Plant-available Nitrogen Research Articles

Effect of zeolite application on soil enzyme activity of potted sandy soil cultivated with Swiss chard and cabbage

A zeolite pot experiment was conducted at the Agricultural Research Council Infruitec-Nietvoorbij in Stellenbosch, South Africa, under greenhouse conditions. The experiment aimed to investigate the impact of zeolite application on soil enzyme activities in sandy soils cultivated with Swiss chard (Beta vulgaris Var. cicla) and cabbage (Brassica oleracea Var. capitata L.) over two years (2018-2019). Different zeolite-to-soil ratios (0:1, 1:9, 2:8, and 3:7 w/w) were used, with each pot containing 12 kg of soil. The experiment involved 72 pots for each vegetable, arranged in a randomized complete block design (RCBD). Soil enzyme activities, including acid phosphatase, β-glucosidase, and urease, as well as soil chemical properties (pH, total plant-available nitrogen, organic carbon, and phosphorus), were analyzed. Key findings indicate that the effect of zeolite application on enzyme activities varied between the vegetable species. Zeolite application significantly increased (P

Spaceborne imaging spectroscopy enables carbon trait estimation in cover crop and cash crop residues

PurposeCover crops and reduced tillage are two key climate smart agricultural practices that can provide agroecosystem services including improved soil health, increased soil carbon sequestration, and reduced fertilizer needs. Crop residue carbon traits (i.e., lignin, holocellulose, non-structural carbohydrates) and nitrogen concentrations largely mediate decomposition rates and amount of plant-available nitrogen accessible to cash crops and determine soil carbon residence time. Non-destructive approaches to quantify these important traits are possible using spectroscopy.MethodsThe objective of this study was to evaluate the efficacy of spectroscopy instruments to quantify crop residue biochemical traits in cover crop agriculture systems using partial least squares regression models and a combination of (1) the band equivalent reflectance (BER) of the PRecursore IperSpettrale della Missione Applicativa (PRISMA) imaging spectroscopy sensor derived from laboratory collected Analytical Spectral Devices (ASD) spectra (n = 296) of 11 cover crop species and three cash crop species, and (2) spaceborne PRISMA imagery that coincided with destructive crop residue collections in the spring of 2022 (n = 65). Spectral range was constrained to 1200 to 2400 nm to reduce the likelihood of confounding relationships in wavelengths sensitive to plant pigments or those related to canopy structure for both analytical approaches.ResultsModels using laboratory BER of PRISMA all demonstrated high accuracies and low errors for estimation of nitrogen and carbon traits (adj. R2 = 0.86 − 0.98; RMSE = 0.24 − 4.25%) and results indicate that a single model may be used for a given trait across all species. Models using spaceborne imaging spectroscopy demonstrated that crop residue carbon traits can be successfully estimated using PRISMA imagery (adj. R2 = 0.65 − 0.75; RMSE = 2.71 − 4.16%). We found moderate relationships between nitrogen concentration and PRISMA imagery (adj. R2 = 0.52; RMSE = 0.25%), which is partly related to the range of nitrogen in these senesced crop residues (0.38–1.85%). PRISMA imagery models were also influenced by atmospheric absorption, variability in surface moisture content, and some presence of green vegetation.ConclusionAs spaceborne imaging spectroscopy data become more widely available from upcoming missions, crop residue trait estimates could be regularly generated and integrated into decision support tools to calculate decomposition rates and associated nitrogen credits to inform precision field management, as well as to enable measurement, monitoring, reporting, and verification of net carbon benefits from climate smart agricultural practice adoption in an emerging carbon marketplace.

Manipulating soil resource availability to alter microbial communities for weed management in agroecosystems

The growing resistance of weeds to herbicides demands innovative strategies that harness soil biology for effective weed control. We examined the use of carbon amendments to stimulate microbial immobilization of soil nitrogen for weed control. We hypothesized that increased carbon availability will stimulate soil microbial growth, leading to greater nitrogen immobilization, which consequently decreases plant-available nitrogen and suppresses the growth of nitrogen-responsive weed species. We buried 80 19-L pots in a research farm field and added sawdust and sucrose to soils as a high carbon treatment and used unamended soils as a control. We examined eight different weed species separately, and measured plant growth, soil carbon, available nitrate, microbial carbon and nitrogen, and microbial community composition after 11 weeks of treatment. The carbon amendments altered plant-microbial competition for nitrogen, resulting in reduced biomass for most weed species. The carbon-amended soils had higher microbial biomass carbon and nitrogen, slower nitrogen cycling, and less available soil nitrogen, indicating enhanced nitrogen immobilization. The carbon treatment altered the beta diversity of soil fungi and bacteria and reduced fungal alpha diversity estimated by the Shannon index. The study results indicate that high carbon substrates can be used to modify plant-microbial competition for soil nitrogen with important implications for developing sustainable weed management practices.

Quantitative importance of subsoil nitrogen cycling processes in Andosols and Cambisols under temperate forests

Nitrogen availability often limits plant growth in forest ecosystems. Plants, including trees, utilize soil inorganic nitrogen transformed via nitrogen cycling processes, including mineralization and nitrification. While most plant fine roots are distributed in surface soil layers, plants take up nitrogen even from subsurface soil layers in addition to the surface soil layers, especially under high nutrient competition. However, there is still limited knowledge about nitrogen cycles within deeper soil layers. In this study, we investigated the vertical profiles (0–60 cm) of the net nitrogen mineralization and nitrification rates at four Japanese forest sites with two different soil types (Andosols and Cambisols). The partial least square path modeling (PLS-PM) was used to determine factors affecting nitrogen cycling processes. The net nitrogen mineralization and nitrification rates per unit soil weight were considerably higher in the surface soil layer than in the deeper soil layers in Andosols but not in Cambisols. PLS-PM analysis showed that microbial biomass and soil organic matter quantities were the important factors influencing the net nitrogen mineralization and nitrification rates, indicating that a similar mechanism, which drives the spatial variations of nitrogen cycling processes in the surface soil layer, predominantly regulates the vertical variations of the processes. Moreover, it was estimated that the net nitrogen mineralization rate could be comparable at all soil types and depths when the rate was expressed per unit soil volume. Therefore, subsoil layers could be a quantitatively important source of plant-available nitrogen in Andosols and Cambisols.

Short-term effects of brassica cover crops on soil quality indicators in organic production in high tunnels

The use of cover crops is aimed at sustaining soil health and productivity in the context of agricultural intensification and accompanying soil degradation. While cover crops have been extensively studied in field production systems, limited research has been conducted concerning their application in high-tunnel vegetable production. This study aimed to assess the effects of turnip (Brassica napus subsp. napobrassica (L.) Jafri) and swede Brassica rapa subsp. Rapifera Metzg) cover crops (CCs) on soil physicochemical and biological properties in an organic high tunnel system in southern Poland in 2017–2019. The planting sequence was as follows: winter cover crops/pumpkin/romaine lettuce/broad bean/chilli pepper. Soil analyses included measurements of bulk density, water capacity, soil aggregation, soil organic carbon (SOC), available soil nutrients, as well as microbial abundance and diversity. Rape crops produced a higher aboveground dry biomass (4.11 t ha−1) than swede (2.85 t ha−1), and the N content in their biomass was 101 kg N ha−1 and 75 kg N ha−1, respectively. The results presented that CC residue significantly contributed to soil organic carbon stock, retention of plant-available nitrogen, and improvement of soil physical properties, especially wet aggregate stability. Soils with the highest SOC concentrations were associated with the highest bacterial and fungal abundance. The most significant number of mesophilic bacteria was detected in the soil where turnip was grown as a cover crop (7.6 × 107 cfu g−1 DM soil). Moreover, a higher abundance of the tested nitrogen cycle bacteria was found in the soils after CC cultivation compared to the control soils, particularly bacteria reducing NH4 +-N and NO₃⁻-N. These findings highlight the importance of cover crop management practices in high tunnels, as they influence the composition of the total bacterial community and the abundance of N-cycling microbial guilds.

Diazotrophic nitrogen fixation through aerial roots occurs in Avicennia marina: implications for adaptation of mangrove plant growth to low-nitrogen tidal flats.

Nitrogen limitation of primary production is common in coastal ecosystems. Mangrove trees maintain high levels of nitrogen fixation around their roots. The interior aerial space of mangrove roots, in which atmospheric gas is supplied through lenticels, could be efficient sites for nitrogen fixation. We measured tidal variations of partial pressure of N2 in root aerenchyma and conducted field experiments using 15 N2 as a tracer to track N2 movement through aerial roots of Avicennia marina. We used the acetylene reduction assay to identify the root parts harboring diazotrophs. The nitrogenase activity and estimated nitrogen fixation through aerenchyma were higher in pneumatophores and absorbing roots than in cable roots. Positive correlations between root nitrogen contents and turnover rates of root nitrogen derived from N2 through aerenchyma suggested that the internal supply of N2 to diazotrophs could be the main source for nitrogen assimilation by A. marina roots. Our results confirmed that N2 is supplied to diazotrophs through aerial roots and that nitrogen fixation occurs in A. marina roots. The aerial root structures, which occur across families of mangrove plants, could be an adaptation to survival in not only low-oxygen environments but also tidal flats with little plant-available nitrogen.

Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction.

Plants uptake and assimilate nitrogen from the soil in the form of nitrate, ammonium ions, and available amino acids from organic sources. Plant nitrate and ammonium transporters are responsible for nitrate and ammonium translocation from the soil into the roots. The unique structure of these transporters determines the specificity of each transporter, and structural analyses reveal the mechanisms by which these transporters function. Following absorption, the nitrogen metabolism pathway incorporates the nitrogen into organic compounds via glutamine synthetase and glutamate synthase that convert ammonium ions into glutamine and glutamate. Different isoforms of glutamine synthetase and glutamate synthase exist, enabling plants to fine-tune nitrogen metabolism based on environmental cues. Under stressful conditions, nitric oxide has been found to enhance plant survival under drought stress. Furthermore, the interaction between salinity stress and nitrogen availability in plants has been studied, with nitric oxide identified as a potential mediator of responses to salt stress. Conversely, excessive use of nitrate fertilizers can lead to health and environmental issues. Therefore, alternative strategies, such as establishing nitrogen fixation in plants through diazotrophic microbiota, have been explored to reduce reliance on synthetic fertilizers. Ultimately, genomics can identify new genes related to nitrogen fixation, which could be harnessed to improve plant productivity.

Long term conservation agriculture impact on soil nitrogen fractions and wheat (Triticum aestivum) yield in subtropical Inceptisol

The present study was carried out at ICAR-Indian Agricultural Research Institute (IARI), New Delhi over two consecutive years (2020 and 2021) to evaluate the influence of conservation agriculture (CA) and nitrogen management strategies on wheat yield in an intensified maize (Zea mays L.)-wheat (Triticum aestivum L.)-mungbean (Vigna radiata L.) cropping system. Results indicated that grain and straw yields of wheat in CA plots were higher, reaching 4829 and 7231 kg/ha, respectively. However, these yields were statistically comparable to those obtained from conventionally tilled plots (4502 and 6611 kg/ha, respectively). Significantly higher wheat grain and straw yields were observed in plots receiving nitrogen fertilizer. Interestingly, the harvest index remained unaffected by both tillage practices and nitrogen management strategies. After two seasons of wheat cultivation, CA plots had significantly higher soil nitrogen fractions, including mineral, alkali-permanganate, potentially mineralizable, microbial biomass N and total nitrogen, compared to conventionally tilled plots. Moreover, all nitrogen-receiving treatments demonstrated significantly higher nitrogen fractions at both soil depths (0–5 and 5–15 cm) compared to the control. Notably, plots treated with urea super granules exhibited superior results in enhancing plant-available nitrogen. In conclusion, this study underscores the importance of CA and various nitrogen management strategies for increasing wheat crop yield and promoting plant-available nitrogen fractions in the soil. These findings providevaluable insights for farmers and researchers looking for sustainable and efficient agricultural practices to optimize wheat production and soil health.

Interaction of Filth Flies and Epigeal Arthropods with Soil Nitrogen and Gas Emissions in Grazing Systems under a Legacy of Low Fertilization

During the summers of 2021 and 2022, we conducted a study in four Georgia Piedmont pastures to assess the effect of the presence of filth flies and epigeal arthropods on carbon and nitrogen emissions and soil nitrogen retention from lax rotational grazing systems under a legacy of low fertilization. Carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3) emissions were measured from dung on days 0, 4, 8, and 15 following depositions. Soil and manure samples were collected on days 0 and 16 and analyzed for ammonium (NH4+), nitrate (NO3−), plant-available nitrogen (PAN), and potentially mineralizable nitrogen (PMN). Manure samples were analyzed for total Kjeldahl nitrogen (TKN). The numbers of filth flies ovipositing and emerging from manure, fire ants, and epigeal arthropods around the manure were determined. Our results indicated that more than 12 ovipositing filth flies per manure pat can reduce PMN by up to 14.7 kg of nitrogen per hectare, while an increase in the biodiversity and abundance of predators may help to increase PAN and PMN in grazing systems, as well as decrease the number of emerging filth flies.

Carbon Sources for Anaerobic Soil Disinfestation in Southern California Strawberry

Anaerobic soil disinfestation (ASD) has been adopted in over 900 ha in California strawberry production as an alternative to chemical fumigation. Rice bran, the predominant carbon source for ASD, has become increasingly expensive. In 2021–22 and the 2022–23 field studies, we evaluated 20–30% lower-priced wheat middlings (Midds) and dried distillers’ grain (DDG) at 21,800 kg ha−1 (in 2021) and 17,000 kg ha−1 (in 2022) as alternative carbon sources to rice bran. The study was placed at Santa Paula, California in September of each season in preparation for strawberry planting in October. Soil and air temperatures were 18–26 °C during that time. After the incorporation of carbon sources into the top 30 cm of bed soil, beds were reshaped, and irrigation drip lines were installed and covered with totally impermeable film (TIF) to prevent gas exchange. Beds were irrigated to saturate the bed soil within 48 h after TIF installation. Anaerobic conditions were measured with soil redox potential (Eh) sensors placed at 15 cm depth in all plots. Both DDG and Midds plots maintained Eh at −180 to 0 mV during the two ASD weeks, while untreated soil was aerobic at 200 to 400 mV. Permeable bags with inocula of Macrophomina phaseolina, a lethal soil-borne pathogen of strawberry, and tubers of a perennial weed Cyperus esculentus were placed 15 cm deep in the soil at ASD initiation and retrieved two weeks later for analyses. Two weeks after that, holes were cut to aerate beds and ‘Victor’ or ‘Fronteras’ bare-root strawberries were transplanted into them. ASD with DDG reduced viable microsclerotia of M. phaseolina by 49% in the first season and 75 to 85% with both carbon sources in the second season. Both ASD treatments reduced tuber germination of C. esculentus 86–90% compared to untreated soil in one of two years. Additionally, Midds and DDG provided greater sufficiency of plant-available nitrogen and phosphorus compared to untreated soil with synthetic pre-plant fertilizer and improved fruit yields by 11–29%. ASD with these carbon sources can suppress soil pathogens and weeds and help sustain organic strawberry production in California.

Effects of limed manure digestate application in sandy soil on plant nitrogen availability and soil N2O emissions

Anaerobically-digested manure is frequently applied to agricultural soil to enhance plant growth and reduce the need for chemical fertilizers. This practice also stimulates microbial nitrogen transformations and often results in N2O emissions. A single mesophilic anaerobic digestion is insufficient for pathogen removal or inactivation and therefore, a post treatment is required for its stabilization and hygienization. Here, we examined the effects of limed manure-digestate as a nitrogen source for plant growth and on N2O emission compared with compost. A plant growth experiment was conducted in a sandy soil and N2O emissions were monitored throughout the experiment. Plants were irrigated with freshwater or liquid-N fertilizer. The combination of compost application and liquid-N fertilizer resulted in surface N2O fluxes over 0.7 ​mg ​m−2 d−1, which were correlated with ammonium concentration in the soil. The presence of N2O in the rhizosphere was only detected in compost-amended soil 2–10 days after plantation. A significantly-lower surface N2O flux of 0.4 ​mg ​m−2 d−1 was recorded with application of limed-digestate, probably due to its effects on nitrogen-transforming microorganisms. Both compost and limed-digestate enhanced plant growth, with a more distinct effect in the freshwater treatment. Our observations demonstrate that limed-digestate can be an efficient substitute for compost as it effectively supports plant growth with substantially-lower N2O emissions.

Impact of Integrating Annual and Perennial Legumes under Coffea arabica on Sloping Land

Above-ground biomass cover under Coffea arabica on sloping land is beneficial but difficult to sustain. Interplanting annual and perennial legumes can sustain the above-ground biomass cover, and improve soil fertility, yield, and profitability. This was tested on 26 sloping farms in a four-growing season experiment on undersowing C. arabica with new crop combinations: Mucuna pruriens var. utilis (T1); Millettia dura Dunn (T2); a combination of M. pruriens and M. dura (T3); and the control with a no-cover legume (T4). On each farm, all treatments followed a randomized single-block design. T3 produced 8.7 mt/ha/yr above-ground biomass that was significantly (p < 0.01) higher than other treatments and was increasing with the seasons. Under T3, plant-available nitrogen (N) and potassium (K) increased more than in other treatments. During the fourth season, coffee yield in T3 was 54%, 22%, and 11% higher than in T4, T2, and T1, respectively. The gross profit under T3 was 86% higher than in T4 in the fourth season. This indicates that interplanting a combination of M. pruriens and M. dura under C. arabica on sloping land can sustainably increase above-ground biomass cover, soil’s plant-available N and K, coffee yield, and profitability. Based on the results, the combination of M. pruriens and M. dura is recommended to optimize coffee production under the described conditions.

Plant nitrogen availability and crosstalk with phytohormones signallings and their biotechnology breeding application in crops.

Nitrogen (N), one of the most important nutrients, limits plant growth and crop yields in sustainable agriculture system, in which phytohormones are known to play essential roles in N availability. Hence, it is not surprising that massive studies about the crosstalk between N and phytohormones have been constantly emerging. In this review, with the intellectual landscape of N and phytohormones crosstalk provided by the bibliometric analysis, we trace the research story of best-known crosstalk between N and various phytohormones over the last 20 years. Then, we discuss how N regulates various phytohormones biosynthesis and transport in plants. In reverse, we also summarize how phytohormones signallings modulate root system architecture (RSA) in response to N availability. Besides, we expand to outline how phytohormones signallings regulate uptake, transport, and assimilation of N in plants. Further, we conclude advanced biotechnology strategies, explain their application, and provide potential phytohormones-regulated N use efficiency (NUE) targets in crops. Collectively, this review provides not only a better understanding on the recent progress of crosstalk between N and phytohormones, but also targeted strategies for improvement of NUE to increase crop yields in future biotechnology breeding of crops.

Nitrogen fertilizer driven nitrous and nitric oxide production is decoupled from microbial genetic potential in low carbon, semi-arid soil

IntroductionNitrous oxide (N2O) emission from soil is a major concern due to its contribution to global climate change and its function as a loss mechanism of plant-available nitrogen (N) from the soil. This is especially true in intensive agricultural soils with high rates of N fertilizer application such as those on the semi-arid Southern High Plains, USA.MethodsThis study examined emissions of N2O, pore-space concentrations of N2O and nitric oxide (NO), soil chemical properties, water content, and the genetic potential for N cycling five years after conservation system and N management implementation.ResultsFor these semi-arid soils with low N, carbon, and water contents, large soil N2O emissions (up to 8 mL N2O-N m-2 day-1) are directly related to the application of N fertilizer which overwhelms the N2O reducing capacity of the soil. When this fertilizer N is depleted, N2O flux is either low, non-existent, or net-negative and has been observed as early as mid-season for preplant applied N fertilizer (-0.1 mL N2O-N m-2 day-1). Soil pore-space gas concentrations (N2O and NO) remained relatively constant across the growing season (average N2O: 0.78 µL N2O L-1 soil air; NO: 3.3 µL NO L-1 soil air, indicating a base-level of N-cycle activity, but was not directly related to surface emissions of N2O which decreased across the growing season. In addition, genetic potential for N cycle activities increased across the growing season simultaneously with stagnant/reduced N cycle activity. This reflects the difficulty in relating genetic potential to in-situ activity in field research.ConclusionIt is likely that in a nutrient and carbon-poor soil, such as the semi-arid agricultural soil in this study, the microbial processes associated with N cycling are mostly limited by inorganic-N and less directly related to genetic potential at the time of sampling.

Local vehicles add nitrogen to moss biomonitors in a low-traffic protected wilderness area as revealed by a long-term isotope study

Public use of protected areas is typically encouraged, but visitors arriving by vehicles may alter the natural areas they seek. Vehicle emissions add nitrogen oxides (NOx) and ammonia (NH3) to the air, which can increase the amount of plant-available (reactive) nitrogen, a limiting nutrient. Changes in ecosystem processes as a result of increases in nitrogen availability are at odds with the goals of many protected wilderness areas that are typically accessed by vehicles. In this multi-year study (2003–2019), we tested whether emissions from local vehicles entered the forest ecosystem adjacent to a highway in a protected wilderness valley near a mid-sized city (Calgary, Alberta, Canada). We examined the concentration of NO2 in the air and the abundance of combustion-derived nitrogen isotopes (δ15N) in naturally-occurring forest moss (Hylocomium splendens and Pleurozium schreberi) within 20 m of the highway as a function of traffic levels that varied independently at two scales: along the highway and among years. Within the valley, we observed a gradient in the number of vehicles that was greatest where vehicles enter the valley, with a corresponding pattern for NO2 concentrations in air. Traffic volume also varied among years, with the highest year having almost twice as many vehicles in the summer as the lowest year. δ15N values in forest moss displayed similar patterns as traffic both within and among years, signalling that nitrogen from vehicle emissions entered the local ecosystem corresponding to local traffic levels. Because vehicle emissions enter natural ecosystems that are intended to be conserved, vehicle use must be considered in the management of protected natural areas.

Plasma-Treated Nitrogen-Enriched Manure Does Not Impose Adverse Effects on Soil Fauna Feeding Activity or Springtails and Earthworms Abundance

Plasma treatment of animal manure is a new technology, enriching the manure with plant-available nitrogen. Therefore, the product is termed nitrogen-enriched organic fertilizer (NEO). The producer (N2 Applied) claims that NEO can be a sustainable alternative to conventional fertilizers used in agriculture. However, the effect of this product on soil-dwelling organisms is unknown. This study investigates and compares the effects of NEO on changes in soil fauna feeding activity, the abundance of springtails, and the abundance and weight of earthworms to mineral fertilizer, organic fertilizer (cattle slurry), and no fertilizer in pot and field experiments with sandy clay loam soil. Early effect evaluation (week 7) indicated influences on soil fauna feeding activity; among treatments, higher amounts of fertilizers went along with lower feeding activity, regardless of fertilizer type. However, the initial fertilizer application stimulation was transient and stabilized with time after fertilization towards mid-term (week 14) and late effect evaluations (week 21). Accordingly, differences between feeding activities were less than five percent at late effect evaluation. Similarly, none of the fertilizers used imposed adverse effects on the abundance of springtails and the abundance and weight of earthworms; these parameters were almost identical among all fertilizing treatments. After two years of application in field trials and in a pot experiment, NEO and the other used fertilizers seem not to harm the selected soil-dwelling organisms.

Quantitative genetic analysis reveals potential to breed for improved white clover growth in symbiosis with nitrogen-fixing Rhizobium bacteria.

White clover (Trifolium repens) is integral to mixed pastures in New Zealand and temperate agriculture globally. It provides quality feed and a sustainable source of plant-available nitrogen (N) via N-fixation through symbiosis with soil-dwelling Rhizobium bacteria. Improvement of N-fixation in white clover is a route to enhancing sustainability of temperate pasture production. Focussing on seedling growth critical for crop establishment and performance, a population of 120 half-sibling white clover families was assessed with either N-supplementation or N-fixation via inoculation with a commercial Rhizobium strain (TA1). Quantitative genetic analysis identified significant (p < 0.05) family additive genetic variance for Shoot and Root Dry Matter (DM) and Symbiotic Potential (SP), and Root to Shoot ratio. Estimated narrow-sense heritabilities for above-ground symbiotic traits were moderate (0.24–0.33), and the strong (r ≥ 0.97) genetic correlation between Shoot and Root DM indicated strong pleiotropy or close linkage. The moderate (r = 0.47) phenotypic correlation between Shoot DM under symbiosis vs. under N-supplementation suggested plant growth with mineral-N was not a strong predictor of symbiotic performance. At 5% among-family selection pressure, predicted genetic gains per selection cycle of 19 and 17% for symbiotic traits Shoot DM and Shoot SP, respectively, highlighted opportunities for improved early seedling establishment and growth under symbiosis. Single and multi-trait selection methods, including a Smith-Hazel index focussing on an ideotype of high Shoot DM and Shoot SP, showed commonality of top-ranked families among traits. This study provides a platform for proof-of-concept crosses to breed for enhanced seedling growth under Rhizobium symbiosis and is informative for other legume crops.

Compost Composition and Application Rate Have a Greater Impact on Spinach Yield and Soil Fertility Benefits Than Feedstock Origin

Rapid urbanization results in the accumulation of food wastes that can be composted and diverted from landfills. Previous lab incubations demonstrated that food-based composts can increase soil N relative to manure-based composts, but these benefits were not tested within a crop system. We assessed soil fertility and yield of spinach (Spinacia oleracea L.) grown in two different soils in a greenhouse, comparing two food- and two manure-based composts added at the recommended N rate (101 kg N ha−1). We quantified soil N mineralization and resin-extractable phosphorus, spinach biomass (root and shoot), and crop nutrient concentrations and accumulation. Nitrogen mineralization generally peaked four weeks after application, and one food-based compost (but no manure-based composts) increased soil phosphorus at harvest compared to an unamended control. One manure-based compost and one food-based compost produced a higher yield and greater nitrogen, phosphorus, and potassium accumulation than the unamended control, whereas only the food-based compost increased spinach phosphorus and potassium concentrations. There was a positive relationship between yield and compost inputs of potassium and plant-available nitrogen (especially nitrate), suggesting that potassium inputs may also explain differences observed among composts. Our results suggest that food-based compost provides more nutrients than composts made from cow manure fiber.

Mineral nitrogen and microbial responses to soil heating in burned grassland

Fire is widely understood to be an important ecological process in grasslands around the world, but little research has been done on soil heating and nutrient and microbe responses to prescribed fire in the northern Great Plains of North America. We investigated plant-available nitrogen responses to soil heating in semi-arid grassland in southwestern North Dakota, USA. We sought to describe the range of temperatures reached at the soil surface and in the plant canopy during five prescribed burns, measure ammonium NH4+ and nitrate NO3- responses to soil heating, and explore relationships between soil heating, nutrient responses, and temperature profiles below the soil surface. We also used phospholipid fatty acid (PLFA) markers to measure soil microbial abundance and community composition responses to fire. We observed statistically-significantly higher NH4+ immediately (1 day) after burns and statistically-significantly higher NO3- 7 months after burns, which follows the pattern for each N species widely described in the literature. The abundance and community composition of soil microbes were both unchanged by fire. Soil heating models indicate that the highest temperatures (above 100°C) were limited to the top 2 cm. Together, these data suggest well-managed prescribed fire plays an important role in enhancing ecological function of managed grasslands by releasing nutrients and promoting nutrient cycling without contributing to soil degradation.

Printed Potentiometric Nitrate Sensors for Use in Soil.

Plant-available nitrogen, often in the form of nitrate, is an essential nutrient for plant growth. However, excessive nitrate in the environment and watershed has harmful impacts on natural ecosystems and consequently human health. A distributed network of nitrate sensors could help to quantify and monitor nitrogen in agriculture and the environment. Here, we have developed fully printed potentiometric nitrate sensors and characterized their sensitivity and selectivity to nitrate. Each sensor comprises an ion-selective electrode and a reference electrode that are functionalized with polymeric membranes. The sensitivity of the printed ion-selective electrodes was characterized by measuring their potential with respect to a commercial silver/silver chloride reference electrode in varying concentrations of nitrate solutions. The sensitivity of the printed reference electrodes to nitrate was minimized with a membrane containing polyvinyl butyral (PVB), sodium chloride, and sodium nitrate. Selectivity studies with sulphate, chloride, phosphate, nitrite, ammonium, calcium, potassium, and magnesium showed that high concentrations of calcium can influence sensor behavior. The printed ion-selective and reference electrodes were combined to form a fully printed sensor with sensitivity of −48.0 ± 3.3 mV/dec between 0.62 and 6200 ppm nitrate in solution and −47 ± 4.1 mV/dec in peat soil.