Non-rhizosphere reinforces the contributions of Feammox and anammox to nitrogen loss than rhizosphere in riparian zones.

The emergence of anaerobic ammonium oxidation (anammox) coupled to iron reduction (named Feammox) refreshes the microbial pathways for nitrogen (N) loss. However, the ecological role of Feammox, compared with conventional denitrification and anammox, in microbial N attenuation in ecosystems remains unclear. Here, the specific contribution of Feammox to N loss and the underlying microbiome interactive characteristics in a riparian ecosystem were investigated through 15N isotope tracing and molecular analysis. Feammox was highlighted in the riparian interface soils and maximally contributed 14.2% of N loss. Denitrification remained the dominant contributor to N loss (68.0%-95.3%), followed by anammox (5.7%-19.1%) and Feammox (0-14.2%). The rates of Feammox and anammox significantly decreased in rhizosphere soils (0.15 ± 0.08 µg N g-1 d -1 for Feammox, 0.80 ± 0.39 µg N g-1 d -1 for anammox) compared with those in non-rhizosphere soils; however, the activities of denitrification remarkably increased in the rhizosphere (13.17 ± 3.71 µg N g-1 d -1). In rhizosphere soils, the competition between bioavailable organic matter (e.g., amino acids and carbohydrates) and ammonium for electron acceptor [i.e., Fe(III)] was the vital inducement for restricted Feammox, while the nitrite consumption boosted by heterotrophic denitrifiers was responsible for weakened anammox. The functional gene of autotrophic Acidimicrobiaceae bacterium A6, instead of heterotrophic Geobacteraceae spp., was significantly positively correlated with Feammox activity. Rare iron-reducing bacteria showed higher node degrees in the non-rhizosphere network than in the rhizosphere network. A syntrophic relationship was found between iron-reducing bacteria (e.g., Anaeromyxobacter, Geobacter) and iron-oxidizing bacteria (e.g., Sideroxydans) in the non-rhizosphere network and facilitated the Feammox pathway. This study provides an in-depth exploration of microbial driven N loss in a riparian ecosystem and introduces new insights into riparian management practices toward high-efficient N pollution alleviation.

Response of maize yield and nitrogen leaching to combining controlled-release urea and normal urea under different surface mulching.

BACKGROUND: A one-off application of combining controlled-release urea (CRU) and conventional urea has been recommended for the reduction of nitrogen (N) loss and improvement of grain yield. However, the effects of combining CRU and urea with different surface mulching has not been studied in detail, and the underlying agronomical and physiological mechanisms need to be more clearly understood. RESULT: A 3-year field study was conducted to determine the effects of combining CRU and urea with different surface mulching on dry matter, N accumulation and translocation, nitrate nitrogen (NO3 - -N) residuals and loss in maize grown under rain-fed conditions. Three surface mulching [plastic film mulching (FM), straw mulching (SM) and no mulching (NM)] as well as three N fertilization [combining CRU and urea with 1:2 as the baseline application (NC), a split urea application with 4:3:3 (NU) and a N control (N0)] were used. The FM under NC fertilization increased N uptake, decreased NO3 - -N residual in the deep soil layer, and decreased N loss. The FM, SM and NM under NC fertilization increased 3-year mean grain yields by 5.8%, 4.0% and 4.6%, respectively, compared to that under NU fertilization. The FM under NC fertilization showed the highest grain yield and economic return. CONCLUSION: Properly managing N application by mixing CRU and urea in a one-off application combined with plastic film mulching may have the potential to provide a better compromise among grain yield, N loss and economic returns for maize in rain-fed farmland. © 2021 Society of Chemical Industry.

Effects of boric acid on urea-N transformation and 3,4-dimethylpyrazole phosphate efficiency.

BACKGROUND: 3,4-Dimethylpyrazole phosphate (DMPP) is a nitrification inhibitor which can restrict nitrate (NO3 - ) production. Boric acid is a substance which inhibits urease activity. However, few studies have focused on the inhibitory effect of boric acid on urea hydrolysis and the possible synergistic effect with DMPP. Thus, an incubation trial was conducted to determine the impact of boric acid and DMPP addition on urea-N transformation, and their synergistic effects, in chernozem soil (Che) and red soil (RS). Four treatments were set up in each soil: urea only (U); urea combined with DMPP (UD); urea combined with boric acid (UB); and urea combined with both DMPP and boric acid (UDB). RESULTS: Compared to U, adding DMPP (UD) increased NH3 emissions by 11% and 13% and decreased soil NO3 - -N concentration by 38% and 13% in Che and RS, respectively. Boric acid addition (UB) effectively prolonged the half-life time of urea by 0.8 and 0.4 days, reduced NH3 volatilizations by 11% and 16% and delayed the occurrence of NH3 emission peaks for 3 and 4 days in contrast to U treatment in Che and RS, respectively. UDB treatment mitigated the NH3 volatilizations caused by the addition of DMPP (UD) by 16% and 29% in Che and RS, respectively. Additionally, a better nitrification inhibition rate was found in the UDB treatment compared to other treatments in both soils. CONCLUSIONS: There is potential to develop a new N transformation inhibition strategy with the use of a combination of boric acid and DMPP. © 2020 Society of Chemical Industry.

How much nitrogen does Africa need to feed itself by 2050?

Nitrogen (N) fertilizers are very important for global food self-sufficiency (FSS), particularly for Africa, where the N input in agriculture is very low. This is the first work which studies and calculates the amount of N fertilizer that each country in Africa needs to feed itself by 2050. In this study, we used five different scenarios of inorganic fertilizer N (IFN) use and human diets to calculate the amount of N fertilizer needed to achieve FSS in Africa by 2050 and analyze the changes in N budget; N losses and N use efficiency (NUE). These scenarios include 1) business as usual (BAU), 2) equitable diet (EqD; self-sufficiency), 3) an IFN input 20% less than the EqD (S1), 4) an IFN input 40% less than the EqD (S2), and 5) a 20% increase in IFN input relative to the EqD (S3). Under the BAU scenario, production trends continue as they have over the past five decades, including an unhealthy human diet. In the EqD scenario, the priority is to meet the local demand for both animal and plant proteins with a healthy human diet. Under the EqD scenario, increasing the total N input from 35 kg N ha-1 yr-1 to 181 kg N ha-1 yr-1 during 2016-2050 is needed to achieve FSS in Africa. This increase in N fertilizer use represents unprecedented N inputs to African terrestrial ecosystems - at least 52 Tg N yr-1 - which would lead to inevitable increases in N losses. We also found that the NUE would decrease from 63% during 2010-2016 to 50% by 2050, whereas the total N surplus would increase from 13 kg N ha-1 yr-1 to 90 kg N ha-1 yr-1 by 2050. The estimated gaseous emissions would increase from 8 kg N ha-1 yr-1 to 61 kg N ha-1 yr-1 by 2050. Our findings conclude that, it is very important to consider the high N losses in Africa if the EqD scenario is applied. The S1 and S2 scenarios result in much less environmental N loss, and better NUE compared with the EqD scenario. Therefore, based on these findings we can recommend the implementation of the S2 scenario with an IFN dose of 77 kg N ha-1 yr-1, in parallel with the use of modern agricultural techniques and the increased use of organic inputs.

Integrated systematic approach increase greenhouse tomato yield and reduce environmental losses.

High input - high output greenhouse vegetable systems are responsible for nutrient surpluses and environmental losses. Integrated strategies that improve soil, crop and nutrient management are needed to ensure more sustainable production systems. We conducted a two-year field experiment to evaluate the potential of integrated soil-crop system management (ISSM) practices to improve the productivity and environmental outcomes from an intensive greenhouse tomato production system in the Yangtze River Basin, China. Four treatments were tested: i) farmers' practice (FP); ii) soil remediation (SR), where lime nitrogen with compost addition was the only management strategy; iii) a treatment that combined soil remediation with optimized crop planting density (SRCO), which increased planting density for improving crop yield; and iv) integrated soil-crop system management (ISSM), as a systematic integrated approach, which included the combined optimization of soil remediation, crop optimization, and nutrient management. In the integrated soil-crop system management treatment, nutrient management was optimized through adoption of the most appropriate type (formula) of fertilizer for the crop, rate and application timing of synthetic fertilizer, and by substituting poultry manure with compost. Our results indicated that the fruit yield of the integrated soil-crop system management treatment was 104 t ha-1, 13.4%-37.3% higher than that of the other three treatments. The mean reactive nitrogen loss (81.1 kg N ha-1) and the greenhouse gas emissions (6495 kg CO2-eq ha-1) in the farmers' practice treatment were much higher than in the other three treatments (reactive nitrogen loss: 47.9-54.3 kg N ha-1; and greenhouse gas emissions: 4926-5468 kg CO2-eq ha-1, respectively). The mean nitrogen and carbon footprints of the integrated soil-crop system management treatment were significantly lower than those of other treatments, as a result of both the lower fertilizer nitrogen use and the greater yield. This study indicates that integrated soil-crop system management could produce greater yields and increase net profit with reduced nitrogen inputs, whilst reducing the environmental cost associated with conventional farmers' practice in plastic-greenhouse vegetable production systems.

Demographic quantification of carbon and nitrogen dynamics associated with root turnover in white clover.

As well as capturing resources, roots lose resources during their lives. We quantified carbon (C) and nitrogen (N) losses associated with root turnover in white clover (Trifolium repens L.). We grew contrasting cultivars for 18 weeks in soil microcosms. Using repeated in situ observations, destructive sampling, and demographic analysis, we measured changes in C and N concentrations in dry matter of 1st- or 2nd-order (terminal) roots to derive C and N fluxes into and out of root cohorts. C and N fluxes from roots during turnover depended on cohort age and order. Ninety per cent of losses occurred from 2nd-order cohorts younger than 18 weeks. Losses were greater from roots of the larger, faster growing cultivar Alice than from the smaller lower yielding cultivar S184. C:N ratios of roots and lost material were similar within each order and between cultivars but smaller in 2nd- compared with 1st-order roots. C and N losses during root turnover could be equivalent to at least 6% of aboveground dry matter production in S184 and 12% in Alice at the field scale. C and N losses associated with root turnover will have potentially significant and previously unrecognized impacts on crop productivity, resource dynamics, and long-term soil fertility.

Green manuring alters reactive N losses and N pools in arable soils: A meta-regression study.

Green manuring is a conservation agricultural practice that improves soil quality and crop yield. However, increasing the active nitrogen (N) and carbon (C) pools during green manure (GM) amendment may accelerate soil N transformation and stimulate N loss. Previous studies have reported the effects of cover crop incorporation on N2O emission; however, the driving mechanisms and other N losses remain unclear. Therefore, we conducted a comprehensive meta-analysis of 109 published articles (517 paired observations) to clarify the effects of GM amendment on soil reactive N (Nr) losses (N2O emissions, NH3 volatilization, and N leaching and runoff), N pools, and N cycling functional gene abundance. The results showed that green manuring increased soil microbial biomass N (MBN) and NO3--N concentrations and stimulated N2O emission but significantly lowered N leaching and yield-scaled NH3 volatilization. Practices of green manuring made a dominant contribution to the variation in N2O emissions and NH3 volatilization after GM application. Furthermore, applying legume-based GM, using N derived from GM (GMN) as an additional input, and short-term GM amendment each stimulated N2O emissions. In contrast, adopting non-legume GM, using GMN to partially substitute mineral N, and applying GM to the soil surface or paddy field mitigated NH3 loss during GM amendment. Additionally, the variation in NH3 volatilization was positively related to soil pH and N application rate (NAR) but had a negative relationship with mean annual precipitation (MAP). This study highlighted the marked effects of green manuring on soil N retention and loss. Agricultural operations that adopt GM amendment should select suitable GM species and optimize mineral N inputs to minimize N loss.

[Analysis on Driving Factors, Reduction Potential, and Environmental Effect of Inorganic Fertilizer Input in Chongqing].

In this study, we sought to quantify the effect of planting structure change on fertilizer input and environmental cost in Chongqing and develop scientific and rational strategies for chemical fertilizer reduction. Based on the crop fertilizer quota standard and large sample farmer survey data under the medium productivity level in Chongqing, we evaluated and analyzed the application reduction potential and environmental benefits of fertilizer with the difference method and life cycle assessment. The results showed that:① since Chongqing became a municipality directly under the central government (1997), Chongqing crop planting structure had greatly changed, and the proportion of food crop (rice, corn, wheat, bean, and potato) decreased by 21%. The area of fruits and vegetables increased from 3.36×105 hm2 to 1.05×106 hm2, and their proportion increased by 20%. ② Nearly 55% of fertilizers had been consumed by vegetable (37%) and citrus production systems, and 11%, 12%, and 12% of fertilizers were consumed by rice, corn, and potato, respectively. ③ The total fertilizer reduction of the Chongqing planting industry could reach up to 1.69×105 tons during the period of "the 14th Five-Year Plan," with a fertilizer reduction potential of 18.6%. The fertilizer reduction potential (reduction amount) of rice, corn, citrus, and vegetables would reach 0.3% (2.9×102 tons), 12% (1.45×104 tons), 21% (3.65×104 tons), and 30% (1.18×105 tons), respectively. On the other hand, the rape system was insufficient in phosphorus potassium fertilizers, and the corn tended to be insufficient in potash fertilizer. ④ The current production level was low, and the nitrogen loss, greenhouse gas emissions, and eutrophication potential in the planting industry of Chongqing reached 1.81×105 tons (N), 1.43×107 tons (CO2-eq), and 1.74×105 tons (PO4-eq). With the increase in the realization degree of the crop quota standard (60%-100%), the reactive nitrogen loss, greenhouse gas emissions, and eutrophication potential decreased by 14.9%-24.9%, 10.1%-16.7%, and 13.8%-23%, respectively. The structure of the planting industry in Chongqing significantly changed, the total fertilizer consumption in Chongqing tended to decline gradually, and the fertilization intensity of commercial crops stayed at a high level. The agricultural fertilizer reduction potential and the reactive nitrogen and greenhouse gas emission reduction potential were large, especially for citrus and vegetable production systems. However, it is also necessary to pay attention to insufficient corn potash fertilizer and rape phosphorus potassium fertilizer investment and carry out collaborative promotion of fertilizer reduction.

Modeling Nitrogen Fate and Water and Nitrogen Use Efficiencies under Different Greenhouse Vegetable Production Systems Using the WHCNS-Veg Model.

Quantitative evaluation of the effects of diverse greenhouse vegetable production systems (GVPS) on vegetable yield, soil water consumption, and nitrogen (N) fates could provide a scientific basis for identifying optimum water and fertilizer management practices for GVPS. This research was conducted from 2013 to 2015 in a greenhouse vegetable field in Quzhou County, North China. Three production systems were designed: conventional (CON), integrated (INT), and organic (ORG) systems. The WHCNS-Veg model was employed for simulating vegetable growth, water dynamics, and fates of N, as well as water and N use efficiencies (WUE and NUE) for four continuous growing seasons. The simulation results revealed that nitrate leaching and gaseous N emissions constituted the predominant N loss within GVPS, which separately accounted for 11.5-59.4% and 6.0-21.1% of the N outputs. The order of vegetable yield, N uptake, WUE, and NUE under different production systems was ORG > INT > CON, while the order of nitrate leaching and gaseous N loss was CON > INT > ORG. Compared to CON, ORG exhibited a significant increase in yield, N uptake, WUE, and NUE by 24.6%, 24.2%, 26.1%, and 89.7%, respectively, alongside notable reductions in nitrate leaching and gaseous N loss by 67.7% and 63.2%, respectively. The ORG system should be recommended to local farmers.

Patterns of δ15N in forest soils and tree foliage and rings between climate zones in relation to atmospheric nitrogen deposition: A review.

The stable nitrogen (N) isotope ratio (δ15N) of forest samples (soils, tree foliage, and tree rings) has been used as a powerful indicator to explore the responses of forest N cycling to atmospheric N deposition. This review investigated the patterns of δ15N in forest samples between climate zones in relation to N deposition. Forest samples exhibited distinctive δ15N patterns between climate zones due to differences in site conditions (i.e., N availability and retention capacity) and the atmospheric N deposition characteristics (i.e., N deposition rate, N species, and δ15N of deposited N). For example, the δ15N of soil and foliage was higher for tropical forests than for other forests by >1.2 ‰ and 4 ‰, respectively due to the site conditions favoring N losses coupled with relatively low N deposition for tropical forests. This was further supported by the unchanged or increased δ15N of tree rings in tropical forests, which contrasts with other climate zones that exhibited a decreased wood δ15N since the 1920s. Subtropical forests under a high deposition of reduced N (NHy) had a lower δ15N by 2-5 ‰ in the organic layer compared with the other forests, reflecting high retention of 15N-depleted NHy deposition. At severely polluted sites in East Asia, the decreased δ15N in wood also reflected the consistent deposition of 15N-depleted NHy. Though our data analysis represents only a subset of global forest sites where atmospheric N deposition is of interest, the results suggest that the direction and magnitude of the changes in the δ15N of forest samples are related to both atmospheric N and site conditions particularly for tropical vs. subtropical forests. Site-specific information on the atmospheric N deposition characteristics would allow more accurate assessment of the variations in the δ15N of forest samples in relation to N deposition.

The fate of nitrogen from different sources in a rice-wheat rotation system - A 15N labeling study.

High loss and low nitrogen (N) efficiency in agricultural production is severe. Also, ammonia volatilization and N leaching aggravated environmental pollution. The eutrophication of surface water and the emissions of N2O increased, hence green fertilization management urgently needs to be rationalized. Coordinating N supply from different sources has been shown to reduce environmental pollution. Therefore, this study was dedicated to clarifying the transport of N sources in the rice-wheat rotation system. The stable isotope tracer technology was used to label fertilizer (F), soil (T), and straw (J) with 15N, respectively. The utilization of N by crops (the N ratio in organs), as well as the residual N in soil and loss status, were measured. According to the potential of response to N, all the wheat cultivars were divided into groups with high (HNV) and low efficiency (LNV). The N contribution ratio showed that 43.28%~45.70% of total N accumulation was from T, while 30.11%~41.73% and 13.82%~24.19% came from F and J. The trend in soil N residue (T > F > J) was consistent with the above, while it was the opposite in N loss (T< F< J). The seasonal effectiveness showed that T achieved the highest N utilization efficiency (31.83%~44.69%), followed by F (21.05%~39.18%) and J (11.02%~16.91%). The post-season sustainability showed that T decreased the most in soil N residue (2.08%~12.53%), and F decreased the most in N accumulation (9.64%~18.13%). However, J showed an increase in N recovery rate (2.87%~5.89%). N translocation and distribution showed that N from different sources in grains was significantly higher than that in stems, glumes, and leaves. The ratio of HNV (75.14%~79.62%) was higher than that of LNV (71.90%~74.59%) in grain, while it was the opposite in other organs. Plant N accumulation, soil N supply, and straw N transformation were determined jointly by the three N sources, thus reducing N loss and N2O production. Therefore, the results will highlight the insights for constructing local N and emission reduction models.

DMPP reduces nitrogen fertilizer application rate, improves fruit quality, and reduces environmental cost of intensive apple production in China.

In China, excessive application of nitrogen (N) fertilizer is common in intensive apple production. To resolve issues of benefit reduction and environmental pollution caused by excessive N, a two-year trial was conducted in an apple orchard with a split-plot design, in which the main factor was the N level (500, 400, 300, and 200 kg N ha-1 year-1, expressed as TN, TN80%, TN60%, and TN40%, respectively) and the deputy factor was whether or not to add 3,4-dimethylpyrazole phosphate (DMPP, expressed as +D). The effects of N reduction combined with DMPP on soil N transformation, fruit quality, economic benefits, and environmental effects were investigated. The results showed that DMPP reduced the production of nitrate and its vertical migration by inhibiting the abundance of AOB amoA and decreased N2O emission by reducing nirKC1 levels. Moreover, N reduction combined with DMPP improved N use efficiency (26.67-49.35%) and reduced N loss rate (15.25-38.76%). Compared with TN, TN60% + D increased the content of anthocyanin and soluble sugar by 21.15% and 13.09%, respectively, and decreased environmental costs caused by NH3 volatilization and N2O emission by 33.84%, while maintaining yield and N utilization rate at relatively high levels. Considering the agronomic, economic and environmental benefits, on the basis of traditional N application rate, 40% N reduction combined with DMPP (TN60% + D) could ensure target yield, corresponding quality and economic benefits, maintain soil N fertility, and reduce the risk of N losses to the environment. The present research could provide references for green, efficient, and sustainable development of apple production.

Global reactive nitrogen loss in orchard systems: A review.

Orchards account for about 5% of the agricultural land in the world, however the amount of nitrogen (N) fertilizer input in orchards is relatively large. Little is known about N input and its impact in orchards at the global scale. Therefore, in this study we systematically evaluated reactive nitrogen (Nr) loss in global orchards. A meta-analysis of 97 studies reported from 2000 to 2021 from different countries showed that the mean global N fertilizer input in orchards was 303 kg N ha-1 yr-1, and the estimated emission factor (EF) of nitrous oxide (N2O) and ammonia (NH3) were 1.39% and 3.64%, respectively. Also, during the same period, orchard nitrate leaching factor (LF) reached 18.5%, and the runoff N loss factor (RF) and net fruit N removal factor (NRF) were estimated to be 2.75% and 5.31%, respectively. The apparent N balance of the global orchard system reached 68.4% of N input. N application increased the Nr loss in various pathways in the orchard. The N2O and NH3 emission and nitrate leaching were linearly correlated with N fertilizer application, and overuse of N resulted in substantial Nr loss. Regionally, the total Nr loss in developing countries was higher than developed countries. Average N input (405 kg N ha-1 yr-1) and Nr loss (102 kg N ha-1 yr-1) of orchards in Asia were the highest. The NH3 volatilization and runoff N loss of deciduous orchards were significantly higher than that of evergreen orchards. N application increased fruit yield, but excessive N input reduced the net fruit N removal (FNR). The results reported here fill an important knowledge gap of N balance analysis of orchards at a global scale and provided a framework for optimizing N management to achieve sustainable fruit production.

Effects of Urea-Ammonium Nitrate Solution on Yield, N2O Emission, and Nitrogen Efficiency of Summer Maize Under Integration of Water and Fertilizer.

In order to clarify the effects of urea-ammonium nitrate solution (UAN) on the yield, nitrogen-use efficiency (NUE), and N2O emissions of summer maize under the condition of water and fertilizer integration, different types of nitrogen fertilizer were selected, namely, ordinary urea (urea) and UAN. Our results showed that the application of UAN was beneficial to improve the dry matter accumulation and the distribution of summer maize. Compared with urea treatment, the total nitrogen accumulation of UAN treatment was increased by 15.8%, and the harvest index was increased by 5.5%. The partial productivity, agronomic use efficiency, and recovery rate of nitrogen for UAN treatment were also increased by 9.1, 19.8, and 31.2%, respectively, compared to those of urea treatment. The soil nitrogen dependence rate treated with UAN was significantly decreased by 13.6%, compared to that of urea treatment. In addition, UAN was beneficial to reduce N2O emissions. The N2O warming potential (GWPN2O) and N2O greenhouse gas intensity (GHGIN2O) of urea treatment were 39.3 and 52.4% higher, compared to those of UAN treatment. The improvement of dry matter accumulation and distribution and nitrogen efficiency for UAN treatment were beneficial to increase the grain yield by 9.1%, compared to that of urea treatment. In conclusion, under the fertigation, the application of UAN favors higher yield and nitrogen uptake, with less soil nitrogen residue, higher NUE, and better environmental effect.

Soil extracellular enzyme activities and the abundance of nitrogen-cycling functional genes responded more to N addition than P addition in an Inner Mongolian meadow steppe.

Nitrogen (N) and phosphorus (P) availability in soils commonly limit belowground biological processes in terrestrial ecosystems. Soil extracellular enzyme activities (EEAs) and microbial functional groups play critical roles in soil biological processes and nutrient cycling, yet their response to nutrient addition are poorly understood. To address this issue, we applied six fertilization treatments composed of combinations of N (0, 1.55, 13.95 g N m-2 yr-1) and P (0, 5.24 g P m-2 yr-1) for two years in a meadow steppe of Inner Mongolia. Soils were collected from each plot in July and August and analyzed for abundances of N-cycling genes and EEAs, and their relationships with treatments. The addition of N significantly increased C-acquisition enzyme activity and enzyme C:N and C:P ratios. Enzymatic stoichiometry indicated that N addition alleviated microbial demand for N, while it increased microbial C limitation. Microbial C and N limitation were significantly correlated with NH4+-N in July, yet they were correlated with soil water content (SWC) in August. The abundance of amoA significantly increased with N addition and was positively related to mineral-N accumulation. The abundance of denitrifier genes and gaseous N loss potential were accelerated by N addition in July, while a neutral effect was observed in August. Nitrate leaching potential was significantly increased by N addition, yet it declined with P addition in July. P addition also suppressed amoA abundance of ammonia oxidizing bacteria. Partial least squares path modelling indicated that N addition positively affected microbial-C limitation, soil N-loss potential and negatively affected microbial-N limitation. P addition negatively affected soil N-loss potential. Ultimately, this study highlights the importance of soil N availability in regulating microbial metabolism and soil N-loss potential, and enhances our understanding of the mechanisms responsible for variation in microbial nutrient cycling in meadow steppe soils.

Effectiveness of Nutrient Management on Water Quality Improvement: A Synthesis on Nitrate-Nitrogen Loss from Subsurface Drainage.

Nutrient management, as described in NRCS Code 590, has been intensively investigated, with research largely focused on crop yields and water quality. Yet, due to complex processes and mechanisms in nutrient cycling (especially the nitrogen (N) cycle), there are many challenges in evaluating the effectiveness of nutrient management practices across site conditions. We therefore synthesized data from peer-reviewed publications on subsurface-drained agricultural fields in the Midwest U.S. with corn yield and drainage nitrate-N (NO3-N) export data published from 1980 to 2019. Through literature screening and data extraction from 43 publications, we obtained 577 site-years of data with detailed information on fertilization, corn yields, precipitation, drainage volume, and drainage NO3-N load/concentration or both. In addition, we estimated flow-weighted NO3-N concentrations ([NO3-N]) in drainage for those site-years where only load and volume were reported. Furthermore, we conducted a cost analysis using synthesized and surveyed corn yield data to evaluate the cost-effectiveness of different nutrient management plans. Results from the synthesis showed that N fertilizer rate was strongly positively correlated with corn yields, NO3-N loads, and flow-weighted [NO3-N]. Reducing N fertilizer rates can effectively mitigate NO3-N losses from agricultural fields; however, our cost analysis showed negative economic returns for continuous corn production at lower N rates. In addition, organic fertilizers significantly boosted corn yields and NO3-N losses compared to inorganic fertilizers at comparable rates; however, accurate quantification of plant-available N in organic fertilizers is necessary to guide appropriate nutrient management plans because the nutrient content may be highly variable. In terms of fertilizer application methods, we did not find significant differences in NO3-N export in drainage discharge. Lastly, impact of fertilization timing on NO3-N export varied depending on other factors such as fertilizer rate, source, and weather. According to these results, we suggest that further efforts are still required to produce effective local nutrient management plans. Furthermore, government agencies such as USDA-NRCS need to work with other agencies such as USEPA to address the potential economic losses due to implementation of lower fertilizer rates for water quality improvement.

Role of NH3 recycling on nitrogen fractions during sludge composting.

The aim of this study is to reduce nitrogen (N) loss and investigate the role of ammonia (NH3) recycling on N fractions, environmental factors and bacterial communities. In this study, collected NH3 from composting and recycled in it. The results showed that NH3 recycling affected N-cycling processes such as nitrification. Redundancy Analyses (RDA) showed that NH4+-N had significantly negative correlation with denitrifying bacteria in treatment group (p < 0.05), demonstrating that NH3 recycling have influenced on the bacterial community structure. Furthermore, Structural Equation Model (SEM) revealed causal relationships between visual variables. Based on these results, we concluded that NH3 recycling is a novel method to reduce N loss.

Biochar-based nitrogen fertilizers: Greenhouse gas emissions, use efficiency, and maize yield in tropical soils.

The sustainable development of agriculture depends on increasing N use efficiency (NUE) and consequently reducing N losses from different sources, such as NH3 volatilization, NO3- leaching, and N2O emissions. While the chemical and physical properties of biochar (BC) in fertilizers have been evaluated to increase NUE, a lack of information exists regarding the effects of BC amendments in tropical soils. We performed a one-year field experiment with tropical soil to evaluate the effects of BC-based N fertilizers (BN) on maize yield and on greenhouse gas (GHG) emissions. The treatments consisted of five fertilizers: ammonium nitrate (AN), urea (U), BN51/10 (51% BC, 10% N), BN40/17 (40% BC, 17% N), BN29/20 (29% BC, 20% N), and a control (without N fertilizer). The N fertilizers (80 kg N ha-1) were broadcast 20 days after sowing. Yield, grain N uptake, NUE, ammonia volatilization, and GHG emissions were measured. The results demonstrated the potential of BNs to enhance the efficiency of the fertilizers. BN51/10 and BN40/17 had an average maize yield that was 26% higher than that of U, and BN51/10 resulted in a NUE that was 12% higher than what was observed for U. Both the effects on yield and NUE were attributed to lower N release rates of the BN-amended fertilizers compared to that of the conventional soluble N sources. The BC-based fertilizers presented better environmental performance, and BN51/10 showed the lowest emission intensity when C sequestration by BC was not considered, with a value that was 14% lower than that of the U treatment. When considering C sequestration by BC, the emission intensity of the C equivalents demonstrated that all BNs presented C sequestration that differed from that of the mineral N sources. BC-based nitrogen fertilizers may have promising applications for sustainable agricultural development by mitigating N losses and increasing C stocks.

[Denitrification and Anaerobic Ammonium Oxidation in Soil Nitrogen Migration Process in a Farmland of Wanshandang Lake].

To explore the rate variation and contribution to N loss of denitrification and anaerobic ammonia oxidation (ANAMMOX) in the nitrogen migration process of farmland soils in southern China, we assess the physicochemical characteristics soil samples of different soil layers from farmland and different land use types (farmland, river channel, riparian zone, and lake sediment) in a wheat-rice rotation area of Wanshandang Lake. Illumina MiSeq sequencing and quantitative real-time polymerase chain reaction (qPCR) are used to investigate the microbial community composition and functional gene abundances of the samples. The potential denitrification and ANAMMOX rate (calculated by N2) of each sample was determined by an isotope culture experiment. It was demonstrated that the potential denitrification rate was significantly positively correlated with TOC, NH4+-N, and NO3--N (P<0.05), and with the abundances of nirS, nirK, and nosZ (P<0.05). The denitrification rate of surface soils was (11.51±1.04) nmol·(g·h)-1, which was significantly higher than other soil layers and other land use types (P<0.05). While the ANAMMOX rate in farmland soils was the highest in the 20-30 cm layer and reached (0.48±0.07) nmol·(g·h)-1. In addition, denitrification was the main cause of N loss in surface soils of the studied farmland, accounting for 91.9%-99.7% of overall loss, and ANAMMOX played an important role in the production of N2 in deep soils.

Increased abundance of nitrogen transforming bacteria by higher C/N ratio reduces the total losses of N and C in chicken manure and corn stover mix composting.

The aim of this work was to investigate how the initial C/N ratio during composting of chicken manure/corn stover mix affected the succession of dominant bacteria in the mix which led to the reduction of the total losses of N and C in the composting process. 16S rDNA sequencing indicated that the succession of predominant bacteria was significantly affected by the temperature and the initial C/N ratio during composting. Redundancy analysis showed that higher C/N appeared to promote the relative abundance of nitrogen fixing bacteria Thermoactinomyces, Planifilum, Flavobacterium, Bacillaceae, Pseudomonas,Sphingobacterium, Paenibacillus, Bacillus and Thermobifida, while compressing the denitrifying bacteria Pusillimonas, Ignatzschineria, Alcanivorax, Cerasibacillus, Truepera and Erysipelothrix. C/N ratio of 30:1 yielded the least C/N losses in the composting process, indicating that adjustment to the initial C/N ratio could affect nitrogen transforming bacteria to reduce the total losses of N and C and improve compost quality.