficacy of four (4) strains was further investigated using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The results showed that all four strains significantly degraded Chlorpyrifos in Minimum Salt Medium (MSM), Lysinibacillus sp.HBUM206408 (79.52%), Stenotrophomonas maltophilia (71.43%), Pseudomonas putida (73.32%), and Achromobacter insuavis (71.03%), producing 2-Hydroxy-3,5,6-trichloropyridine (TCP) as a metabolite in MSM as the only source of carbon. Therefore, these strains can be used for the bioremediation of Chlorpyrifos in contaminated soil. There is a need for further studies to determine the possible mechanisms and other metabolites of Chlorpyrifos degradation by the isolates obtained in the study. Besides, future studies should explore the efficacy and survival of the organisms in the contaminated environment.

Dairy farm soil presents distinct microbiota and varied prevalence of antibiotic resistance across housing areas

Dairy cattle of different ages experience different living conditions and varied frequency of antibiotic administration that likely influence the distribution of microbiome and resistome in ways that reflect different risks of microbial transmission. To assess the degree of variance in these distributions, fecal and soil samples were collected from six distinct housing areas on commercial dairy farms (n = 7) in Washington State. 16S rRNA gene sequencing indicated that the microbiota differed between different on-farm locations in feces and soil, and in both cases, the microbiota of dairy calves was often distinct from others (P < 0.05). Thirty-two specific antibiotic resistance genes (ARGs) were widely distributed on dairies, of which several clinically relevant ARGs (including cfr, cfrB, and optrA) were identified for the first time at U.S. dairies. Overall, ARGs were observed more frequently in feces and soil from dairy calves and heifers than from hospital, fresh, lactation and dry pens. Droplet-digital PCR demonstrated that the absolute abundance of floR varied greatly across housing areas and this gene was enriched the most in calves and heifers. Furthermore, in an extended analysis with 14 dairies, environmental soils in calf pens had the most antibiotic-resistant Escherichia coli followed by heifer and hospital pens. All soil E. coli isolates (n = 1,905) are resistant to at least 4 different antibiotics, and the PFGE analysis indicated that florfenicol-resistant E. coli is probably shared across geographically-separated farms. This study identified a discrete but predictable distribution of antibiotic resistance genes and organisms, which is important for designing mitigation for higher risk areas on dairy farms.

Isolation and Characterization of Indigenous Lipase Producing Bacteria from Lipid?rich Environment

To isolate and characterize lipase producing bacteria from lipid?rich environment and screen the best lipolytic indigenous bacteria a study was made. For the isolation of bacteria, oil based wastewater and soil were collected from ten different sampling sites. Four different media were used for study the aerobic heterotrophic bacterial count. The highest bacterial count (1.56 × 107 cfu/gm) was observed in dairy farm soil and lowest (8.3 × 102 cfu/ml) in the Buriganga river water. The highest percentage (94.51) of lipase producing bacteria was found in edible oil mill soil and lowest (23.44) in the Buriganga river water. Among the total isolates 30 showed better lipase activity. Potential ten lipase producers were taken for molecular identification. Among them, nine genera were matched with their conventional identification but conventionally identified Acetobacter liquifaciens was found to be as Stenotrophomonas maltophilia. The enzyme produced by the isolated bacteria could be used for the treatment of lipid?rich wastewater.Plant Tissue Cult. &amp; Biotech. 26(2): 243-253, 2016 (December)

The response of ammonia-oxidizing microorganisms to trace metals and urine in two grassland soils in New Zealand.

An incubation experiment was conducted to investigate the response of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and the nitrification rate to the contamination of Cu, Zn, and Cd in two New Zealand grassland soils. The soils spiked with different concentrations of Cu (20 and 50mgkg-1), Zn (20 and 50mgkg-1), and Cd (2 and 10mgkg-1) were incubated for 14days and then treated with 500mgkg-1 urine-N before continuing incubation for a total of 115days. Soils were sampled at intervals throughout the incubation. The nitrification rate in soils at each sampling period was determined, and the abundance of AOB and AOA was measured by real-time quantification polymerase chain reaction (qPCR) assay of the amoA gene copy numbers. The results revealed that moderate trace metal stress did not significantly affect the abundance of AOB and AOA in the two soils, probably due to the high organic matter content of the soils which would have reduced the toxic effect of the metals. Nitrification rates were much greater and the observable nitrification period was much shorter in the dairy farm (DF) soil, in which the AOB and AOA abundances were greater than those of the mixed cropping farm (MF) soil. AOB were shown to grow under high nitrogen conditions, whereas AOA were shown to grow under low N environments, with different metal concentrations. Therefore, nitrogen status rather than metal applications was the main determining factor for AOB and AOA growth in the two soils studied.

New Zealand dairy farm effluent, irrigation and soil biota management for sustainability: Farmer priorities and monitoring

AbstractAgricultural science has produced compelling data to show that soil biota may be exploited to increase agricultural efficiency. However, field application is entirely dependent on farmers’ knowledge. This study assessed current New Zealand dairy farmer’s soil management practices, knowledge on earthworms and soil microbes and their willingness to monitor and manage them for nutrient use efficiency. Farmers indicated that soil quality influences their farms’ overall success with 84% acknowledging that it is enhanced by irrigation and effluent application practices. Although they indicated that earthworms and soil microbes are responsive to management, there were clear gaps in implementation at the farm scale level. For example only 6% of the respondents used soil microbes as soil quality indicators. Scientific findings are not transmitted adequately to farmers, who increasingly rely on scientific expertise to maintain or boost production. Farmers are willing to monitor and use earthworms and soil m...

Effect of different land use and land use change on ammonia oxidiser abundance and N2O emissions

In recent years, there has been a major expansion of dairy farming in New Zealand, largely as a result of land use change from forestry and sheep farming to dairy farming. Possible impacts of different land uses and land use change on ammonia oxidising bacteria (AOB) and archaea (AOA) and N2O emissions are not well understood. A field study was carried out to determine the effects on AOB and AOA abundance by three long-term different land uses, pine tree plantation (30+ years), sheep farming (30+ years) and dairy farming (12+ years), located in close proximity on the same soil type. A laboratory incubation study was carried out to determine the impact of dairy cow urine application (simulating the deposition of dairy cattle urine after the conversion of tree plantation and sheep farming to dairy farming) on AOB and AOA growth and N2O emissions. The results showed that AOB abundance was higher in the dairy and sheep farm soils (P < 0.05) than in the pine tree soil but that the AOA abundance was higher in the sheep farm soil than in the dairy and pine tree soils (P < 0.05). When dairy cow urine was applied in the incubation study, the AOB growth was initially faster in the dairy, followed by sheep and then followed by the pine tree soil, but the growth continued for an extended period in the pine tree soil with the amoA gene copy numbers eventually exceeding those in the sheep and dairy pasture soils. AOA grew following urine application in the sheep soil but did not change in the other soils. Total N2O emissions in the pine tree soil was more than twice those from the dairy and sheep farm soils. These results demonstrate the significant impact of land use and land use change on ammonia oxidiser communities and subsequent impacts on nitrogen transformations and N2O emissions. Further research is needed to verify these results in the field.

Anthropogenic fluorine accumulation in the Waikato and Bay of Plenty regions of New Zealand: comparison of field data with projections

Application of phosphate (P) fertilizers to farmland is projected to be causing worldwide accumulation of fluorine (F) in agricultural soils and associated ecosystems, but wide-scale field data have been lacking. We report results of sampling across two large regions of New Zealand involving soils of 298 native and farmed properties. This has enabled the first wide-scale retrospective estimates of anthropogenic F enrichment in pastoral and horticultural soils. Results validate earlier projections: F accumulation in farmed soils has been comparatively rapid (mean increase 2.1 % per year) and widespread. Over 50 years, average total F concentrations in surface soils have doubled from ~220 to 440 mg/kg. Thresholds protective against chronic fluorosis in grazing animals are being substantively passed, indicating that land may be rendered unsuitable for pastoral production in the mid-term future: when sampled 44 % of dairy farm soil samples exceeded 500 mg/kg total F, and 10 % exceeded 650 mg/kg. Potential for F toxicity to plants and wildlife appear to be significant and marginal, respectively, at current soil F concentrations. Relationships between F and other elements suggest P fertilizers are also a source of several elements geochemically linked to F, and that anthropogenic F modifies soil aluminium (Al) chemistry, potentially opening a broad-scale Al exposure pathway to pollinating insects. Findings signal a need for systematic examination of the range of possible affects that may be linked to increasing soil F, which include various types of ecotoxicity, altered Al chemistry, reduced P availability, and potential for increased dietary intakes of F, Al and aluminofluoride (AlFx) species over time.

Farm system management affects community structure of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are considered to play a pivotal role in organic farming systems as they are known to enhance plant phosphorus (P) uptake from soils low in plant-available P. However, the structure and therefore function of AMF communities may be altered depending on environment and management conditions. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and quantitative real-time PCR (qPCR) were used to explore AMF community structure in soils from perennial forages (Medicago sativa—Phleum pratense) on three pairs of long-term (>20yr) organic and conventional dairy farm soils in Ontario, Canada. There were no significant differences in DGGE band numbers (indicative of species richness) among organic and conventionally managed soils. Analysis of Similarity revealed significant differences in AMF community composition with both farming system management and farm pair location having significant effects (R=0.71 and 0.91, respectively, P<0.0001 for both). Real-time qPCR indicated greater abundance of Funneliformis mosseae under conventional management (P=0.036), while organic management tended to support greater abundance of Claroideoglomus claroideum (P=0.067). Such a compositional shift in AMF communities could have consequences for the growth and P-use efficiency of their host. The results of this study highlight that the structure of AMF community assemblages are co-determined by both local environmental conditions and farming system management, and importantly, demonstrate for the first time differences between organic and conventional management in dairy farm soils from mixed perennial forages.

Effect of synthetic dairy factory effluent containing different acids (H3PO4, HNO3 and CH3COOH) on soil microbial and chemical properties and nutrient leaching

The effects of addition of synthetic dairy factory effluent (DFE) containing phosphoric, nitric or acetic acids as cleaning agents on soil chemical and microbial properties and potential nutrient leaching from a dairy farm soil were studied in an 84-day open incubation/leaching experiment and in a short-term (24 days) closed incubation. Dairy factory effluent resulted in increased leaching of Na+ and Ca2+. The main anion leached in the DFE treatments was Cl−, whilst in the control treatments it was NO 3 − . Leachates from DFE-treated soil had a greater electrical conductivity (EC) and lower pH than those from controls, but type of acid had little effect on the ionic content or composition of leachates. At the conclusion of the experiment, soils from DFE treatments showed a large accumulation of exchangeable Na+, a reduction in exchangeable Ca2+ and significant increases in microbial biomass C, basal respiration and β-glucosidase and arylsulphatase activities. Microbial activity was greatest from the acetic acid-DFE treatment. There was a significant increase in extractable P in the phosphoric acid-DFE treatment, but addition of nitric acid-DFE did not increase leaching of NO 3 − . In the short-term incubation experiment, EC increased over time in all treatments, while pH, microbial biomass and basal respiration decreased. During the first few days after a one-off DFE addition, there was an increase in both microbial biomass C and basal respiration, but these differences dissipated after 3 days. It was concluded that while additions of DFE have significant effects on chemical and microbial soil properties, a change in the form of acid present in the DFE has relatively minor effects on these properties.

Growing maize silage in dairy effluent paddocks for two consecutive seasons - effect on crop yield and soil nitrogen

Nutrient loading can be high in dairy-farm soils that are regularly irrigated with shed effluent, especially when the area treated is small or the farming system has intensified.

Retention capacity of biochar-amended New Zealand dairy farm soil for an estrogenic steroid hormone and its primary metabolite

We examined the retention ability of a New Zealand dairy farm soil amended with 3 types of biochar produced from a variety of feedstocks for a steroid hormone (oestradiol, E2) and its primary transformation product (estrone, E1). Biochars produced from corn cob (CC), pine sawdust (PSD) and green waste (GW) were characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and solid-state 13C nuclear magnetic resonance spectroscopy. Batch sorption studies were performed on soil amended with each biochar (0.5% and 1% by weight) using a complex solvent extraction scheme, and isotherms were fitted to the Freundlich model. All isotherms were highly non-linear, with N values in the range 0.46–0.83 (E2) and 0.66–0.88 (E1) in soil amended with different percentages of biochars. Overall, addition of all 3 biochars was found to increase the soil sorption affinity for the hormones, with E2 sorption being the highest in the soil amended with 1% PSD biochar. There was no marked difference in hormone sorption ability in the other 2 treatments (soil treated with 1% CC biochar and 1% GW biochar). Overall, the effective distribution coefficient (Kdeff) values for E2 at the lowest equilibrium concentration (Cw 0.5 mg/L) ranged from 35 to 311 L/kg in soil amended with the 3 types of biochar. Addition of 0.5% of PSD biochar resulted in ~560% increase in the Kdeff value for E2, while at 1% addition of PSD biochar, uptake of E2 was nearly 1400% higher than the control. For E1, the percentage increase in Kdeff was comparatively smaller than E2; however, it still ranged from 40 to 280%, and 60 to &gt;320% at addition of 0.5% and 1% PSD biochar, respectively, compared with the control soil. Highest treatment temperature and associated greater surface area, low ash content, higher carbon content, and the abundance of polar functional groups (e.g. –OH, C=O) may explain why the soil amended with PSD biochar exhibited high sorptive capacity for the hormones.

Distribution of Tetracycline and Streptomycin Resistance Genes and Class 1 Integrons in Enterobacteriaceae Isolated from Dairy and Nondairy Farm Soils

The prevalence of selected tetracycline and streptomycin resistance genes and class 1 integrons in Enterobacteriaceae (n = 80) isolated from dairy farm soil and nondairy soils was evaluated. Among 56 bacteria isolated from dairy farm soils, 36 (64.3%) were resistant to tetracycline, and 17 (30.4%) were resistant to streptomycin. Lower frequencies of tetracycline (9 of 24 or 37.5%) and streptomycin (1 of 24 or 4.2%) resistance were observed in bacteria isolated from nondairy soils. Bacteria (n = 56) isolated from dairy farm soil had a higher frequency of tetracycline resistance genes including tetM (28.6%), tetA (21.4%), tetW (8.9%), tetB (5.4%), tetS (5.4%), tetG (3.6%), and tetO (1.8%). Among 24 bacteria isolated from nondairy soils, four isolates carried tetM, tetO, tetS, and tetW in different combinations; whereas tetA, tetB, and tetG were not detected. Similarly, a higher prevalence of streptomycin resistance genes including strA (12.5%), strB (12.5%), ant(3'') (12.5), aph(6)-1c (12.5%), aph(3'') (10.8%), and addA (5.4%) was detected in bacteria isolated from dairy farm soils than in nondairy soils. None of the nondairy soil isolates carried aadA gene. Other tetracycline (tetC, tetD, tetE, tetK, tetL, tetQ, and tetT) and streptomycin (aph(6)-1c and ant(6)) resistance genes were not detected in both dairy and nondairy soil isolates. A higher distribution of multiple resistance genes was observed in bacteria isolated from dairy farm soil than in nondairy soil. Among 36 tetracycline- and 17 streptomycin-resistant isolates from dairy farm soils, 11 (30.6%) and 9 (52.9%) isolates carried multiple resistance genes encoding resistance to tetracycline and streptomycin, respectively, which was higher than in bacteria isolated from nondairy soils. One strain each of Citrobacter freundii and C. youngae isolated from dairy farm soils carried class 1 integrons with different inserted gene cassettes. Results of this small study suggest that the presence of multiple resistance genes and class 1 integrons in Enterobacteriaceae in dairy farm soil may act as a reservoir of antimicrobial resistance genes and could play a role in the dissemination of these antimicrobial resistance genes to other commensal and indigenous microbial communities in soil. However, additional longer-term studies conducted in more locations are needed to validate this hypothesis.

PHOSPHATE AND GLYPHOSATE MOBILITY IN SOIL COLUMNS AMENDED WITH ROUNDUP

Sorption of glyphosate and competitive desorption of phosphate in soils has been measured in past studies largely under batch equilibration conditions, which maximize the potential for retention of these anions. The experiments reported here were conducted by applying dilute Roundup® solutions to soil columns, followed by leaching with water and collection of initial leachate. Soils representing a wide range of physical and chemical properties, including total and soluble P, were included in the study. The concentrations of total dissolved P and orthophosphate (PO43−) in column leachates were measured using inductively coupled plasma spectrometry and colorimetry, respectively. Leachate glyphosate was estimated as the difference between total P and PO43−. Column leaching experiments with Roundup showed nearly complete glyphosate retention on the coarse-textured soils initially tested, from 85% to 95% sorption, despite the fact that higher than agronomic rates, 7.4 to 14.8 mg kg−1 of glyphosate, were applied. However, a second identical application 5 days later on one of these soils decreased the retention efficiency to a range of 63% to 73%. The Roundup treatments did not increase dissolved PO43− in leachates from these soils. A forest soil with low P status and a dairy farm soil with high P status were subjected to the same column leaching tests. The leachates from both soils treated with Roundup contained elevated total P compared with controls, shown to be predominantly PO43−. Column leaching experiments with much higher glyphosate application rates showed that glyphosate can displace PO43− from sorption sites on both organic and mineral soils. The experimental results suggest that glyphosate sorption does not necessarily result in PO43− dissolution and that there is only limited competition for sorption sites between glyphosate and PO43−. Strong glyphosate sorption on high-organic matter soils indicates bonding of this anion by a metal bridge to organic functional groups.

Soil microbial respiration responses to repeated urea applications in three grasslands

Grazing animals excrete urine and create transitorily high pH, nitrogen (N)-replete soil patches. Beneath grazed pasture, we postulated the soil microbial community would be highly responsive to N application. Lesser responses were expected of soils beneath grassland without grazing animals. Soil samples were collected near Lincoln, New Zealand (43.6°S, 172.5°E), beneath pasture regularly grazed by dairy cattle, an adjacent pasture set aside from grazing 20 years ago, and a nearby grassland that has never been grazed. Soil microbial respiration responses to repeated urea (500 kg N/ha) applications were determined by laboratory incubation experiments and the soil pH and water-soluble C content were also measured. The first application induced 0.13 ± 0.04 (dairy farm), 0.15 ± 0.05 (set aside), and 0.20 ± 0.04 (ungrazed) g C/kg increases in microbial respiration over 9 days, excluding carbon dioxide production from carbonate hydrolysis. After a second application, 9-day respiration increased by 0.26 ± 0.04 (dairy farm), 0.41 ± 0.04 (set aside) and 0.20 ± 0.07 (ungrazed) g C/kg. For the dairy farm and ungrazed soils, the microbial communities responded differently to repeated urea addition. The responses included transitory changes in pH and reflected the limited amounts of readily decomposable organic matter.