Non-symbiotic Nitrogen Fixation Research Articles

Isolation and Characterization of Rhizobacteria from Soil and Its Efficiency as Plant Growth- Promoting Microbes

Rhizosphere is the soil environment where the plant root is available and is a zone of maximum microbial activity resulting in a confined nutrient pool in which essential macro-and micronutrients are extracted. The microbial population present in the rhizosphere is relatively different from that of its surroundings due to the presence of root exudates that function as a source of nutrients for microbial growth. Among all these interactions, those resulting in symbiotic and non-symbiotic nitrogen fixation are considerably important. In recent years, the use of bacteria (rhizobacteria) to promote plant growth has increased in several regions of the world and has acquired relevant importance in developing countries that are the producers of raw materials for food.In the present study Rhizobacteria was isolated from the soil and the production of IAA and phosphate solubilisatrion was studied. The effect of PGPR was done on Mat seeds (matki) and black-eyed peaseeds (chawali) on the growth of plants.

Genomic insights into a free-living, nitrogen-fixing but non nodulating novel species of Bradyrhizobium sediminis from freshwater sediment: Three isolates with the smallest genome within the genus Bradyrhizobium

Three bacterial strains isolated from a sediment sample collected at a water depth of 4 m from the Huaihe River in China were characterized. Phylogenetic investigation of the 16S rRNA gene and concatenated housekeeping gene sequences assigned the three novel strains in a highly supported lineage distinct from the published Bradyrhizobium species. The sequence similarities of the concatenated housekeeping genes of the three novel strains support their distinctiveness with the type strains of named species. Average nucleotide identity values of the genome sequences (79.9–82.5%) were below the threshold value of 95–96% for bacterial species circumscription. Close relatives to the novel strains are Bradyrhizobium erythrophlei, Bradyrhizobium jicamae, Bradyrhizobium lablabi, Bradyrhizobium mercantei, Bradyrhizobium elkanii and Bradyrhizobium japonicum. The complete genomes of strains S2-20-1T, S2-11-2 and S2-11-4 consist of single chromosomes of size 5.55, 5.45 and 5.47 Mb, respectively. These strains lack a symbiosis island, key nodulation and photosystem genes. Based on the data presented here, the three strains represent a novel species for which the name Bradyrhizobium sediminis sp. nov. is proposed for S2-20-1T as the type strain. Those three strains are proposed as novel species in free-living Bradyrhizobium isolates with the smallest genomes so far within the genus Bradyrhizobium. A number of functional differences between the three isolates and other published genomes indicate that the genus Bradyrhizobium is extremely heterogeneous and has roles within the community including non-symbiotic nitrogen fixation.

Physicochemical and Characterization of Nitrogen Fixing Bacteria from Soil Samples Within the Vicinity of Telecommunication Mast (Site No: 000148) Located at Karfi Town Kura Local Government, Kano State

The telecommunication mast associated-radiation is one of the primary factors influencing the way in which microorganisms interact with ecosystem. This study aims to assess the physicochemical and non-symbiotic nitrogen fixing bacteria (NNFB) from soil samples within the vicinity of telecommunication mast located at Karfi town Kura local government Kano state. Soil samples A, B, and C were collected within the vicinity of the mast at an interval of 10 meters, 20 meters and 30 meters from the mast respectively and control sample (D) was collected from location *(outside the vicinity of the mast)*. Physicochemical parameters of the soil samples were analyzed, isolation and identification of non-symbiotic nitrogen fixing bacteria were carried out using standard procedures. Samples B showed higher values of pH (8.02), phosphorus (23.95mg/kg), organic carbon (1.45%), nitrogen (0.28%) and organic matter content (2.50%) while control sample (D) showed lower values with 6.24, 2.77mg/kg, 0.41%, 0.07% and 0.71% of pH, phosphorus, organic carbon, nitrogen and organic matter content respectively. However, the moisture content(0.21%) of control sample is higher than that of sample A and B with 0.12% and 0.11% respectively The mean count of NNFB of the soil samples were 3.20 ± 0.06, 1.80± 0.12, 1.40±0.23, 1.20±0.20 for sample B, C, A and D respectively. Total of 14 isolates of the species Azomonas agilis 1(7.14%), Azotomonas insolita 1(7.14%), Bacillus megaterium 2(14.28 %), Bacillus azotoformans 1(7.14%), Bacillus mycoides 3(21.42%), Enterobacter cloacae 3(21.42%), and Klebsiella pneumonia 3(21.42%) were obtained. This indicates that the electromagnetic radiation from the mast has no effect on soil physicochemical parameters as well as non symbiotic nitrogen fixing bacteria proliferation.

Effect of CaCO<sub>3</sub> Form on Soil Inherent Quality Properties of Calcareous Soils

Four soil samples different in there CaCO3 forms contents (total, active and active /total CaCO3) were taken from tillage horizon 0-30 cm depth to study the impacts of CaCO3 form on some soil inherent quality indicators in calcareous soils. Result revealed that the total CaCO3 forms have a great influence on particle size distribution to make it coarser in general comparing with the absence of CaCO3 with soil particles. The increase of active /total (A/T CaCO3%) till 50% has a positive effect on increasing soil electrical conductivity E.C ds.m-1, while increment of A/T CaCO3 over 50% till 70% detrimentally reduced soil E.C ds.m-1 hundred fold. The elevation of (A/T CaCO3%) has inverse correlation with soil cation exchange capacity (CEC Cmole.kg soil). the elevation of (A/T CaCO3%) has inverse correlation with soil cation exchange capacity (CEC Cmole.kg soil) the (A/T CaCO3%) ratio over 56% till 69% significantly improves the mean weight diameter and macro aggregate. In general the optimum total CaCO3 for micro aggregate formation may not exceed 20%. The best Total and (A/T CaCO3%) for better aggregate stability is between 20 to 48% . The proper total calcium carbonate for better total heterotrophic aerobic bacterial activity is around 20% . The best growth of the Azotobacter species which is belonging to non-symbiotic nitrogen fixing bacteria is obtained when total CaCO3 ranges between 10-20% or between 48-56% of (A/T CaCO3%).

水位和施氮对若尔盖高寒湿地土壤非共生固氮的影响

水位和施氮对若尔盖高寒湿地土壤非共生固氮的影响

Визначення мікроелементного складу ґрунту за його мікробіологічними та біохімічними показниками трансформації сполук циклу нітрогену

By results of information and analytical researches it was established high informational content of soil microbiological indicators, the reflecting direction and intensity of microbiological processes of nitrogen-containing compounds; the predictive value of indicators of soils integrated biochemical processes that are associated with transformation of soil nitrogen compounds; the effectiveness of using the established informativeness and predictive value of microbiological and biochemical indicators in the various types of soils nitrogen-containing compounds transformation for forecasting of the microelement status and simultaneous account the functional diversity of soil processes. The new method of different genesis soils microelement composition determination is grounded taking into account the orientation of microbiological transformation processes of nitrogen-containing substances, interaction of microbiological and biochemical components of nitrogen compounds of soils. The elaborated algorithm of the method includes: sampling, analysis and data acquisition; determination of soils microelement composition, their microbiological (indicators of the number of basic ecological-trophic microorganisms groups) and biochemical (integral biochemical parameters – non-symbiotic nitrogen fixation, ammonification and nitrification of soil) of the components of nitrogen compounds obtained by known methods; prediction of the soils elemental composition by regression equations, followed by the extension of the metod algorithm to the basic trace elements / heavy metals and soils of different types of a certain natural-climatic zone in the conditions of technogenic pollution and technological load. Due to the use of mathematical and statistical analysis, the establishing of new quantitative relationships of diagnostic indicators of the chemical and biological state of soils provides universality, increase informativeness, accuracy, expressiveness of the method in the background (natural) conditions, the impact of technological load, risk and the presence of technogenic pollution for soils quality management based on microelement composition and soil biogenicity. The patent protection method (patent for utility model № 124819 UA, 2018) provides the expressiveness of prediction of the soils microelement status and biogenicity; increase of accuracy and predictability of the soils qualitative state for the microelement composition.

PEMBERIAN AMELIORAN DAN ISOLAT BAKTERI FIKSASI NITROGEN NON SIMBIOTIK (FNNS) UNTUK MENINGKATKAN PERTUMBUHAN DAN SERAPAN N TANAMAN PADI GOGO (Oryza sativa L.) PADA MEDIUM ULTISOL

The need of rice as the staple food of the people of Indonesia has a deficit every year. Upland rice cultivation in dry land such as Ultisols became one of the alternatives to meeting the needs of rice. However, productivity of crop in Ultisols is low because of some problems of acidity and nutrients deficiency. It is necessary input such as ameliorants like biochar cocopeat of oil palm empty bunch compost (OPEBC) and the use of bacterial non-symbiotic nitrogen fixation (NSNF) to fix the problems. The research aims to study the effect of application of ameliorant and suspensions of bacterial isolates of NSNF on growth and N uptake by upland rice in Ultisols medium. The research was conducted at the Green House of the Faculty of Agriculture, University of Riau, Pekanbaru from Mei to September 2017. The research in form factorial experiment was arranged a completely randomized design (CRD). The first factor were ameliorant, consists of six type (biochar, cocopeat, OPEBC, biochar+cocopeat, biochar+OPEBC, each doses 50 g polybag-1 and without ameliorant as a control). The second factor were suspensions of bacterial isolates of NSNF, consists of three levels (10 and 20 ml polybag-1 and without bacterial isolates as a control). The parameters observed were plant height, number of tillers, weight of dry shoot and roots, N uptake by shoot and roots. The results show that the application of ameliorant (biochar, cocopeat, OPEBC, biochar + cocopeat, biochar + OPEBC), each doses of 50 g polybag-1 and suspensions of bacterial isolates of NSNF doses of 0, 10 and 20 ml polybag-1 increased plant height, number of tillers, weight of dry shoot and N uptake by shoot compared to control and the application of without ameliorant with suspension of bacterial isolates of NSNF doses of 0, 10 and 20 ml polybag-1.Key words : biochar, cocopeat, palm oil empty bunch, upland rice, ultisol

Increased complementarity in water‐limited environments in Scots pine and European beech mixtures under climate change

AbstractManagement of mixedwoods is advocated as an effective adaptation strategy to increase ecosystem resiliency in the context of climate change. Although mixedwoods have been shown to have greater resource use efficiency relative to pure stands, considerable uncertainty remains with respect to the underlying ecological processes. We explored species interactions in Scots pine/European beech mixedwoods with the process‐based model FORECAST Climate. The model was calibrated for two contrasting forests in the southwestern Pyrenees (northern Spain): a wet Mediterranean site at 625 m.a.s.l. and a subalpine site at 1335 m.a.s.l. Predicted mixedwood yield was higher than that for beech stands but lower than pine stands. When simulating climate change, mixedwood yield was reduced at the Mediterranean site (−33%) but increased at the subalpine site (+11%). Interaction effects were enhanced as stands developed. Complementarity dominated the Mediterranean stand but neutral or net competition dominated the subalpine stand, which had higher stand density and water availability. Reduced water demand and consumption, increased canopy interception, and improved water‐use efficiency in mixtures compared to beech stands, suggest a release of beech intraspecific competition. Beech also facilitated pine growth through better litter quality, nonsymbiotic nitrogen fixation, and above‐ and belowground stratification, leading to higher foliar nitrogen content and deeper canopies in pines. In conclusion, mixtures may improve water availability and use efficiency for beech and light interception for pine, the main limiting factors for each species, respectively. Encouraging pine–beech mixtures could be an effective adaptation to climate change in drought‐prone sites in the Mediterranean region.

Dynamics of Microbial Functional Groups in Rhizosphere of Spring Barley

Plant rhizosphere is the portion of soil which is in direct contact with the plant roots. From the microbiological point of view, this area is characterized by strong dynamic of functional groups with high specificity towards the substrate available. Spring barley is a crop with high requirements to the composition of the microflora in the rhizosphere, disturbances produced by agronomic inputs affecting the stability of rhizospheric contact interfaces and ultimately the plant growth. Analysis of changes within the microbial community was carried out with the purpose of defining the disruptive impact of mineral inputs and potential of zeolite to reduce these disruptions. Microbial functional groups were analyzed on the basis of the CO2 export under the specific conditions of soil inoculation on specific substrates over a time period of incubation. Microresp detection plates allow evaluation of a large number of samples under identical conditions of inoculation and the establishment of dynamics of the entire microbial community. The dynamics of the entire microbial communities (basal respiration) is stimulated to increase in case of unilateral application of zeolite and zeolite as a buffer for urea fertilization. General growth trend of microbial communities follows proportional the associated application of zeolite with urea, the most powerful non-symbiotic nitrogen fixation processes being stimulated by this combination of fertilizers. Simultaneously, an increase in the dynamics of denitrifiers was observed, also the decomposition of lignin and cellulose and biological crust formation due to the proliferation of cyanobacteria. Rhizosphere of barley plants is characterized by the presence of actinomycetes as dominant in functional microbial community of all experimental variants analyzed with a high capacity for biological degradation and raised mineralization of organic matter.

Impact of Some Pesticides on Total Counts of Soil Non-Symbiotic Nitrogen-Fixing Bacteria, Particularly Azotobacter sp

A pot experiment was conducted to evaluate the effect of glyphosate herbicide (n-phosphonomethyl glycine), mancozeb fungicide ([[1,2-ethanediylbis- [carbamodithioato]](2-)] manganese mixture with [[1,2-ethanediylbis- [carbamodithioato]]-(2- )] zinc) anddiazinon insecticide (O, O-diethyl O-[6- methyl-2- (1-methylethyl)- 4-pyrimidynyl]), threesoil orders and two soil moisture contents (50% and 100% of field capacity) and theircombinations on soil total non-symbiotic nitrogen-fixing bacteria particularlyAzotobacter sp. counts. This experiment last for two months from the 6 th of Jun until the8 th of August 2011 with five sampling periods at biweekly intervals. Factorial experiment(4×3×2) with Completely Randomized Design (CRD) and three replications was usedand the means were compared using Revised Least Significant Differences (R.LSD) atthe level of significant of 0.05. Significant results were obtained at the last two scheduledperiod’s sampling of 4 th and 5 th , and the results showed that: Mancozeb fungicidedecreased total Azotobacter sp.; Diazinon insecticide decreased both total non-symbioticnitrogen-fixing bacteria and total Azotobacter sp.; Agholan soil (order Entisols) showedthe greatest increase in soil total non-symbiotic nitrogen-fixing bacteria. 50% soilmoisture content revealed the greatest reduction total Azotobacter sp. while, 100% soilmoisture content showed the greatest increase in soil total Azotobacter sp. count. Thecombinations among: glyphosate, Agholan soil and 100% moisture combination showedthe greatest reduction in total non-symbiotic nitrogen-fixing bacteria and totalAzotobacter sp.

English

In Lesotho, agriculture remains a major source of income for more than 80% of rural population. The arable land accounts for about 9% of the total land area and the current crop yields are half the level achieved in the late 1970s. Despite its contribution to Lesotho’s development, the rural economy has been languishing due to poor land management and farming practices, declining soil fertility, poor weather conditions and poor management of water resources. Communities living in marginal lands and whose livelihoods are highly dependent on natural resources are among the most vulnerable to climate change. In Lesotho, about six farming technologies, namely, block farming, mono-cropping, conservation farming, keyhole garden, double digging and the Machobane Farming systems are practiced. We assessed the distribution and diversity of Bacillus spp., the non-symbiotic Nitrogen Fixing Bacteria (NFB) and physico-chemical variables including soil texture, pH, organic carbon, and available phosphorus as quality indicators of soils from various farming systems in Lesotho in an attempt to elucidate the adaptive capacity of various farming systems to climate change. Amongst the six farming systems assessed, the Machobane Farming System (MFS) practicing fields exhibited significant level of soil quality improvement in microbial composition and physico-chemical property compared to other farming systems. These findings provide, for the first time, scientific evidence that the MFS, which combines indigenous knowledge and technology, may show better resilience to climate change for high and sustainable production of variety of crops throughout the year. Key words: Indigenous farming technology, adaptability, traditional knowledge, farming practices in Lesotho, soil microorganisms, soil fertility.

Non-symbiotic nitrogen fixation in the intestine of click beetle larvae (Coleoptera, Elateridae).

92 One of poorly studied aspects of trophism of soil� inhabiting invertebrates is the evaluation of nitrogen sources and the role of microorganisms in their nutri� tion, particularly in groups specializing in consuming plant food. The most widespread view is that the main food source of soil phytovores and saprovores is soil microorganisms, which is proved by presence of numerous specialized microbophages in the content of soil population, particularly among microarthro� pods. However, zoomicrobial relationships in pedo� bionts are characterized by a wide spectrum of interac� tions, from trophic to obligate mutualistic. Parietal and cavernous groups are distinguished in the intesti� nal complexes of microorganisms in soil invertebrates; symbiotic nature of parietal forms and selective diges� tion of microbial cells have been shown [1].

Describing Paenibacillus mucilaginosus strain N3 as an efficient plant growth promoting rhizobacteria (PGPR)

AbstractBacterium Paenibacillus mucilaginosus strain N3 was isolated from agricultural farm soil (located at Boriavi village, Gujarat, India). Isolate showed an evidence of non-symbiotic nitrogen fixation, when grown in nitrogen-free bromothymol blue growth medium. It was tested positive for direct plant-growth-promoting traits like Indole-3-acetic acid production, solubilization of Tri-calcium-phosphate, and ammonia production. Further, N3 isolate was tested positive for siderophore production of catecholate type and catalase production as an indirect plant-growth-promoting trait. Biochemical tests along with 16s rRNA gene sequence analysis confirmed the strain N3 to be P. mucilaginosus. To determine its efficacy as a plant-growth-promoting rhizobacteria (PGPR), its talc-based biofertilizer was prepared and tested on the growth of green gram (Vigna radiata). Seeds treated with this biofertilizer showed an increase in overall dry biomass by 17% and sapling length by 28% (as compared to non-treated control...

Баланс азота в земледелии Балтасинского района Республики Татарстан

On the basis of 45 years data, the economic dynamics of nitrogen balance was represented, calculated in four different ways, which are defined by correspondence of accounting of credit and debit articles of nitrogen balance. When calculating the balance according to the first embodiment, we limited by comparison of economic takeaway of nitrogen, including agricultural crops (excluding biological nitrogen fixation, including symbiotic) with the receipt of it as part of mineral and organic fertilizers. In the second embodiment of nitrogen balance calculation, the economic takeaway was calculated, taking into account the symbiotic nitrogen fixation, the dimensions of which were taken equal to 2/3 of the economic removal of nitrogen by legumes. In the following two variants of calculation the authors attempted to better reflection of credit and debit articles of nitrogen balance: precipitation leaching, losses due to soil erosion, loss of gaseous nitrogen, symbiotic and non-symbiotic nitrogen fixation, nitrogen in the delivery of seeds and precipitation, according to the recommendations, which differ only by different approaches to the calculation of the size of symbiotic nitrogen fixation. Regardless of the calculation method, the fluctuations in the dynamics of nitrogen balance were about the same and had a wavy character. Nitrogen deficiency in the cycle I changed to a surplus in the next four cycles (1971-1995), but the last three cycles characterized by a negative balance again. Such dynamics of economic nitrogen balance was mainly due to changes in the flow of nitrogen in fertilizer and takeaways with crops. The highest correlation was found between the first and third embodiments of the calculation (r = 0,994), which may give a more realistic economic dynamics of the nitrogen balance.

Nitrogen cycling in summer active perennial grass systems in South Australia: non-symbiotic nitrogen fixation

Non-symbiotic nitrogen (N2) fixation by diazotrophic bacteria is a potential source for biological N inputs in non-leguminous crops and pastures. Perennial grasses generally add larger quantities of above- and belowground plant residues to soil, and so can support higher levels of soil biological activity than annual crops. In this study, the hypothesis is tested that summer-active perennial grasses can provide suitable microsites with the required carbon supply for N2 fixation by diazotrophs, in particular during summer, through their rhizosphere contribution. In a field experiment on a Calcarosol at Karoonda, South Australia, during summer 2011, we measured populations of N2-fixing bacteria by nifH-PCR quantification and the amount of 15N2 fixed in the rhizosphere and roots of summer-active perennial grasses. Diazotrophic N2 fixation estimates for the grass roots ranged between 0.92 and 2.35 mg 15N kg–1 root day–1. Potential rates of N2 fixation for the rhizosphere soils were 0.84–1.4 mg 15N kg–1 soil day–1 whereas the amount of N2 fixation in the bulk soil was 0.1–0.58 mg 15N kg–1 soil day–1. Populations of diazotrophic bacteria in the grass rhizosphere soils (2.45 × 106 nifH gene copies g–1 soil) were similar to populations in the roots (2.20 × 106 nifH gene copies g–1 roots) but the diversity of diazotrophic bacteria was significantly higher in the rhizosphere than the roots. Different grass species promoted the abundance of specific members of the nifH community, suggesting a plant-based selection from the rhizosphere microbial community. The results show that rhizosphere and root environments of summer-active perennial grasses support significant amounts of non-symbiotic N2 fixation during summer compared with cropping soils, thus contributing to biological N inputs into the soil N cycle. Some pasture species also maintained N2 fixation in October (spring), when the grasses were dormant, similar to that found in soils under a cereal crop. Surface soils in the rainfed cropping regions of southern Australia are generally low in soil organic matter and thus have lower N-supply capacity. The greater volume of rhizosphere soil under perennial grasses and carbon inputs belowground can potentially change the balance between N immobilisation and mineralisation processes in the surface soils in favour of immobilisation, which in turn contributes to reduced N losses from leaching.

English

A study was undertaken in three blocks of Manipur viz. Haorang, Wangoi and Sawombung after rice harvest covering upland, midland and lowland areas. The oxidizable organic carbon (OC) of these soils was found to be fairly good and ranged from 5.0 to 18.1 g/kg. The average pH values of 5.72, 5.45 and 5.33 were noticed in the soils of Haorang, Wangoi and Sawombung blocks respectively. Significant relationships were observed between the organic carbon and mineralized nitrogen pools. The NO3-N content was found to be positively correlated with oxidizable OC (r = 0.335*), total N (r = 0.480**) and NH4-N (r = 0.818**) of these soils. The colony forming unit (CFU) of total viable bacteria (TVB), aerobic Non-Symbiotic nitrogen fixing bacteria (ANFB), phosphate solubilizing bacteria(PSB), actinomycetes and fungi varied widely. There was fair increase of microbial populations at pH=5.7 and effect of pH was more for PSB and ANFB.The abundance of microbes in the three land types was as follows: upland–ANFB>TVB>PSB >actinomycetes> fungi; Midland- TVB> ANFB>PSB>actinomycetes> fungi; and lowland –PSB>TVB>ANFB>actinomycetes> fungi. Key words: Organic carbon (OC), nitrogen pool, microbial abundance, rice soil.

Potential Production and Application of Biofertilizers in Sudan

INTRODUCTION During the last decades, the increased costs of fertilizer production coupled with the progressively increasing use of chemical fertilizers are adding to the cost of crop cultivation. In addition, chemical fertilizers are harmful when they persist in the soil and enter the food chain. Instead, an approach is adopted to introduce into the soil potential microorganism, a practice known as inoculation. The inoculants are also known as biofertilizers. Several microorganisms and their association with crop plants are being exploited in the production of biofertilizers. The microorganisms which are potential biofertilizers are symbiotic and nonsymbiotic nitrogen fixing microorganisms, phosphorous solubilizing microorganisms and silicate bacteria. The potential uses of biofertilizers in agriculture play an important role of providing an economically viable level for achieving the ultimate goal to enhance productivity. On the other hand, the value of organic materials as a source of plant nutrients is greatly enhanced by composting. Composted materials are also more stable and pleasant to handle. In this paper the discussion is restricted to a review of the main groups of microbial biofertilizers in addition to fertilizers from the organic origin.

Short-term effects of forest restoration management on non-symbiotic nitrogen-fixation in western Montana

Forest restoration treatments involving selection harvest and prescribed fire have been applied throughout the Rocky Mountain West with only a limited understanding of how these treatments influence plant community composition and soil processes. Forest restoration treatments, especially those involving fire, have the potential to reduce N capital on site. Unfortunately there has been only limited effort to investigate the effects of forest restoration treatments on forest ecosystem N inputs, especially free living N-fixation in soil and woody residues. Recent studies have highlighted the potential for decaying woody roots to serve as hot spots for N-fixation. The fire and fire surrogates (FFS) study site at Lubrecht Experimental Forest in Western Montana provided a unique opportunity to investigate the effect of restoration treatments on N-fixation. We set out to examine how prescribed fire, selection harvest, and a combination of both influence free living N-fixing bacteria that colonize decomposing woody roots, mineral soil, and soil crusts. Soil, root, and soil crust samples were collected from replicated treatment plots in August 2005 and soil samples were recollected in May 2006 just following snowmelt. Acetylene reduction assays were run on all samples, and extractable inorganic N and potentially mineralizable N (PMN) were measured in mineral soil. While restoration treatments caused an increase in dead roots associated with stumps and fire killed trees, N-fixation rates were nearly non-existent in these root systems. Nitrogen-fixation rates were not significantly influenced by treatments in decomposing woody roots or in mineral soil, but were slightly greater ( P < 0.10) in soil crusts when the control stand was compared to treated plots. Nitrogen-fixation rates were also greater in mineral soil than in roots. Soil collected in August exhibited greater rates of N-fixation than soil collected in May which we attributed to higher moisture and an increase in available N following spring thaw. Average rates of free living N-fixation across the treatment plots at Lubrecht were low (0.26 kg N ha −1 year −1), but over time we estimate that these sources, along with the sparse population of symbiotic N-fixing plants and wet N deposition, would replenish soil N lost through fire or harvesting in approximately 40–100 years.

Gardian and Pivot Herbicide Effect on Some Non-Symbiotic Nitrogen Fixing Bacteria

ABSTRACTStudying the ecological risk of the herbicides used in modern agriculture is very important for environment protection from pollution. Therefore investigations of herbicide effect on important for soil fertility and plant nutrition microorganisms is actual and necessary. An ecological assessment of two herbicides/gardian and pivot/was done by measuring the bacterial growth of non-symbiotic nitrogen fixing bacteria—Azotobacter chroococcum 18 and two strains of Azospirillum brasilense—Sp. 7 and Sp. 107. Inhibition of bacterial growth is observed and it depends on the herbicide used, its concentration and the bacterial strain. Three rates of herbicides were studied. Gardian inhibition on the bacterial growth varies from 22 % to 75%. The decrease of the size of bacterial colonies of A. brasilense Sp. 7, when the highest concentration is used is 75%; in case of A. brasilense Sp. 107 - it is 50%. In case of pivot application A. brasilense Sp. 107 is more resistant again/inhibition varies from 17% to 50%/; for A. brasilense Sp. 7 it is respectively 33% and 56%. In case of A. chrococcum the inhibition of the highest concentration of gardian is 56% and of pivot - 50%. The results show that gardian is more toxic than pivot as concerning the growth of the bacterial species studied.

Potential for non-symbiotic N2-fixation in different agroecological zones of southern Australia

Nitrogen fixation by symbiotic and non-symbiotic bacteria can be a significant source of nitrogen in cropping systems. However, contributions from non-symbiotic nitrogen fixation (NSNF) are dependent on available carbon in the soil and environmental conditions (soil moisture and temperature). In Australia, measurements of NSNF have been made in the field by quantifying nitrogenase activity. These studies have included determinations of the moisture and temperature requirements for NSNF and for crop residue decomposition that supplies carbon to NSNF bacteria. Other studies have determined the N input by NSNF using N budget calculations. These data together with information about carbon supply and environmental conditions were used to estimate potential NSNF in the cropping zones of southern Australia. Using the ArcviewGIS Spatial Analyst (v3.1), maps of Australia showing estimates of NSNF in different cropping zones as determined by rainfall and temperature or carbon availability were generated. In Western Australia (represented by Wongan Hills) and South Australia (represented by Avon), where summers are dry, estimates of NSNF were generally low (10–15 kg N/ha from January to June) due to limitations of soil moisture. In New South Wales, particularly in the north where summer rainfall patterns develop (represented by Gunnedah), the warm, moist conditions produced higher estimates of NSNF (totaling 32–38 kg N/ha from January to June). In this region, the majority of estimated NSNF occurred in January and February leading to the depletion of carbon supplies and reduced NSNF in autumn (March–June). Information about potential supplies of N from NSNF across the cropping zones should be useful for researchers to select and study areas that are most likely to benefit from NSNF. It should also help agronomists and extension officers explain changes in N status within paddocks or within specific farming systems and to provide more accurate advice on N fertiliser requirements, particularly in low-input farming systems.