production of synthetic fertilizers. These chemicals provide the soil with the amount ofnitrogen needed for crops to reach the levels of production required to feed the world. We have reached a degree of dependence that, without fertilizers, half the planet would not have to eat. The consumption of these compounds already exceeds 100 million tons per year andthe consequences of this excess are generating diverse and serious environmental problems, making of modern agriculture an unsustainable practice. In this context, leguminous plants (peanut, peanuts, peas, soybeans, alfalfa, etc.) take a leading role in agriculture, as they are able to obtain nitrogen through an elegant biological mechanism known as nitrogen fixing symbiosis, making unnecessary the use of fertilizers for their growth. For this reason, the United Nations has proclaimed 2016 as the International Year of Legumes (http://www.fao.org/pulses-2016/en/). The present article aims to publicize the importance of this initiative through a historical view ofthenitrogen problem in agriculture, taking as a central axis the biological nitrogen fixation.
short and long term, that result in a geographic mosaic (Aller, 1997). The long-term ecological research station ofthe central abyssal plain is affected by the yearly flux. The decrease in C/N a from 12.0 (in 2002) to 7.7 (in 2005) in the abyssal plain reflects a mixture of continental organic matter from the Mississippi through turbidity currents (Bouma, 1972; Bryant et al., 1991) and gravity fluxes (Normark et al., 1993; Morse and Beazley, 2008) with predominantly pelagic materials exported in 2002 (Gordon and Goñi, 2004). A similar pattern was recorded by Rabiela-Alonso (2006) in macrofaunal density values that can be linked to the C/N ratios of this study by bioturbation and remineralization. El Niño years contribute with organic matter export to the deep sea in the Gulf of Mexico (Escobar-Briones, 2003) and, as recorded in other basins, may generate inter-yearly changes in the flux to the seafloor (Smith and Druffel, 1998). 5.5. Variability in response to the sedimentation conditions
Denitrifiers are typically facultative organotrophs, which utilize organic carbon as an energy source.50 Some authors have observed denitrification in compost-biofilters.51– 55 At low NO concentrations, the quantity of compost used in these studies provided adequate carbon and energy sources for removal and degradation. However, at higher NO concentrations, the amount of available carbon substrates became limited andthe addition of an exogenous carbon source was required to maintain efficient NO reduction. As high as 90% removal efficiency was observed for a 500 ppm NO gas stream at an EBRT of 1.3 min when treated in the presence of a phosphate buffer containing either lactate or dextrose compared with 20% removal in a non- supplemented biofilter.53, 56–58 Lactate, glucose, dextrose and molasses, as well as labile organic material inherent in compost, have all been used as carbon sources in NO denitrifying systems. Several volatile organic compounds can also be used as carbon and energy sources, and denitrification activity has been observed in a superficially aerobic toluene-treating biofilter.59 In such a system, the presence of a thick biofilm creating anaerobic underlayers allowed denitrification to nitrogen gas. Removal efficiencies of 75% of 60 ppm NO streams were reported for an EBRT of 6 min. Also, the removal of NO from a simulated wet-scrubbed combustion gas was investigated with different packing materials (compost, perlite and biofoam). The results showed that all three packing materials performed well, reaching more than 85% NO removal at EBRT of 70–80 s. The compost performed better than the other packings at shorter EBRT of 13–45 s. However, inert carrier materials such as perlite and biofoam are known to offer long term stability and reduced back-pressure compared with organic filter beds as compost.60 The experimental data suggest that the compost, perlite and biofoam systems, subject to further optimization, offer potential for the biological removal of NOx from gas streams.61
laboratory determinations, one-way analysis of variance (ANOVA) was performed separately for each year. For the NUE components, the control treatment was used to perform the calculations, andthe four fertilized treatments were compared to each other. Therefore, in this case differences among the two components of NUE were tested by ANOVA two-way factorial analysis including as factors: fertilizer type and rate. Data normality and variance homogeneity were verified before the analysis. Means were separated by Duncan´s test at 0.05 probability level (P ≤ 0.05). The N mineralization potential model was fitted to the cumulative N mineralized using a non-linear regression procedure. All statistical analyses were performed using the StatGraphics Centurion XVI software (StatPoint Technologies Inc, Warrenton, VA, USA).
Nitrogen (N) is an essential macronutrient available to plants mainly as nitrate in agricultural soils. Besides its role as a nutrient, inorganic and organic N sources play key roles as signals that control genome-wide gene expression in Arabidopsis and other plant species. Genomics approaches have provided us with thousands of genes whose expression is modulated in response to N treatments in Arabidopsis. Recently, systems approaches have been utilized to map the complex molecular network that plants utilize to integrate metabolic, cellular, and developmental processes to successfully adapt to changing N availability. The challenge now is to understand the molecular mechanisms underlying N regulation of gene networks and bridge the gap between N sensing, signaling, and downstream physiological and developmental changes. We discuss recent advances in this direction.
The objective of this work was to evaluate the influence ofnitrogen fertilization on the expression of yield and grain protein content in wheat in different environments ofthe semiarid Pampa region. The field experiments were carried out in Embajador Martini, Macachín and Anguil. The treatments were: control (0N), fertilization at seeding with 40 kg N.ha 1 (40+0) and 80 kg N.ha 1 (80+0), delayed fertilization with 40 kg N.ha 1 (between Z3.9 and Z5.0) (0+40) and divided fertilization (40+40). The treatments were arranged in a completely randomized block design with four replicates. Five filed experiments were carried out in each site and yield, grain protein content, water use efficiency andnitrogen use efficiency were determined. The sites with IMO> 4,5% had more response to yields in comparation with control, than the sites with IMO>4,5%. The soils with >50% A+L had grater soil potential fertility, and there were significant differences between the control and 80 kg.ha 1 at seeding o divided fertilization. Instead, the soils with <50% A+L did not show significant differences in the yields between treatments. The lowest yields in these soils were translated in higher protein grain content, reaching 11%. More soil nitrogen content increases the grain nitrogen content but decreases nutrient use efficiency. Although, rainfalls are the main restriction of this region, with a good water availability, the wheat productivity is limited by low nitrogen content.
The depletion of phosphate rock reserves makes necessary the finding and characterization of new phosphorus (P) sources to ensure a sustainable P fertilization. This research deals with the effect ofthe application of wastes derived from the winery and distillery industries on P availability in two calcareous soils. Soils were treated with five wastes providing different amounts of P: two raw wastes (exhausted grape marc and grape stalk) and three composts made with different proportions of these materials or including lees cake as well. The soils were incubated for 16 weeks determining soil pH, dissolved organic carbon and Olsen P in five samplings along time. At the end ofthe incubation, inorganic P was fractionated to NaOH-NaCl-P, citrate-bicarbonate- dithionite-P (CBD-P), and HCl-P andthe P sorption index (PSI) and degree of P saturation (DPS) were also determined. The increment in Olsen P was firstly positively related to the amount of P applied, being higher in the composted materials, but along time the effect of other factors such as the organic matter incorporation influenced these changes. After 16 weeks of incubation, the enhancement of Olsen P produced by the different wastes began to equalize (7.1 mg kg -1 on average), despite ofthe different amounts of P applied
the data are slightly lower for nitrogenand almost identical for fluorine. A lower error band value has been obtained for these physical properties andthe values ofthe composition-property gradient for both glass systems are all ofthe same order of magnitude, consistent with the previously published results while expanding the range of compositions into this new system with mixed modifiers and with a significantly different cation ratio.
Trees are important for the spatial variation of SOC andnitrogen pools within the SPS of Rivas. Areas under and around the trees have larger total SOC andnitrogen pools than open pasture, so trees in SPS enhance carbon storage. There were interesting differences between the two tree species. For G. ulmifolia plots the largest SOC andnitrogen pools were found in the leaf litter cone, while for C. alata plots the largest pools were found under the canopy. A probable explanation for this lies in the differences in weight ofthe leaves, flowers and fruits. C. alata has thick leaves and heavy fruit and flowers, which are not taken by the wind and drop under or very close to the tree. G. ulmifolia has lighter leaves, which can be easily blown for several meters by the wind, increasing the litter supply for soil microbes outside the tree canopy. The two G. ulmifolia individuals on Haplusterts clearly illustrate this. Both trees were older than other individuals. Other studies have shown that tree age affects the size ofthe SOC pool (Oelbermann et al. 2004). The two G. ulmifolia individuals have had ample time to affect the surrounding soil. The SOC pool in the leaf litter cone was about 50% larger than in the other two areas. Leaf litter has most probably been the most important contributor to this difference.
The diversity of diazotrophic prokaryotes present in the microbial mat throughout the thermal gradient was determined using nifH gene clone libraries. PCR amplifications ofthe nifH gene were performed using the universal primers PolF/PolR (Poly et al., 2001) that cover most ofthe known diazotrophic organisms (Bacteria and Archaea), including cyano- bacteria (Mårtensson et al., 2009; Díez et al., 2012). These primers amplify fragments 360 bp in length. The PCR products were purified (Wizard Clean-Up System; Promega, Madison, WI, USA) and cloned using the commercial pJET1.2/blunt Cloning Kit (Thermo Scientific) according to the manufacturer's instructions. Clones with the proper insert sequence were validated using the primer vector set pJetF/ pJetR (amplicon length ~ 550–600 bp). Fifty to one hundred clones obtained from each library (12 clone libraries in total) were selected for cyanobacterial- specific nifH gene amplifications using the primers CNF and CNR (Olson et al., 1998). These primers amplify a fragment within the insert generated by the
The maize crop fertilization is directly related to grain yield. There are alternative fertilizers to increase production, however unknown effect on the same. The aim of this study was to determine the effect of foliar fertilizers Quilt, Amminostim, Nutribond, Lixiviados and Control, with varying levels of N (100, 200 y 300 kg ha -1 ) in hybrids P1684w, PUMA1167, H-40, H-51AE, H-57, M8092, FAISAN and SYN1806 in Valles Altos of Mexico State, on productivity and morphological characters, which used a randomized block design in plots divided, large plot to be managed as foliar fertilizer and a small plot ofnitrogen levels, while blocking criterion was considered the hybrid. Analysis of variance was performed with the GLM procedure and comparison using the Tukey test with α = 0.05. Hybrid Faisan the best values record 5.5 t ha -1 and 7.1 t ha -1 , respectively, surpassing grain yield 1.7 t to lower yielding hybrid PUMA 1167. The foliar fertilizer application did not increase the yield of straw and grain nor its morphological components, only an increase in plant height and cob with Nutribond fertilizer application. The use of a nitrogen level of 200 and 300 kg ha -1 favored the grain and straw yields exceeding 1.1 t and 976.6 kg nitrogen level of 100 kg, respectively.
alkalinity, salinity, nutrient deficiency and toxicity stresses are potentially harmful to plants. The role ofnitrogen as an essential nutrient and structural component of amino acids, proteins, nucleic acids and other essential components for the development has been widely documented in several species because ofthe importance in the processes of growth and agricultural production. However, at present, there is little literature the effect ofnitrogen deficiency and toxicity on osmoregulators compounds as indicators of stress in plants. So the aim of this work was to study nitrogen compounds indicators of stress (proline, glycine betaine and choline) in response to toxic doses of N and deficient in green beans developed in a culture chamber under controlled conditions.
frost tolerance of roots, seedlings were placed in a modified cultivation tray in which the wall ofthe cells was replaced by a 2-mm plastic mesh that allowed the plug to be fully frozen. To prevent root desiccation, the plants were watered the day before andthe plug was wrapped in aluminum foil during freezing tests. Shoots were insulated from frost by the same polystyrene cover used to isolate the root system.
Replacing bare-fallow with cover crops may improve the control on weed species (den Hollander et al. 2007), erosion (Bowman et al. 2000) and nitrate leaching (Gabriel et al. 2012a). From a biological point of view, cover crops contribute to the soil disease control and perform as a reservoir for beneficial insects (Mojtahedi et al. 1999). Besides, they supply an additional input of organic matter to the soil (Kuo et al. 1997), increasing the stability of its aggregates and ameliorating the physical properties in compacted soils (Reeves 1994). Furthermore, they are used as a source of forage in integrated agricultural systems (Hartwig and Ammon 2002) and in the future they might be exported from the system, sold and integrated in animal feeding industrial processes (Liu et al. 2008). All these potential benefits are defined as ecosystems services (Díaz et al. 2007) andthe capability of a particular cover crop to provide certain benefits might depends on characteristics of its growth pattern, nutrient exchange and chemical composition. However, these benefits are not usually required as a whole, but farmers should first determine the primary benefits desired, an in which combination and degree. In addition, if cover crops are improperly managed or selected they may have a negative effect in the cash crop, either by competing for water and nutrients, building up diseases or retarding seed germination (Thorup-Kristensen et al. 2003). Proper management and choice of cover crops are therefore essential to maximize advantages and minimize drawbacks and we should consider cover crop selection as targeted for the specific needs ofthe farmer andthe agrosystem. Improving cover crops characterization might provide tools to the stakeholders for selecting the species that are most suitable for reaching the ecological services required in a particular agrosystem.
The O3 effects on pasture biomass were related to the observed response of gas exchange rates since reductions of NEE up to 28% were recorded. Similar results were observed when NEE was expressed based on dry biomass or on ground surface area. Thus O3 effects on NEE at canopy level were partially explained by the 03- induced reduction in biomass, but photosynthetic and/or respira- tion rates ofthe pasture were also affected. Indeed, O3 increased dark respiration when calculated on biomass weight basis, but ef- fects on photosynthetic rates cannot be disregarded (O3 effects on photosynthesis at leaf level are presented elsewhere: Calvete-Sogo et al., 2013). Dark CO2 fluxes include aboveground plant respiration, plant root respiration and soil microbial respiration, representing a combination of plant and soil processes. Since aboveground biomass was responsible of 70% ofthe observed dark respiration at the late phenological stage, effects on plant metabolism could mask the effects on soil processes. A test with a limited amount of replicated measurements showed that O3 strongly increased bare soil dark respiration (-3.9 (imol CO2 i r r 2 s _ 1 in NFA + compared