Application of nitrolim, which contains 57% calcium cyanamide, to the soil surface completely inhibited germination of sclerotia of Sclerotinia sclerotiorum, whether buried or placed on the soil surface, over a period of at least 20 weeks at 20°C, whereas most sclerotia on untreated soil germinated within 5 weeks, producing apothecia 2–6 weeks later. Temperature markedly influenced the germination rate of sclerotia. On untreated soil, sclerotia failed to germinate at 10° after 4 weeks, and at 15° only one-third had germinated. Hydrogen cyan-amide was a less effective inhibitor of germination than nitrolim. Benlate and benzotriazole inhibited germination of sclerotia over a period of at least 20 weeks at 20° but parabanic acid had no effect. Initial inhibition by maleic acid hydrazide was followed by normal germination and the formation of apothecia.
The complex dielec ric constant has been measured at five audio frequencies over the temperature range 5.5-390 K for various concentrations of Ce, Eu, Gd, and Er in Sr${\mathrm{F}}_{2}$. Three principal relaxations are observed, two of which have been studied by previous workers. The shift in relative population between the two peaks with ion size, observed previously, has been verified and the ratio of the dipole moment is found to be approximately 2.8, which is consistent with the identification of the two relaxations as type-I and type-II dipoles. In addition, under the assumption of thermal equilibrium, enthalpy differences for the two species in Sr${\mathrm{F}}_{2}$: Gd and Sr${\mathrm{F}}_{2}$: Eu are found to be 0.049 and 0.078 eV, respectively, which is also consistent with the previous identifications. The thrid relaxation is a low-activation-energy process which occurs for large concentrations (> 0.1 mol%) of small rare-earth ions. Consequently, it is concluded that the new relaxation is cluster-associated. A similar relaxation, ${R}_{\mathrm{III}}$, is known to occur for small rare earths in calcium fluoride; however, the relaxation exists at smaller concentrations in calcium fluoride and is and is stable for larger rare earths in strontium fluoride.
Context While multi-year field experiments remain a cornerstone of agricultural research, their requirement warrants critical examination. Objective This perspective analyses the scientific rationale behind multi-year experiment expectations and proposes a framework for determining appropriate experimental duration based on research objectives, mechanistic understanding and environmental dependencies. Results and conclusions Field experiments offer distinct advantages over laboratory studies by capturing environmental complexity, including weather variations, soil biological dynamics, pest pressures, and the effects across spatial scales. Multi-year experiments enhance research robustness through increased reliability, better understanding of treatment effects under varying conditions, and greater statistical power. However, significant limitations include increased costs and resource demands, which can create barriers particularly for researchers in low- and middle-income countries, early career researchers, and those working on time-sensitive agricultural issues. We argue that certain research contexts (some of which are the same for short-term mesocosm and incubation scale experiments), such as mechanistic studies with clear process understanding, innovative technology validation, or time-sensitive investigations (including double and triple cropping systems), should warrant acceptance of single-year experiments when accompanied by robust supporting evidence and comprehensive metadata. Significance A more flexible and nuanced approach to determining study duration could better serve agricultural science advancement while maintaining research rigour, especially for studies combining detailed mechanistic investigations with field validation, that could, and should, be systematically integrated into future meta-analyses.
The distribution and diversity of RNA viruses in soil ecosystems are largely unknown, despite their significant impact on public health, ecosystem functions, and food security. Here, we characterise soil RNA viral communities along an altitudinal productivity gradient of peat, managed grassland and coastal soils. We identified 3462 viral contigs in RNA viromes from purified virus-like-particles in five soil-types and assessed their spatial distribution, phylogenetic diversity and potential host ranges. Soil types exhibited minimal similarity in viral community composition, but with >10-fold more viral contigs shared between managed grassland soils when compared with peat or coastal soils. Phylogenetic analyses predicted soil RNA viral communities are formed from viruses of bacteria, plants, fungi, vertebrates and invertebrates, with only 12% of viral contigs belonging to the bacteria-infecting Leviviricetes class. 11% of viral contigs were found to be most closely related to members of the Ourmiavirus genus, suggesting that members of this clade of plant viruses may be far more widely distributed and diverse than previously thought. These results contrast with soil DNA viromes which are typically dominated by bacteriophages. RNA viral communities, therefore, have the potential to exert influence on inter-kingdom interactions across terrestrial biomes.
The leaching of base cations in acidic soils can result in calcium (Ca2+) and magnesium (Mg2+) deficiencies, which are important for microbial cell function. We aimed to determine if microbial carbon use efficiency (CUE) and microbial biomass carbon (MBC) were limited in acidic soils due to a lack of base cations. Microbial CUE across a range of agricultural soils (n = 970; pHCa 3.4–7.9) treated with either deionised H2O (control) or a solution of 300 mM CaCl2 + 300 mM MgCl2 (+Base cations) was determined using a14C radioisotope tracer approach. Our results showed that the addition of base cations significantly increased microbial CUE (by up to 20%) at pHCa < 4.7; which coincided with a steep increase in exchangeable acidity. Base cation addition significantly increased MBC in nil-limed soils (pHCa 4.6) from 494 mg C kg−1 to 769 mg C kg−1 when plant residue was added, but not in limed soils (pHCa 6.2). Our findings indicate that the addition of base cations to highly acidic soils can increase microbial growth, thus aiding with carbon sequestration in these agricultural soils.
The cell walls of Sclerotinia sclerotiorum (Lib.) de Bary have been examined by electron microscope, infrared and biochemical techniques. The rind walls of the sclerotia have a rough outer electron-dense layer which is absent from the other walls. The hyphal walls do not have definite layers, but the pseudo-parenchymatous walls possess a relatively thin electron-dense inner wall surrounded by a substantially thicker outer electron-transparent layer. Microfibrils, probably of chitin, are present in all walls. Whereas β-glucan and chitin are constituents of the hyphal walls, and of the pseudoparenchymatous and rind walls of the sclerotia, a melanin was found in the rind walls only. Enzyme studies with culture filtrates from two lytic soil micro-organisms suggested that the β-glucan was similar to laminarin, a β (1→3) glucan. In addition the presence of β ( 1→6) linkages was indicated in the pseudoparenchymatous walls. Acid-hydrolysis products of the pseudoparenchymatous and hyphal walls were similar and included amino-acids, amino-sugar and glucose with some mannose. Phenol oxidase was present in the rind cells and in an exudate from the sclerotial surfaces. The product of the activity of this enzyme on catechol differed from the melanin pigment of the rind walls.
Wetting up either air‐dried or field moist soil to predetermined moisture contents resulted in substantial changes in the composition of soil solution. Solute concentrations were generally reduced following a 24‐hour equilibration period. The magnitude of these changes was dependent upon the amount of water added and the element involved. Air‐drying soil for 14 days at 25°C resulted in increased concentrations of most determined elements upon rewetting. Both physical and chemical changes in the soil occurred during the sample preparation and the centrifugation process. Soil solution should be separated from field moist soil as quickly as possible after sample collection.
Nitrogen (N) leaching from coarse-textured soils frequently leads to productivity losses and negative environmental consequences. Historically, clay amendment has been used on coarse-textured soils to decrease water repellence and nutrient leaching. More recently, biochar has been proposed as an alternative soil amendment to decrease N leaching while simultaneously storing carbon. As biochar has a greater nutrient-retention capacity, we hypothesised that biochar derived from Eucalyptus marginata would be a more effective amendment than clay at minimising N leaching. The soil used was a coarse-textured agricultural sand with the following treatments: (1) biochar incorporated homogenously into the 0–10 cm soil layer, (2) clay incorporated similarly, (3) biochar added as a layer at 10 cm depth, (4) clay added similarly, or (5) a control. Amendments were added at 25 t/ha and watered periodically over 21 days and watered with the equivalent to 30 mm. Clay and biochar amendments significantly decreased cumulative NH4+ leaching by ~20% and NO3– leaching by 25%. Biochar decreased NO3– leaching significantly more than clay, possibly due to decreased nitrification. Dissolved organic N leaching was not influenced by any treatment. Leaching of N was unaffected by amendment application method. We conclude that to decrease N leaching, land managers should apply the most readily available of the amendments in the most convenient manner.
Plants and microorganisms intensely compete for nitrogen (N) at many stages of the terrestrial N cycle. In particular, the dissolved organic N (DON) pool, and competition for low molecular weight dissolved organic N (LMWDON) compounds such as amino acids and peptides (and LMW dissolved organic matter; LMWDOM as a whole) has received significant recent research interest. However, as LMWDON compounds contain both N and carbon (C), a question that remains is whether soil microorganisms are primarily taking up LMWDON mainly for the C or the N contained therein. We investigated microbial uptake rates of the model peptide l-trialanine as a rapidly cycling LMWDON compound in temperate grassland soils of differing fertility using 14C labelling to assess how soil fertility status influenced microbial uptake of LMWDON. We then imposed an excess of C as glucose and/or N as NH4Cl to ask whether the uptake of the peptide was affected by C or N excess. Our results demonstrate that l-trialanine is taken up rapidly from the soil solution (t½ < 1.5 min), and that an excess of C, rather than N, resulted in a reduced uptake of the peptide. From this, we conclude that LMWDON is taken up primarily to fulfil the C requirement of soil microorganisms, indicating that they exist in a C-limited state, and are able to respond quickly to a transient influx of an easily metabolisable resource.
Escherichia coli O157:H7 is a potentially lethal pathogen which has been responsible for several outbreaks of milk-borne illness in recent years. The objective of this study was to evaluate the survival and metabolic activity (indexed by bioluminescence) of a chromosomally lux -marked strain of Esch. coli O157:H7 in raw, pasteurized and microfiltered pasteurized milk at 4 and 20°C for up to 14 d. Results showed that the population of Esch. coli O157:H7 and its metabolic activity decreased in all samples during storage at 4°C, with no significant differences in numbers observed between the different milk types; but metabolic activity was significantly higher ( P <0·05) in the microfiltered pasteurized milk than that in raw milk. At 20°C, Esch. coli O157:H7 counts and cell activity peaked at day 2, and then declined progressively. At 20°C, survival and metabolic activity were significantly lower in raw milk compared with pasteurized milk. We conclude that storage temperature is more important in regulating the survival of Esch. coli O157 in contaminated milk than its origin/pre-treatment conditions.
Urine patches contribute greatly to greenhouse gas emissions within livestock grazed ecosystems. The effective area of a ruminant urine patch comprises the wetted area, the diffusional area and the pasture response area. This study specifically assesses the importance of considering the diffusional area for monitoring urine patch N2O emissions. Spatial and temporal changes in N2O emissions and potential drivers of emissions (soil pH, EC, redox potential, dissolved organic carbon and nitrogen, NO3− and NH4+) were measured in sheep urine amended Eutric Cambisol mesocosms, maintained at 50% or 70% water-filled pore space (WFPS). At 70% WFPS, over 10 weeks, the emission factor (EF) was greater when considering the wetted area plus a 9 cm diffusional area (EF = 2.75 ± 0.72% of applied N) than when considering the wetted area alone (EF = 1.44 ± 0.30% of applied N); differences were not statistically significant at 50% WFPS. Redox potential, total extractable N and WFPS contributed significantly to the observed variation in daily N2O fluxes from the urine patch. We conclude that the urine patch diffusional area is an extremely important source of emissions from urine patches. This has implications when measuring EFs, as the lateral diffusion of solutes may be restricted by chamber walls resulting in an underestimate of N2O emissions, particularly at higher soil moisture contents. Site-specific assessments of the urine patch diffusional area should be made, and accounted for, prior to monitoring emissions and calculating emission factors from urine patches applied within chambers.
Presented are multiepoch Very Long Baseline Interferometry (VLBI) observations on Southern Hemisphere radio stars phase-referenced to background radio sources. The differential astrometry analysis results in high-precision determinations of proper motions and parallaxes. The astrophysical implications and astrometric consequences of these results are discussed.
The addition of calcium carbonate to catchments or watercourses--liming--has been used widely to mitigate freshwater acidification but the abatement of acidifying emissions has led to questions about its effectiveness and necessity. We conducted a systematic review and meta-analysis of the impact of liming streams and rivers on two key groups of river organisms: fish and invertebrates. On average, liming increased the abundance and richness of acid-sensitive invertebrates and increased overall fish abundance, but benefits were variable and not guaranteed in all rivers. Where B-A-C-I designs (before-after-control-impact) were used to reduce bias, there was evidence that liming decreased overall invertebrate abundance. This systematic review indicates that liming has the potential to mitigate the symptoms of acidification in some instances, but effects are mixed. Future studies should use robust designs to isolate recovery due to liming from decreasing acid deposition, and assess factors affecting liming outcomes.
