Agronomic Management of Indigenous Mycorrhizas

Many of the advantages conferred to plants by arbuscular mycorrhiza (AM) are associated to the ability of AM plants to explore a greater volume of soil through the extraradical mycelium. Sieverding (1991) estimates that for each centimetre of colonized root there is an increase of 15 cm3 on the volume of soil explored, this value can increase to 200 cm3 depending on the circumstances. Due to the enhancement of the volume of soil explored and the ability of the extraradical mycelium to absorb and translocate nutrients to the plant, one of the most obvious and important advantages resulting from mycorrhization is the uptake of nutrients. Among of which the ones that have immobilized forms in soil, such as P, assume particular significance. Besides this, many other benefits are recognized for AM plants (Gupta et al, 2000): water stress alleviation (Augé, 2004; Cho et al, 2006), protection from root pathogens (Graham, 2001), tolerance to toxic heavy metals and phytoremediation (Audet and Charest, 2006; Göhre and Paszkowski, 2006), tolerance to adverse conditions such as very high or low temperature, high salinity (Sannazzaro et al, 2006), high or low pH (Yano and Takaki, 2005) or better performance during transplantation shock (Subhan et al, 1998). The extraradical hyphae also stabilize soil aggregates by both enmeshing soil particles (Miller e Jastrow, 1992) and producing a glycoprotein, golmalin, which may act as a glue-like substance to adhere soil particles together (Wright and Upadhyaya, 1998). Despite the ubiquous distribution of mycorrhizal fungi (Smith and Read, 2000) and only a relative specificity between host plants and fungal isolates (McGonigle and Fitter, 1990), the obligate nature of the symbiosis implies the establishment of a plant propagation system, either under greenhouse conditions or in vitro laboratory propagation. These techniques result in high inoculum production costs, which still remains a serious problem since they are not competitive with production costs of phosphorus fertilizer. Even if farmers understand the significance of sustainable agricultural systems, the reduction of phosphorus inputs by using AM fungal inocula alone cannot be justified except, perhaps, in the case of high value crops (Saioto and Marumoto, 2002). Nurseries, high income horticulture farmers and no-agricultural application such as rehabilitation of degraded or devegetated landscapes are examples of areas where the use of commercial inoculum is current. Another serious problem is quality of commercial available products concerning guarantee of phatogene free content, storage conditions, most effective application methods and what types to use. Besides the information provided by suppliers about its inoculum can be deceiving, as from the usually referred total counts, only a fraction may be effective for a particular plant or in specific soil conditions. Gianinazzi and Vosátka (2004) assume that progress should be made towards registration procedures that stimulate the development of the mycorrhizal industry. Some on-farm inoculum production and application methods have been studied, allowing farmers to produce locally adapted isolates and generate a taxonomically diverse inoculum (Mohandas et al, 2004; Douds et al, 2005). However the inocula produced this way are not readily processed for mechanical application to the fields, being an obstacle to the utilization in large scale agriculture, especially row crops, moreover it would represent an additional mechanical operation with the corresponding economic and soil compaction costs. It is well recognized that inoculation of AM fungi has a potential significance in not only sustainable crop production, but also environmental conservation. However, the status quo of inoculation is far from practical technology that can be widely used in the field. Together a further basic understanding of the biology and diversity of AM fungi is needed (Abbott at al, 1995; Saito and Marumoto, 2002). Advances in ecology during the past decade have led to a much more detailed understanding of the potential negative consequences of species introductions and the potential for negative ecological consequences of invasions by mycorrhizal fungi is poorly understood. Schwartz et al, (2006) recommend that a careful assessment documenting the need for inoculation, and the likelihood of success, should be conducted prior to inoculation because inoculations are not universally beneficial. Agricultural practices such as crop rotation, tillage, weed control and fertilizer apllication all produce changes in the chemical, physical and biological soil variables and affect the ecological niches available for occupancy by the soil biota, influencing in different ways the symbiosis performance and consequently the inoculum development, shaping changes and upset balance of native populations. The molecular biology tools developed in the latest years have been very important for our perception of these changes, ensuing awareness of management choice implications in AM development. In this context, for extensive farming systems and regarding environmental and economic costs, the identification of agronomic management practices that allow controlled manipulation of the fungal community and capitalization of AM mutualistic effect making use of local inoculum, seem to be a wise option for mycorrhiza promotion and development of sustainable crop production

Activities of Rhizosphere Microorganisms as Affected by Application of Organic Amendments in a Calcareous Loamy Soil. 2. Nitrogen Transformations

The activities of some nitrogen transforming microorganisms in the rhizosphere of both alfalfa and wheat growing in a calcareous loamy soil of Saudi Arabia as affected by organic amendments have been studied in a greenhouse experiment. The organic amendments were sludge (narrow C/N ratio) and wheat straw (wide C/N ratio), applied at 2% wt./wt. to the soil. The asymbiotic nitrogen fixers, either aerobic or anaerobic, as well as the nitrfying bacteria, were determined in the rhizosphere and nonrhizosphere soils periodically for 7 weeks. Total nitrogen, organic carbon, ammonium, and nitrate nitrogen were determined in the same samples. Results showed that treatment of the calcareous loamy soil with organic amendments significantly enhanced the microbial population transforming nitrogen (asymbiotic N2-fixers and nitrifying bacteria) in the rhizosphere and nonrhizosphere soils of both plants with high values for the former during most of' the experiment periods. However, the rhizosphere effect was not obvious in the case of Azotobacter densities. The highest stimulative effect for the asymbiotic N2-fixers and nitrifying bacteria was observed in the soil amended with sludge, especially in the early periods of plant growth. Also, the microbial numbers were more influenced by their proximity to the alfalfa roots than to wheat roots. Total nitrogen in the rhizosphere and nonrhizosphere soils of alfalfa and wheat significantly increased with application of organic amendments. The increase was especially evident in the rhizosphere region. Ammonium nitrogen values in the soils amended with organic matter were higher in the root regions of both plants than in unamended soil, indicating a high ammonification rate for the former by heterotrophic microorganisms. Amendment of soil with 2% sludge (narrow C/N ratio) enhanced the mineralization of organic nitrogen and nitrification processes. Amendment of soil with straw (wide C/N ratio) increased immobilizaition of mineral nitrogen. Using the sewage sludge (2% w/w) as an organic amendment to the loamy soil did not retard the proliferation and activities of the asymbiotic, N2-fixers and nitrifying bacteria in the soil but enhanced the processes

Effect of Salinity on Survival and Symbiotic Performance Between Rhizobium meliloti and Medicago sativa L. in Saudi Arabian Soils.

The effect of salinity on the growth and survival of different local and imported strains of Rhizobium meliloti in liquid media for 72 h was studied in the laboratory. The rhizobial strains were-tested for their symbiotic efficiencies with lucerne grown in salinized sand culture and in natural Saudi Arabian soils of different salinities in the greenhouse. Results have shown that growth of all rhizobial strains investigated in liquid media was adversely affected by high salinity with relatively slight salt tolerance in the local rhizobial strains. Salinization of sand culture to high concentration (100-250 mM NaCl) greatly affected noditlation and symbiotic N2-Fixation of lucerne plants grown in it. Growing lucerne in sand of high salt concentration (250 mM NACl) campletely prevented the formation of nodules. Inoculation of lucerne plants grown in sand culture with local isolates of.R.meliloti has shown slight salt tolerance up to 100 mM NaCl. These local isolates gave relatively higher symbiotic N2-Fixation than the rest of the inoculated rhizobial strains. High salinity of natural soils (9.1 and 14.1 ds m-1) deleteriously affected the nodule formation and the symbiotic N2-Fixation in lucerne plants inoculated with all rhizobial strains. Inoculation of lucerne plants with rhizobial strains showing tolerance to salinity in sand culture did not show the same tolerance in natural saline soils, and this could be attributed to the competitive potentiality of the strain used in the soil

Virtual reality interface for HVDC substation and DC breaker design and maintenance

For HVDC links, the substation is a major cost factor. 3D visualization using virtual reality has the potential to play a significant part in cost reduction. This paper outlines the problem and gives two examples: the use of visualization for planning internal drone inspection; and the application of visualization to the design of a superconducting fault-current limiter breaker.</p

A data-driven approach to automatic extraction of professional figure profiles from Résumés

The process of selecting and interviewing suitable candidates for a job position is time-consuming and labour-intensive. Despite the existence of software applications aimed at helping professional recruiters in the process, only recently with Industry 4.0 there has been a real interest in implementing autonomous and data-driven approaches that can provide insights and practical assistance to recruiters. In this paper, we propose a framework that is aimed at improving the performances of an Applicant Tracking System. More specifically, we exploit advanced Natural Language Processing and Text Mining techniques to automatically profile resources (i.e. candidates for a job) and offers by extracting relevant keywords and building a semantic representation of résumés and job opportunities