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Agricultural soils often receive annual applications of manure for long periods. Our objective was to quantify the effects of 19 consecutive years of pig (Sus scrofa) slurry (PS) application to a loamy soil (loamy, mixed, frigid Aeric Haplaquept) on N2O emissions. Soil surface N2O fluxes (FN2O) were measured 36 times in 1 yr. Nitrous oxide concentration profiles, soil NH+4‐ and NO−3‐N contents, denitrifying enzyme activity (DEA), and denitrification rate (DR) in soil were also determined to explain the variation in FN2O Long‐term (19 yr) treatments on continuous silage maize (Zea mays L.) were 60 (PS60) and 120 Mg ha−1 yr−1 (PS120) of pig slurry and a control receiving mineral fertilizer at a dose of 150 kg ha−1 each of N, P2O5, and K2O. Denitrifying enzyme activity, soil N2O concentrations, and FN2O (<25 ng m−2 s−1) were low in the control plots receiving mineral fertilizer. Annual applications of PS to the soil for 18 yr had positive residual effects on the DEA compared with the long‐term fertilized control plots. Following PS application, there was a strong and rapid increase of FN2O (up to 350 ng m−2 s−1) on manured plots. The PS‐induced FN2O increased with increasing quantity of PS, probably as the result of a greater availability of NO−3‐N for denitrification. The effects of PS on FN2O were mostly limited to the 30 d following application, with low fluxes (<10 ng m−2 s−1) during the rest of the measurement period. Total N2O–N emissions represented 0.62, 1.23, and 1.65% of total N applied in control, PS60, and PS120 plots, respectively. These emission factors for the PS plots agreed with values previously suggested for N‐fertilized soils (1.25%).

Biofertilizers, namely Rhizobium and biocontrol agents such as Pseudomonas and Trichoderma have been well established in the field of agricultural practices for many decades. Nevertheless, research is still going on in the field of inoculant production to find methods to improve advanced formulation and application in fields. Conventionally used solid and liquid formulations encompass several problems with respect to the low viability of microorganisms during storage and field application. There is also lack of knowledge regarding the best carrier in conventional formulations. Immobilization of microorganisms however improves their shelf-life and field efficacy. In this context, microencapsulation is an advanced technology which has the possibility to overcome the drawbacks of other formulations, results in extended shelf-life, and controlled microbial release from formulations enhancing their application efficacy. This review discusses different microencapsulation technologies including the production strategies and application thereof in agricultural practices.

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Biological nitrogen fixation is a phenomenon occurring in all known ecosystems. Symbiotic nitrogen fixation is dependent on the host plant genotype, the Rhizobium strain, and the interaction of these symbionts with the pedoclimatic factors and the environmental conditions. Extremes of pH affect nodulation by reducing the colonization of soil and the legume rhizosphere by rhizobia. Highly acidic soils (pH <4.0) frequently have low levels of phosphorus, calcium, and molybdenum and high concentrations of aluminium and manganese which are often toxic for both partners; nodulation is more affected than host-plant growth and nitrogen fixation. Highly alkaline soils (pH >8.0) tend to be high in sodium chloride, bicarbonate, and borate, and are often associated with high salinity which reduce nitrogen fixation. Nodulation and N -fixation are observed under a wide range of temperatures with optima between 20-30°C. Elevated temperatures may delay nodule initiation and development, and interfere with nodule structure and functioning in temperate legumes, whereas in tropical legumes nitrogen fixation efficiency is mainly affected. Furthermore, temperature changes affect the competitive ability of Rhizobium strains. Low temperatures reduce nodule formation and nitrogen fixation in temperate legumes; however, in the extreme environment of the high arctic, native legumes can nodulate and fix nitrogen at rates comparable to those observed with legumes in temperate climates, indicating that both the plants and their rhizobia have successfully adapted to arctic conditions. In addition to low temperatures, arctic legumes are exposed to a short growing season, a long photoperiod, low precipitation and low soil nitrogen levels. In this review, we present results on a number of structural and physiological characteristics which allow arctic legumes to function in extreme environments.

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Abstract. Penicillin-binding proteins (PBPs) are membrane proteins involved in the final stages of peptidoglycan synthesis and represent the targets of b-lactam antibiotics. Enterococci are naturally resistant to these antibiotics because they produce a PBP, named PBP5fm in Enterococcus faecium, with low-level affinity for b-lactams. We report here the crystal structure of the acyl-enzyme complex of PBP5fm with benzylpenicillin at a resolution of 2.4 Å. A characteristic of the active site, which distinguishes PBP5fm from other PBPs of known structure, is the topology of the loop 451 -465 defining the left CMLS, Cell. Mol. Life Sci. 59 (2002) 1223 -1232 1420-682X/02/071223-10 $ 1.50 + 0.20/0 © Birkhäuser Verlag, Basel, 2002 CMLS Cellular and Molecular Life Sciencesedge of the cavity. The residue Arg464, involved in a salt bridge with the residue Asp481, confers a greater rigidity to the PBP5fm active site. In addition, the presence of the Val465 residue, which points into the active site, reducing its accessibility, could account for the low affinity of PBP5fm for b-lactam. This loop is common to PBPs of low affinity, such as PBP2a from Staphylococcus aureus and PBP3 from Bacillus subtilis. Moreover, the insertion of a serine after residue 466 in the most resistant strains underlines even more the determining role of this loop in the recognition of the substrates.

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