Pasture Soils Research Articles

Biological nitrification inhibition by Brachiaria grasses mitigates soil nitrous oxide emissions from bovine urine patches

High nitrogen (N) concentration in bovine urine, which generally exceeds plant N uptake rates, results in the formation of hotspots of N loss when bovine urine is deposited on grazed pasture soils. High spatial variability in the distribution of urine patches in grazed pastures poses a major challenge to mitigate N losses. Some exudates from the roots of several tropical forage grasses were shown to inhibit the activity of soil nitrifiers; a process known as biological nitrification inhibition (BNI). We hypothesized that nitrate (NO3−) production and nitrous oxide (N2O) emissions from urine patches deposited on soils under forage grasses with high BNI capacity are lower than those with forage grasses with low BNI capacity. This hypothesis was tested using field plots of two tropical forage grass cultivars, Brachiaria humidicola cv. Tully (BT) and interspecific Brachiaria hybrid cv. Mulato (BM) which, correspondingly, have high and low BNI capacity. Nitrification rates and amoA gene copy numbers of ammonia oxidizing archaea (AOA) and bacteria (AOB) in soils under the two forage grasses were quantified before and after urine and water (control) application, as well, an additional experiment was conducted to quantify denitrification potential. Moreover, soil N2O emissions from simulated urine (0.123 kg N m−2) and water patches were monitored over a 29-day period. Results showed a greater suppression of nitrification, denitrification and AOA abundance in soils under BT than those under BM. Positive relationships (p < 0.05) existed between AOA and AOB abundance and NO3− contents in soils under BM. Bovine urine resulted in higher cumulative N2O fluxes from soils under BM (80 mg N2O-N m−2) compared to those under BT (32 mg N2O-N m−2). Consequently, N2O emission factors were higher for soils under BM (0.07%) than under BT (0.00002%). We conclude that tropical forage grasses with high BNI capacity play a key role in mitigating N2O emissions from bovine urine patches in archaea-dominated soils. This suggests that wide-spread adoption of tropical forage grasses with high BNI capacity may have a great potential to tighten N cycling in grazed pastures.

On-irrigator pasture soil moisture sensor

In this paper, we presented the development of a proximal soil moisture sensor that measured the soil moisture content of dairy pasture directly from the boom of an irrigator. The proposed sensor was capable of soil moisture measurements at an accuracy of ±5% volumetric moisture content, and at meter scale ground area resolutions. The sensor adopted techniques from the ultra-wideband radar to enable measurements of ground reflection at resolutions that are smaller than the antenna beamwidth of the sensor. An experimental prototype was developed for field measurements. Extensive field measurements using the developed prototype were conducted on grass pasture at different ground conditions to validate the accuracy of the sensor in performing soil moisture measurements.

Distribution of Diverse Escherichia coli between Cattle and Pasture.

Escherichia coli is widely considered to not survive for extended periods outside the intestines of warm-blooded animals; however, recent studies demonstrated that E. coli strains maintain populations in soil and water without any known fecal contamination. The objective of this study was to investigate whether the niche partitioning of E. coli occurs between cattle and their pasture. We attempted to clarify whether E. coli from bovine feces differs phenotypically and genotypically from isolates maintaining a population in pasture soil over winter. Soil, bovine fecal, and run-off samples were collected before and after the introduction of cattle to the pasture. Isolates (363) were genotyped by uidA and mutS sequences and phylogrouping, and evaluated for curli formation (Rough, Dry, And Red, or RDAR). Three types of clusters emerged, viz. bovine-associated, clusters devoid of cattle isolates and representing isolates endemic to the pasture environment, and clusters with both. All isolates clustered with strains of E. coli sensu stricto, distinct from the cryptic species Clades I, III, IV, and V. Pasture soil endemic and bovine fecal populations had very different phylogroup distributions, indicating niche partitioning. The soil endemic population was largely comprised of phylogroup B1 and had a higher average RDAR score than other isolates. These results indicate the existence of environmental E. coli strains that are phylogenetically distinct from bovine fecal isolates, and that have the ability to maintain populations in the soil environment.

The effect of land use on soil permeability in Vojvodina

In order to get a comprehensive overview of the effect of land use on soil physical properties, this study was conducted on the selected representative soil samples collected at the territory of Autonomous Province of Vojvodina and included 6 types of soil present in this area. Undisturbed soil samples were taken from 61 localities, from the surface horizon (0 -30 cm) using the Kopetzky cylinders in three replications. The rate of water flow through soil was determined by the constant flow rate method. The velocities of water flow and filtration coefficients were calculated (K-Darcy), while statistical analysis confirmed a positive correlation between soil use and soil permeability. The results showed that soils used for agricultural production have lower permeability compared to soils in forests, meadows, and pastures.

Enzyme activity of Chromic Luvisols under different degree of erosion and land use

Soil erosion is a serious environmental problem and a threat to the sustainable agriculture production. Little information is available on enzyme activities of eroded soils in Bulgaria, especially on their relations to the degree of erosion and soil properties. In this work, slightly, moderately and severely eroded Chromic Luvisols under different land use (pasture, crop field and virgin) were studied. Enzyme activities (invertase, catalase and phosphatase), total nitrogen, total carbon, available phosphorus contents and soil particle distribution were determined and possible relations between them were examined. Data showed that enzyme activities tended to lower with increasing the degree of erosion. This was better pronounced for invertase and phosphatase in pasture and virgin soils. Depending on land use, all enzyme activities decreased in the order pasture > virgin > crop field soils, showing positive impact of soil cover and negative effect of cultivation practices. Soil invertase and phosphatase activities were in close relations with soil carbon content. The activities of catalase and phosphatase correlated positively with soil clay. Invertase only was in positive relation with soil silt and in negative relation with the sand content. Data obtained are intended to contribute to development of biological indicators of eroded soils.

Factor Analysis of Influence of Parameters of Water Regime and Hydrological Changes on Pastures

According to basic tabular data (DEFRA-commissioned project BD1310. Final report to the Department for Environment, Food and Rural Affairs) steady regularities between biochemical substances of the soil of pastures and hydrological parameters of their water mode are revealed shows the ranking methodology affecting and dependent factors and identification of deterministic models of the relationship between the 10 factors according to the general equation consisting of the sum of two biotechnical laws.

Impact of Grazing Intensity and Seasons on Greenhouse Gas Emissions in Tropical Grassland

Greenhouse gases (GHG) can be affected by grazing intensity, soil, and climate variables. This study aimed at assessing GHG emissions from a tropical pasture of Brazil to evaluate (i) how the grazing intensity affects the magnitude of GHG emissions; (ii) how season influences GHG production and consumption; and (iii) what are the key driving variables associated with GHG emissions. We measured under field conditions, during two years in a palisade-grass pasture managed with 3 grazing intensities: heavy (15 cm height), moderate (25 cm height), and light (35 cm height) N2O, CH4 and CO2 fluxes using static closed chambers and chromatographic quantification. The greater emissions occurred in the summer and the lower in the winter. N2O, CH4, and CO2 fluxes varied according to the season and were correlated with pasture grazing intensity, temperature, precipitation, % WFPS (water-filled pores space), and soil inorganic N. The explanatory variables differ according to the gas and season. Grazing intensity had a negative linear effect on annual cumulative N2O emissions and a positive linear effect on annual cumulative CO2 emissions. Grazing intensity, season, and year affected N2O, CH4, and CO2 emissions. Tropical grassland can be a large sink of N2O and CH4. GHG emissions were explained for different key driving variables according to the season.

УЛААНБААТАР ХОТЫН ХӨРСНИЙ БОХИРДОЛ

According by soil investigation of Ulaanbaatar city area in 2012 soil heavy metal contamination generally was low. In some areas revealed anomaly high content of Chromium, Lead and Zink exceeding maximum allowed content. But this points a sporadic distributed not covered big area and 7.5-2.7 % of samples are exceeding standard level. The soil ammonium and sulfate content is high comparing with non-polluted pasture soils. Soil ammonium pollution more closely connected with big open markets and “ger horoolol” area. Primary source of sulfate content is air pollution and coal burning. Soil microbiological pollution, E.Coli and anaerobic bacteria level is high. The “ger horoolol” district area becoming main source of microbiological pollution. Improvement of solid waste management and “ger horoolol” area planning is challenging issue to solve a soil pollution problem of Ulaanbaatar city area.

Erratum: Phylogenetic and functional potential links pH and N2O emissions in pasture soils.

Scientific Reports 6: Article number: 35990; published online: 26 October 2016; updated: 06 December 2016.

Carbon dioxide, nitrous oxide and methane emissions from the Waimate District (New Zealand) pasture soils as influenced by irrigation, effluent dispersal and earthworms

Effects of wet/dry cycles in inducing greenhouse gas emissions are well documented. However, the effects of field drying and rewetting events remain poorly understood. This study investigated the i...

The chemical nature of organic phosphorus that accumulates in fertilized soils of a temperate pasture as determined by solution 31P NMR spectroscopy

AbstractInefficiency of fertilizer phosphorus (P) use in grazing systems is often associated with the accumulation of inorganic and organic P in fertilized soil. However, the chemical nature of the accumulated organic P remains poorly understood. The aim of this study was to use solution 31P nuclear magnetic resonance (NMR) spectroscopy on sodium hydroxide–ethylenediaminetetraacetic acid (NaOH‐EDTA) extracts to identify the chemical nature of organic P in soils from a medium‐term (13 years) permanent pasture field experiment. This included an unfertilized pasture (P0), and treatments designed to maintain soil P fertility at near ‘optimum' (P1) and ‘supra‐optimum' (P2) levels for pasture growth; pastures at all levels of soil P fertility were continuously grazed with either a moderate or high stocking rate (SR09 and SR18). Approximately 20% of the fertilizer P added to pastures was recovered as organic P in NaOH‐EDTA extracts at the P1 level of soil P fertility in the 0–10 cm soil layer, and the majority (≈ 65%) of this was detected as the broad phosphomonoester signal. In addition, several specific forms of phosphomonoesters (myo‐ and scyllo‐inositol hexakisphosphate, α‐ and β‐glycerophosphate, and RNA mononucleotides) and phosphodiesters were detected across all soils but at low concentrations. This study shows that phosphate fertilization of pastures primarily results in the accumulation of complex forms of phosphomonoesters rather than that of specific forms of recognizable biomolecules (e.g., myo‐inositol hexakisphosphate).

Response of ammonia oxidizers and denitrifiers to repeated applications of a nitrification inhibitor and a urease inhibitor in two pasture soils

The nitrification inhibitor 3,4-dimethylpyrazol-phosphate (DMPP) and the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) can mitigate N losses through reducing nitrification and ammonia volatilization, respectively. However, the impact of repeated applications of these inhibitors on nitrogen cycling microorganisms is not well documented. This study aimed to investigate the changes in the abundance and community structure of the functional microorganisms involved in nitrification and denitrification in Australian pasture soils after repeated applications of DMPP and nBTPT. Soil was collected in autumn and spring, 2014 from two pasture sites where control, urea, urea ammonium nitrate, and urea-coated inhibitors had been repeatedly applied over 2 year. Soil samples were analyzed to determine the potential nitrification rates (PNRs), the abundances of amoA, narG, nirK and bacterial 16S rRNA genes, and the community structure of ammonia oxidizers. Two years of urea application resulted in a significantly lower soil pH at Terang and a significant decrease in total bacterial 16S rRNA gene abundance at Glenormiston and led to significantly higher PNRs and abundances of ammonia oxidizers compared to the control. Amendment with either DMPP or nBTPT significantly decreased PNRs and the abundance of amoA and narG genes. However, there was no fertilizer- or inhibitor-induced change in the community structure of ammonia oxidizers. These results suggest that there were inhibitory effects of DMPP and nBTPT on the functional groups mediating nitrification and denitrification, while no significant impact on the community structure of ammonia oxidizers was observed. The application of nitrification or urease inhibitor appears to be an effective approach targeting specific microbial groups with minimal effects on soil pH and the total bacterial abundance.

N2O and CO2 dynamics in a pasture soil across the frozen period

Since the process of gas dynamics in agricultural soils is mainly studied during plant growth, only a few studies have focused on these dynamics in frozen soils covered with snow. Nevertheless, gas...

Phylogenetic and functional potential links pH and N2O emissions in pasture soils.

Denitrification is mediated by microbial, and physicochemical, processes leading to nitrogen loss via N2O and N2 emissions. Soil pH regulates the reduction of N2O to N2, however, it can also affect microbial community composition and functional potential. Here we simultaneously test the link between pH, community composition, and the N2O emission ratio (N2O/(NO + N2O + N2)) in 13 temperate pasture soils. Physicochemical analysis, gas kinetics, 16S rRNA amplicon sequencing, metagenomic and quantitative PCR (of denitrifier genes: nirS, nirK, nosZI and nosZII) analysis were carried out to characterize each soil. We found strong evidence linking pH to both N2O emission ratio and community changes. Soil pH was negatively associated with N2O emission ratio, while being positively associated with both community diversity and total denitrification gene (nir & nos) abundance. Abundance of nosZII was positively linked to pH, and negatively linked to N2O emissions. Our results confirm that pH imposes a general selective pressure on the entire community and that this results in changes in emission potential. Our data also support the general model that with increased microbial diversity efficiency increases, demonstrated in this study with lowered N2O emission ratio through more efficient conversion of N2O to N2.

Changes in the Bacterial Community Structure of Remediated Anthracene-Contaminated Soils.

Mixing soil or adding earthworms (Eisenia fetida (Savigny, 1826)) accelerated the removal of anthracene, a polycyclic aromatic hydrocarbon, from a pasture and an arable soil, while a non-ionic surfactant (Surfynol® 485) inhibited the removal of the contaminant compared to the untreated soil. It was unclear if the treatments affected the soil bacterial community and consequently the removal of anthracene. Therefore, the bacterial community structure was monitored by means of 454 pyrosequencing of the 16S rRNA gene in the pasture and arable soil mixed weekly, amended with Surfynol® 485, E. fetida or organic material that served as food for the earthworms for 56 days. In both soils, the removal of anthracene was in the order: mixing soil weekly (100%) > earthworms applied (92%) > organic material applied (77%) > untreated soil (57%) > surfactant applied (34%) after 56 days. There was no clear link between removal of anthracene from soil and changes in the bacterial community structure. On the one hand, application of earthworms removed most of the contaminant from the arable soil and had a strong effect on the bacterial community structure, i.e. a decrease in the relative abundance of the Acidobacteria, Chloroflexi and Gemmatimonadetes, and an increase in that of the Proteobacteria compared to the unamended soil. Mixing the soil weekly removed all anthracene from the arable soil, but had little or no effect on the bacterial community structure. On the other hand, application of the surfactant inhibited the removal of anthracene from the arable soil compared to the untreated soil, but had a strong effect on the bacterial community structure, i.e. a decrease in the relative abundance of Cytophagia (Bacteroidetes), Chloroflexi, Gemmatimonadetes and Planctomycetes and an increase in that of the Flavobacteria (Bacteroidetes) and Proteobacteria. Additionally, the removal of anthracene was similar in the different treatments of both the arable and pasture soil, but the effect of application of carrot residue, earthworms or the surfactant on the bacterial community structure was more accentuated in the arable soil than in the pasture soil. It was found that removal of anthracene was not linked to changes in the bacterial community structure.

Diversity and biogeographical patterns of legumes (Leguminosae) indigenous to southern Africa.

The principal aim of this study was to establish biogeographical patterns in the legume flora of southern Africa so as to facilitate the selection of species with agricultural potential. Plant collection data from the National Herbarium, South Africa, were analysed to establish the diversity and areas covered by legumes (Leguminosae/Fabaceae) indigenous to South Africa, Lesotho and Swaziland. A total of 27,322 records from 1,619 quarter degree grid cells, representing 1,580 species, 122 genera and 24 tribes were included in the analyses. Agglomerative hierarchical clustering was applied to the presence or absence of legume species in quarter degree grid cells, the resultant natural biogeographical regions (choria) being referred to as leguminochoria. The description of the 16 uniquely formed leguminochoria focuses on defining the associated bioregions and biomes, as well as on the key climate and soil properties. Legume species with a high occurrence in a leguminochorion are listed as key species. The dominant growth form of key species, species richness and range within each leguminochorion is discussed. Floristic links between the leguminochoria are established, by examining and comparing key species common to clusters, using a vegetation classification program. Soil pH and mean annual minimum temperature were found to be the main drivers for distinguishing among legume assemblages. This is the first time that distribution data for legumes has been used to identify biogeographical areas covered by leguminochoria on the subcontinent. One potential application of the results of this study is to assist in the selection of legumes for pasture breeding and soil conservation programs, especially in arid and semi-arid environments.

The effect of irrigation and urine application on phosphorus losses to subsurface flow from a stony soil

Diffuse losses of phosphorus (P) from agricultural land via subsurface flow (viz leaching) can result in degradation of surface water quality. Factors such as irrigation and soil pH can increase the solubility of P and its subsequent loss to water. Urine patches are known to alter pH by up to 3 units, but it is unknown if this increases P loss. This study investigated subsurface P loss from a stony soil subjected to different rates of irrigation (12, 25, 50mmh−1) with or without the application of urine (600kgNha−1), a typical N loading rate under a cattle urine patch, using intact lysimeters. Results showed that despite receiving urine, average total P (TP), filtered reactive P (FRP) and filtered unreactive P (FURP) concentrations were significantly (P<0.05) lower (27, 3, 7μgL−1) than non-urine treatments (40, 8, 11μgL−1). Increasing the rate (not amount) of irrigation did not affect the load of P lost. Total P loads were generally low (0.070–0.167kgha−1) compared to other studies where P loss has been measured in drainage from pasture soils after P fertiliser application. The lack of differences observed with increasing irrigation rates was thought to be due to attenuation as P moved from preferential flow pathways in the topsoil to matrix flow in the subsoil gravels. The lower P losses following urine application were due to: 1) the buffering effect of the soil negating any significant pH-induced solubilisation of P; and 2) enhanced P uptake and decreased drainage (due to greater evapotranspiration) as dry matter production increased in response to the nitrogen applied in urine. However, despite this soil having only a moderate Olsen P concentration, typical of productive landuses in the region, FRP and TP concentrations still exceeded guidelines for good surface water quality. Strategies should be considered to decrease these losses, especially where drainage occurs via preferential flow pathways that negate attenuation of P losses, or are well connected to surface waters such as using precision irrigation.

Soil moisture deficit selects for desiccation tolerant Rhizobium leguminosarum bv. trifolii

Tolerance to desiccation is a highly desirable attribute for Rhizobium spp., which are widely used as symbionts of pasture legumes. Poor survival of Rhizobium spp. is of particular concern during the commercial formulation and seed application phase, but also when sown into dry fields and during saprophytic survival. Efforts have been made to protect Rhizobium spp. from desiccation, either by use of desiccation protectants in formulations, or by triggering generalised mechanisms of cellular stress tolerance. This study looked at the potential to isolate desiccation tolerant strains of Rhizobium leguminosarum bv. trifolii that are intrinsically tolerant to desiccation. We investigated the influence of long term exposure to dry soil conditions, and rapid soil drying, as factors in selection of desiccation tolerance. Pasture soils were collected from 26 sites in New Zealand that ranged in soil moisture deficits (SMD) from 149days per year (very dry) to 0 (wet). Rhizobium leguminosarum bv. trifolii populations were quantified (most probable number; MPN) in the field-fresh and dried (48h forced air) samples from each site, and the percentage population survival determined. Rhizobium leguminosarum bv. trifolii survival after soil drying was strongly correlated to SMD (P<0.001; R2=0.42), providing evidence for strong selection for desiccation tolerant phenotypes in dry environments. Desiccation tolerance of R. leguminosarum bv. trifolii isolated from nodules taken from white clover plants grown in fresh and dried soils from three sites was compared in a micro-droplet assay. Strains from plants grown in the dried soils were more tolerant to rapid drying under in vitro conditions (P<0.001). Screening of a subset of strains on a range of osmolytes (phenotype microarray), showed desiccation tolerance was associated with tolerance to the salts sodium nitrite, sodium nitrate, and ammonium sulphate, and ethylene glycol. Growth in the presence of ethylene glycol maybe useful surrogate indicators of desiccation tolerance in R. leguminosarum bv. trifolii. Overall, these results show that environmental conditions can provide a basis for selection of populations with desiccation tolerance, and plant-based baiting can be used to recover strains with improved characteristics.

An assessment of the effect of contact time on cadmium phytoavailability in a pasture soil.

The length of time cadmium (Cd) is in contact with the soil has been recognised as a factor affecting phytoavailability, but the extent of this process is currently poorly understood. This study used isotopic dilution techniques (E and L values) to determine the effect of contact time on Cd phytoavailability from soil collected from a long-term phosphorus (P) fertiliser trial. Cadmium phytoavailability was determined in soil that was last fertilised with soluble Cd from P fertiliser 17years prior to sampling (residual plots) and soil that received annual applications of P fertiliser until sampling (continuous plots). It was found that both E values and L values increased with P fertiliser (viz Cd) inputs and were significantly related to each other (r 2=0.82 P<0.005). There was however no significant difference (P<0.05) in the percentage of total Cd that was phytoavailable calculated using E values (E%) between the continuous (mean 51%) and the residual plots (mean 51%). There was also no significant difference (P<0.05) in the percentage of total soil Cd that was phytoavailable calculated using L values (L%) between the continuous (mean 77%) and residual plots (mean 87%). These results suggest that despite Cd being in contact with the soil for 17years, there was no difference in the size of the phytoavailable Cd pool compared to recent Cd inputs. This study should be repeated for other soil types and factored into any analysis for the long-term implications of ongoing Cd accumulation in soil on future landuse.

Aluminum Forms in Solid Phase of Soils Developed over Schists as a Function of Land Use

ABSTRACTLand use may modify certain soil properties while soil physicochemical characteristics can influence metal partitioning in soils. Therefore, the total content and various forms of aluminum (Al) in solid phase of schist-developed topsoils (0–20 cm) in NW Spain under different land uses (i.e., forest, pasture, and cultivation) were evaluated to identify the Al-bearing phases. Aluminum fractionation was performed, using a six-step sequential extraction procedure with ammonium acetate, hydroxylamine hydrochloride, ammonium oxalate in darkness, hydrogen peroxide, ammonium oxalate under ultraviolet radiation, and acid digestion. Mean concentrations of total Al were similar in the soils under three land uses. Mean percentage of the various Al forms in all soils were in the following order: residual fraction > amorphous compounds > crystalline compounds > water-soluble/exchangeable/specifically adsorbed > bound to oxidizable organic matter > manganese oxides. The forest soils contained considerably higher contribution of amorphous compounds (16.3%) to total Al concentration compared with the soils under other two uses (mean about 9%). Maximum mean concentration of exchangeable Al was also observed in forest soils (mean 8.8% of total Al vs. about 4% in pasture soils and cultivated soils); this is attributed to lower pH and higher organic matter content of the forest soils. Thus, this study revealed the impact of land use on the Al-bearing phases and, hence, in its bioavailability to plants.