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1.
The potential for using the composting process to sanitize plant waste infected with one of three plant pathogens was investigated using bench‐scale composting equipment. Two of these pathogens, the potato wart disease fungus Synchytrium endobioticum and Potato spindle tuber viroid (PSTVd) are currently subject to European quarantine regulations. The third, Polymyxa betae, a parasite of sugar beet, is regulated in some European countries when in association with Beet necrotic yellow vein virus (BNYVV), the causal organism of rhizomania disease of sugar beet. Survival of test organisms following various combinations of compost temperature, exposure time and moisture was determined using RNA‐based detection methodology and/or plant‐based bioassays. Mathematically definable relationships between compost treatment (temperature/time) and organism viability were identified for P. betae and S. endobioticum; these give some indication of the practicality of using composting for dealing with infected wastes. However, for PSTVd, the considerable variability in measured susceptibility of the viroid to the composting process meant that no such definable relationship could be determined and further work would be needed to extrapolate to practical situations.  相似文献   
2.
Ullucus tuberosus (ulluco) is a tuber-forming species that has become a novel crop in highland and temperate maritime climates. Eight viruses have been previously reported infecting Ullucus, including Andean potato latent virus (APLV), a quarantine virus within the European Union. No reference sequences have been published for the viruses previously described from U. tuberosus. Plants grown in the UK for the internet trade were tested for the presence of quarantine viruses using ELISA and real-time RT-PCR. ELISA positive results were obtained for APLV and multiple other viruses. A similar suite of viruses was detected at a second outbreak site linked to horticultural trade. Virus identification was by high-throughput sequencing (HTS) using a ribosomal RNA (rRNA)-depleted total RNA approach. Analysis of viral contigs indicated the presence of several novel viruses closely related to, but not consistent with, the viruses indicated by ELISA. Further confirmatory testing by real-time RT-PCR indicated that two tymoviruses, tentatively named Ullucus tymovirus 1 and Ullucus tymovirus 2, were more closely related to each other (85% identity), than to APLV or Andean potato mild mosaic virus (63–66% identity). APLV could not be confirmed from either site by either HTS or PCR. A novel tobamovirus (Ullucus tobamovirus 1) was only detected at the initial outbreak site. A novel polerovirus (Ullucus polerovirus 1) and a distinct genotype of Papaya mosaic virus were detected from both outbreak sites. Deploying HTS during a plant health outbreak demonstrates the potential of this approach to give rapid, accurate diagnosis.  相似文献   
3.
Field experiments were conducted on four acid soils which were typical of the eastern section of the cropping region in southeastern Australia. The response of three cereal varieties to application of limestone or elemental S was measured as a function of soil pH. The cereals were selected to cover the known range of tolerance to acidity: Triticale (×Triticosecale wittmack cv. Currency) (tolerant); wheat (Tritcum aestivum cv. Matong) (moderately tolerant) and barley (Hordeum vulgare cv. Schooner) (sensitive). A two asymptote logistic equation was used to describe the relationship between soil pH and rates of limestone and elemental sulphur. The upper asymptotes for the four sites were well below the pH of lime saturation as the agriculturally practiced rates of lime were lower than the rates that could achieve the maximum pH in the field. The same equation was used to fit higher rates of lime application to a similar soil type to one of the four sites in this study and resulted in an upper asymptote of 7.26. Crop yield responses to lime application were well described by soil pHCa (0.01 M CaCl2). Soil pHCa ranges which gave 95% of maximum yield were pHCa 4.3–5.6 for Matong wheat, 4.4–4.8 for Currency triticale and 4.7–5.8 for Schooner barley. It was found that rainfall played an important role in limiting the yield response of crops to lime application. Lime reaction, lime requirement and grain yield models should include rainfall and soil water content as these influence the rate and extent of dissolution of limestone and subsequent plant response in a semi-arid environment.  相似文献   
4.
Precision Agriculture - Precision nutrient management requires accurate assessment of crop nutrient status. This is common for assessing N status, but much less so for other nutrients. Because...  相似文献   
5.
Twenty microsatellites (simple sequence repeats, SSR) were used to discriminate wild boar from domestic pig and to identify mixtures of the two. Reference groups of wild boar and pig samples were collected from the UK and Europe for genetic assignment tests. Bayesian Analysis of Populations software (BAPs) gave 100% correct assignment for blind wild boar and pig samples and correctly identified mixed samples. DNA was extracted from 12 commercial food samples (11 labeled as containing wild boar) including patés, salamis, and sausage, and good SSR profiles were obtained. Eleven samples were correctly assigned as pig, and two as mixed meats. One sample sold as wild boar meat was clearly assigned as pig. A further 10 blind samples of meat cuts were analyzed, eight wild boar and two pig, and all were correctly assigned.  相似文献   
6.
 To ascertain the cause of the decrease in pH with depth through the surface 15 cm of moderately acidic soils, pH was monitored in layers of an initially mixed surface soil (to a nominal depth of 10 cm) during two consecutive seasons under fallow, wheat, and subterranean-clover plots. Variation of pH-influencing processes within soil layers to 15 cm depth was measured during the first season. Initially, soil pH was relatively uniform within the surface 7.5 cm, although there was an average 0.53 unit decrease of pH from 0–2.5 cm to 10–15 cm depth. Under all plots, residual lime reaction, net organic anion association and oxidation, net manganese oxidation and reduction, and particularly net N mineralisation and subsequent nitrification, tended to decrease with depth through the surface 15 cm of soil. In wheat and subterranean-clover plots, the alkalinity added with the return of 3.9–4.7 t ha–1 of plant residue dry matter was predominantly released within the surface 2.5 cm of soil. The dominant pH-influencing processes were net N mineralisation and subsequent nitrification, and the return of alkaline plant residues. In the fallow plots, the surface 10 cm of soil tended to acidify due to nitrification. However in wheat and clover plots, alkalinity added to the surface 2.5 cm of soil from plant residues exceeded acidification resulting from nitrification at this depth. The magnitude of the pH gradient through 0–15 cm depth was therefore maintained under wheat, increased under clover, and decreased under fallow. Received: 11 October 1999  相似文献   
7.
Recently, soil carbon sequestration in agro-ecosystems has been attracting significant interest as soil organic carbon (SOC) can potentially offset some atmospheric carbon dioxide. The objectives of this study were to use the RothC model to simulate soil carbon sequestration and determine the proportion of pasture production as carbon input for SOC sequestration under different pasture types and pasture management in a long term experiment established in 1992. There were two types of pastures, annual and perennial pastures, with or without application of limestone. Simulation results showed that with an initial setting for the stubble retention factor of 0.65 and root/shoot ratio of 0.5 for annual pasture and 1.0 for perennial pasture, RothC can adequately simulate SOC for both pasture types, especially annual pasture. Using an inverse modelling technique, the root/shoot ratio was determined as 0.49 and 0.57 for annual pasture and 0.72 and 0.76 for perennial pasture with and without limestone application, respectively. There was a large improvement in model performance for perennial pasture with and without limestone application. The root mean squared errors (RMSE) reduced from 3.19 and 2.99 t C ha−1 in the initial settings to 2.09 and 2.10 t C ha−1, while performance efficiency (PE) increased from 0.89 and 0.91 to the same value of 0.95 when the root/shoot ratio of 0.72 and 0.76 were used for limed and unlimed perennial pastures. However, there was little improvement for annual pasture as RMSE had little change and PE was the same. As the stubble retention factor and root/shoot ratio can be combined into one factor that measures an equivalent amount of total above-ground pasture production allocated for soil carbon input, the modelled results can be summarised as 1.2 times and 1.4 times the above-ground dry matter for annual and for perennial pasture, respectively, regardless of liming. Our results provide useful information for simulation of soil carbon sequestration under continuous pasture systems.  相似文献   
8.
Agricultural management can affect soil organic matter chemistry and microbial community structure, but the relationship between the two is not well understood. We investigated the effect of crop rotation, tillage and stubble management on forms of soil phosphorus (P) as determined by solution 31P nuclear magnetic resonance spectroscopy and microbial community composition using fatty acid methyl ester analysis in a long-term field experiment (26 years) on a Chromic Luvisol in New South Wales, Australia. An increase in soil organic carbon, nitrogen and phosphorus compared to the beginning of the experiment was found in a rotation of wheat and subterranean clover with direct drill and mulching, while stubble burning in wheat–lupin and wheat–wheat rotations led to soil organic matter losses. Microbial biomass was highest in the treatment with maximum organic matter contents. The same soil P forms were detected in all samples, but in different amounts. Changes in organic P occurred mainly in the monoester region, with an increase or decrease in peaks that were present also in the sample taken before the beginning of the experiment in 1979. The microbial community composition differed between the five treatments and was affected primarily by crop rotations and to a lesser degree by tillage. A linkage between soil P forms and signature fatty acids was tentatively established, but needs to be verified in further studies.  相似文献   
9.
The Murrumbidgee River catchment is a major region of both dryland and irrigated agricultural production in eastern Australia. The salinity of water in the lower reaches of the river is the subject of concern; changing land management upstream is one option to minimise accessions of salt to the river but this must be done in a way that provides an adequate quantity of water for downstream users and the environment.

We examined 30 years of sporadic data on the ionic composition of water for 7 subcatchments contributing to the mid-Murrumbidgee River and for 2 gauging stations on the river itself. Despite the common local presumption that salinity, measured as electrical conductivity (EC), is primarily due to NaCl from cyclic marine salt, we found that NaCl was the dominant salt in only some streams. The presence of HCO3−'s of Ca2+ and Mg2+ in all streams, and their dominance in 2 streams, indicates that mineral weathering is also a major contributor to the salt load of water in the catchment. However, Ca2+ and Mg2+ bicarbonates have limited solubility and so their concentrations will not become a cause of osmotic stress when the water is used for drinking or irrigation. Therefore, in our efforts to prioritise lower order catchments of the Murrumbidgee River for changed land management, it will be necessary to examine the nature of the salts they discharge, not just EC. By distinguishing between Cl−/Na+ dominated streams and Ca2+, Mg2+/HCO3− dominated streams we can refine our search for sources of osmotic stress which might potentially worsen with time. This will enable us to target particular land management units so as to obtain the maximum reduction in downstream salinity with a minimal decrease in flow volume and minimal area of land undergoing changed landuse.  相似文献   

10.
 In the field, surface soil pH gradients were observed under senescing plants over late spring and summer. A soil incubation experiment was conducted (119 days, 20  °C) to provide direct evidence of the influence of plant residue incorporation on soil pH. This was investigated in terms of plant residue type (wheat and subterranean clover) and dry matter addition rate (0, 6.25, 12.5 and 25.0 g kg–1), as well as the soil layer of incorporation (0–2.5 and 7.5–10 cm) and moisture regime (continuously moist and moist-dry cycles). During incubation, moist unamended soils slowly acidified. In contrast, the addition of plant residue resulted in a rapid (day 0–7) increase of soil pH due to the association, and particularly oxidation, of added organic anions. This was followed by a gradual (day 7–119) pH decline attributed to the mineralization and subsequent nitrification of added organic N. The addition of 12.5–25.0 g kg–1 of cereal crop residues, and 6.25–25.0 g kg–1 of legume-based pasture residues, resulted in a net alkalization of the surface 2.5 cm of soil. It was therefore concluded that surface soil pH gradients observed in the field were largely attributable to an increase of pH at the surface 2.5 cm in response to plant residue return. The magnitude of such gradients will be particularly large with the return of large quantities of plant residues of high ash alkalinity in soils of relatively low initial pH and biological activity, and when the surface of the soil is exposed to moist-dry cycles. Received: 11 October 1999  相似文献   
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