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Conservation agriculture (CA) has been proposed as a viable strategy to enhance soil health and the resilience of farms to climate change, and to support the sustainability of agricultural production systems. While CA is a well-established approach, research results are lacking regarding its long-term impact on nitrogen (N) dynamics in the soil–plant system. In this study, a 20-year experiment was used to investigate the long-term effects of no-tillage in CA on soil organic carbon (SOC) and nitrogen (N) mineralization, plant N uptake, grain yields, and the grain quality of durum wheat. A CA system based on no-tillage (NT) was evaluated and compared with conventional tillage (CT) used for wheat/legumes biennial crop rotation. Results showed that soil samples from CA plots experienced significantly more N mineralization than those under CT, which was attributed to increased SOC and N. Topsoil sampled from the CA plots 20 years after the implementation of the experiment had 43% more absolute potentially mineralizable N (N0) than the CT plots, with no significant differences observed in deeper soil layers (15–30 cm and 30–45 cm). The absolute potentially mineralizable carbon (C0) in soils from the CA system was 49% and 35% higher than in soils from the CT system, at soil depths of 0–15 and 15–30 cm, respectively. Furthermore, CA resulted in higher amounts of remobilized N and higher rates of N uptake during the critical growth stages of durum wheat. The amount of N remobilized during the kernel-filling phase under CA was 59% higher than under CT. Total N uptake in wheat plants was 45% greater under CA compared to CT. The most significant differences in N uptake between the CA and CT systems were observed during two critical growth stages: late tillering to heading (1.7 times higher in CA than CT) and heading to anthesis (1.5 times higher in CA than CT). The most significant differences for N uptake were shown during the late tillering to heading stage and the heading to anthesis stage. The amount of N remobilized during the kernel filling phase under CA was 59% higher than CT. CA adoption resulted in 21% and 35% higher grain and straw yields, respectively, compared to CT. The grain and straw N yields were 21% and 51% higher, respectively, under CA than CT. Moreover, the CA system exhibited higher partial factor productivity of nitrogen fertilizer (PFP N) for both grain and straw yields. Thousand kernel weight (TKW) and hectoliter weight were also significantly higher under CA than CT. The grain protein content, wet gluten content, vitreousness, and falling number were similar between the CA and CT systems. These results highlight the benefits of long-term CA adoption to increase soil N mineralization, providing a substantial base for N uptake during the critical growth stages of durum wheat, thus leading to increased crop yield. The findings underscore the potential of CA systems in promoting sustainable agriculture and mitigating the impacts of soil degradation. [ABSTRACT FROM AUTHOR]

Fertilization guidelines for organic watermelon transplant production are rare. We investigated the effect of four commercial organic fertilizers and seven organic fertilizer blends, along with one conventional fertilizer (Peter's Professional 20-20-20) on watermelon transplants. The four organic fertilizers were Nature Safe (fertilizer label: 7-7-7), Miracle-Gro (8-8-8), Dr. Earth fertilizer tea (4-4-4), and Drammatic (2-4-1). The seven blended organic fertilizers were created by supplementing Drammatic with nitrogen (N)-rich and/or potassium (K)-rich fertilizers to balance its N:phosphorus (P):K ratios. Watermelon 'Jubilee' was sown in organic substrate, and fertilizer treatments were applied weekly with a total of 0.4 g nitrogen/L substrate. Miracle-Gro and Drammatic had the highest N mineralization rate after 21 days and the highest inorganic N concentration, respectively, and resulted in the highest shoot dry weight among organic fertilizers. Miracle-Gro also resulted in the highest root dry weight. Dr. Earth fertilizer tea supplied the lowest N and P, and resulted in stunted transplants. Our results indicated that nitrate concentration was the most important factor influencing both shoot and root growth. Supplementing Drammatic with N-rich and/or K-rich fertilizers to balance its N:P:K ratio did not affect shoot and root dry weight. Combined, we concluded that nitrogen availability rather than nutrient balance is the key factor influencing watermelon transplant growth. [ABSTRACT FROM AUTHOR]

While the influence of canopy trees on soils in natural and restored forest environments is well studied, the influence of understory species is not. Here, we evaluate the effects of outplanted native woody understory on invasive grass biomass and soil nutrient properties in heavily grass-invaded 30 + year-old plantations of a native N-fixing tree Acacia koa in Hawai'i. We analyze soils from under A. koa trees with versus without planted woody understory and compare these to soils from under remnant pasture trees of the pre-deforestation dominant, Metrosideros polymorpha where passive recruitment of native woody understory has occurred since the cessation of grazing. Simultaneously, we experimentally planted understory species at three times the density used by managers to see if this could quickly decrease grass biomass and change soil nutrient dynamics. We found that invasive grass biomass declined with understory planting in surveyed and experimental sites. Yet, woody understory abundance had no effect on N cycling. Short-term N availability and nitrification potential were higher under A. koa than M. polymorpha trees regardless of understory. Net N mineralization either did not differ (~ 1 mo) between canopy species or was higher (171 day incubations) under remnant M. polymorpha where organic matter was also higher. The only influence of understory on soil was a positive correlation with loss-on-ignition (organic matter) under M. polymorpha. We also demonstrate differential controls over N cycling under the two canopy tree species. Overall, understory restoration has not changed soil characteristics even as invasive grass biomass declines. [ABSTRACT FROM AUTHOR]

Using predicted potential N mineralization (PNM) from its relationship with CO2 flush at 1 d incubation (CF) of soil samples in recommended N rates can reduce N fertilization rates for crops. This study used predicted PNM at the 0–15 cm depth to reduce N fertilization rates and examined spring wheat (Triticum aestivum L.) yields at two sites (Froid and Sidney) in Montana, USA. Cropping sequences at Froid were fall and spring till continuous spring wheat (FSTCW), no-till continuous spring wheat (NTCW1), no-till spring wheat–pea (Pisum sativum L.) (NTWP1), and spring till spring wheat–fallow (STWF). At Sidney, cropping sequences were conventional till spring wheat–fallow (CTWF), no-till spring wheat–fallow (NTWF), no-till continuous spring wheat (NTCW2), and no-till spring wheat–pea (NTWP2). Soil samples collected to a depth of 15 cm in September 2021 at both sites were analyzed for CF, PNM, and NO3-N contents, from which the reduction in N fertilization rate (RNFA) and the amount of N fertilizer applied (ANFA) to 2022 spring wheat were determined. In April 2022, spring wheat was grown with or without predicted PNM and annualized crop yields were compared. The CF and PNM were 114–137% greater for NTWP1 than STWF at Froid and 26–80% greater for NTCW2 than CTWF and NTWF at Sidney. The reduction in N fertilization rate was 26–102% greater for NTWP1 at Froid and 8–10% greater for NTCW2 and NTWF than other cropping sequences at Sidney. Annualized crop yield was 26–60% lower for crop–fallow than continuous cropping, but was not significantly different between with or without PNM at both sites. Using PNM can significantly reduce N fertilization rates for crops while sustaining dryland yields. [ABSTRACT FROM AUTHOR]

Background and aims: Several lines of evidence indicate that arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) associations can have different effects on soil nutrient dynamics. Some lineages of ECM fungi can extract N from organic matter, with varying impacts on decomposers, soil carbon pools, mineral N availability, and plants that lack ECM. However, these effects are not always observed, and it is not clear how they are mediated by environmental factors. Methods: We used Plant Root Simulator probes to compare soil availability of a wide range of nutrients beneath replicated 30-yr old plantations of Chilean Nothofagus (ECM) and Cupressaceae (Austrocedrus, Fitzroya: AM) on a lowland temperate site. Probes were buried for two 8-week periods in early spring and late summer. We also compared understorey composition beneath plantations, to test for evidence of different successional trajectories beneath Nothofagus and Cupressaceae. Results: Soil organic carbon, total N and total phosphorus did not differ significantly between Nothofagus and Cupressaceae stands. Redundancy analysis revealed significant effects of both plantation type (Nothofagus vs. Cupressaceae) and season on overall mineral nutrient availability. Mineral N availability did not differ significantly between Nothofagus and Cupressaceae plots, but pH and calcium availability were significantly lower beneath Nothofagus. Manganese (Mn) was much more available beneath Nothofagus stands, which might reflect abundant Mn-peroxidase, a key enzyme involved in breakdown of lignin by ECM fungi. Understorey composition varied considerably between individual plantations, but did not differ significantly between Nothofagus and Cupressaceae plantations. Conclusions: Despite an overall effect on the stoichiometry of nutrient availability, we found little evidence of modification of the local N cycle by ECM fungi, or of divergent regeneration patterns beneath AM and ECM plantations. This might reflect the relatively N-rich character of this site, and/or mycorrhizal effects being counteracted by leaf trait differences between Chilean Cupressaceae and Nothofagus species. [ABSTRACT FROM AUTHOR]

Using predicted potential N mineralization (PNM) from its relationship with CO2 flush at 1 d incubation (CF) of soil samples in recommended N rates can reduce N fertilization rates for crops. This study used predicted PNM at the 0–15 cm depth to reduce N fertilization rates and examined spring wheat (Triticum aestivum L.) yields at two sites (Froid and Sidney) in Montana, USA. Cropping sequences at Froid were fall and spring till continuous spring wheat (FSTCW), no-till continuous spring wheat (NTCW1), no-till spring wheat–pea (Pisum sativum L.) (NTWP1), and spring till spring wheat–fallow (STWF). At Sidney, cropping sequences were conventional till spring wheat–fallow (CTWF), no-till spring wheat–fallow (NTWF), no-till continuous spring wheat (NTCW2), and no-till spring wheat–pea (NTWP2). Soil samples collected to a depth of 15 cm in September 2021 at both sites were analyzed for CF, PNM, and NO3-N contents, from which the reduction in N fertilization rate (RNFA) and the amount of N fertilizer applied (ANFA) to 2022 spring wheat were determined. In April 2022, spring wheat was grown with or without predicted PNM and annualized crop yields were compared. The CF and PNM were 114–137% greater for NTWP1 than STWF at Froid and 26–80% greater for NTCW2 than CTWF and NTWF at Sidney. The reduction in N fertilization rate was 26–102% greater for NTWP1 at Froid and 8–10% greater for NTCW2 and NTWF than other cropping sequences at Sidney. Annualized crop yield was 26–60% lower for crop–fallow than continuous cropping, but was not significantly different between with or without PNM at both sites. Using PNM can significantly reduce N fertilization rates for crops while sustaining dryland yields.

To investigate the impact of pre-treating on mineralized nitrogen production, we carried out an anaerobic incubation following five pre-treatment sets: (1) 5 g soil/50 ml water (Control), (2) 5 g soil/50 ml water/80℃/ 4 hours (Hot water), (3) 2.5 g soil/50 ml water/80℃/4 hours + 2.5 g soil (Mixed hot water), (4) 5 g soil/ 50 ml water/ultrasound 37 Hz/30 minutes (Ultrasound), and (5) 2.5 g soil/50 ml water/ultrasound 37 Hz/30 minutes + 2.5 g soil (Mixed ultrasound). Inorganic nitrogen was extracted before incubation (Initial In-N) and after 4 weeks of anaerobic incubation (Total Min-N and Net Min-N). The results reveal that Initial In-N ranged from 21.8 to 23.5 mg N/kg and was similar among four pre-treatment methods. Interestingly, Net Min-N was promoted by heating hot water; meanwhile, ultrasound pre-treatment did not enhance soil mineralization potential. This indicates that pre-treating soil with hot water could be a promising method to enhance soil nitrogen mineralization.

Efficient water management is critical to sustainable crop production in arid and semi-arid southwestern United States. A study was designed to evaluate the variations in soil water content (SWC) and nitrogen (N) dynamics within the 0–100 cm soil profile and forage maize (Zea mays L.) and sorghum (Sorghum bicolor) yields in winter cover crop integrated crop rotations in a semi-arid environment using a Root Zone Water Quality Model (RZQWM2). The cover cropping treatments were no cover crop (NCC), a mixture of grasses, brassicas, and legumes (GBL), a mixture of grasses and brassicas (GB), and a mixture of grasses and legumes (GL) under maize and sorghum silage production. The root mean square error (RMSE), index of agreement (d), and Nash-Sutcliffe model efficiency coefficient (NSE) were used to evaluate the effectiveness and efficiency of the model. The observations and simulations showed that the soil water content was greater and soil temperature was lower under cover crops than under NCC. Simulated N mineralization in maize and sorghum with cover cropping was 41.1–44.2 % and 41.9–42.3 % greater than NCC. Also, the model simulated that cover crops improved the plant N uptake by 15.4–17.3 % in maize and 13.6–14.7 % in sorghum compared to NCC. Simulated aboveground biomass yields of maize and sorghum were 8.11–24.2 % and 5.68–21.3 % greater with cover crops than with NCC. Integrating cover crops in maize and sorghum silage production systems can conserve soil water and improve N uptake, increasing silage yield under semi-arid irrigated conditions in the southwestern United States.

Sewage sludge can be used as an organic amendment as long as it is ensured that there is no risk of environmental contamination or risk to public health. In this study, sewage sludge from two wastewater treatment plants (WWTPs) subjected to two disinfection and stabilization treatments [40% (mass/mass), calcium oxide, and calcium hydroxide] and their respective untreated sewage sludge were used. Three control treatments were also added: conventional farmyard manure (FYM), a nitrogen (N) mineral fertilizer (ammonium nitrate 34.5% N) applied at a rate of 50 kg N ha−1 (N50) (the same rate of all organic amendments), and an unfertilized control (N0), totaling nine treatments. Lettuce (Lactuca sativa L.) was cultivated in pots for two growing cycles. The dry matter yield (DMY) was higher in the N50 treatment (13.5 and 10.6 g plant−1 in the first and second growing cycles, respectively), followed by sewage sludge (10.8 to 12.4 and 8.4 to 8.7 g plant−1), FYM (8.5 and 7.2 g plant−1), and the control (7.7 and 6.0 g plant−1). The DMY was related to the N provided by the different treatments, assessed by the N and nitrate concentrations in tissues, N uptake, and apparent N recovery (ANR). Sewage sludge, due to its high N concentration and low carbon (C)/N ratio, mineralized rapidly, providing a significant amount of N to plants, as well as other nutrients, such as phosphorus (P) and boron (B). FYM, with a higher C/N ratio, provided less N to plants, also due to the short duration of the lettuce growing cycle. Alkalized sewage sludge increased soil pH and calcium (Ca) availability for plants. Fertilizer treatments minimally influenced cationic micronutrients. Heavy metals in the initial sewage sludge were below the threshold values established in international legislation, and the levels in soil and lettuce tissues were generally not higher than those in other treatments. Both of the sewage sludges used in this study showed high fertilizing value and very reactive behavior, making nutrients available much more quickly than FYM. This information is relevant to consider in defining their agricultural use. [ABSTRACT FROM AUTHOR]

Rhizosphere environments play a vital role in the nutrient cycling of crops and soil organic nitrogen mineralization. Sugar beet is a highly nitrogen (N)-demanding crop, and it is necessary to explore the relationship between the sugar beet root exudates, the microbial community, and nitrogen utilization. In this study, a special separation method was employed to create rhizosphere (H3) and non-rhizosphere (H2 and H1) environments for sugar beet. After 50 d of cultivation in nearly inorganic-free soil, the microbial diversity and its correlation with root metabolites and N were examined. The results showed that in H3, the inorganic N content was over 23 times higher than in H1 and H2, with a 13.1% higher relative abundance of ammonia-oxidizing bacteria compared to H2 and a 32% higher abundance than H1. The relative abundance of nitrite-oxidizing bacteria was also 18.8% higher than in H1. Additionally, a significant positive correlation was observed between inorganic nitrogen content and serine (Ser) and isoleucine (Ile). The organic nitrogen content exhibited positive correlations with glycine (Gly), alanine (Ala), and tyrosine (Tyr) but displayed negative correlations with certain amino acids, organic acids, and glucose. The co-linearity network indicated that the microbial composition in H3 also exhibited higher node connectivity. It can be inferred that under the influence of sugar beet root exudates, the changes in the rhizosphere's microbial diversity were more intricate, thereby benefiting soil nitrogen cycling and inorganic N accumulation. These findings provide profound insight into sugar beet soil organic nitrogen mineralization and contribute to the sustainable and environmentally friendly development of modern agriculture. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Guangxi Normal University - Natural Science Edition is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To predict the mineralization of nitrogen(N) in organic amendments in paddy fields, we applied data obtained from incubation experiments under waterlogged conditions by a hierarchical Bayesian model using acid-detergent-soluble organic N (ADSON) as a model input. Each of 20 organic amendments (6 cattle manure composts, 3 swine manure composts, 3 poultry manure composts, 2 oil cakes, 2 rice brans, 1 fish meal, 1 sludge fertilizer, and 2 mixed commercial organic fertilizers) was mixed with paddy soil, and the N mineralization curves obtained after 1, 2, 4, 8, and 12 weeks of waterlogging were incorporated into the model to obtain values of the model parameters ki, α1, and Q10. All model parameters converged with a mean absolute error (MAE) of 0.044 g N kg−1, a root mean square error (RMSE) of 0.060 g N kg−1, and a model efficiency (EF) of 0.96. These values were comparable to or slightly better than those of a previous model for upland soil conditions. Most of the observed values were within the 95% Bayesian prediction interval, indicating that the model performed well with the observed data. Although it is generally believed that livestock manure composts decompose more slowly than organic fertilizers such as oil cake, the livestock manure composts had a large value of the rate constant ki, presumably because of the initial rapid decomposition of the small amounts of organic N present in them. In paddy fields, the soil conditions are aerobic between the application of organic amendments and water entry. In such a case, we propose the use of the upland field model to predict the mineralization of organic N during the period of aerobic soil conditions and of this study's model during the period of waterlogging, subtracting the amount of already mineralized N from the parameters Nin and ADSON. The model devised here is expected to be useful for fertilization design in organic agriculture and in the reduction of the use of inorganic fertilizer. [ABSTRACT FROM AUTHOR]

The management of understory vegetation and anthropogenic nitrogen (N) deposition has significantly resulted in a nutrient imbalance in forest ecosystems. However, the effects of canopy nitrogen addition and understory vegetation removal on N transformation processes (mineralization, nitrification, ammonification, and leaching) along with seasonal variations (spring, summer, autumn, and winter) remain unclear in subtropical forests. To fill this research gap, a field manipulation experiment was conducted with four treatments, including: (i) CK, control; (ii) CN, canopy nitrogen addition (25 kg N ha−1 year−1); (iii) UR, understory vegetation removal; and (iv) CN+UR, canopy nitrogen addition plus understory vegetation removal. The results revealed that CN increased net mineralization and nitrification by 294 mg N m−2 month−1 in the spring and 126 mg N m−2 month−1 in the winter, respectively. UR increased N mineralization and nitrification rates by 618 mg N m−2 month−1 in the summer. In addition, CN effectively reduced N leaching in the spring, winter, and autumn, while UR increased it in the spring and winter. UR increased annual nitrification rates by 93.4%, 90.3%, and 38.9% in the winter, spring, and summer, respectively. Additionally, both net N ammonification and annual nitrification rates responded positively to phosphorus availability during the autumn. Overall, UR potentially boosted nitrification rates in the summer and ammonification in the spring and winter, while CN reduced N leaching in the spring, winter, and autumn. Future research should integrate canopy nitrogen addition, understory vegetation removal, and phosphorus availability to address the global N deposition challenges in forest ecosystems. [ABSTRACT FROM AUTHOR]

Sewage sludge should primarily find use in agriculture, reducing the quantity directed towards alternative disposal methods like incineration or deposition in municipal landfills. This study evaluated the agronomic value and the risk of soil and plant tissue contamination with heavy metals in sewage sludge obtained from two wastewater treatment plants (WWTP). The experiment was arranged as a 2 × 5 factorial (two sewage sludges, five sanitation treatments), involving lettuce cultivation in pots over two growing cycles. The two sewage sludges were sourced from the WWTPs of Gelfa and Viana do Castelo and underwent five sanitation and stabilization treatments (40% and 20% calcium oxide, 40% and 20% calcium hydroxide, and untreated sewage sludge). The Gelfa sewage sludge, characterized by a higher initial nitrogen (N) concentration, resulted in greater dry-matter yield (DMY) (12.4 and 8.6 g plant−1 for the first and second growing cycles, respectively) compared to that from Viana do Castelo (11.0 and 8.1 g plant−1), with N release likely being a major factor influencing crop productivity. The high N concentration and the low carbon (C)/N ratio of sewage sludge led to rapid mineralization of the organic substrate, which additionally led to a higher release of other important nutrients, such as phosphorus (P) and boron (B), making them available for plant uptake. Alkalizing treatments further stimulated sewage sludge mineralization, increasing soil pH and exchangeable calcium (Ca), thereby enhancing Ca availability for plants, and indicating a preference for use in acidic soils. Cationic micronutrients were minimally affected by the sewage sludge and their treatments. The concentrations of heavy metals in the sewage sludge, soils, and lettuce tissues were all below internationally established threshold limits. This study highlighted the high fertilizing value of these sewage sludges, supplying N, P, and B to plants, while demonstrating a low risk of environmental contamination with heavy metals. Nevertheless, the safe use of sewage sludge by farmers depends on monitoring other risks, such as toxic organic compounds, which were not evaluated in this study. [ABSTRACT FROM AUTHOR]

Problems of salt-affected soils can be alleviated by organic amendments, but their nitrogen (N) mineralization pattern, crucial to providing proper N synchronization with crop demand, can differently be influenced by salinity and sodicity. An incubation study was carried out objectively to investigate the mineralization and kinetic release of N in three organic wastes (OWs) – rice husk (RH), rice straw (RS), burnt rice husk (BRH) in saline-sodic (SS) and sodic (Sod) soils. The OWs were mixed into the soils and inorganic N was measured under aerobic condition (field capacity) for 28 days followed by waterlogged condition until day-112. The mineral N mineralized from all OWs was, on average, <20% of N input released into the mineral N pool with RS mineralized the highest. Mineralization occurred less in SS than in Sod soil. Nitrogen mineralization peaked at 28 days with net immobilization observed after 21-day of waterlogged condition. The mineralization rate and mineralizable N pool of these OWs had a better fit to two-pool than first-order model, showing the highest quantities in respective RS, RH and BRH and fast N pools constant rate greater in SS than in Sod soils. Net N mineralization differed among OWs, soils and incubation times. The N mineralization pattern of OWs was a function of both N sources and soil salinity. The pool and rate of mineralizable N were predicted from the initial material's total N. The findings can lead to proper N management for jasmine rice in salt-affected soils using inorganic wastes to partially supply N. [ABSTRACT FROM AUTHOR]

Soil organic nitrogen (N) mineralization not only supports ecosystem productivity but also weakens carbon and N accumulation in soils. Recalcitrant (mainly mineral‐associated organic matter) and labile (mainly particulate organic matter) organic materials differ dramatically in nature. Yet, the patterns and drivers of recalcitrant (MNrec) and labile (MNlab) organic N mineralization rates and their consequences on ecosystem N retention are still unclear. By collecting MNrec (299 observations) and MNlab (299 observations) from 57 15N tracing studies, we found that soil pH and total N were the master factors controlling MNrec and MNlab, respectively. This was consistent with the significantly higher rates of MNrec in alkaline soils and of MNlab in natural ecosystems. Interestingly, our analysis revealed that MNrec directly stimulated microbial N immobilization and plant N uptake, while MNlab stimulated the soil gross autotrophic nitrification which discouraged ammonium immobilization and accelerated nitrate production. We also noted that MNrec was more efficient at lower precipitation and higher temperatures due to increased soil pH. In contrast, MNlab was more efficient at higher precipitation and lower temperatures due to increased soil total N. Overall, we suggest that increasing MNrec may lead to a conservative N cycle, improving the ecosystem services and functions, while increasing MNlab may stimulate the potential risk of soil N loss. [ABSTRACT FROM AUTHOR]

Biochar is a promising material to improve soil quality. Effects of coconut shell biochar on tropical soil nitrogen mineralization and microbial community were less reported. The incubation experiment was conducted to observe the required effects. Biochar rates in latosol were 0%, 1%, 2% and 5% (w/w), respectively. Results showed: (1) soil pH and CEC improved with biochar rate; (2) urease activity was increased at the lower biochar rate (<2%) but reduced at the 5% rate, while acid phosphatase activity was not changed by biochar; (3) biochar addition reduced soil microbial diversity. The bacterial population like Proteobacteria, Gemmatimonadetes, Planctomycetes, Verrucomicrobia and Bacteroidetes enhanced by more biochar addition, while Actinobacteria and Chloroflexi were found less at the high biochar rate. Fungal strains like Ascomycota decreased by biochar addition, but Basidiomycota and Chytridiomycota increased at high biochar rates. Genus of Haematonectria, Chaetomium, Gibberella, Aspergillus, Fusarium and Eupenicillium decreased effectively under biochar addition; (4) soil nitrogen mineralization with biochar amendment was described well by the exponential model (R2>0.95, P<0.01), but soil nitrogen mineralization potential was found to be less due to biochar application. Thus, the addition of biochar derived from coconut shells had positive effects on soil characteristics, microorganisms, and nitrogen mineralization. [ABSTRACT FROM AUTHOR]

Invasive plants often alter ecosystem function and processes, especially soil N cycling. In eastern United States forests, the shrub Rosa multiflora ("rose") is a dominant invader, yet potential effects on N cycling are poorly understood. Moreover, invasive plant management can impact soil N cycling by decreasing plant N uptake and disturbing the soil. The objectives of this study were to evaluate N cycling along a gradient of rose invasion (observational) and investigate potential changes to N cycling (manipulative) under four different management strategies: (1) do nothing (the control), (2) invasive plant removal, (3) removal followed by native seed mix addition, (4) removal, native seed mix, and chipped rose stem addition. We selected three forest sites experiencing a Low, Medium, or High amount of shrub invasion, and measured N cycling in the early (June) and late (September) growing seasons. We found N was immobilized in June and mineralized in September. One year after experimental management, removal alone had no effect on N cycling compared to control plots, but addition of native seed mix and chipped stems reduced early-season nitrification in our Medium invasion site. Our findings suggest that rose invasion may increase N cycling rates when soils are dry, which may occur more frequently with future climate change. In addition, N cycling responds differentially to management in the year following invasive plant removal, but most noticeably under moderate rose invasion. [ABSTRACT FROM AUTHOR]

Summary: High‐latitude ecosystems are warming faster than other biomes and are often dominated by a ground layer of Ericaceous shrubs, which can respond positively to warming. The carbon‐for‐nitrogen (C‐for‐N) exchange between Ericaceous shrubs and root‐associated fungi may underlie shrub responses to warming, but has been understudied.In a glasshouse setting, we examined the effects of warming on the C‐for‐N exchange between the Ericaceous shrub Empetrum nigrum ssp. hermaphroditum and its root‐associated fungi. We applied different 13C and 15N isotope labels, including a simple organic N form (glycine) and a complex organic N form (moss litter) and quantified their assimilation into soil, plant biomass, and root fungal biomass pools.We found that warming lowered the amount of 13C partitioned to root‐associated fungi per unit of glycine 15N assimilated by E. nigrum, but only in the short term. By contrast, warming increased the amount of 13C partitioned to root‐associated fungi per unit of moss 15N assimilated by E. nigrum.Our study suggests that climate warming affects the short‐term exchange of C and N between a widespread Ericaceous shrub and root‐associated fungi. Furthermore, while most isotope tracing studies use labile N sources, we demonstrate that a ubiquitous recalcitrant N source may produce contrasting results. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fertilization guidelines for organic watermelon transplant production are rare. We investigated the effect of four commercial organic fertilizers and seven organic fertilizer blends, along with one conventional fertilizer (Peter’s Professional 20-20-20) on watermelon transplants. The four organic fertilizers were Nature Safe (fertilizer label: 7-7-7), Miracle-Gro (8-8-8), Dr. Earth fertilizer tea (4-4-4), and Drammatic (2-4-1). The seven blended organic fertilizers were created by supplementing Drammatic with nitrogen (N)-rich and/or potassium (K)-rich fertilizers to balance its N:phosphorus (P):K ratios. Watermelon ‘Jubilee’ was sown in organic substrate, and fertilizer treatments were applied weekly with a total of 0.4 g nitrogen/L substrate. Miracle-Gro and Drammatic had the highest N mineralization rate after 21 days and the highest inorganic N concentration, respectively, and resulted in the highest shoot dry weight among organic fertilizers. Miracle-Gro also resulted in the highest root dry weight. Dr. Earth fertilizer tea supplied the lowest N and P, and resulted in stunted transplants. Our results indicated that nitrate concentration was the most important factor influencing both shoot and root growth. Supplementing Drammatic with N-rich and/or K-rich fertilizers to balance its N:P:K ratio did not affect shoot and root dry weight. Combined, we concluded that nitrogen availability rather than nutrient balance is the key factor influencing watermelon transplant growth.

To investigate the dynamic changes of nitrogen mineralization of tobacco-planting soil in central Henan and explore the response characteristics of soil microbial diversity and nitrogen cycle function genes to soil moisture condition, the tobacco-planting soil from Xuchang were cultured under 50% (H-50%), 65% (H-65%), 80% (H-80%) water conditions to analyze the difference of functional diversity of bacterial and fungal communities. The results showed that the mineralization amount and mineralization rate of soil inorganic nitrogen in H-65% treatment were higher than those in other treatments. Proteobacteria, Actinobacteria, Chloroflexi, Firmicutes, Acidobacteria, Planctomycotes, and Germatimonades were the dominant bacteria at phylum level relative abundance >3%). The relative abundance of Proteus in H-80% treatment was significantly higher than other treatments, while the relative abundance of Firmicutes was vice versa. The relative abundances of Actinomyces and Curvularia in H-50% treatment were significantly higher than those in other treatments. Ascomycota accounted for more than 90% of the fungal OTUs (operational taxonmic units), and its relative abundance showed an inverted "V" trend with the increasing of soil moisture content. The results of LEfSe (LDA effect size) analysis for bacterial showed that 6 active biomarkers (LDA value >3.5) were detected at the genus level. The bacterial community showed abundant functional diversity, the primary functional layer was more active in metabolism, and the functional gene abundance of the secondary functional layer changed obviously under different water content conditions. The relative abundances of nifK, nifD, nifH genes involved nitrogen fixation process showed H-50%>H-65%>H-80%, and the relative abundances of norB, nirK, nosZ genes involved denitrification process were the highest in H-65% treatment. Collectively, the reasonable regulation of soil moisture content might effectively regulate the dynamic change of soil nitrogen mineralization, the functional diversity of soil microbial community and the change of functional genes relating to nitrogen cycle in central Henan tobacco growing areas. [ABSTRACT FROM AUTHOR]

Soil mineral nitrogen is an important component of soil nitrogen, plays an important role in the transformation of soil nitrogen, and is a major indicator reflecting soil fertility, mainly including nitrate nitrogen and ammonium nitrogen. The accumulation of soil mineral nitrogen is closely related to soil microorganisms, fertilization, temperature, water, tillage and land use. The loss of soil mineral nitrogen may cause the decline of soil fertility, the eutrophication of surface water and the release of nitrous oxide, which will lead to the greenhouse effect and ultimately affect the survival and development of human beings. This paper summarized the composition and source of soil mineral nitrogen, the factors affecting nitrogen mineralization, the extraction and testing of mineral nitrogen, and the impact on the environment, and compared various testing methods in order to provide a basis for the study of soil mineral nitrogen. [ABSTRACT FROM AUTHOR]

Aims: Kura clover living mulch (KCLM) is thought to provide in-season nitrogen (N) to the cash crop. Because of interactions between cropping system and crop performance, the magnitude of in-season N inputs from KCLM cannot be quantified using common N rate research methods. We aim to quantify the timing and magnitude of these N inputs using clover biomass and decomposition data. Methods: This research measured the temporal distribution of clover biomass with intensive sampling, vertical biomass distribution using bead tracer analysis, and residue decomposition using in situ litter bags. These data were used as inputs to a model that estimated the in-season N contributions from KCLM. Results: Our results found that spring management contributed 7–23 kg N ha−1 during the first 6 weeks of the growing season, while shade suppression contributed 59 – 84 kg N ha−1 from mid-June to mid-October. Daily N inputs peaked on 8 August at 1.14 kg N ha−1 d−1. When these estimates were added to fertilizer N inputs and analyzed against crop N uptake, we found that the maize took up 88% of the total N inputs and fertilizer recovery efficiency was 56%. Conclusions: This study provides a methodology which generates estimates that may be used in research related to N cycling and management in KCLM and other legume intercropping systems. [ABSTRACT FROM AUTHOR]

Nitrohumic acids (NHAs) are considered as promising slow-release N fertilizers. In this study, NHA was produced from six organic feedstocks, including coal, leonardite, municipal waste compost, sewage sludge, and apple and beech biochars via nitration using nitric acid. The nitration process was conducted in two ways: (i) after humic acid (HA) extraction (NHAD), and (ii) before HA extraction (NHAID). The prepared NHAs were then characterized using FT-IR and CHNS analysis. Additionally, N mineralization of NHAs was investigated in a sandy loam soil sample. The FT-IR spectra showed that both methods of nitration loaded nitro (NO2) groups into the HA structure. However, the CHNS analysis indicated the highest rate of N increase for NHAD (106%) and NHAID (113%) extracted from leonardite. Moreover, on average, the total acidity and carboxylic groups of the HAs increased by 7.5% and 14.5% after the nitration processes, respectively. The highest extraction yields of NHAD (26.1%) and NHAID (42.1%) were also obtained from leonardite. Although the extraction yield of NHAID was on average two times higher than that of NHAD, NHAD indicated a higher soil N availability (1.4 times). We concluded that the NHAD extracted from leonardite could be considered as an alternative slow-release N fertilizer. [ABSTRACT FROM AUTHOR]

Nitrate nitrogen (nitrate-N) is crucial for the development of tobacco quality. However, how to enhancing soil nitrification in tobacco plantation is still an immediate concern that requires attention. This study aimed to examine the impact of mixed organic manure on soil nitrification in tobacco cultivation regions. We selected an Ultisols field, which was planted with tobacco from Yunnan province, to explore the impact of adding various organic manures (F1-F6: regular organic manures, F7: mixed organic compost which was derived from crop residues), on soil gross N mineralization and nitrification. This study was conducted through a 75-day indoor leaching experiment, with constant temperature (25°C) and humidity (65% of field water capacity). The results showed that F4 significantly (p <.05) enhanced soil N mineralization, and had the highest mineralized-N and potentially releasable mineralized-N (N0) due to its highest organic carbon (OC) and total-N, which amounted to 422 mg kg−1 and 705.7 mg kg−1, respectively. F7 exhibited a significant increase (p <.05) in the rate of soil N mineralization, with the highest first-order mineralization rate constant (k1) of 0.090 d−1. Moreover, it displayed a substantial increase (p <.05) in nitrate-N content and potentially releasable nitrate-N (Np), measuring 41.5 mg kg−1 and 41.3 mg kg−1, respectively. Furthermore, F7 exhibited the highest first-order nitrification rate constant (k2) of 0.076 d−1. It also demonstrated a considerably higher net nitrate-N/mineralized-N ratio of 33.5%, which was significantly (p <.05) greater than that of F1-F6 (nitrate-N/mineralized-N ratio: −7.06 to 1.86%). At day 15 and day 45, F7 exhibited the highest nitrate-N concentration and nitrate-N/mineralized-N ratio (28.1 mg kg−1 and 49.7%) in comparison to F1-F6, which had lower nitrate-N concentrations (ranging from 0.4 to 6.9 mg kg−1) and nitrate-N/mineralized-N ratios (ranging from 0.4 to 11.9%). These results indicate that the addition of mixed organic compost significantly enhances soil nitrification compared to regular organic manures. Therefore, it suggests that incorporating mixed organic compost improves soil nitrification in Ultisols. [ABSTRACT FROM AUTHOR]

Agricultural crops grown in the irrigated semi-arid region of southern Idaho account for almost two-thirds of the median household income in the region. The impacts of climate change on cropping systems and the availability of water for irrigation would be a serious challenge for the state's economic dependence on agriculture. The objective of the study was to simulate the future impact of climate change on a crop rotation of spring wheat-potato-spring barley-sugarbeet grown in the semi-arid region of southern Idaho using conventional management practices and a high dairy manure application. The Root Zone Water Quality Model (RZWQM2) simulations used bias-corrected and spatially disaggregated projections from the World Climate Research Program's coupled model inter-comparison project phase 5 to generate 40 GCM projections for the time from 2071-2099. The 28-yr scenarios were designed to simulate the impact of temperature and CO2 regimes on crop production, soil nitrogen mineralization, nitrogen seepage, deep seepage of water, and nitrous oxide emissions. Data from a field experiment in southern Idaho with conventional fertilizer practices and annual applications of 52 Mg ha-1 dairy manure with a crop rotation of spring wheat-potato-spring barley-sugarbeet were used in the RZWQM2 simulations. Results were compared to a baseline scenario of conventional management practices, historical weather data, and ambient CO2. Spring wheat yield increased by 22% and 16% for manure and fertilizer treatments, respectively, compared to the baseline scenario. Using the same comparison, potato tuber yield decreased by 65% and 60% in the manure and fertilizer treatments, respectively, for the highest temperature and CO2 increase scenarios. Spring barley produced a 33% higher yield with increased temperature and CO2. However, yield decreased when temperature increased, but CO2 remained unchanged. Sugarbeet yields decreased by 16% and 18% for manure and fertilizer treatments, respectively, compared to the baseline scenario. Nitrogen mineralization, N seepage from the profile, and nitrous oxide emissions were strongly influenced by the manure applications, and there was little simulated impact of climate change on these processes. These simulation results indicate that genetic enhancements or alternative management will be needed to maintain potato and sugar beet production levels in semi-arid areas, while spring barley and wheat yields may increase, assuming adequate irrigation water supplies are available. [ABSTRACT FROM AUTHOR]

Background and aims: Cover crops are an integral constituent of sustainable subtropical agroecosystems. Using grass/legume mixtures as opposed to monocultures has the potential to maximize their multifunctionality. This project aimed to understand temporal patterns of nitrogen (N) release of cover crop monocultures and mixtures in a subtropical vegetable production system. Methods: A litterbag experiment was established to study N release patterns of two commonly used grasses, two legumes, four two-species mixture each with one grass and one legume, and one four-species mixture. This field experiment was complemented by two laboratory incubations to quantify soil N mineralization after the termination of cover crops in 2020 and 2021. Results: The majority of residue N (> 60%) was lost in the first month of decomposition, suggesting no or minimal N release from cover crops beyond one cropping season. Mixtures enhanced N release relative to monocultures within the first two months; however, the timing of this synergistic effect depended on grass species in the mixture. Initial residue N concentration reasonably predicted the N loss trajectory of all residue types (r = -0.72; p < 0.05). Legumes showed the highest N mineralization rate, followed by mixtures and lastly grasses. Conclusions: Our findings reveal significant temporal variability in N release among different cover crop mixtures, despite the rapid decomposition across all cover crop treatments. Selection of appropriate species in cover crop mixtures helps to facilitate the synchronization of N release and crop update in subtropical systems where N management is extremely time sensitive. [ABSTRACT FROM AUTHOR]

Boreal forests harbor as much carbon (C) as the atmosphere and significant amounts of organic nitrogen (N), the nutrient most likely to limit plant productivity in high‐latitude ecosystems. In the boreal biome, the primary disturbance is wildfire, which consumes plant biomass and soil material, emits greenhouse gasses, and influences long‐term C and N cycling. Climate warming and drying is increasing wildfire severity and frequency and is combusting more soil organic matter (SOM). Combustion of surface SOM exposes deeper older layers of accumulated soil material that previously escaped combustion during past fires, here termed legacy SOM. Postfire SOM decomposition and nutrient availability are determined by these layers, but the drivers of legacy SOM decomposition are unknown. We collected soils from plots after the largest fire year on record in the Northwest Territories, Canada, in 2014. We used radiocarbon dating to measure Δ14C (soil age index), soil extractions to quantify N pools and microbial biomass, and a 90‐day laboratory incubation to measure the potential rate of element mineralization and understand patterns and drivers of legacy SOM C decomposition and N availability. We discovered that bulk soil C age predicted C decomposition, where cumulatively, older soil (approximately −450.0‰) produced 230% less C during the incubation than younger soil (~0.0‰). Soil age also predicted C turnover times, with old soil turnover 10 times slower than young soil. We found respired C was younger than bulk soil C, indicating most C enters and leaves relatively quickly, while the older portion remains a stable C sink. Soil age and other indices were unrelated to N availability, but microbial biomass influenced N availability, with more microbial biomass immobilizing soil N pools. Our results stress the importance of legacy SOM as a stable C sink and highlight that soil age drives the pace and magnitude of soil C contributions to the atmosphere between wildfires. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rhizosphere environments play a vital role in the nutrient cycling of crops and soil organic nitrogen mineralization. Sugar beet is a highly nitrogen (N)-demanding crop, and it is necessary to explore the relationship between the sugar beet root exudates, the microbial community, and nitrogen utilization. In this study, a special separation method was employed to create rhizosphere (H3) and non-rhizosphere (H2 and H1) environments for sugar beet. After 50 d of cultivation in nearly inorganic-free soil, the microbial diversity and its correlation with root metabolites and N were examined. The results showed that in H3, the inorganic N content was over 23 times higher than in H1 and H2, with a 13.1% higher relative abundance of ammonia-oxidizing bacteria compared to H2 and a 32% higher abundance than H1. The relative abundance of nitrite-oxidizing bacteria was also 18.8% higher than in H1. Additionally, a significant positive correlation was observed between inorganic nitrogen content and serine (Ser) and isoleucine (Ile). The organic nitrogen content exhibited positive correlations with glycine (Gly), alanine (Ala), and tyrosine (Tyr) but displayed negative correlations with certain amino acids, organic acids, and glucose. The co-linearity network indicated that the microbial composition in H3 also exhibited higher node connectivity. It can be inferred that under the influence of sugar beet root exudates, the changes in the rhizosphere’s microbial diversity were more intricate, thereby benefiting soil nitrogen cycling and inorganic N accumulation. These findings provide profound insight into sugar beet soil organic nitrogen mineralization and contribute to the sustainable and environmentally friendly development of modern agriculture.

Sewage sludge can be used as an organic amendment as long as it is ensured that there is no risk of environmental contamination or risk to public health. In this study, sewage sludge from two wastewater treatment plants (WWTPs) subjected to two disinfection and stabilization treatments [40% (mass/mass), calcium oxide, and calcium hydroxide] and their respective untreated sewage sludge were used. Three control treatments were also added: conventional farmyard manure (FYM), a nitrogen (N) mineral fertilizer (ammonium nitrate 34.5% N) applied at a rate of 50 kg N ha−1 (N50) (the same rate of all organic amendments), and an unfertilized control (N0), totaling nine treatments. Lettuce (Lactuca sativa L.) was cultivated in pots for two growing cycles. The dry matter yield (DMY) was higher in the N50 treatment (13.5 and 10.6 g plant−1 in the first and second growing cycles, respectively), followed by sewage sludge (10.8 to 12.4 and 8.4 to 8.7 g plant−1), FYM (8.5 and 7.2 g plant−1), and the control (7.7 and 6.0 g plant−1). The DMY was related to the N provided by the different treatments, assessed by the N and nitrate concentrations in tissues, N uptake, and apparent N recovery (ANR). Sewage sludge, due to its high N concentration and low carbon (C)/N ratio, mineralized rapidly, providing a significant amount of N to plants, as well as other nutrients, such as phosphorus (P) and boron (B). FYM, with a higher C/N ratio, provided less N to plants, also due to the short duration of the lettuce growing cycle. Alkalized sewage sludge increased soil pH and calcium (Ca) availability for plants. Fertilizer treatments minimally influenced cationic micronutrients. Heavy metals in the initial sewage sludge were below the threshold values established in international legislation, and the levels in soil and lettuce tissues were generally not higher than those in other treatments. Both of the sewage sludges used in this study showed high fertilizing value and very reactive behavior, making nutrients available much more quickly than FYM. This information is relevant to consider in defining their agricultural use.

Rising global temperatures have the potential to increase soil nitrogen (N) mineralization from soil organic matter (SOM). By increasing SOM over time, management practices that increase SOM through the addition of soil amendments, such as compost, have been recognized as effective strategies for mitigating the effects of climate change and building resilience in agricultural ecosystems. However, the effects of these strategies on temperature-induced changes to soil N cycling are unclear, particularly when soils are managed to increase SOM. To determine how agricultural management history and compost amendments affect net N mineralization, net nitrification, and nitrous oxide (N2O) production, we performed a laboratory incubation of soils with two distinct agricultural management histories under three incubation temperatures. Three compost treatments (green-waste compost, food-waste compost, and no compost) were applied, each with and without the addition of synthetic urea fertilizer. We found that organically managed soil exhibited higher rates of net N mineralization and nitrification than conventionally managed soil, leading to greater nitrate production. The rate of N mineralization in organically managed soil was also more sensitive to temperature increases. Although compost addition stimulated microbial activity, it did not affect the N-cycling processes measured in this study at any temperature. Therefore, the implementation of climate change resilience and mitigation strategies aimed at augmenting stocks of soil carbon may render agricultural soils more susceptible to increased N mineralization and subsequent losses under warming, particularly if plant uptake of the mineralized N does not occur concurrently. Moreover, the effects of compost application to stimulate the immobilization of excess N is likely limited in soils with low background C.

Abstract Boreal forests harbor as much carbon (C) as the atmosphere and significant amounts of organic nitrogen (N), the nutrient most likely to limit plant productivity in high‐latitude ecosystems. In the boreal biome, the primary disturbance is wildfire, which consumes plant biomass and soil material, emits greenhouse gasses, and influences long‐term C and N cycling. Climate warming and drying is increasing wildfire severity and frequency and is combusting more soil organic matter (SOM). Combustion of surface SOM exposes deeper older layers of accumulated soil material that previously escaped combustion during past fires, here termed legacy SOM. Postfire SOM decomposition and nutrient availability are determined by these layers, but the drivers of legacy SOM decomposition are unknown. We collected soils from plots after the largest fire year on record in the Northwest Territories, Canada, in 2014. We used radiocarbon dating to measure Δ14C (soil age index), soil extractions to quantify N pools and microbial biomass, and a 90‐day laboratory incubation to measure the potential rate of element mineralization and understand patterns and drivers of legacy SOM C decomposition and N availability. We discovered that bulk soil C age predicted C decomposition, where cumulatively, older soil (approximately −450.0‰) produced 230% less C during the incubation than younger soil (~0.0‰). Soil age also predicted C turnover times, with old soil turnover 10 times slower than young soil. We found respired C was younger than bulk soil C, indicating most C enters and leaves relatively quickly, while the older portion remains a stable C sink. Soil age and other indices were unrelated to N availability, but microbial biomass influenced N availability, with more microbial biomass immobilizing soil N pools. Our results stress the importance of legacy SOM as a stable C sink and highlight that soil age drives the pace and magnitude of soil C contributions to the atmosphere between wildfires.

Age-old traditional farming practices are generally followed by tribal inhabitants using locally available organic sources of plant nutrients. The aim of the present study was to determine the kinetics and rate of mineralization of different local organic sources of North East region of India. An incubation study of 100 days was carried out using locally available organic sources, i.e. farmyard manure (FYM; T1), poultry manure (T2), pig manure (T3) and vermicompost (T4) at the rate of 120 kg N/ha (considering recommended dose of fertilizer of rice as 120 kg N/ha). Bulk soil sample of Typic kandihumultis at 0-15 cm was collected from the College of Post Graduate Studies in Agricultural Sciences, Umiam, Meghalaya research farm and treated with organic sources and kept in an incubator at field capacity soil moisture and 25°C temperature. Observations were taken at 10 days interval up to 100 days of incubation (DOI). A control treatment (T0) of no organic source was used for comparison. The results showed that the average nitrogen mineralization rate (Nmin) of T3 was highest (64.88%), followed by T2 (57.77%), T4 (42.98%) and T1 (35.24%). The highest Nmin rate of T3 and T2 was noted at 60 DOI as 79.37% and 76.10% respectively. At 50-60 DOI, total nitrogen, available nitrogen and nitrogen fractions (ammonical nitrogen and nitrate nitrogen) released were the highest irrespective of the organic sources. R² (coefficient of determinate) of first-order kinetics of all organic sources was found to be: 0.91 (T3) > 0.90 (T2) > 0.89 (T4) > 0.88 (T1), while R² of second-order kinetics was: 0.66 (T3) > 0.65 (T2) > 0.64 (T1 and T4). It has been concluded that T3 is the best organic nutrient source among the treatments considered for this study. [ABSTRACT FROM AUTHOR]

1.Experimental studies across biomes demonstrate that herbivores can have significant effects on ecosystem functioning. Herbivore effects, however, can be highly variable with studies demonstrating positive, neutral or negative relationships between herbivore presence and different components of ecosystems. Mixed effects are especially likely in the soil, where herbivore effects are largely indirect mediated through effects on plants.2.We conducted a long‐term experiment to disentangle the effects of non‐native moose in boreal forests on plant communities, nutrient cycling, soil composition and soil organism communities.3.To explore the effect of moose on soils, we conduct separate analyses on the soil organic and mineral horizons. Our data come from 11 paired exclosure‐control plots in eastern and central Newfoundland, Canada that provide insight into 22–25 years of moose herbivory. We fit piecewise structural equations models (SEM) to data for the organic and mineral soil horizons to test different pathways linking moose to above‐ground and below‐ground functioning.4.The SEMs revealed that moose exclusion had direct positive impacts on adult tree count and an indirect negative impact on shrub percent cover mediated by adult tree count. We detected no significant impact of moose on soil microbial C:N ratio or net nitrogen mineralization in the organic or mineral soil horizon. Soil temperature and moisture, however, was more than twice as variable in the presence (i.e. control) than absence (i.e. exclosure) of moose. Overall, we observed clear impacts of moose on above‐ground forest components with limited indirect effects below‐ground. Even after 22–25 years of exclusion, we did not find any evidence of moose impacts on soil microbial C:N ratio and net nitrogen mineralization.5.Our long‐term study and mechanistic path analysis demonstrates that soils can be resilient to ungulate herbivore effects despite evidence of strong effects above‐ground. Long‐term studies and analyses such as this one are relatively rare yet critical for reconciling some of the context‐dependency observed across studies of ungulates effects on ecosystem functions. Such studies may be particularly valuable in ecosystems with short growing seasons such as the boreal forest. [ABSTRACT FROM AUTHOR]

The mineralization of urea fertilizer significantly impacts nitrogen movement in the soil. An incubation study was done on a lab scale basis to examine nitrogen dynamics in soil inoculated with plant growth-promoting bacteria (PGPB) supplemented with varying levels of nitrogen fertilizer in the form of urea (0% N, 25% N, 50% N, 75% N, and 100% N). In the present experiment, sandy clay loam soil was used and incubated for four weeks, and the concentrations of NH4+¯N and NO3-¯N were monitored using the destructive method (Kjeldahl) to determine the mineralization rate of urea. Results showed higher NH4+¯N (11.880 mg/kg mineralized with UPMRB9N50 treatment) and NO3-¯N (20.060 mg/kg mineralized with UPMRB9N50 treatment) concentrations in the bacteriatreated soil compared to the uninoculated control. Urea-N remains higher (0.0353% and 0.0253% from UPMRB9N50 treatment in the first and second weeks, respectively) in bacteria-treated soil during the first two weeks, then gradually becomes zero towards the end of the observing period. Nitrogen (N) leaching loss was lower in bacterial inoculated soil compared to the control, and the leaching loss of N was greater with the increased N fertilizer rates. Cumulative N leaching loss is higher (29.797 mg/kg) in 100% N-treated soil than in other treatments. The findings observed that the beneficial bacteria could enhance the N mineralization to make the nutrient available for the crop while, at the same time, reducing leaching losses of fertilizer when supplied with a minimum amount of chemical fertilizer, thereby saving the input cost and protecting the environment. [ABSTRACT FROM AUTHOR]

Anticipated permafrost thaw in upcoming decades may exert significant impacts on forest soil nitrogen (N) dynamics. The rate of soil N mineralization (Nmin) plays a crucial role in determining soil N availability. Nevertheless, our understanding remains limited regarding how biotic and abiotic factors influence the Nmin of forest soil in response to permafrost thaw. In this study, we investigated the implications of permafrost thaw on Nmin within a hemiboreal forest based on a field investigation along the degree of permafrost thaw, having monitored permafrost conditions for eight years. The results indicate that permafrost thaw markedly decreased Nmin values. Furthermore, Nmin demonstrated positive associations with soil substrates (namely, soil organic carbon and soil total nitrogen), microbial biomass carbon and nitrogen, and soil moisture content. The decline in Nmin due to permafrost thaw was primarily attributed to the diminished quality and quantity of soil substrates rather than alterations in plant community composition. Collectively, our results underscore the pivotal role of soil substrate and microbial biomass in guiding forest soil N transformations in the face of climate-induced permafrost thaw. [ABSTRACT FROM AUTHOR]

Afforestation on degraded lands is an effective measure to control desertification and soil erosion, but these functions are often constrained by soil nitrogen (N) availability. Moreover, soil N availability usually shifts along plantation development, yet we have a limited understanding of factors driving this shift. Here, we examined dynamics of soil N mineralization and nitrification rates along plantation development, and explored mechanisms behind these dynamics from the perspective of N‐cycling microbes. We measured needle litter quality, N‐hydrolyzing enzyme activity, biomass and community composition of soil microbes (phospholipid fatty acid analysis) and ammonia oxidizers (real‐time quantitative PCR and high‐throughput sequencing), and net N mineralization and nitrification rates along a chronosequence of Pinus sylvestris var. mongolica stands with six age classes ranging from 15‐ to 61‐year‐old in the Three‐North region of China. Results showed that stand development increased net N mineralization rate by 54%, nitrate‐N concentration by 106%, and nitrate‐N:ammonium‐N ratio from 1.09 to 2.63. Gram‐positive:gram‐negative bacterial ratio and β‐N‐acetylglucosaminidase activity initially increased and subsequently decreased along stand development with the highest values in 40‐year‐old stands, while fungal:bacterial ratio showed the opposite pattern with the lowest value in 40‐year‐old stands. These shifts in soil microbial properties were associated with age‐related changes in needle litter C:N ratio and soil pH. Net N mineralization rate was positively related to β‐N‐acetylglucosaminidase activities, but not to soil microbial biomass and community composition. Net nitrification rate was negatively correlated with ammonia‐oxidizing archaeal abundances and positively with ammonia‐oxidizing bacterial abundances. Collectively, our results indicate that soil N availability increases and N cycling accelerates with plantation growth, and suggest that microbial N recycling driven by β‐N‐acetylglucosaminidase is tightly related to soil N dynamics along stand development. [ABSTRACT FROM AUTHOR]

Fresh-market tomatoes (Lycopersicon esculentum Mill.) are increasingly produced with subsurface drip irrigation in California, as growers adapt to decreased water availability. Drip irrigation improves water use efficiency, but may reduce the soil volume where conditions are optimal for microbial and root activity. This poses complications for organic growers, whose cropping systems are dependent on microorganisms to convert the nitrogen (N) from organic sources into plant-available N. To investigate grafting as a potential practice to increase access to N, grafted and non-grafted "Brandywine" heirloom tomatoes were grown with drip irrigation in a two-year field trial. The three rootstocks were "Maxifort," "Fortamino," and "DRO138TX." Prior to each growing season, a legume cover crop mix was grown and labeled with 15N ammonium sulfate to track tomato N uptake from cover crop residues. There were no significant differences in yield, N uptake and N partitioning in the plants due to rootstock treatments. Leaf analyses suggested that the tomato plants were not N deficient in either year. However, there was a significant difference in total N uptake from cover crop residues between years. This was caused by large differences in N concentration in the cover crop. Plants responded to a lower N availability by producing less vine biomass, while producing the same fruit yield. A budget revealed that the tomato plants accessed a considerable amount of N from the soil below 60 cm of the profile to cover their demand. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a key limiting nutrient in terrestrial ecosystems, but there remain critical gaps in our ability to predict and model controls on soil N cycling. This may be in part due to lack of standardized sampling across broad spatial–temporal scales. Here, we introduce a continentally distributed, publicly available data set collected by the National Ecological Observatory Network (NEON) that can help fill these gaps. First, we detail the sampling design and methods used to collect and analyze soil inorganic N pool and net flux rate data from 47 terrestrial sites. We address methodological challenges in generating a standardized data set, even for a network using uniform protocols. Then, we evaluate sources of variation within the sampling design and compare measured net N mineralization to simulated fluxes from the Community Earth System Model 2 (CESM2). We observed wide spatiotemporal variation in inorganic N pool sizes and net transformation rates. Site explained the most variation in NEON's stratified sampling design, followed by plots within sites. Organic horizons had larger pools and net N transformation rates than mineral horizons on a sample weight basis. The majority of sites showed some degree of seasonality in N dynamics, but overall these temporal patterns were not matched by CESM2, leading to poor correspondence between observed and modeled data. Looking forward, these data can reveal new insights into controls on soil N cycling, especially in the context of other environmental data sets provided by NEON, and should be leveraged to improve predictive modeling of the soil N cycle. Plain Language Summary: Nitrogen (N) is not only a key limiting nutrient that often constrains plant growth but also a major pollutant in places where supply exceeds demand. However, we lack the ability to accurately predict and model rates of soil N cycling. This paper introduces a first of its kind, standardized and publicly available data set of soil inorganic N pools and net transformation rates spanning the United States. We describe the data set in detail, then examine spatiotemporal trends in N pools and fluxes and how those measurements compare to predictions from an Earth system model. Key Points: The National Ecological Observatory Network (NEON) measures soil inorganic nitrogen (N) pools and net flux rates at continental scaleThe most N cycle variation is observed at the site level, followed by plots within sites. Organic horizons have high N pools and flux ratesThe Community Earth System Model 2 poorly predicts temporal trends in net N mineralization. NEON data can be used to improve predictive power [ABSTRACT FROM AUTHOR]

Copyright of Forest Research is the property of Forest Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)