Inorganic Nitrogen Fertilizer Research Articles

Integration effects of soil amendments and cover crops on dryland no‐till corn

AbstractA field study was carried out at the Mississippi Agricultural and Forestry Experiment Station near Pontotoc to evaluate the synergistic impacts of broiler litter (BL) and inorganic fertilizer nitrogen (N) with flue gas desulfurization (FGD) gypsum and lignite in the presence of winter cover crops (WCCs) on dryland no‐till corn (Zea mays L.) in Falkner silt loam soil. The experimental design was a split‐plot randomized complete block design with three replications. The main plots were WCC and winter fallow (WF), and the subplots were fertilization treatments. Fertilization treatments included BL, inorganic fertilizer N, FGD gypsum and lignite with BL, FGD gypsum and lignite with inorganic fertilizer N, and an unfertilized control. BL, FGD gypsum, and lignite were applied at the rates of 13.4, 3.4, and 3.4 Mg ha−1, respectively. Inorganic fertilizer N was applied to corn at 168 kg N ha−1. BL increased soil carbon (C), soil infiltration, and resulted in higher corn grain yield compared to both inorganic fertilizer N and unfertilized control in 2020 and 2022. Averaged across fertilization treatments, WCC improved soil moisture, soil C, and soil infiltration by 16%, 19%, and 25% at the 0‐ to 15‐cm depth, respectively, and increased corn grain yield by 25% as compared to WF in 2022. Cover crops boosted corn grain yield during drier years. The combination of FGD gypsum and lignite with BL increased corn grain yield by 15% in 2020 and 13% in 2022 compared to BL alone. This approach can be considered to promote the sustainability of agroecosystems.

Yak and Tibetan sheep dung increase the proportional biomass of grasses and alleviate soil nitrogen limitation in degraded Tibetan alpine grassland

The dung of Tibetan livestock serves as a natural fertilizer that plays a crucial role in maintaining plant productivity and restoration of degraded alpine grasslands. However, research on how livestock dung affects vegetation composition and soil quality in Tibetan alpine grassland on the time scale remains uncertain. We established three types of nutrients (yak dung, Tibetan sheep dung and urea) and control on a Tibetan alpine grassland in 2017, and measured the vegetation (species composition, aboveground biomass, composition of functional group biomass, and species diversity) and soil characteristics (soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP)), and calculated the SOC/TN, SOC/TP and TN/TP ratios) at the end of August 2017, 2018, and 2019. The study aimed to compare the effect organic fertilizers (two Tibetan livestock dungs) and inorganic nitrogen fertilizer (urea) on vegetation characteristics and soil chemical properties, and to assess whether the livestock dung can improve soil nutrient availability level in degraded Tibetan alpine grassland. Our results showed that: (1) Tibetan sheep dung delayed the increase of aboveground biomass, and urea increased the aboveground biomass in 2017 and 2018; (2) yak and Tibetan sheep dungs and urea increased proportional biomass of aboveground grasses and plant species richness index in the three years; and (3) livestock dungs increased SOC, TN, the ratios of SOC/TP and TN/TP in 2018. Our study implies that yak and Tibetan sheep dung stimulated plant growth and altered soil nutrients, while alleviating soil nitrogen limitation in degraded alpine grasslands. The return of livestock dung to soil may be a sustainable alternative to chemical fertilizers in near-natural recovery of degraded Tibetan alpine grasslands.

Organic Nitrogen Effects on Root Architecture in Rice Seedlings

Organic Nitrogen Effects on Root Architecture in Rice Seedlings

Effect of nitrogen reduction by chemical fertilization with green manure (Vicia sativa L.) on soil microbial community, nitrogen metabolism and and yield of Uncaria rhynchophylla by metagenomics.

Uncaria rhynchophylla is an important herbal medicine, and the predominant issues affecting its cultivation include a single method of fertilizer application and inappropriate chemical fertilizer application. To reduce the use of inorganic nitrogen fertilization and increase the yield of Uncaria rhynchophylla, field experiments in 2020-2021 were conducted. The experimental treatments included the following categories: S1, no fertilization; S2, application of chemical NPK fertilizer; and S3-S6, application of chemical fertilizers and green manures, featuring nitrogen fertilizers reductions of 0%, 15%, 30%, and 45%, respectively. The results showed that a moderate application of nitrogen fertilizer when combined with green manure, can help alleviate soil acidification and increase urease activity. Specifically, the treatment with green manure provided in a 14.71-66.67% increase in urease activity compared to S2. Metagenomics sequencing results showed a decrease in diversity in S3, S4, S5, and S6 compared to S2, but the application of chemical fertilizer with green manure promoted an increase in the relative abundance of Acidobacteria and Chloroflexi. In addition, the nitrification pathway displayed a progressive augmentation in tandem with the reduction in nitrogen fertilizer and application of green manure, reaching its zenith at S5. Conversely, other nitrogen metabolism pathways showed a decline in correlation with diminishing nitrogen fertilizer dosages. The rest of the treatments showed an increase in yield in comparison to S1, S5 showing significant differences (p < 0.05). In summary, although S2 demonstrate the ability to enhance soil microbial diversity, it is important to consider the long-term ecological impacts, and S5 may be a better choice.

Boosting Crop Growth Rates of Hybrid Rice (Pukhraj) through Synergistic Use of Organic Nitrogen Sources in Conjunction with Urea Nitrogen

In Northwestern Pakistan’s rice-based cropping systems, the prevalent reliance on inorganic nitrogen fertilizers (INF) has led to insufficient nitrogen (N) contributions from soil organic manures (OM). This study aims to evaluate the impact of organic sources (OS), including animal manures (AM) and crop residues (CR), on crop growth rates (CGR) in a rice-wheat rotation. A two-year field experiment involving hybrid rice (Oryza sativa L., Pukhraj) was conducted in Batkhela, Khyber Pakhtunkhwa. Various OS and inorganic-N (urea) combinations were applied, emphasizing their influence on CGR. The findings highlight poultry manure (PM) application as the most impactful on CGR, while wheat straw (WS) application resulted in the lowest CGR among the six OS investigated. Additionally, the use of AM showcased superior CGR compared to CR. In the initial year, the highest CGR occurred, with 75% of N sourced from urea and 25% from OS. In the second year, a balanced 50% N application from each source yielded the highest CGR. Urea and PM demonstrated the most robust CGR among OS combinations, while urea and WS yielded the lowest. Notably, onion leaves, a cost-effective option, delivered promising results comparable to berseem residues, indicating their potential as organic manure, especially in sulfur-deficient soils. These findings underscore the viability of onion residue management as a cost-effective alternative to ammonium sulfate fertilizers with global applicability. The abstract recommends promoting organic sources, particularly poultry manure and onion leaves, alongside inorganic-N fertilizers to enhance CGR and reduce dependence on costly alternatives. However, further research and field trials are necessary to explore the long-term impacts of these organic sources on soil health, nutrient cycling, and the sustainability of rice-based cropping systems in Northwestern Pakistan and beyond. In conclusion, this study investigates the influence of organic sources on CGR in rice-wheat rotations, emphasizing the superiority of poultry manure and onion leaves. The findings highlight cost-effective alternatives to conventional fertilizers, emphasizing the need for further research to validate long-term sustainability and applicability beyond the study area.

Long-Term Fertilization Contributes to Carbon Saturation in Neutral-To-Alkaline Soils but not in Acidic Soils

ABSTRACT The study investigated the adsorption of dissolved organic carbon (DOC) on Chinese soils from four long-term experiments involving five treatments: (1) no fertilization (control), (2–4) inorganic nitrogen (N), phosphorus (P), and potassium (K) fertilization (N, NP, and NPK), (5) NPK plus manure (NPKM). The results showed that DOC adsorption followed a modified Langmuir isotherm model effectively (R2 = 0.912 ~ 0.991). The maximum adsorption capacity (Q max ) (i.e. saturation deficits) generally increased with increasing soil organic carbon (SOC) due to fertilization in Luvic Phaeozem, Haplic Gypsisols, and Eutric Cambisols. However, it decreased significantly in acidic soils (Haplic Acrisols) from 15.59 g/kg for control, to 13.96, 13.03, 9.30 and 8.02 g/kg for N, NP, NPK and NPKM, respectively. Moreover, long-term fertilization, particularly with organic fertilization (e.g. NPKM), resulted in an increase of carbon (C) saturation by 1.42 g/kg (5.52%) in Luvic Phaeozem, 9.27 g/kg (44.29%) in Haplic Gypsisols, and 3.75 g/kg (27.66%) in Eutric Cambisols; however, there was a slight decrease by 1.70 g/kg (−7.49%) in Haplic Acrisols. Canonical correlation analysis (CCA) revealed that clay content and soil available iron (AFe) might be the crucial factors controlling C deficits, and subsequently, C saturation, along with current SOC. In conclusion, long-term fertilization contributed to C saturation in neutral-to-alkaline soils, but not in acidic soils. Thus, further attention should be paid to the long-term effects of fertilization on C saturation.

Assessing the Impact of Organic-Inorganic Nitrogen Application on Maize Yield and Nitrogen Leaching Using the DNDC Model

In order to optimize maize yield and minimize nitrogen leaching, field experiments and DNDC model simulations assessed various organic-inorganic nitrogen application treatments. Trials were conducted in the Hetao irrigation area of Inner Mongolia, comparing six treatments: no nitrogen (CK), solely inorganic nitrogen (U1), and combinations where 25%, 50%, 75%, and 100% of inorganic nitrogen was replaced with organic nitrogen (U3O1, U1O1, U1O3, O1). The DNDC model was calibrated using the U1 treatment data from 2018-2020 and validated with other treatments. Results indicated the model accurately simulated maize yield (NRMSE &lt; 5°%) and nitrate nitrogen leaching (NRMSE &lt; 15%). Simulation outcomes demonstrated that increasing inorganic nitrogen application reduced crop yield and significantly increased nitrate leaching. Conversely, higher proportions of organic nitrogen, along with adjusted irrigation and frequency of inorganic nitrogen fertilization, increased maize yield while reducing nitrate leaching. At a fixed nitrogen application rate of 240 kg hm−2, maize yield initially rose and then declined with increasing organic nitrogen ratios, while nitrate nitrogen leaching decreased consistently. Optimal results were achieved with a 3:2 ratio of organic to inorganic nitrogen, yielding 12578 kg hm−2 with nitrate nitrogen leaching at 15.7 kg NO-3-N hm−2, indicating this ratio as the preferred method for combined nitrogen application in the region.

The Effect of Inorganic Nitrogen Fertilizers on the Quality of Forage Composed of Various Species of Legumes in the Northern Part of a Temperate Climate Zone.

This study focuses on the effect of inorganic nitrogen fertilizers on the quality of perennial grasses. Both grasses and legumes are important in swards, and each type of grass has different biological and ecological properties. Legumes in multi-species swards, especially in their early ages, benefit other Poaceae grasses by improving their growth. When evaluating individual cuts over a three-year period, it was determined that the quality indicators of the forage were significantly influenced by the year of use, N fertilizer application, and the different species compositions of the swards. In many cases, N fertilizers significantly reduced the CP content while tending to increase MADF and NDF. Monoculture grass swards had the highest WSC content; in most cases, N fertilizers increased the WSC content in the forage. DMD was the lowest in the first year of use, specifically in the first cut. Our three-year experiment, which investigated twelve swards with different species compositions, demonstrated that legume grasses improved the quality indicators of forage and contributed to maintaining a more stable overall forage yield over the years. As the climate continues to become warmer, there is a growing need to study a wide range of plant species and different varieties suitable for local growth conditions.

Biochar amendments to tropical paddy soil increase rice yields and decrease N2O emissions by modifying the genes involved in nitrogen cycling

Water management strategies are critical in regulating nitrous oxide (N2O) emissions from paddy soils under rice cultivation. Biochar is widely used as an amendment to decrease soil N2O emissions. However, the impacts of biochar amendment on N2O emissions under different water management strategies in paddy soils have not been investigated thoroughly, and the underlying mechanisms remain poorly understood. In particular, the effects of mid-season water drainage, a strategy used for water conservation, need to be better understood. In this study, a pot experiment was conducted including six treatments: alternating dry-wet conditions during the mid-season period without and with 2% (w/w) biochar (AWD1 and AWD2, respectively), continuous flooding during the mid-season period without (CF1) and with 2% (CF2) biochar, and regular mid-season drainage during the mid-season period without (CON1) and with 2% (CON2) biochar. All treatments received inorganic nitrogen, phosphorus and potassium fertilizers (NPK) administered in a split application. We found that fluxes of N2O emission peaked after the two fertilizers’ additions. No significant difference in the first N2O flux peak was found among different treatments. There also was no difference in the second N2O flux peak in both CF treatments, whereas biochar addition significantly decreased the second N2O flux peak in AWD2 and CON2 treatments. This was mainly due to increased nosZ gene copies and decreased ratios of denitrification and amoA genes to nosZ gene copies. Biochar amendments resulted in significant stimulation of nifH gene copies in the AWD2 treatment. Lastly, biochar increased rice yields in all treatments. Our study suggested that AWD2 was the optimal management strategy for mitigating N2O emissions and improving rice production in this tropical paddy soil.

Short term effects of digestate and composted digestate on soil health and crop yield: Implications for sustainable biowaste management in the bioenergy sector

Composting mitigates environmental risks associated with using solid digestate as fertilizer. However, evidence is lacking on benefits of using composted digestate as fertilizer in enhancing soil health and increasing agronomic yield compared to non-composted digestate (hereafter, digestate). A field study was conducted consisting of digestate, composted digestate, co-composted digestate with biogas feedstocks (corn [Zea mays L.] silage, poultry litter, corn silage + poultry litter or food processing by-product), inorganic nitrogen fertilizer, and control (no treatment applied) on soil microbial biomass, enzyme activities (EA), soil organic carbon (SOC), bioavailable P (P), total nitrogen (TN), soil health index (SHI), and sunflower (Helianthus annuus L.) yield. The Partial Least Square Path Model (PLS-PM) was used to predict: 1) nutrient cycling in response to changes in microbial growth and EA and 2) agronomic yield in response to SHI and soil nutrients dynamics. Composted digestate had equivalent soil health benefits with most of co-composted materials and digestate, albeit agronomic yield was greatest with composted digestate, which was 40 % and 100 % greater than with inorganic nitrogen fertilizer and digestate, respectively, indicating composted digestate's potential to replace the synthetic N fertilizer. Moreover, composts from a sole digestate, rather than the ones from co-composted with fresh feedsstocks, can be promising organic amendments and fertilizers for growing sunflower. The PLS-PM model identified that triggered microbial biomass growth and EA, following digestate and composted digestate applications, catalyzed organic matter decomposition, resulting in enhanced nutrients contents and soil health. However, the model revealed that improved SHI did not predict agronomic yield, as opposed to P and TN, suggesting agronomic performance may have been more sensitive to changes in specific soil nutrients status than the overall soil health condition. We conclude that the benefits of composted digestate as fertilizer hint the significance of digestate valorization via post-digestate composting and compost utilization for sustainability of the bioenergy sector.

Effect of various doses of cowdung and nitrogen on the yield performance of mustard in coastal area of Bangladesh (Brassica sp.)

The experiment was conducted at the agriculture field laboratory of Noakhali Science and Technology University during the period from October 2021 to January 2022 to observe the effect of various doses of cowdung and nitrogen on the performance of mustard. The experiment comprised of two factors viz: cowdung and nitrogen. One organic fertilizer like different level of cowdung-control 0 t ha-1 (C0), 15 t ha-1 (C1), 30 t ha-1 (C2), 45 t ha-1 (C3) and another inorganic fertilizer nitrogen - control 0 kg ha-1 (N0), 100 kg ha-1 (N1), 200 kg ha-1 (N2), 300 Kg ha-1 (N3). The experiment was laid out in Randomized Complete Block Design (RBCD) with three replications. Application of different doses of cowdung and nitrogen significantly influenced the Plant height (cm), branches plant-1 (no.), effective siliqua plant-1 (no.), seeds siliqua-1 (no.), 1000-seed weight (g), seed yield (t ha-1), stover yield (t ha-1), biological yield (t ha-1) and harvest index (%) of mustard. The maximum plant height, number of branches plant-1, number of effective siliqua plant-1, siliqua length, number of seeds siliqua-1, 1000-seed weight, seed yield, stover yield, biological yield and harvest index was obtained with the application of 45 t ha-1 cowdung (C3). On the other hand, with the application of 300 kg ha-1 N the maximum plant height, number of branches plant-1, number of effective siliqua plant-1, siliqua length, number of seeds siliqua, 1000-seed weight, seed yield, stover yield, biological yield was found except the harvest index. In case of the interaction effect of treatment, the highest seed yield (1.77 t ha-1) was obtained from the treatment combination of C3N3 (45 t ha-1 cowdung + 300 kg ha-1 N) and the lowest seed yield (0.93 t ha-1) was found from the control (C0N0) treatment. Res. Agric. Livest. Fish. Vol. 10, No. 2, August 2023: 109-122

Linking microbial carbon‐degrading potential to organic carbon sequestration in fertilized soils: Insights from metagenomics

AbstractThe capacity of soils to store organic carbon (SOC) is vital for agricultural productivity. Soil microorganisms exert a critical role in carbon (C) flow and potentially influence C balance through the decomposition of plant and microbial dead biomass. However, the connection between the microbial degradation potential of plant‐derived and microbial‐derived C and soil organic carbon sequestration (SOCSR) under organic and inorganic nitrogen (N) fertilization treatments remains largely unexplored using metagenomics. In this study, metagenomics was used to investigate the effects of 4 years inorganic (N1: 250 kg N ha−1 yr−1 and N3: 450 kg N ha−1 yr−1) and organic N (O1: N1 + 11,250 kg ha−1 yr−1 sheep manure and O3: N1 + 18,750 kg ha−1 yr−1 sheep manure) fertilizer application on plant biomass decomposition genes, microbial biomass decomposition genes, and microbial properties related to different sources of C decomposition (species composition and diversity). Furthermore, the study explored the relationship between organic matter decomposition genes, microorganisms, and SOCSR. The results revealed that compared with N1 treatment, the increased application of inorganic N fertilizer (N3) significantly enhanced the abundance of genes related to plant and microbial biomass decomposition and microbial diversity involved in SOC decomposition, resulting in reduced SOC content. Conversely, the increased application of organic N fertilizer (O1 and O3) had a minor effect on the abundance of genes related to different sources of C decomposition and C decomposing microbial diversity, but reduced microbial entropy (the ratio of microbial biomass carbon to SOC) and increased SOC content. The random forest model highlighted that plant biomass decomposition genes and bacterial community composition were important factors affecting SOCSR. The Mantel test also indicated that the genes involved in the decomposition of lignin, cellulose, and hemicellulose were closely related to SOCSR. These findings highlighted that increased inorganic N fertilizers greatly enhanced the microbial capacity for SOC decomposition, resulting in reduced SOC accumulation. While the increased application of organic N fertilizer increased SOC stability and reduced the mineralization potential of SOC, contributing to SOCSR. Overall, these findings provide a greater understanding of the relationship between soil C turnover and microbial C‐degrading potential under short‐term fertilization. And in a long time, they may have important implications for global strategies aimed at increasing SOCSR to restore fertility and facilitate sustainable agricultural development.

Assessing the synergistic effect of acidified carbon, inorganic fertilizer, and biofertilizer on fenugreek antioxidant levels, and quality traits

The use of inorganic fertilizers has become increasingly necessary due to the depletion of soil fertility. Inadequate nutrient levels in both plants and soil can be remedied with the application of fertilizers. However, to achieve optimal results, it is recommended to supplement inorganic fertilizers with organic alternatives such as biochar. Despite its benefits, the high pH of activated carbon presents a significant challenge to its use in alkaline soil. Recent studies have shown that acidified carbon can be used instead of alkaline activated carbon. Moreover, the use of biofertilizers is crucial for maintaining soil quality. The purpose of the current study was to investigate the effects of using biofertilizers, inorganic nitrogen fertilizer, and acidified carbon fertilizer in combination on fenugreek growth and chlorophyll concentrations. A pot experiment was conducted using calcium ammonium nitrate (CAN) and three levels of acidified carbon (BC) at 0, 0.75, and 1.50%, with and without the addition of biofertilizer (BF). The results revealed that 1.50CANBC + BF was the most effective supplement for improving soil characteristics such as pH, EC, and overall organic matter. The application of 0.75CANBC + BF was found to be a successful treatment for promoting fenugreek growth and enhancing nitrogen absorption. To achieve better fenugreek quality by reducing electrolyte leakage and MDA, and increasing chlorophyll levels, gardeners are advised to use 1.50CANBC + BF. However, to establish 1.50CANBC + BF as the optimal method for fenugreek growth in poor fertility and high pH soils, further experimental studies in various agro-climatic conditions are necessary.

Effects of long-term organic and inorganic fertilization on greenhouse gas emissions and soil nutrient stoichiometry in a rice–rice–fallow cropping system

Long-term use of organic and inorganic fertilizers can have a negative impact on greenhouse gas (GHG) emissions and nutrient stoichiometry in paddy soil. However, production of sufficient crops to meet food and feed demands globally requires the use of fertilizer in crop production. In the present study, we assessed the environmental impacts of five fertilizer treatments in a rice–rice–fallow cropping system: no fertilizer (CK); inorganic nitrogen, phosphorus, and potassium fertilizers (NPK); manure (M); inorganic phosphorus and potassium fertilizers with manure (PKM); and inorganic nitrogen, phosphorus, and potassium fertilizers with manure (NPKM). Soil parameters were analyzed to examine the relationships between GHG emissions, net ecosystem carbon budgets (NECBs), and soil nutrient stoichiometric ratios. Both the PKM and NPKM treatments increased grain yield and the soil carbon–nitrogen (C:N), carbon–phosphorus (C:P), and nitrogen–phosphorus (N:P) ratios compared to the CK treatment; they also decreased the nitrogen–potassium (N:K) ratio. In the combined fertilization treatments, the fallow season accounted for 9–13% of annual methane (CH4) emissions, whereas early rice accounted for 55–62 % and late rice contributed 38–45 %. Compared to the CK, PKM and NPKM fertilization increased the annual nitrous oxide (N2O) emissions by 52–73 % and 103–115 %, respectively, in both the rice and fallow seasons. In early rice, the C:P ratio and GHG intensity (GHGI) were negatively correlated with CH4 and N2O emissions, whereas both yield and CH4 emissions had strong positive associations with global warming potential (GWP). In the late rice season, GHGI was negatively correlated with carbon dioxide (CO2) and CH4 emissions, and N2O had strong positive associations with GWP. CO2 and N2O emission levels were greater from late rice than from early rice, although CH4 emissions from early rice contributed more to the annual GWP, resulting in higher carbon equivalent emissions but a lower carbon efficiency ratio in early rice output. A Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) optimization analysis suggested that PKM was the best fertilization method to improve yield while minimizing negative environmental impacts, followed in descending order by the NPKM, NPK, and M treatments.

Analysis on Change in Soil Organic Carbon Content of Farmland in Yangtze River Economic Belt Under Different Fertilizing Measures

The literature from a long-term fertilization experiment in the Yangtze River Economic Belt from January 1992 to May 2022 was collected, and the data of farmland soil organic carbon were extracted and integrated. Using the normalization treatment and the analysis method of relative annual variation, the overall change in soil organic carbon content in farmland in the Yangtze River Economic Belt under different long-term fertilization measures was studied, and the change differences of soil organic carbon content under three tillage modes were compared so as to judge and analyze the influence of the duration of the experiment on soil organic carbon dynamics. The results showed that under different long-term fertilization measures, the organic carbon content of farmland soil in the Yangtze River Economic Belt in China showed an overall upward trend. The NP, NPK, O, and NPKO treatments all increased the organic carbon content of agricultural soils, with that of the NPKO treatment being the largest. The sole application of inorganic nitrogen fertilizer reduced the organic carbon content of the soil. The rates of change in soil organic carbon content were 0.22 g·(kg·a)-1, 0.24 g·(kg·a)-1, and 0.16 g·(kg·a)-1for dryland, paddy, and water-dry rotation farmland, respectively. Additionally, the relatively rapid increase effect of organic carbon brought by the O and NPKO treatments could last for no more than 28 years in dryland soil but could still last for more than 28 years in paddy field and paddy-upland rotation soil. There was some variation in the rate of change of soil organic carbon content between soil types. The average rate of change of organic carbon was 0.25 g·(kg·a)-1for red soils, 0.14 g·(kg·a)-1 for brown soils, 0.19 g·(kg·a)-1 for tidal soils, and 0.15 g·(kg·a)-1 for rice soils. The trend of NPKO>O>NPK>NPK>NP>N was basically maintained for the rate of change in soil organic carbon content. The NPKO treatments were all significantly higher than the chemical fertilizer (N, NP, and NPK) treatments alone. The N treatment showed a reduction in organic carbon content in both red soil and rice soils. Considering the carbon fixation of farmland soil, the combined application of organic and inorganic fertilizers is a more suitable fertilization method in this area.

A combination of organic fertilizers partially substitution with alternate wet and dry irrigation could further reduce greenhouse gases emission in rice field

Alternate wet and dry (AWD) irrigation and organic fertilizers substitution (OFS) have contrasting effects on CH4 and N2O emissions in rice cultivation. Combining these two practices may be feasible for simultaneous reduction of CH4 and N2O emission from paddy. Hence, we conducted a two-year field experiment to explore the reduction of greenhouse gases under the combination of AWD and OFS. The field experiment which was designed with two irrigation methods (continuous flooding (CF) irrigation and AWD irrigation), and five nitrogen regimes (N0, N135, and N180 represent 0, 135, and 180 kg N ha-1, respectively, ON25 and ON50 represent 25% and 50% OFS for inorganic fertilizer, respectively). The results showed a single-peak emission for CH4 fluxes during the whole rice growing season in all water and nitrogen treatments while the N2O fluxes peak only observed during tillering period with AWD irrigation. AWD irrigation and OFS showed a limited reduction in global warming potential (GWP). These were owing to that AWD irrigation reduced 38.3% CH4 emissions while increase 145.9% N2O emissions when compared to CF irrigation, and the low rate (25%) OFS only reduced CH4 emission by 29.4% while high rate (50%) only reduce N2O emission by 38.8% when compared to conventional inorganic nitrogen fertilizer (N180). Combined AWD and ON25 could maximize the reduction in GWP and yield-scaled GWP, which were reduce 58.0% and 52.5%, respectively, compare to the conventional water and nitrogen management (CF and N180). Furthermore, the structural equation modelling (SEM) indicated that the soil dissolved organic carbon (DOC) and rice aboveground biomass showed a significant positive effect on CH4 fluxes while soil NH4+ with a negative effect, and the soil NH4+, nitrification potential, denitrification potential significant affected N2O fluxes with a positive effect while DOC with a negative effect. These results investigated that 25% OFS rate for inorganic fertilizer could further reduce warming potential in AWD irrigation rice field.

Leaching is the main pathway of nitrogen loss from a citrus orchard in Central China

Due to the high application rates and low utilization efficiency of inorganic nitrogen (N) fertilizer, conventional citrus orchards tend to cause N losses and extensive pollution. In order to address these issues, it is essential to identify the leading cause of N loss by citrus orchard N mass balance. In the present study, a two-year field experiment was performed on 4 different treatments (CK: no N fertilizer; CF: conventional N fertilizer; NR: 70% of conventional N fertilizer; OM: NR with organic manure) to quantify the pathways of N loss in citrus orchards in Hubei Province, China. Our findings revealed that leaching (17.0%) was the dominant N loss pathway in the conventional citrus orchard of central China, followed by runoff (2.9%), NH3 volatilization (2.3%), and N2O emission (0.5%). Reduced N fertilizer rates (−30.0%) led to a significant reduction in gaseous N loss (−34.9%), runoff N loss (−20.3%), and N leaching (−13.0%) via the reduced content of soil NH4+ and soil NO3-. Interestingly, the presence of organic manure reduced 15.2% of runoff N loss, 3.8% of N leaching and 6.9% of total N loss via reduced soil NO3-, but increased 39.6% of gaseous N loss via increased soil DOC. On the other hand, the low N fertilizer rates suppressed N uptake of citrus by reducing the content of soil NO3-, while organic manure promoted N uptake of citrus via the increased content of soil DOC. Overall, using organic manure as a substitute provides a better solution to fertilization for the citrus orchards in central China compared to reducing N fertilizer rates.

Can the co-application of biochar and different inorganic nitrogen fertilizers repress N2O emissions in acidic soil?

The sole application of nitrogen (N) fertilizer with lower N2O emission potential or combined with biochar may help for mitigating N2O production. However, how biochar applied with various inorganic N fertilizers affected N2O emission in acidic soil remains unclear. Thus, we examined N2O emission, soil N dynamics and relating nitrifiers (i.e., ammonia-oxidizing archaea, AOA) in acidic soil. The study contained three N fertilizers (including NH4Cl, NaNO3, NH4NO3) and two biochar application rates (i.e., 0% and 0.5%). The results indicated that the alone application of NH4Cl produced more N2O. Meanwhile, the co-application of biochar and N fertilizers enhanced N2O emission as well, especially in the combined treatment of biochar and NH4NO3. Soil pH was decreased with the application of various N fertilizers, especially with NH4Cl, and the average decrease rate was 9.6%. Meanwhile, correlation analysis showed a negative relationship between N2O and pH, dramatically, which might indicate that the alteration of pH was one factor relating to N2O emission. However, there was no difference between the same N addition treatments with or without biochar on pH. Interestingly, in the combined treatment of biochar and NH4NO3, the lowest net nitrification rate and net mineralization rate appeared during days 16–23. Meanwhile, the highest emission rate of N2O in the same treatment also appeared during days 16–23. The accordance might indicate that N transformation alteration was another factor relating to N2O emissions. In addition, compared to NH4NO3 alone application, co-applied with biochar had a lower content of Nitrososphaera-AOA, which was a main contributor to nitrification. The study emphasizes the importance of using a suitable form of N fertilizers and further indicates that two factors, namely alteration of pH and N transformation rate, are related to N2O emission. Moreover, in future studies, it is necessary to explore the soil N dynamics controlled by microorganisms.

Biochar enhancement of nitrification processes varies with soil conditions

Application of inorganic nitrogen (N) fertilizers in agriculture can increase emissions of nitrous oxide, a potent greenhouse gas, leaching of nitrate (NO3−), a groundwater contaminant hazardous to human health, and soil acidification. Soil amendment with biochar potentially mitigates these losses and undesirable outcomes. However, there have been considerable inconsistencies in reported impacts, likely owing to variable physiochemical characteristics of the biochar materials and/or the soil environment. This study methodically evaluated the impact of biochar soil incorporation on N transformation and underlying microbial processes using soils with varying biochar types, soil texture, soil moisture, and manure compost co- amendments. Laboratory incubations were conducted to monitor the fate of urea fertilizer N spiked in biochar amended and unamended soils by assaying soil ammonium (NH4+), nitrite (NO2−), and NO3− concentrations, pH, and abundances of soil nitrifiers; ammonia oxidizing bacteria and archaea (AOB and AOA) and Nitrospira with the capacity to perform complete ammonia oxidation (comammox). Soil moisture was a critical factor affecting N transformation processes, more so than biochar, but biochar did result in significantly different concentrations of N species in response to urea application. Biochar enhanced nitrification, more significantly in drier conditions and in sandy soil. Biochar offered some buffering potential in the neutral-alkaline, unsaturated soils, preventing >1 unit drop in pH compared to unamended soils. Co-application of biochar with manure composts enhanced nitrification slightly, which was evidenced by higher abundances of some soil nitrifiers at 4 weeks, although increases in nitrification rates were not statistically significant. Soil nitrifier populations tended to increase in response to a pinewood biochar, but trends differed for saturated soil, in soils of differing textures, or when different biochar materials were evaluated. Thus, when evaluating implications of biochar on the fate of mineral N fertilizer, soil moisture and other environment conditions should be considered.

A Review of Combined Use of Biochar with Nitrogen Fertilizer as an Instrument for Improving Maize Yield and Soil Fertility

The decline of soil fertility is one of the major problems around the world for producing crops and ensuring food security. Therefore, the review's objective was to examine how biochar and inorganic nitrogen fertilizers affect soil physicochemical characteristics, as well as maize production and growth parameters. Similarly, biochar is a product of the thermochemical decomposition of biomass produced under limited oxygen. It has potential benefits in agriculture, such as improving soil fertility, water retention. The nutrient composition of biochar produced is determined by the type of feedstock used and the pyrolysis conditions. A study showed that adding biochar and nitrogen fertilizer decreased soil bulk density and enhanced water-holding capacity and soil chemical properties like pH, nitrogen, phosphorus, potassium, organic carbon, calcium, ECEC, and base saturation. Moreover, the review reported that the addition of N fertilizer and biochar greatly promoted crop N uptake and N content, which then increased leaf photosynthetic efficiency, dry matter accumulation, and grain yields. The findings discovered that when the rate of biochar and nitrogen increased, crop productivity and soil properties also increased significantly. It is concluded that applying biochar along with nitrogen fertilizer increased maize crop productivity as well as soil attributes more than applying biochar and nitrogen fertilizer separately. Therefore, farmers and agricultural experts should consider incorporating these practices into their land management strategies to improve overall agricultural sustainability.