Enriched rice husk biochar superior to commercial biochar in ameliorating ammonia loss from urea fertilizer and improving plant uptake.

Adding value to agricultural leftovers and turning them into biochar is a viable way to replenish soil nutrients and boost crop productivity. To further validate the efficacy of enriched rice husk biochar, an incubation study and a pot experiment were conducted: (1) to describe the effect of enriched rice husk biochar addition on soil total N, soil exchangeable NH4 + and available NO3 - and (2) to describe the effect of enriched rice husk biochar on improving N, P, K, Ca, and Mg uptake, use efficiency, and dry matter production of rice plants. The amount of NH3 loss that was considerably reduced by rice husk biochar at 5 and 10 t ha-1 was 34 % lower than the control. The availability of soil total N, exchangeable NH4 +, available NO3 -, available P, and exchangeable cations was greatly enhanced by the addition of rice husk biochar. Due to the effective nutrient uptake that occurs with an increase in soil nutrient level, the physical growth of the rice plant (height, tiller number, greenness, and panicle number) increeased significantly in treatments supplemented with 5 t ha-1 rice husk biochar. When rice plants were treated with 5 t ha-1 rice husk biochar, their absorption of N, P, and K increased by >80 %, respectively. The production of dry matter in rice plants increased as a result of the increased N intake. The application of 5 t ha-1 of rice husk biochar enhanced the soil nutrients by reducing NH3 loss and augmenting soil nutrients for efficient plant absorption, as demonstrated by the favourable enhancement of soil macro- and micronutrients and biomass of rice plants.

[Effects of water-nitrogen interactions on NH3 and N2O emissions and yield in winter wheat cropland]. / 水氮互作对冬小麦农田NH3和N2O排放及产量的影响.

To investigate the effects of different irrigation and nitrogen application modes on nitrogen gaseous loss in winter wheat farmland, we conducted a field experiment at Changqing Irrigation Experiment Station in Shandong Province, with two irrigation levels (80%-90% θf(I1) and 70%-80% θf(I2)) and three nitrogen application levels (conventional nitrogen application of 240 kg·hm-2(N1), nitrogen reduction of 12.5% (N2), and nitrogen reduction of 25% (N3)). The results showed that ammonia volatilization and nitrous oxide emission rate peak appeared within 2-4 days after fertilization or irrigation. The ammonia volatilization rate during the chasing fertilizer period was significantly higher than that during the basal fertilizer period. Compared with other treatments, the ave-rage ammonia volatilization rate of I2N2 treatment during the chasing fertilizer period was reduced by 10.1%-51.6%, and the average nitrous oxide emission rate over the whole growth period was reduced by 15.4%-52.2%. The ammonia volatilization rate was significantly positively associated with surface soil pH value and ammonium nitrogen content, while the nitrous oxide emission rate was significantly positively associated with nitrate content in topsoil. The accumulation amount of soil ammonia volatilization and nitrous oxide emission ranged from 0.83-1.42 and 0.11-0.33 kg·hm-2, respectively. Moderate reduction of irrigation water and nitrogen input could effectively reduce cumulative amounts of ammonia volatilization and nitrous oxide emission from winter wheat farmland. The cumulative amounts of ammonia volatilization and nitrous oxide emission under I1N3 and I2N2 treatments were signi-ficantly lower than those under other treatments. The highest winter wheat yield (5615.6 kg·hm-2) appeared in I2N2 treatment. The irrigation water utilization efficiency of I2 was significantly higher than that of I1, with the maximum increase rate of 45.2%. Compared with N1 and N3 treatments, the maximum increase rate of nitrogen fertilizer productivity and agricultural utilization efficiency in N2 reached 15.2% and 31.8%, respectively. In conclusion, the treatment with 70%-80% θf irrigation level and 210 kg·hm-2 nitrogen input could effectively improve the utilization efficiency of irrigation water and nitrogen fertilization and reduce gaseous loss from winter wheat farmland.

Modeling maize growth and nitrogen dynamics using CERES-Maize (DSSAT) under diverse nitrogen management options in a conservation agriculture-based maize-wheat system.

Agricultural field experiments are costly and time-consuming, and often struggling to capture spatial and temporal variability. Mechanistic crop growth models offer a solution to understand intricate crop-soil-weather system, aiding farm-level management decisions throughout the growing season. The objective of this study was to calibrate and the Crop Environment Resource Synthesis CERES-Maize (DSSAT v 4.8) model to simulate crop growth, yield, and nitrogen dynamics in a long-term conservation agriculture (CA) based maize system. The model was also used to investigate the relationship between, temperature, nitrate and ammoniacal concentration in soil, and nitrogen uptake by the crop. Additionally, the study explored the impact of contrasting tillage practices and fertilizer nitrogen management options on maize yields. Using field data from 2019 and 2020, the DSSAT-CERES-Maize model was calibrated for plant growth stages, leaf area index-LAI, biomass, and yield. Data from 2021 were used to evaluate the model's performance. The treatments consisted of four nitrogen management options, viz., N0 (without nitrogen), N150 (150 kg N/ha through urea), GS (Green seeker-based urea application) and USG (urea super granules @150kg N/ha) in two contrasting tillage systems, i.e., CA-based zero tillage-ZT and conventional tillage-CT. The model accurately simulated maize cultivar's anthesis and physiological maturity, with observed value falling within 5% of the model's predictions range. LAI predictions by the model aligned well with measured values (RMSE 0.57 and nRMSE 10.33%), with a 14.6% prediction error at 60 days. The simulated grain yields generally matched with measured values (with prediction error ranging from 0 to 3%), except for plots without nitrogen application, where the model overestimated yields by 9-16%. The study also demonstrated the model's ability to accurately capture soil nitrate-N levels (RMSE 12.63 kg/ha and nRMSE 12.84%). The study concludes that the DSSAT-CERES-Maize model accurately assessed the impacts of tillage and nitrogen management practices on maize crop's growth, yield, and soil nitrogen dynamics. By providing reliable simulations during the growing season, this modelling approach can facilitate better planning and more efficient resource management. Future research should focus on expanding the model's capabilities and improving its predictions further.

Microplastic Has No Effect on Rice Yield and Gaseous N Emission from an Infertile Soil with High Inorganic N Inputs.

Microplastic might affect the crop yield, nitrogen (N) use efficiency and reactive N losses from agricultural soil systems. However, evaluation of these effects in infertile soil planted with different rice cultivars is lacking. We conducted a soil column experiment to determine the influence of a typical microplastic polyethylene (PE) input into an infertile soil with 270 kg N ha-1 and planted with two rice cultivars, i.e., a common rice Nangeng 5055 (NG) and a hybrid rice Jiafengyou 6 (JFY). The results showed that JFY produced a significantly (p < 0.05) greater grain yield than NG (61.6-66.2 vs. 48.2-52.5 g pot-1) but was not influenced by PE. Overall, PE hardly changed the N use efficiency of NG and JFY. Unexpectedly, PE significantly (p < 0.05) increased the total amino acid content of NG. Compared with JFY, NG volatilized significantly (p < 0.05) more ammonia (NH3) (0.84-0.92 vs. 0.64-0.67 g N pot-1) but emitted equal nitrous oxide (N2O). PE exerted no effect on either NH3 volatilization or the N2O emission flux pattern and cumulative losses of the rice growth cycle, whether with NG or JFY. Some properties of tested soils changed after planting with different rice cultivars and incorporating with microplastic. In conclusion, the rice production, N use efficiency, NH3 volatilization and N2O emission from the N-fertilized infertile soil were pronouncedly influenced by the rice cultivar, but not the PE. However, PE influenced the grain quality of common rice and some properties of tested soils with both rice cultivars.

Biochar and hydrochar application influence soil ammonia volatilization and the dissolved organic matter in salt-affected soils.

Biochar, which including pyrochar (PBC) and hydrochar (HBC), has been tested as a soil enhancer to improve saline soils. However, the effects of PBC and HBC application on ammonia (NH3) volatilization and dissolved organic matter (DOM) in saline paddy soils are poorly understood. In this research, marsh moss-derived PBC and HBC biochar types were applied to paddy saline soils at 0.5 % (w/w) and 1.5 % (w/w) rates to assess their impact on soil NH3 volatilization and DOM using a soil column experiment. The results revealed that soil NH3 volatilization significantly increased by 56.1 % in the treatment with 1.5 % (w/w) HBC compared to the control without PBC or HBC. Conversely, PBC and the lower application rate of HBC led to decrease in NH3 volatilization ranging from 2.4 % to 12.1 %. Floodwater EC is a dominant factor in NH3 emission. Furthermore, the fluorescence intensities of the four fractions (all humic substances) were found to be significantly higher in the 1.5 % (w/w) HBC treatment applied compared to the other treatments, as indicated by parallel factor analysis modeling. This study highlights the potential for soil NH3 losses and DOM leaching in saline paddy soils due to the high application rate of HBC. These findings offer valuable insights into the effects of PBC and HBC on rice paddy saline soil ecosystems.

Soil amendments reduce CH4 and CO2 but increase N2O and NH3 emissions in saline-alkali paddy fields.

Limited research has been conducted on ammonia (NH3) volatilization and greenhouse gases (GHGs) emissions in saline-alkali paddy fields, along with complex interaction involving various genes (16sRNA, amoA, narG, nirK, nosZ, and nifH). This study employed mesocosm-scale experiment to investigate NH3 volatilization and GHGs emissions, focusing on bacterial communities and genic abundance, in saline-alkali paddy fields with desulfurized gypsum (DG) and organic fertilizer (OF) amendments. Compared to the control (CK) treatment, DG and OF treatments reduced methane (CH4) and carbon dioxide (CO2) emissions by 78.05 % and 26.18 %, and 65.84 % and 11.62 %, respectively. However, these treatments increased NH3 volatilization by 26.26 % and 45.23 %, and nitrous oxide (N2O) emission by 41.00 % and 12.31 %. Notably, NH3 volatilization primarily stemmed from ammonia nitrogen (NH4+-N), rather than total nitrogen (TN) in soil and water. N2O was mainly produced from nitrate nitrogen (NO3--N) in soil and water, as well as NH4+-N in water. The increase in NH3 volatilization and N2O emission in DG and OF treatments, was attributed to the reduced competition among bacterial communities, rather than the increased bacterial activity and genic copies. These findings offer valuable insights for managing nutrient loss and gaseous emissions in saline-alkali paddy fields.

Reducing the environmental impact of rice production in subtropical India by minimising reactive nitrogen loss.

The future of reactive nitrogen (N) for subtropical lowland rice to be characterised under diverse N-management to develop adequate sustainable practices. It is a challenge to increase the efficiency of N use in lowland rice, as N can be lost in various ways, e.g., through nitrous oxide (N2O) or dinitrogen (N2) emissions, ammonia (NH3) volatilization and nitrate (NO3-) leaching. A field study was carried out in the subsequent wet (2021) and dry (2022) seasons to assess the impacts of different N management strategies on yield, N use efficiency and different N losses in a double-cropped rice system. Seven different N-management practices including application of chemical fertilisers, liquid organic fertiliser, nitrification inhibitors, organic nutrient management and integrated nutrient management (INM) were studied. The application of soil test-based neem-coated urea (NCU) during the wet season resulted in the highest economic yield, while integrated nutrient management showed the highest economic yield during the dry season. Total N losses by volatilization of NH3, N2O loss and leaching were 0.06-4.73, 0.32-2.14 and 0.25-1.93 kg ha-1, corresponding to 0.06-5.84%, 0.11-2.20% and 0.09-1.81% of total applied N, respectively. The total N-uptake in grain and straw was highest in INM (87-89% over control) followed by the soil test-based NCU (77-82% over control). In comparison, recovery efficiency of N was maximum from application of NCU + dicyandiamide during both the seasons. The N footprint of paddy rice ranged 0.46-2.01 kg N-eq. t-1 during both seasons under various N management. Ammonia volatilization was the process responsible for the largest N loss, followed by N2O emissions, and NO3- leaching in these subtropical lowland rice fields. After ranking the different N management practices on a scale of 1-7, soil test-based NCU was considered the best N management approach in the wet year 2021, while INM scored the best in the dry year 2022.

Treatment of nitrogen and phosphorus from sewage tailwater in paddy rice wetlands: concept and environmental benefits.

Domestic sewage tailwater (DSTW) reuse for crop irrigation is considered a promising practice to reduce water demand, mitigate water pollution, and substitute chemical fertilization. The level of the above environmental benefits of this water reuse strategy, especially when applied to paddy wetlands, remains unclear. In this study, soil column experiments were conducted to investigate the nitrogen and phosphorus fate in paddy wetlands subjected to different tailwater irrigation and drainage strategies, specifically, (i) TW1 and TW2 for regular or enhanced irrigation-drainage without N fertilization, (ii) TW3 and TW4 for regular irrigation with base or tillering N fertilizer, (iii) conventional fertilization N210, and (iv) no-fertilization controls N0. The results showed that the total nitrogen (TN), nitrate (NO3-), and total phosphorus (TP) removal rates from the paddies irrigated by DSTW ranged between 51.92 and 59.34%, 68.1 and 83.42%, and 85.69 and 86.98% respectively. Ammonia emissions from the DSTW-irrigated treatments were reduced by 14.6~47.2% compared to those paddies subjected to conventional fertilization (N210), similarly for TN emissions, with the exception of the TW2 treatment. Overall, it is established that the paddy wetland could effectively remove residual N and P from surface water runoffs, while the partial substitution of chemical fertilization by DSTW could be confirmed. The outcome of this study demonstrates that DSTW irrigation is a promising strategy for sustainable rice production with a minimized environmental impact.

Nitrogen-loss and carbon-footprint reduction by plant-rhizosphere exudates.

Low-carbon approaches to agriculture constitute a pivotal measure to address the challenge of global climate change. In agroecosystems, rhizosphere exudates are significantly involved in regulating the nitrogen (N) cycle and facilitating belowground chemical communication between plants and soil microbes to reduce direct and indirect emissions of greenhouse gases (GHGs) and control N runoff from cultivated sites into natural water bodies. Here, we discuss specific rhizosphere exudates from plants and microorganisms and the mechanisms by which they reduce N loss and subsequent N pollution in terrestrial and aquatic environments, including biological nitrification inhibitors (BNIs), biological denitrification inhibitors (BDIs), and biological denitrification promoters (BDPs). We also highlight promising application scenarios and challenges in relation to rhizosphere exudates in terrestrial and aquatic environments.

Improving Fertilizer Use Efficiency-Methods and Strategies for the Future.

This editorial introduces our Special Issue entitled "Improving Fertilizer Use Efficiency-Methods and Strategies for the Future". The fertilizer use efficiency (FUE) is a measure of the potential of an applied fertilizer to increase the productivity and utilization of the nutrients present in the soil/plant system. FUE indices are mainly used to assess the effectiveness of nitrogen (N), phosphorus (P), and potassium (K) fertilization. This is due to the low efficiency of use of NPK fertilizers, their environmental side effects and also, in relation to P, limited natural resources. The FUE is the result of a series of interactions between the plant genotype and the environment, including both abiotic and biotic factors. A full recognition of these factors is the basis for proper fertilization in farming practice, aimed at maximizing the FUE. This Special Issue focuses on some key topics in crop fertilization. Due to specific goals, they can be grouped as follows: removing factors that limit the nutrient uptake of plants; improving and/or maintaining an adequate soil fertility; the precise determination of fertilizer doses and application dates; foliar application; the use of innovative fertilizers; and the adoption of efficient genotypes. The most important nutrient in crop production is N. Hence, most scientific research focuses on improving the nitrogen use efficiency (NUE). Obtaining high NUE values is possible, but only if the plants are well supplied with nitrogen-supporting nutrients. In this Special Issue, particular attention is paid to improving the plant supply with P and K.

Mitigating ammonia volatilization in rice cultivation: The impact of partial organic fertilizer substitution.

Optimizing water and nitrogen management to minimize NH3 volatilization from paddy fields has been extensively studied. However, there is limited research on the combined effect of different rates of organic fertilizer substitution (OFS) and irrigation methods in rice cultivation, exploring an effective water and nitrogen combination is beneficial to mitigate NH3 volatilization. To address this gap, we conducted a two-year field experiment to investigate NH3 volatilization under different OFS rates (0%, 25%, and 50%) combined with continuous flooding irrigation (CF) and alternate wet and dry irrigation (AWD). Our findings revealed that NH3 fluxes exhibited similar emission patterns after each fertilization event and significantly decreased with increasing rates of OFS during the basal stage. Compared to no substitution (ON0), the low (ON25) and high (ON50) rates of OFS reduced cumulative NH3 emissions by 18.9% and 16.6%, and lowed NH3 emission factors (EFs) by 26.7% and 23.3%, respectively. Although OFS resulted in a slight reduction in rice yield, yield-scaled NH3 emissions were significantly reduced by 11.9% and 6.5% under the low and high substitution rates, respectively. This reduction was mainly attributed to the slight yield reduction observed at the low substitution rate. Furthermore, when combined with ON0, AWD irrigation had the potential to increase NH3 volatilization. However, this increase was not observed when combined with ON25 and ON50. During each fertilization stage, floodwater + concentration emerged as the prominent environmental factor influencing NH3 volatilization, showing a stronger and more positive correlation compared to other factors such as floodwater pH, soil pH, and NH4+ concentration. Based on our findings, we recommend implementing effective water and nitrogen management strategies to minimize NH3 volatilization in rice cultivation. This involves applying a lower rate of organic fertilizer substitution during the basal stage, maintaining high water levels during fertilization, and implementing mild AWD irrigation during non-fertilization periods.

The increasing risk of ammonia volatilization in farmland from the recovery product of magnesium-modified biochar after nitrogen and phosphorus adsorption.

Many studies have shown that magnesium modified biochar (MgBC) can recover nutrients from wastewater and be applied as an excellent slow-release fertilizer in farmland. However, the recovery products (NP-loaden MgBC), represented by struvite or magnesium phosphate, have a high degree of self-alkalinity, which may significantly increase the ammonia (NH3) volatilization in farmland. In this study, the optimal adsorption parameters, self-alkaline regulation process and co-adsorption mechanism of MgBC for ammonium ion (NH4+) and phosphate ion (PO43-) were studied through batch experiments. A field experiment was conducted with three treatments, including local conventional fertilization (N1B0) and the application of 5 t·ha-1 or 10 t·ha-1 NP-loaden MgBC in combination with local conventional fertilization (N1B1 and N1B2, respectively), to determine the impact of NP-loaden MgBC on NH3 volatilization, surface water c(NH4+-N) and pH. The results indicated that the maximum NH4+ and PO43- synergistic recovery of MgBC under the optimal adsorption parameters (dosage of 0.6 g·L-1; initial NH4+ and PO43- concentrations of 120 and 60 mg·L-1 and pH of 8) were 59.96 and 98.60 mg·g-1, respectively. Self-regulating alkaline MgBC maintained pH suitable for struvite, and precipitation mechanism controlled the adsorption. The presence of NP-loaden MgBC raised the pH levels in surface water during the basal fertilization stage and increased c(NH4+-N) in surface water during the topdressing stages. This, in turn, led to a significant increase in NH3 volatilization loss during the entire rice-growing period, with N1B1 and N1B2 experiencing a 23.87 % and 48.91 % increase respectively, compared to N1B0. Therefore, it is imperative to take into account the adverse impact of NP-laden MgBC on NH3 loss in paddy fields when considering its application in future field studies.

Nitrification and urease inhibitors mitigate global warming potential and ammonia volatilization from urea in rice-wheat system in India: A field to lab experiment.

The efficacy of alternative nitrogenous fertilizers for mitigating greenhouse gas and ammonia emissions from a rice-wheat cropping system in northern India was addressed in a laboratory incubation experiment using soil from a 10-year residue management field experiment (crop residue removal, CRR, vs. incorporation, CRI). Neem coated urea (NCU), standard urea (U), urea ammonium sulfate (UAS), and two alternative fertilizers, urea + urease inhibitor NBPT (UUI) and urea + urease inhibitor NBPT + nitrification inhibitor DMPSA (UUINI) were compared to non-fertilized controls for four weeks in incubation under anaerobic condition. Effects of fertilizers on global warming potential (GWP) and ammonia volatilization were dependent on residue treatment. Relative to standard urea, NCU reduced GWP by 11 % in CRI but not significantly in CRR; conversely, UAS reduced GWP by 12 % in CRR but not significantly in CRI. UUI and UUINI reduced GWP in both residue treatments and were more effective in CRI (21 % and 26 %) than CRR (15 % and 14 %). Relative to standard urea, NCU increased ammonia volatilization by 8 % in CRI but not significantly in CRR. Ammonia volatilization was reduced most strongly by UUI (40 % in CRI and 37 % in CRR); it was reduced 28-29 % by UUINI and 12-15 % by UAS. Overall, the urease inhibitor, alone and in combination with the nitrification inhibitor, was more effective in mitigating greenhouse gas and ammonia emissions than NCU. However, these products need to be tested in field settings to validate findings from the controlled laboratory experiment.

Effects of the Combining Straw Return with Urease Inhibitor on Ammonia Volatilization, Nitrogen Use Efficiency, and Rice Yield in Purple Soil Areas.

Straw return in rice (Oryza sativa L.) paddy has been heavily criticized for its potential to influence ammonia (NH3) volatilization loss due to irrational fertilizer N application. Therefore, improving the N fertilization strategies within residue straw systems is necessary to reduce N loss from NH3 volatilization. This study investigated how the incorporation of oilseed rape straw and the urease inhibitor affected NH3 volatilization, fertilizer N use efficiency (FNUE), and rice yields over two growing seasons (2018-2019) in the purple soil region. This study arranged eight treatments combined straw (2, 5, 8 ton ha-1, named 2S, 5S, 8S, respectively), with urea or urease inhibitor (UI, 1% NBPT) with three replicates, which included control (CK), UR (Urea, 150 kg N ha-1), UR + 2S, UR + 5S, UR + 8S, UR + 2S + UI, UR + 5S + UI, UR + 8S + UI, based on the randomized complete block method. Our results indicated that incorporating oilseed rape straw increased NH3 losses by 3.2-30.4% in 2018 and 4.3-17.6% in 2019 than the UR treatment, attributing to the higher NH4+-N content and pH value within floodwater. However, the UR + 2S + UI, UR + 5S + UI and UR + 8S + UI treatments reduced NH3 losses by 3.8%, 30.3%, and 8.1% in 2018 and 19.9%, 39.5%, and 35.8% in 2019, separately compared to their corresponding UR plus straw treatments. According to the findings, adding 1% NBPT significantly decreased NH3 losses while incorporating 5 ton ha-1 oilseed rape straw. Furthermore, adding straw, either alone or in conjunction with 1% NBPT, increased rice yield and FNUE by 0.6-18.8% and 0.6-18.8%, respectively. Otherwise, NH3 losses scaled by yield in the UR + 5S + UI treatment decreased significantly between all treatments in 2018 and 2019. These results suggest that optimizing the oilseed rape straw rate combined with 1% NBPT applied with urea efficiently increased rice yield and reduced NH3 emissions in the purple soil region of Sichuan Province, China.

Fate of nitrogen and phosphorus from source-separated human urine in a calcareous soil.

Human urine concentrates 88% of the nitrogen and 50% of the phosphorus excreted by humans, making it a potential alternative crop fertilizer. However, knowledge gaps remain on the fate of nitrogen in situations favouring NH3 volatilization and on the availability of P from urine in soils. This study aimed at identifying the fate of nitrogen and phosphorus supplied by human urine from source separation toilets in a calcareous soil. To this end, a spinach crop was fertilized with 2 different doses of human urine (170 kgN ha-1 + 8.5 kgP ha-1 and 510 kgN ha-1 + 25.5 kgP ha-1) and compared with a synthetic fertilizer treatment (170 kgN ha-1 + 8.5 kgP ha-1) and an unfertilized control. The experiment was conducted in 4 soil tanks (50-cm depth) in greenhouse conditions, according to a randomized block scheme. We monitored soil mineral nitrogen over time and simulated nitrogen volatilization using Hydrus-1D and Visual Minteq softwares. We also monitored soil phosphorus pools, carbon, nitrogen and phosphorus (CNP) in microbial biomass, soil pH and electrical conductivity. Only an excessive input of urine affected soil pH (decreasing it by 0.2 units) and soil conductivity (increasing it by 183%). The phosphorus supplied was either taken up by the crop or remained mostly in the available P pool, as demonstrated by a net increase of the resin and bicarbonate extractable P. Ammonium seemed to be nitrified within about 10 days after application. However, both Visual Minteq and Hydrus models estimated that more than 50% of the nitrogen supplied was lost by ammonia volatilization. Overall, our results indicate that direct application of urine to a calcareous soil provides available nutrients for plant growth, but that heavy losses of volatilized nitrogen are to be expected. Our results also question whether long-term application could affect soil pH and salinity.

Crop-specific ammonia volatilization rates and key influencing factors in the upland of China - A data synthesis.

Ammonia (NH3) is an important alkaline reactive nitrogen (Nr) species which is involved in global nitrogen (N) biogeochemical cycling, but which has negative impacts on the environment and human health. In order to better understand and control the NH3 loss potential in soil-upland crop systems in China, an integrated data analysis including 1302 observations from 236 published articles between 1980 and 2021 was conducted. The typical NH3 volatilization rate (AVR) and the main factors influencing AVR in the major Chinese upland crops (maize, wheat, openfield vegetables and greenhouse vegetables and others) were estimated and analyzed. The mean AVR for maize, wheat, openfield vegetables and greenhouse vegetables were 7.8%, 5.3%, 8.4% and 1.8%. The most important influencing factors were fertilizer placement, meteorological conditions (especially temperature and rainfall) and soil properties (especially SOM). Subsurface N application produced a significantly lower AVR compared to surface application. High N recovery efficiency and N agronomic efficiency were generally associated with low AVRs. In conclusion, high N application rates, inefficient application methods and the use of loss-prone N fertilizer types are the main factors responsible for high AVRs in major Chinese croplands.

Arbuscular Mycorrhizal Fungi Shift Soil Bacterial Community Composition and Reduce Soil Ammonia Volatilization and Nitrous Oxide Emissions.

Arbuscular mycorrhizal fungi (AMF) establish mutualistic relationships with the majority of terrestrial plants, increasing plant uptake of soil nitrogen (N) in exchange for photosynthates. And may influence soil ammonia (NH3) volatilization and nitrous oxide (N2O) emissions directly by improving plant N uptake, and/or indirectly by modifying soil bacterial community composition for the soil C availability increasing. However, the effects of AMF on soil NH3 volatilization and N2O emissions and their underlying mechanisms remain unclear. We carried out two independent experiments using contrasting methods, one with a compartmental box device (in 2016) and the other with growth pot experiment (in 2020) to examine functional relationships between AMF and soil NH3 volatilization and N2O emissions under varying N input. The presence of AMF significantly reduced soil NH3 volatilization and N2O emissions while enhancing plant biomass and plant N acquisition, and reducing soil NH4+ and NO3-, even with high N input. The presence of AMF also significantly reduced the relative abundance within the bacterial orders Sphingomonadales and Rhizobiales. Sphingomonadales correlated significantly and positively with soil NH3 volatilization in 2016 and N2O emissions, whereas Rhizobiales correlated positively with soil N2O emissions. High N input significantly increased soil NH3 volatilization and N2O emissions with increasing relative abundance of Sphingomonadales and Rhizobiales. These findings demonstrate the contribution of AMF in regulating NH3 and N2O emission by improving plant N uptake and altering soil bacterial communities. They also suggest that altering the rhizosphere microbiome might offer additional potential for restoration of N-enriched agroecosystems.

Environmental risk of microplastics after field aging: Reduced rice yield without mitigating yield-scale ammonia volatilization from paddy soils.

Microplastics (MPs, <5 mm) are enriched in paddy ecosystems as emerging environmental pollutants. Biochar (BC) is a controversial recalcitrant carbon product that poses potential environmental risks. The presence of these two exogenous organic substances has been demonstrated to have impacts on soil nitrogen cycling and crop production. However, the after-effects of MPs and BC on soil ammonia (NH3) volatilization and rice yield after field aging remain unexplored. In this study, two common MPs, including polyethylene (PE) and polyacrylonitrile (PAN), and BC were selected for rice growing season observations to study the impacts on soil NH3 volatilization and rice yield after field aging. The results showed that the reduction of cumulative soil NH3 losses by MPs was around 45% after one-year field aging, which was within the range of 40-57% in the previous rice season. Abatement of NH3 volatilization by MPs mainly occurred in basal fertilization and was related to floodwater pH. Besides, the reduction rate of NH3 volatilization by BC and MPs + BC was enhanced after field aging (63% and 50-57%) compared to that in the previous rice season (5% and 11-19%), with the abatement process occurring in the first supplementary fertilization. There was a significant positive correlation between cumulative NH3 volatilization and soil urease activity. Notably, field aging removed the positive effect of MPs and MPs + BC in reducing yield-scale NH3 losses in the previous rice season (∼62%). Furthermore, despite BC affecting rice yield insignificantly after field aging, the presence of MPs led to a significant 17-19% reduction in rice yield. Our findings reveal that differences in the after-effects of BC and MPs in field aging emerge, where the negative impacts of MPs on soil NH3 abatement and crop yield are progressively becoming apparent and should be taken into serious consideration.

Effectiveness of mixing poultry litter compost with rice husk biochar in mitigating ammonia volatilization and carbon dioxide emission.

Nitrogen-rich materials such as poultry litter (PL) contributes to substantial N and C loss in the form of ammonia (NH3) and carbon dioxide (CO2) during composting. Biochar can act as a sorbent of ammonia (NH3) and CO2 emission released during co-composting. Thus, co-composting poultry litter with rice husk biochar as a bulking agent is a good technique to mitigate NH3 volatilization and CO2 emission. A study was conducted to evaluate the effects of composting the mixtures of poultry litter with rice husk biochar at different ratios on NH3 and CO2 emissions. Four mixtures of poultry litter and rice husk biochar at different rate were composted at 0:1, 0.5:1, 1.3:1 and 2.3:1 ratio of rice husk biochar (RHB): poultry litter (PL) on a dry weight basis to achieve a suitable C/N ratio of 15, 20, 25, and 30, respectively. The results show that composting poultry litter with rice husk biochar can accelerate the breakdown of organic matter, thereby shortening the thermophilic phase compared to composting using poultry litter alone. There was a significant reduction in the cumulative NH3 emissions, which accounted for 78.38%, 94.60%, and 97.30%, for each C/N ratio of 20, 25, and 30. The total nitrogen (TN) retained relative was 75.96%, 85.61%, 90.24%, and 87.89% for each C/N ratio of 15, 20, 25, and 30 at the completion of composting. Total carbon dioxide lost was 5.64%, 6.62%, 8.91%, and 14.54%, for each C/N ratio of 15, 20, 21, and 30. In addition, the total carbon (TC) retained were 66.60%, 72.56%, 77.39%, and 85.29% for 15, 20, 25, and 30 C/N ratios and shows significant difference as compared with the initial reading of TC of the compost mixtures. In conclusion, mixing and composting rice husk biochar in poultry litter with C/N ratio of 25 helps in reducing the NH3 volatilization and CO2 emissions, while reducing the overall operational costs of waste disposal by shortening the composting time alongside nitrogen conservation and carbon sequestration. In formulating the compost mixture with rice husk biochar, the contribution of C and N from the biochar can be neglected in the determination of C/N ratio to predict the rate of mineralization in the compost because biochar has characteristic of being quite inert and recalcitrant in nature.

Regulation of denitrification/ammonia volatilization by periphyton in paddy fields and its promise in rice yield promotion.

BACKGROUND: Nitrogen (N) is the most limiting nutrient in rice production. N loss via denitrification and ammonia (NH3 ) volatilization decreases N utilization efficiency. The effect of periphyton (a widespread soil surface microbial aggregate in paddy soil) on N-cycling processes and rice growth in paddy soils remain unclear. The purpose of this study was to reveal the interactions of periphyton with the overlying water and sediment in paddy soils on denitrification/NH3 emissions and rice yield by combining pot experiments and path analysis modeling. RESULTS: The sediment exerted significant direct and positive effects on denitrification. The periphyton both directly and indirectly enhanced denitrification, mainly by regulating the ammonium (NH4 + )-N content in the sediment. The total contribution of periphyton to denitrification was stronger than that of the overlying water but smaller than that of the sediment. The pH in the overlying water and the NH4 + -N content in the sediment had a strong positive effect on NH3 volatilization. Although the periphyton biomass and chlorophyll a directly prohibited NH3 emissions, this was counterbalanced by the indirect stimulation effects of the periphyton due to its positive alteration of the pH. Moreover, periphyton facilitated rice yield by 10.2% by releasing N. CONCLUSION: Although the periphyton may have driven N loss by regulating the NH4 + -N content in the sediment and the pH in the overlying water, our study also found that the periphyton was considered a temporary N sink and provided a sustained release of N for rice, thus increasing the rice yield. © 2022 Society of Chemical Industry.