Plant-available Nitrogen Research Articles

Biochar influences nitrogen availability in Andisols of north Idaho forests

Biochar application in forest soils can influence tree growth and forest productivity through mediating plant-available nitrogen (N) pools. However, how soil N availability and related transformations respond to biochar addition in cold–temperate forest ecosystems is not well understood. Our study assessed the effect of a hardwood forest residue biochar on soils taken from an elevational gradient within a cold–temperate, north Idaho forest. Forest soils were incubated at 0%, 10% and 20% biochar amendments in a greenhouse for 120 days. We measured soil small organic N (amino compound) and inorganic N (ammonium and nitrate) pools, enzyme activities, small organic N turnover, N mineralization and nitrification rates. Biochar decreased small organic N and inorganic N concentrations in most elevations. Enzyme analysis shows biochar increased the activity of aminopeptidase, but decreased the activity of N-acetyl-β-d-glucosaminidase, β-glucosidase and acid phosphatase. Biochar did not influence small organic N turnover and N mineralization rates, but decreased nitrification rate. In conclusion, hardwood forest residue biochar application in cold–temperate forests has important impact on short-term soil N cycling.

Nitrous oxide fluxes of a boreal abandoned pasture do not significantly differ from an adjacent natural bog despite distinct environmental conditions

Land-use conversion of pristine boreal peatlands for agricultural purposes is an ongoing process and projected to become more intensive with rising population growth and increased demands for food production. However, agricultural use of peatlands affects the production and emission of nitrous oxide (N2O), a very potent greenhouse gas currently gaining more attention in the global assessment of greenhouse gases. While the intensity of N2O emissions depends on a range of environmental factors, including hydrological parameters, temperature and the availability of nitrogen in soils, key driving processes remain poorly understood. In order to understand the effects of land-use change on the peatland ecosystem, we quantified N2O fluxes under different land-use in a comparative study between a natural bog and an adjacent abandoned pasture in Newfoundland, Canada. We conducted in situ gas flux measurements using the static chamber method over five growing seasons. In addition, we measured photosynthetic rates and environmental parameters, namely soil temperature and moisture, water table and concentrations of total nitrogen and dissolved organic carbon in pore waters. According to previous studies, we hypothesized higher N2O emissions from the abandoned pasture due to drainage compared to the natural bog. However, despite significant differences of environmental parameters and photosynthetic rates, we found no significant difference of N2O fluxes between the two sites. We argue that N2O production at the abandoned pasture was inhibited due to exhaustion of plant-available nitrogen as a result of increased gross primary production compared to the natural bog. We conclude that the effect of drainage and fertilization on N2O fluxes during the growing season was superposed by vegetation composition change effects at the abandoned pasture, leading to similar N2O fluxes at both sites.

Grassland harvesting alters ant community trophic structure: An isotopic study in tallgrass prairies.

Disturbances have long been recognized as important forces for structuring natural communities but their effects on trophic structure are not well understood, particularly in terrestrial systems. This is in part because quantifying trophic linkages is a challenge, especially for small organisms with cryptic feeding behaviors such as insects, and often relies on conducting labor‐intensive feeding trials or extensive observations in the field. In this study, we used stable isotopes of carbon and nitrogen to examine how disturbance (annual biomass harvesting) in tallgrass prairies affected the trophic position, trophic range, and niche space of ants, a widespread grassland consumer. We hypothesized that biomass harvest would remove important food and nesting resources of insects thus affecting ant feeding relationships and trophic structure. We found shifts in the feeding relationships inferred by isotopic signatures with harvest. In particular, these shifts suggest that ants within harvest sites utilized resources at lower trophic levels (possibly plant‐based resources or herbivores), expanded trophic breadth, and occupied different niche spaces. Shifts in resource use following harvest could be due to harvest‐mediated changes in both the plant and arthropod communities that might affect the strength of competition or alter plant nitrogen availability. Because shifts in resource use alter the flow of nutrients across the food web, disturbance effects on ants could have ecosystem‐level consequences through nutrient cycling.

Effects of emergent aquatic plants on nitrogen transformation processes and related microorganisms in a constructed wetland in northern China

Wetland plants affect ammonia-oxidation rate (AOR) and nitrogen-fixation rate (NFR), resulting in changes in plant-available nitrogen and wetland nitrogen-cycling. This study aims to investigate the underlying mechanisms and influencing factors associated with ammonium oxidation and nitrogen fixation in response to wetland-emergent aquatic plants. A field experiment was conducted to study the response of activity, abundance, and community structure of ammonia-oxidizers and diazotrophs to three wetland-emergent aquatic plants in summer and autumn. The root exudates and soil physicochemical properties were determined due to their important role in rhizosphere interactions. AOR and NFR were significantly higher in rhizosphere than in bulk soils. The increases of AOR and NFR in rhizosphere were significantly positively affected by oxidation-reduction potential, additionally, NFR was also significantly affected by sugar-containing root exudates. Furthermore, NFR strongly correlated with diazotroph abundance, whereas AOR was linearly correlated with ammonia-oxidizing archaea (AOA) activity and mostly determined by a specific AOA taxon. Emergent plant rhizosphere exhibited strong positive effects on AOR and NFR by altering community structure and abundance of related microorganisms. Release of available oxygen and carbon in plant rhizospheres is vital for promoting ammonium oxidation and nitrogen fixation and might further mediate wetlands nitrogen-cycling.

Hybrid systems combining manures and cover crops can substantially reduce nitrogen fertilizer use

ABSTRACTManures allow for nitrogen (N) and phosphorus (P) recycling but low N:P ratios result in P over-fertilization when applying manures to meet crop N demand. Such stoichiometric imbalances can result in inefficient use of non-renewable P resources as well as aquatic eutrophication. On average, P surpluses in wheat (Triticum aestivum L.) and corn (Zea mays L.) systems of the United States vary between 1.4 and 3.1 kg P per kg of plant-available nitrogen (PAN) applied. Hybrid systems combining manures and biological N2-fixation from cover crops can limit P over-fertilization and reduce synthetic N fertilizer inputs. On average, about 40–48% of corn and 69–75% of wheat crop N demand could be met by manures and legume cover crops in the United States. However, the range of their possible N contribution to a specific system is wide given the variability in nutrient concentrations/availability and transfer to a subsequent crop. The adoption of hybrid systems is also limited by other constraints, most notably the spatial decoupling between animal and crop production.

Physiological responses and small RNAs changes in maize under nitrogen deficiency and resupply.

Maize is an important crop in the world, nitrogen stress severely reduces maize yield. Although a large number of studies have identified the expression changes of microRNAs (miRNAs) under N stress in several species, the miRNAs expression patterns of N-deficient plants under N resupply remain unclear. The primary objective of this study was to identify miRNAs in response to nitrogen stress and understand relevant physiological changes in nitrogen-deficient maize after nitrogen resupply. Physiological parameters were measured to study relevant physiological changes under different nitrogen conditions. Small RNA sequencing and qRT-PCR analysis were performed to understand the response of miRNAs under different nitrogen conditions. The content of chlorophyll, soluble protein and nitrate nitrogen decreased than CK by 0.52, 0.49 and 0.82 times after N deficiency treatment and increased than ND by 0.52, 1.36 and 0.65 times after N resupply, respectively. Conversely, the activity of superoxide dismutase (SOD) and peroxidase (POD) increased by 0.67 and 1.64 times than CK after N deficiency, respectively, and decreased by 0.09 and 0.35 times than ND after N resupply. A total of 226 known miRNAs were identified by sRNA sequencing; 106 miRNAs were differentially expressed between the control and N-deficient groups, and 103 were differentially expressed between the N-deficient and N-resupply groups (P < 0.05). Real-time quantitative PCR (qPCR) was used to further validate and analyze the expression of the identified miRNAs. A total of 1609 target genes were identified by target prediction, and some differentially expressed miRNAs were predicted to target transcription factors and functional proteins. Gene Ontology (GO) analysis was used to determine the biological function of these targets and revealed that some miRNAs, such as miR169, miR1214, miR2199, miR398, miR408 and miR827 might be involved in nitrogen metabolism regulation. Our study comprehensively provides important information on miRNA functions and molecular mechanisms in response to N stress. These findings may assist to improve nitrogen availability in plants.

Amount of Rain Until Third Leaf Explain Differences in Irrigated Durum Wheat Yield Between a Conventional and No-Tillage System in a Long-Term Crop Rotation System in Mediterranean Environment

Crop yields usually respond to crop rotation, but they may interact with tillage system and year (as an integration of variables, mainly in terms of temperature and precipitation). The objective of this study was to evaluate the determinants of the irrigated durum wheat yield under long-term tillage system × crop rotation (2000–2008). Tillage factor considered two levels: moldboard plow plus disk harrow (CT) and no-till (NT) and crop rotations factor had three levels: wheat–fallow–canola (W–F–C), wheat–maize (W–M) and wheat–fallow (W–F). Last year, we evaluate a maize crop as a physical soil quality indicator. The tillage system × crop rotation interaction was not significant, and the lowest durum wheat yield and biomass were observed in the W–M rotation experimental year (reduction of 18.7%). Tillage system × year interaction was significant for wheat yield. Partial least squares analysis indicated that precipitation was high between sowing and 3rd leaf was determinant for yield, and a negative correlation between these variables was observed. Despite the above, no differences were observed in the maize yield directly attributable to physical soil properties. Our study shows that rainfall distribution appears to cause of the tillage system × year interaction for durum wheat yield. When the precipitation was higher (160 mm) between sowing and 3rd leaf, yield decreased in NT by 37% compared to CT possible due to a hypoxia condition and/or low plant-available soil nitrogen, with a negative effect over tillering, affecting in the long-term spike number per square meter.

Tomato plants rather than fertilizers drive microbial community structure in horticultural growing media

Synthetic fertilizer production is associated with a high environmental footprint, as compounds typically dissolve rapidly leaching emissions to the atmosphere or surface waters. We tested two recovered nutrients with slower release patterns, as promising alternatives for synthetic fertilizers: struvite and a commercially available organic fertilizer. Using these fertilizers as nitrogen source, we conducted a rhizotron experiment to test their effect on plant performance and nutrient recovery in juvenile tomato plants. Plant performance was significantly improved when organic fertilizer was provided, promoting higher shoot biomass. Since the microbial community influences plant nitrogen availability, we characterized the root-associated microbial community structure and functionality. Analyses revealed distinct root microbial community structure when different fertilizers were supplied. However, plant presence significantly increased the similarity of the microbial community over time, regardless of fertilization. Additionally, the presence of the plant significantly reduced the potential ammonia oxidation rates, implying a possible role of the rhizosheath microbiome or nitrification inhibition by the plant. Our results indicate that nitrifying community members are impacted by the type of fertilizer used, while tomato plants influenced the potential ammonia-oxidizing activity of nitrogen-related rhizospheric microbial communities. These novel insights on interactions between recovered fertilizers, plant and associated microbes can contribute to develop sustainable crop production systems.

Modeling growing season and annual cumulative nitrous oxide emissions and emission factors from organically fertilized soils planted with barley in Lethbridge, Alberta, Canada

The widely used Denitrification-Decomposition (DNDC) model does not explicitly account for the influence of microbes in organic fertilizer. However, applying organic fertilizers to soils may increase N2O emissions because organic fertilizers can contain appreciable levels of the plant-available nitrogen (N), and contain many types of microbes including denitrifiers. In this study, the DNDC model was extended to include a microbial factor to account for the enhancement of microbial contents by the organic fertilizer input, and applied to two organically fertilized (digestate and manure) soils planted with barley in Lethbridge, Alberta, Canada. The growing season cumulative N2O emissions at the recommended N rate of digestate and manure were used to calibrate the model, while the emissions at the double recommended N loadings were used for validation. The results show that the growing season cumulative N2O emissions at recommended N loadings were calculated to be 1.90, 1.62, 3.50, and 2.55 kg-N ha−1 for digestate, and 0.45, 0.17, 0.35, and 0.74 kg-N ha−1 for manure in 2008, 2009, 2010, and 2011 respectively. The corresponding emission factors (EFs) are 0.937, 0.444, 1.947, and 0.510, as well as 0.095, 0.035, 0.072, and 0.083 for manure in 2008, 2009, 2010, and 2011 respectively. The average four-year relative errors of N2O emissions and EFs of validated cases are 32.3% and 34.3% for digestate, as well as 66.9% and 126% for manure, respectively. Two-factor hyperbolic and quadratic models of emissions and EFs correlating N loadings and weather conditions were developed and applied to N2O emission data at recommended N loadings. The coefficients of determination of modeled EFs to measured values are 0.887 and 0.982 for digestate and manure, respectively. The two-factor hyperbolic model predicted that N2O EFs would range from 0.085% to 1.1% for digestate with N loadings ranging from 100 to 800 kg-N ha−1, and product of average precipitation and air temperature during the growing season ranging from 18 to 36 mm × oC. The corresponding emissions ranged from 1.0 to 5.1 kg-N ha−1. We conclude that N2O emissions and EFS could be effectively modeled by a two-factor hyperbolic equation for digestate, and quadratic equation for manure.

Effect of Rates and Time of Nitrogen Application on Growth, Yield, and Yield Components of Wheat (Triticum aestivum L.) in Eastern Hararghe, Ethiopia

Wheat is a highly valued crop in the national diet of Ethiopians, and widely produced in the country. However, its productivity is constrained by low plant-available soil nitrogen due to depleting soil organic matter content and high leaching losses of mineralized nitrogen during the rainy seasons. This problem is compounded by low rates and inappropriate-timing of N fertilizer applications in the country. Therefore, field experiments were carried out during the 2013 main cropping season from July to November in Meta and Haramaya districts of eastern Ethiopia on a farmer’s field and on the research field of Haramaya University, respectively. The objectives of the study was to investigate the effect of rate and time of nitrogen application on growth, yield, grain protein content, and N use efficiency of bread wheat. The treatments consisted of six levels of nitrogen (0, 46, 69, 92, 115 and 138 kg N ha -1 ) and four application times ( 1 / 2 dose at planting + ½ dose at mid-tillering;½ dose at mid-tillering + ½ at anthesis; 1 / 3 rd dose each at planting, mid-tillering + anthesis, and 1 / 4 th dose at planting + ½ dose at mid-tillering + 1 / 4 th dose at anthesis. The experiments were laid out in factorial arrangement in RCBD with three replications. All the parameters evaluated were affected by the main effect of N fertilizer rate and time of N application. However, grain yield, harvest index, hectolitre weight, number of kernels per spike, total biomass yield, and total number of tillers at Haramaya and harvest index, were not significantly affected by the time of N fertilizer application. Days to heading and physiological maturity were prolonged in response to increasing the rate of nitrogen application at both sites. The highest biomass yield and plant height were recorded at 138 kg N ha -1 at both sites. Most of the parameters including grain yield exhibited maximum performances under this rate of N supply. The highest spike length was obtained at split application of 138 kg N ha -1 applied ( 1 / 4 th dose at planting, ½ at mid-tillering and 1 / 4 th at anthesis). Similarly, the tallest plants were recorded under similar rate N ha -1 applied ( 1 / 2 dose at planting and ½ dose at anthesis) at Haramaya. The nitrogen use efficiency decreased with increased N rate at both sites. In general, at Haramaya, plots treated with 46 and 115 kg N ha -1 at two equal splits at mid-tillering and at anthesis produced high grain yields, coupled with the best economic benefit or profitability. Whereas, at Meta, plots treated with 46 and 92 kg N ha -1 at two equal splits at mid-tillering and at anthesis and at three splits ( 1 / 4 th at planting + ½ at mid-tillering + 1 / 4 th at anthesis), respectively produced optimum grain yields, coupled with the best economic benefit or profitability. It could, thus, be concluded that application of 46 and 115 kg N ha -1 in two splits at mid-tillering and at anthesis and 92 kg N ha -1 in three splits ( 1 / 4 th at planting + ½ at mid-tillering + 1 / 4 th at anthesis) enhanced yield, yield components and N use efficiency of bread wheat. This implies the change of the blanket recommendation of 64 kg N ha -1 in the study area to this rate and time of application to improve the yield and N use efficiency of the crop in the study area. Keywords:- nitrogen fertilizers , yield and wheat DOI : 10.7176/JNSR/9-11-01 Publication date :June 30 th 2019

Plant Available Nitrogen Estimation Tools for a Biosolids‐Amended, Clayey Urban Soil

Core Ideas Biosolids produced by heat‐drying and Cambi process had higher plant available N. Biosolids blended with woody byproducts had lower plant available N. Soil nitrate and 7‐d anaerobic incubation were the best indicators of N availability. Soil test reliability may have been reduced by high clay and low C and N of urban soil. Improving mineralizable N estimates from exceptional quality (EQ) biosolids products is important for making more reliable N recommendations to rehabilitate disturbed urban soils for vegetative production. The objectives of this study were to compare the N fertilizer equivalency method and several chemical (NH4–N, NO3–N, total N, and organic N) and biological (7 d anaerobic incubation [7‐AI] and Solvita CO2 Burst) tests for quantifying plant available nitrogen (PAN) and organic N mineralization of EQ biosolids used to grow tall fescue (Schedonorus arundinaceus Schreb.) in a clayey urban degraded soil. The EQ biosolids were products of thermal hydrolysis plus anaerobic digestion (Blue Plains exceptional quality biosolids; BLOOM), blending of BLOOM with woody mulch (BM), blending of BLOOM with sand and sawdust (Blue Pains exceptional quality biosolids + sand + sawdust; BSS), composting (Livingston compost; LBC), and heat drying (OCB; OceanGro thermally dried). The EQ biosolids were applied at agronomic N rates, and the inorganic fertilizer was applied at four N rates in a field study. The N fertilizer equivalency method predicted considerably lower organic N mineralization than calculated for BM (7.1%), BSS (–12%), and LBC (4.6%). Treatments BLOOM, BM, and OCB had the highest 7‐AI organic N mineralization. Correlations between tall fescue N uptake and soil N tests showed that soil NO3–N and 7‐AI were the best indicators of biosolids N availability in our urban soil. However, the relatively low correlations between soil N indicators and tall fescue N uptake was likely due to low residual soil N, high soil clay content, and possible low microbial activity of the low organic matter‐containing anthropogenic soil.

Cover crops prove effective at increasing soil nitrogen for organic potato production

Many farms in northeast California are experimenting with organic production to take advantage of price premiums and niche markets. A common challenge in organic farming is finding dependable nitrogen sources to meet the needs of vegetable and grass crops, especially in fields with low soil nitrogen. This study assessed the use of cover crops and organic amendments for increasing soil nitrogen for potato production at the Intermountain Research and Extension Center in Tulelake. Researchers evaluated several cover crop species, three planting dates and multiple cover crop mixes. Amendments included composts, manures, bloodmeal and soymeal. The data collected in the study included total nitrogen from cover crops and amendments, plant-available nitrogen in the soil, potato petiole nitrate and crop yield and quality. Vetches and field peas, managed as green manure, were successful at satisfying potatoes' in-season nitrogen demand. These cover crops, grown alone or in mixes with non-legume species, produced potato crops whose yield and quality were similar to crops grown with conventional fertilizers. The cover crops' influence on potato pest pressure was neutral. Chicken manure was the most cost-effective amendment for satisfying potatoes' in-season nitrogen demand.

Biological and thermochemical conversion of human solid waste to soil amendments

Biological and thermochemical sanitization of source-separated human solid waste (HSW) are effective technologies for unsewered communities. While both methods are capable of fecal pathogen sterilization, the agronomically-beneficial properties of waste sanitized between methods remains unclear. Therefore, this study compared recovery and quality of soil amendments produced by compostation, torrefaction, and pyrolysis of HSW, established their financial value, and quantified tradeoffs between product value and conversion efficiency. Temperature and associated mass losses significantly affected the physical and chemical properties of thermochemically-treated HSW. Thermophilic composting, a biological sanitation method practiced in informal settlements in Nairobi, Kenya, produced an amendment that contained between 16 and 858-fold more plant-available nitrogen (N; 214.5 mg N/kg) than HSW pyrolyzed between 300 and 700 °C (0.2–15.2 mg N/kg). Conversely, HSW pyrolyzed at 600 °C had four-fold higher plant-available phosphorus (P; 3117 mg P/kg) and five-fold higher plant-available potassium (K; 7403 mg K/kg) than composted HSW (716 mg P/kg and 1462 mg K/kg). Wide variation between international fertilizer prices on the low end and regional East African prices on the high end resulted in broad-spaced quantiles for the value of agronomic components in HSW amendments. Phosphorus and K comprised a disproportionate amount of the value, 52–87%, compared to plant-available N, which contributed less than 2%. The total value of treated HSW, summed across all agronomic components per unit weight amendment, was greatest for thermochemically-treated HSW at 600 °C, averaging 220 USD/Mg, more than four-fold that of composted HSW, 53 USD/Mg. In contrast, torrefaction provided the highest monetary value per unit weight feedstock, 144 USD/Mg, as low heating temperatures engender minimal mass loss and higher nutrient densities per unit weight feedstock, compared to composted or pyrolyzed HSW. When benchmarked against total N, P, and K of eight commonly-applied organic amendments, including sewage-sludge (Milorganite), compost, and alfalfa meal, HSW pyrolyzed at 700 °C was of greatest value per unit weight of amendment, 365 USD/Mg, compared to 89 USD/Mg for composted HSW, and contained 2.9% total N (0.5 mg available N/kg), 3.1% total P (7640 mg available P/kg), 3.5% total K (17,671 mg available K/kg).

Fertile cities: Nutrient management practices in urban agriculture

Cities are increasingly targeted as centers for sustainable development and innovation of food systems. Urban agriculture (UA) is advocated by some as a multi-faceted approach to help achieve urban sustainability goals as it provides possible social, economic and environmental benefits. The role of UA in restoring resource cycles receives increasing attention, especially with regard to assimilating urban waste. However, there is little information on how nutrients are managed in UA in industrialized countries. To examine nutrient management in UA, data was collected from a total of 25 ground-based UA initiatives in the Netherlands on i) preferences for types of fertilizers, and ii) quantity and quality of fertilizers used including nutrient composition and organic matter content. The main inputs at urban farms were compost and manure, high in organic matter content. The total nutrient inputs were compared to nutrient demand, based on crop nutrient uptake, in order to determine nutrient balances. Results show that mean nutrient inputs exceeded mean crop demand by roughly 450% for total nitrogen, 600% for phosphorus and 250% for potassium. Mean inputs for plant-available nitrogen were comparable to crop uptake values. The surpluses, particularly for phosphorus, are higher than fertilizer application limits used for conventional farming in The Netherlands. While nutrient input calculations were subject to several uncertainties, e.g., due to lack of accuracy of the data supplied by the farmers, results show a salient indication of over-fertilization and thus a suboptimal nutrient use. If UA continues to expand across cities these observed nutrient surpluses may pose a risk for local surface waters and groundwater as well as soil quality. The need to improve nutrient management in UA is evident. Soil tests, harvest logging and book keeping of nutrient inputs would improve data quality and may help balance nutrient inputs with nutrient outputs.

Plant silicon effects on insect feeding dynamics are influenced by plant nitrogen availability

AbstractAlthough there is growing evidence that silicon (Si)‐based plant defenses effectively reduce both the palatability and digestibility of leaves, and thus impact nutrient assimilation by insect herbivores, much less is known about how this is affected by extrinsic and intrinsic factors. For example, do herbivores exhibit compensatory feeding on poor‐quality diets with Si or are Si defenses less effective in agroecosystems where high N availability increases plant quality? To investigate the interactive effects of N and Si on insect feeding, we conducted insect performance and compensatory feeding bioassays using maize, Zea mays L. (Poaceae), and the true armyworm, Pseudeletia unipuncta Haworth (Lepidoptera: Noctuidae). In the performance assay, the addition of Si alone resulted in increased larval mortality compared with the controls, likely because early instars with poorly developed mandibles could not feed effectively. However, larvae fed on plants treated with both Si and N survived better than on plants treated with Si only, although pupal mass did not differ between treatments. In our compensatory assay, Si addition reduced maize consumption, but increased both armyworm approximate digestibility and N assimilation efficiency, suggesting that enhanced post‐ingestion feeding physiology, rather than compensatory food intake, could have accounted for the lack of Si effects on pupal weight. Overall, our results demonstrate that, similar to other chemical and mechanical defenses, the effectiveness of plant Si defense is influenced by plant nutrient status and consumer compensatory ability.

Nutrients in Saltmarsh Soils Are Weakly Related to those in Adjacent Coastal Waters

Saltmarshes provide a broad range of high-value ecosystem services and can be sensitive to eutrophication, but elucidating such impacts at broad spatial scales demands a better understanding of the underlying nutrient linkages between saltmarsh soil and tidal waters. We used existing water quality data and field surveys of 15 saltmarshes across a broad trophic gradient of coastal waters, but similar biogeographic setting (in Ireland) to investigate if phosphorus and nitrogen pools in saltmarsh soils are related to those in tidal water across saltmarshes. We also investigated if the strength of such relationships is inversely related to ground elevation, which approximates the degree of tidal inundation. Plant-available phosphorus and nitrogen pools in soil were related to water nutrients, albeit only weakly. We did not find any support for the moderating influence of elevation, indicating that it may be obscured by internal cycling and external sources. We also found evidence for effect of birds on the saltmarsh nutrient pool. Saltmarsh soils are unlikely to serve as general sentinels of nutrient conditions in their corresponding water bodies and may need separate assessment criteria and management tools, which in turn require disentangling localised and whole-saltmarsh sources of variation in nutrient concentrations.

Impact of different rhizobial strains and reduced nitrogen supply on growth, yield and nutrient uptake in cowpea grown hydroponically

One of the strategies that contributes to more sustainable crop production in greenhouses is the reduction of nitrogen input without compromising yield. In legume crops, this goal can be achieved by using efficient rhizobial strains capable of biologically fixing atmospheric nitrogen to inoculate the seeds or the young seedlings. In soilless culture, inoculation of legumes with rhizobia can considerably reduce the input of inorganic nitrogen when preparing nutrient solutions. However, the practical application of this approach faces some difficulties. On the one hand, the supply of plant-available nitrogen is important at the early growth stage, when the rhizobia are still not functional in terms of N(2) fixation. On the other hand, inorganic nitrogen and especially nitrate N inhibits rhizobium colonization. To cope with these two contrasting needs, fine tuning of the nitrogen supply is needed, whereby legumes grown in soilless culture are inoculated with relevant rhizobial strains. In the present study, two different indigenous rhizobia, Bradyrhizobium sp. VULI1.1 and Ensifer sp. VUKA2, and a mixture of them were used to inoculate cowpea [Vigna unguiculata (L.) Walp.] grown in Perlite and supplied with different nitrogen levels to test their inoculation and nitrogen-fixation ability. Plants were supplied with either full-N (total-N 11.2 mM) or 60% of full-N until the flowering stage. Afterwards, the nitrogen supply was reduced to either 30 or 0% until the end of the cultivation period. Nodule number and weight per plant were also estimated. The reduction of nitrogen supply to 60% of the full requirements during the vegetative stage and 0% during the reproductive stage led to increased nodule weight but decreased number of nodules per plant, which resulted in reduced growth and yield. However, supplying 60% of the full nitrogen requirements up to the flowering stage and 30% thereafter increased both nodulation and yield in rhizobium-inoculated cowpea plants in comparison with 100% nitrogen supply without rhizobium inoculation throughout the cropping period. These results indicate that applying different rates of inorganic nitrogen before and after the formation of N(2)-fixing nodules could be considered an effective strategy to reduce nitrogen fertilizer supply in hydroponic cowpea crops without compromising yield.

Humic substrates facilitated nitrogen uptake in tea bushes by influencing biochemical and microbiological properties in soil of Northeast India

Several groups of microorganisms are involved in converting applied urea into plant-available nitrate nitrogen (N) in soil. The objective of this study was to evaluate efficacy of humic substrates (HS) for maximizing crop yield by enhancing N availability in soil. In this experiment, HS was applied in soil of tea garden in such a way that active substrate was applied at 0, 400, 800, 1,200, 1,600, and 2,000 g ha−1 in six treatments. Chemical fertilizers were applied in all the treatments (including control) following the recommended doses. This study indicated that applied HS enhanced tea shoot yield and N uptake by tea bushes. Improved biochemical and microbiological properties increased N availability in HS-treated soil and that in turn facilitated N uptake by tea bushes. It was determined that HS substrate application at 1.2 kg ha−1 could enhance the yield of tea shoots up to 18% higher than control treatment.

Flexible Laser-Induced Graphene for Nitrogen Sensing in Soil.

Flexible graphene electronics are rapidly gaining interest, but their widespread implementation has been impeded by challenges with ink preparation, ink printing, and postprint annealing processes. Laser-induced graphene (LIG) promises a facile alternative by creating flexible graphene electronics on polyimide substrates through the one-step laser writing fabrication method. Herein, we demonstrate the use of LIG, created with a low-cost UV laser, for electrochemical ion-selective sensing of plant-available nitrogen (i.e., both ammonium and nitrate ions: NH4+ and NO3-) in soil samples. The laser used to create the LIG was operated at distinct pulse widths (10, 20, 30, 40, and 50 ms) to maximize the LIG electrochemical reactivity. Results illustrated that a laser pulse width of 20 ms led to a high percentage of sp2 carbon (77%) and optimal peak oxidation current of 120 μA during cyclic voltammetry of ferro/ferricyanide. Therefore, LIG electrodes created with a 20 ms pulse width were consequently functionalized with distinct ionophores specific to NH4+ (nonactin) or NO3- (tridodecylmethylammonium nitrate) within poly(vinyl chloride)-based membranes to create distinct solid contact ion-selective electrodes (SC-ISEs) for NH4+ and NO3- ion sensing, respectively. The LIG SC-ISEs displayed near Nernstian sensitivities of 51.7 ± 7.8 mV/dec (NH4+) and -54.8 ± 2.5 mV/dec (NO3-), detection limits of 28.2 ± 25.0 μM (NH4+) and 20.6 ± 14.8 μM (NO3-), low long-term drift of 0.93 mV/h (NH4+ sensors) and -5.3 μV/h (NO3- sensors), and linear sensing ranges of 10-5-10-1 M for both sensors. Moreover, soil slurry sensing was performed, and recovery percentages of 96% and 95% were obtained for added NH4+ and NO3-, respectively. These results, combined with a facile fabrication that does not require metallic nanoparticle decoration, make these LIG electrochemical sensors appealing for a wide range of in-field or point-of-service applications for soil health management.

Affinity of Hyperammonia-Producing Bacteria To Produce Bioammonium/Ammonia Utilizing Five Organic Nitrogen Substrates for Potential Use as an Organic Liquid Fertilizer.

This research was conducted to create a plant-available nitrogen nutrient solution utilizing ruminant bacteria for ultimate use as a liquid nitrogen fertilizer for precision fertigation of vegetable crops. Three hyperammonia-producing ruminant bacteria, Clostridium aminophilum, Peptostreptococcus anaerobius, and Clostridium sticklandii, were cultured anaerobically using five different organic nitrogen substrates to determine their efficiency in producing bioammonium/ammonia (BAA), a term defined here as a biologically produced solution containing both ammonium and ammonia. These bacteria were chosen because of their ability to produce ammonium at rates not experienced by any other bacteria. The five substrates were soy protein isolate (SPI), blood meal, feather meal, dried fish, and yeast extract (Y) used alone and in combination with Y. C. aminophilum and SPI were selected for further experimentation in an attempt to maximize BAA production. These substrates were chosen because they are commonly fed to cattle and they are also used as organic fertilizer amendments. C. aminophilum was cultured with SPI rates from 0.8 g·10 mL–1 salt solution reaching SPI’s maximum solubility level at 1.6 g·10 mL–1 salt solution at 0.2 g intervals, and the BAA content was measured every 24 h for 168 h. It was concluded that there was no significant benefit in culturing C. aminophilum with more than 1.0 g·10 mL–1 for more than 96 h to achieve maximum BAA concentrations.