Soil Nitrogen Leaching Research Articles

Effect of Microplastics and Straw Addition on Nitrogen and Phosphorus Leaching in Orange Orchard Soils

To explore the effects of microplastic input and straw addition on nitrogen and phosphorus leaching in orange orchard soil, indoor soil column leaching simulation experiments were conducted on orange orchard soil in Dangyang City, Hubei Province. The experiment analyzed the effects of different treatments on the leaching characteristics of soil nitrogen and phosphorus. The results showed that： ① The increase in microplastic input increased the leaching capacity of the soil （TN, NO3--N, NH4+-N, and TP） when only microplastic input was added. ② Under the addition of straw, the input of microplastics increased, which reduced the leaching amount of TN and NO3--N in the soil, and increased the leaching amount of NH4+-N and TP in the soil. ③ Under the input of microplastics, the key influencing factors of soil nitrogen and phosphorus leaching were soil bulk density and water content. Under straw addition, it was mainly affected by soil carbon and nitrogen content. Among them, microplastic input and straw addition significantly increased soil pH, but their path coefficients for nitrogen and phosphorus leaching were not significantly correlated. The results showed that the effects of polypropylene microplastic input and straw addition on soil nitrogen and phosphorus leaching were related to the amount of microplastics input and whether straw was added. The results showed that the input of microplastics would increase the amount of soil nitrogen and phosphorus leaching. Although nitrogen leaching loss caused by microplastic input could be reduced under straw addition, soil phosphorus leaching loss was significantly increased.

Comparative research on monitoring methods for nitrate nitrogen leaching in tea plantation soils

Great concern has long been raised about nitrate leaching in cropland due to its possible environmental side effects in ground water contamination. Here we employed two common techniques to measure nitrate leaching in tea plantation soils in subtropical China. Using drainage lysimeter as a reference method, the adaptability of estimating drainage and nitrate leaching by combining the water balance equation with the suction cup technique was investigated. Results showed that the final cumulative leachate volume for the calculated and measured method was 721.43 mm and 729.92 mm respectively during the study period. However, nitrate concentration exerted great influence in the estimation of nitrate leaching from the suction cup-based method. The cumulative nitrate leaching loss from the lysimeter and suction cup-based method was 47.45 kg ha−1 and 43.58 kg ha−1 under lysimeter nitrate concentrations ranging from 7 mg L−1 to 13 mg L−1, 156.28 kg ha−1 and 79.95 kg ha−1 under lysimeter nitrate concentrations exceeding 13 mg L−1. Therefore, the suction cup-based method could be an alternative way of monitoring nitrate leaching loss within a range of 7–13 mg L−1 of nitrate concentrations in leachate. Besides, lower results occurred in suction cup samplers due to lack of representative samples which mainly leached via preferential flow when in strong leaching events. Thus, it is advisable to increase sampling frequency under such special conditions. The results of this experiment can serve as a reference and guidance for the application of ceramic cups in monitoring nitrogen and other nutrient-ion leaching in tea plantation soils.

Soil properties improvement and nitrogen leaching induced compost and mineral fertilization for maximizing grapevines production in arid regions, El-Minia, Egypt

Soil properties improvement and nitrogen leaching induced compost and mineral fertilization for maximizing grapevines production in arid regions, El-Minia, Egypt

Optimizing application of dairy effluent with synthetic N fertilizer reduced nitrogen leaching in clay loam soil

High application rates of dairy effluent and manure are often associated with nitrogen (N) leaching, which can affect groundwater quality. Here, we used a lysimeter to examine N leaching losses and biomass yield following application of dairy effluent and manure under wheat-maize cropping. The field experiment included seven treatments: no N fertilizer (Control); 200/300 kg N ha−1 synthetic N fertilizer only (wheat/maize) (CN); 100/150 kg N ha−1 synthetic N fertilizer plus 100/150 (DE1), 150/200 (DE2) and 250/350 (DE3) kg N ha−1 dairy effluent; 100/150 kg N ha−1 synthetic fertilizer plus 100/150 kg N ha−1 dairy manure (SM1); and 150/225 kg N ha−1 synthetic fertilizer plus 50/75 kg N ha−1 dairy manure (SM2). Compared with CN, DE1 treatment increased maize yield by 10.0 %, wheat N use efficiency (NUE) by 26.5 %, and wheat and maize N uptake by 7.7–16.3 %, while reduced N leaching by 22.4 % in wheat season and by 40.4 % in the maize season. In contrast, DE2 and DE3 treatment increased N leaching by 27.2–241 % and reduced NUE by 26.2–55.2 %. SM2 treatment increased yield and NUE by 8.8 % and 7.8 %, respectively, and reduced N leaching by 42.9 % during the wheat but not the maize season. Annual N leaching losses were 37.6 kg N ha−1 under CN treatment, but decreased to 27.4 kg N ha−1 under DE1. In contrast, N leaching increased to 52.8 and 84.1 kg N ha−1 under DE2 and DE3 treatment, respectively (P < 0.05). Meanwhile, under SM1 and SM2 treatment, N leaching decreased by 71.2 % and 32.0 %, respectively, compared with CN. These results suggest that replacing 50 % and 25 % synthetic N fertilizer with dairy farm effluent and manure could reduce N leaching losses but had varied effects on crop productivity under wheat-maize cropping.

Effects of magnesium-modified biochar on soil nitrogen leaching and growth of Chinese cabbage

Effects of magnesium-modified biochar on soil nitrogen leaching and growth of Chinese cabbage

Short-versus long-term effects of nitrogen addition and warming on soil nitrogen mineralization and leaching in a grass-dominated old field.

Increased atmospheric nitrogen (N) deposition and climate warming are both anticipated to influence the N dynamics of northern temperate ecosystems substantially over the next century. In field experiments with N addition and warming treatments, cumulative treatment effects can be important for explaining variation in treatment effects on N dynamics over time; however, comparisons between data collected in the early vs. later years potentially can be confounded with interactions between treatment effects and inter-annual variation in environmental conditions or other factors. We compared the short-term versus long-term effects of N addition and warming on net N mineralization and N leaching in a grass-dominated old field using in situ soil cores. We added new N addition and warming plots (3 years old) to an existing field experiment (16 years old), which enabled comparison of the treatment effects at both time scales while controlling for potential inter-annual variation in other factors. For net N mineralization, there was a significant interaction between plot age and N addition over the growing season, and for extractable inorganic N there was a significant interaction between plot age and warming over winter. In both cases, the directions of the treatment effects differed among old and new plots. Moreover, the responses in the new plots differed from the responses observed previously when the 16-year-old plots had been new. These results demonstrate how inter-annual variation in responses, independent from cumulative treatment effects, can play an important role in interpreting long-term effects on soil N cycling in global change field experiments.

Replacing chemical fertilizers with biogas slurry is an environment friendly strategy to reduce the risk of soil nitrogen leaching: evidence from the HYDRUS model simulation

Excessive chemical fertilizer use leads to soil nitrogen leaching. Biogas slurry, which is rich in nitrogen, has been proposed as an organic substitute for chemical fertilizer via drip irrigation. However, the dynamics of nitrogen migration and potential threats to biogas slurry return remain unclear. Using a two-year field experiment and HYDRUS software, this study modeled soil moisture and nitrogen migration under biogas slurry drip irrigation. The validated model accurately simulates water and nitrogen migration, predicting nitrogen leaching dynamics. Compared to chemical fertilizer treatment, differences in soil hydraulic parameters under biogas slurry drip irrigation impact moisture and nitrate nitrogen distribution. Increasing biogas slurry proportion enhances nitrate nitrogen content in the root layer, promoting plant nitrogen absorption while reducing leaching by 49.66%. Optimizing the irrigation system involves high concentration substitution in early growth and low concentration in late growth, mitigating nitrogen leaching, and enhancing plant root absorption.

Biochar effects on soil nitrogen retention, leaching and yield of perennial citron daylily under three irrigation regimes

Biochar can serve as a soil amendment to immobilize soil nitrogen (N) and reduce N leaching from cropland without negative effect on crop yield. However, the interaction effect of biochar application and irrigation regimes on soil N status (N retention and N loss) and crop yield is rarely reported in the open perennial vegetable field. A two-years field trial (transplanting in first year and consecutive growth in second year) was conducted in citron daylily vegetable cropping system on a sandy brown alluvial soil. Two biochar application rates (0 and 30 t ha−1) and three irrigation regimes (CDI, conventional drip irrigation; WSDI, water-saving drip irrigation with 80% of full irrigation quota; APRDI, alternate partial root-zone drip irrigation with 80% of full irrigation quota) were included. The response of crop yield and soil N status to both biochar application and irrigation regimes varied across planting years for perennial citron daylily. After the first planting year's harvest, APRDI enhanced flower bud yield by 18–28% compared to CDI and WSDI, likely due to improved nitrate use efficiency evidenced by lower soil nitrate retention in the surface soil (0–20 cm) post-harvest. However, biochar application resulted in a reduction of yield by 27% under APRDI. Additionally, WSDI with reduced yields, decreased soil TN in the sub-surface layer (20–50 cm) with 9–19% by comparison with other two irrigation regimes, resulting in higher TN concentration in the soil solution (14–28%) in and thus an increased risk for N leaching. However, after the second harvest year, there were no variations in crop yield induced by biochar application and irrigation regimes. Irrigation regimes exhibited limited influence on soil N status, while biochar application mitigated soil nitrogen decline in the 0–50 cm layer by enhancing organic nitrogen retention capacity for nearly 16–85%. Furthermore, the lowest TN concentration in the soil solution in the sub-surface layer (20–50 cm) with biochar application under APRDI suggested a reduced risk for N leaching. We conclude that combining biochar application with the APRDI regime could help retain soil N, decrease the risk of N leaching, and enhance crop yield in total for two consecutive planting years. Therefore, this approach is recommended for sustainable N management in long-term planting of perennial crops.

Yield, Quality, and Nitrogen Leaching of Open-Field Tomato in Response to Different Nitrogen Application Measures in Northwestern China.

The overuse of fertilizers in open-field tomato leads to soil deterioration through nutrient leaching and increases the risk of agricultural non-point source contamination. Currently, the combined effects of different fertilization methods on soil nitrogen leaching and tomato production are still unclear. Therefore, the most effective fertilization method for open-field tomato should be discovered by examining how different fertilization methods affected tomato yield and quality, nitrogen use efficiency (NUE), and soil nitrogen leaching. Compared with CK (no fertilization), fertilization significantly increased the yield, total sugar (TS), total soluble solids (TSS), and vitamin C (vC) contents of fruits (p < 0.05), and OPT (optimal fertilization, controlled release nitrogen application, 240 kg ha-1) had the largest effect on increasing yield, quality, and net profit. However, when the fertilizer application rate reached 375 kg ha-1, these indices decreased. Nitrogen leaching concentrations, leaching amount, and titratable acids (TAs) increased with increased nitrogen application rates. Compared with other treatments, OPT reduced the total leaching amounts of total nitrogen (TN), nitrate nitrogen (NO3--N), and ammonia nitrogen (NH4+-N) by 30.09-51.79%, 24.89-50.03%, and 30-65%, respectively. Principal component analysis (PCA) showed that OPT achieved the highest overall score in terms of yield, quality, and nitrogen leaching conditions. The partial least squares path modeling (PLS-PM) further reveals that applications of high amounts of nitorigen have a positive effect on soil nitrogen leaching. The amount of nitrogen leaching vegetatively affects tomato yield and quality, while plant uptake of nitrogen positively affects tomato production. These findings confirm the importance of using controlled-release fertilizers and reducing nitrogen inputs to control nitrogen leaching and enhance open-field tomato yields.

Applications of land surface model to economic and environmental-friendly optimization of nitrogen fertilization and irrigation

Land surface models (LSMs) have prominent advantages for exploring the best agricultural practices in terms of both economic and environmental benefits with regard to different climate scenarios. However, their applications to optimizing fertilization and irrigation have not been well discussed because of their relatively underdeveloped crop modules. We used a CLM5-Crop LSM to optimize fertilization and irrigation schedules that follow actual agricultural practices for the cultivation of maize and wheat, as well as to explore the most economic and environmental-friendly inputs of nitrogen fertilizer and irrigation (FI), in the North China Plain (NCP), which is a typical intensive farming area. The model used the indicators of crop yield, farm gross margin (FGM), nitrogen use efficiency (NUE), water use efficiency (WUE), and soil nitrogen leaching. The results showed that the total optimal FI inputs of FGM were the highest (230 ± 75.8 kg N ha−1 and 20 ± 44.7 mm for maize; 137.5 ± 25 kg N ha−1 and 362.5 ± 47.9 mm for wheat), followed by the FIs of yield, NUE, WUE, and soil nitrogen leaching. After multi-objective optimization, the optimal FIs were 230 ± 75.8 kg N ha−1 and 20 ± 44.7 mm for maize, and 137.5 ± 25 kg N ha−1 and 387.5 ± 85.4 mm for wheat. By comparing our model-based diagnostic results with the actual inputs of FIs in the NCP, we found excessive usage of nitrogen fertilizer and irrigation during the current cultivation period of maize and wheat. The scientific collocation of fertilizer and water resources should be seriously considered for economic and environmental benefits. Overall, the optimized inputs of the FIs were in reasonable ranges, as postulated by previous studies. This result hints at the potential applications of LSMs for guiding sustainable agricultural development.

Combined Effect of Freeze–Thaw Cycles and Biochar Addition on Soil Nitrogen Leaching Characteristics in Seasonally Frozen Farmland in Northeast China

Global climate warming and increased climate variability may increase the number of annual freeze–thaw cycles (FTCs) in temperate zones. The occurrence of more frequent FTCs is predicted to influence soil carbon and nitrogen cycles and increase nitrogen leaching. Biochar has the potential to increase soil organic carbon storage and decrease nitrogen leaching. This study aims to investigate the impact of freeze–thaw cycles (FTCs) on soil nitrogen leaching in temperate zones, considering the potential exacerbation of FTCs due to global climate warming and increased climate variability. This study focuses on how biochar, a carbon-rich material produced from biomass, might mitigate nitrogen leaching by influencing soil characteristics. This study explores the interactions between different laboratory-simulated FTC frequencies (ranging from 0 to 12 cycles) and various biochar addition ratios (0%, 2%, 4%, and 6% w/w) on soil nitrogen leaching based on a total of 60 soil columns. Pearson correlations between the soil quality indicators and nitrogen leaching characteristics were detected, and partial least squares path modeling (PLS-PM) was used to assess the effects of the FTCs, biochar addition ratios, and soil quality indicators on the nitrogen leaching content. The results showed that the amount of leached soil NH4+-N and NO3−-N reached 0.129–1.726 mg and 2.90–7.90 mg, respectively. NH4+-N and NO3−-N first increased and then decreased under the FTCs, with the highest values being observed after the 6th FTC. As the biochar addition ratio increased, the NH4+-N and NO3−-N contents decreased. Correlation analysis showed that the nitrogen leaching content was significantly related to the soil pH, soil organic matter (SOM), NH4+-N content, and microbial biomass carbon content (MBC) (p &lt; 0.01). The results of the conceptual path model revealed that nitrogen leaching characteristics were significantly affected by the pH, SOM, soil nitrogen content, and biochar addition ratio. Our results suggest that biochar addition can help reduce nitrogen leaching in farmland soil in areas with black soil and seasonal freeze–thaw cycles.

Research on Underground Drip Irrigation and Soil Redistribution - Take Heshan District of Yiyang City as an Example

Abstract: The drip flow and the buried depth of drip irrigation zone are not only important parameters of subsurface irrigation design and operation management, but also important factors affecting the migration and redistribution of soil water and fertilizer. Crop growth is closely related to soil water and nitrogen leaching, water and fertilizer transport patterns and redistribution characteristics. It is of great significance to study the migration and redistribution of soil water and fertilizer under subsurface drip irrigation for improving the utilization efficiency of water and fertilizer and improving the system of subsurface drip irrigation. In this paper, the migration mode and redistribution characteristics of water and nitrogen in subsurface drip irrigation were studied and analyzed by means of laboratory soil box experiment, considering the two factors of drip flow and the buried depth of drip irrigation belt. The main research conclusions are as follows: Ⅰ. Different drip flows had effects on soil moisture front, soil moisture content and soil water redistribution. If other conditions remain unchanged, increasing the drip flow can increase the moist body area of soil and increase the moisture content of soil. The distance between vertical and horizontal directions increased with the large drip flow, and the soil water content decreased with the increase of distance. Large drip flow can promote the redistribution of soil water after drip irrigation. Ⅱ. Different drip depth had effects on soil moisture content and soil water redistribution. When the drip depth was 0cm, the surface shape of the wet body was a "horizontal" semi-ellipse after drip irrigation. When the drip depth was 10cm and 20cm, the surface of the wet body was an "upright" semi-ellipse after drip irrigation. The larger the buried depth of the drip can make the distribution of soil moisture more uniform, and the larger the buried depth of the drip can promote the migration of water in the soil. Ⅲ. Different drip discharge had an effect on soil nitrogen redistribution, and large drip discharge promoted soil nitrogen redistribution after drip irrigation. The Nitrate Nitrogen (NO3--N) content in the moist body is lower than that near the edge of the wetting front. The content of Ammonium Nitrogen (NH4+-N) near the edge of the wetting peak is higher than that inside the wetting body. Ⅳ. The redistribution of soil nitrogen was affected by different buried depth of drip head, and the greater buried depth of drip head could promote the redistribution of soil nitrogen. In terms of vertical and horizontal migration of ammonium nitrogen and nitrate nitrogen, on the day after drip irrigation, the cumulative effect of Nitrate Nitrogen (NO3--N) buried at a depth of 20cm was more significant near the wetting front edge at a larger vertical downward distance, and the cumulative effect of Nitrate Nitrogen (NO3--N) buried at a depth of 20cm was more significant inside the wetting body at a larger vertical downward distance. At the same time, the drip buried depth of 20cm can spread the cumulative effect inside the wet body and near the edge of the wet front to a longer horizontal distance.

Reducing nitrogen leaching using wood vinegar treated in urea-fertilized soil.

Wood vinegar (WV) is known to retard the release of ammonium (NH4+) from urea by inhibiting urea hydrolysis. However, the effect of WV on nitrogen leaching in soil is not known, and there are few studies on the effect of WV on microbial activity although WV exhibits antibacterial properties against pathogens in agriculture. Therefore, the purpose of this study was to investigate the effect of WV on controlling nitrogen leaching and soil microbial activity. Soils were treated with urea and WV, and the available inorganic nitrogen concentrations in the soil were compared with those from soils treated with N-(n-butyl)thiophosphoric triamide (NBPT), a commonly used urease inhibitor. The nitrate concentration in the soil was significantly decreased in the WV treatment, although the ammonium concentration was not affected by the WV treatment. Basal soil respiration was significantly increased in the WV and NBPT treatments although the microbial biomass was increased in the urea only treatment. The ammonium nitrogen concentration in the leachate was not significantly different in the WV and urea-treated soil compared to the urea-only treatment. However, the nitrate leaching increased in the soil treated only with urea at 16days after the treatment although there was no statistically significant difference in the total leached nitrate. Therefore, WV can be used to reduce nitrogen leaching and enhance soil microbial activity.

Evaluating the Effects of Controlled Drainage on Nitrogen Uptake, Utilization, Leaching, and Loss in Farmland Soil

Controlling drainage during the growth stage is one of the means to provide suitable water and fertilizer conditions for crops, alleviate environmental pollution, and increase crop yield. Therefore, in this study, we studied three drainage treatments: free drainage (FD) and growth-stage subsurface controlled drainage (CD) at depths of 40 cm (CWT1) and 70 cm (CWT2). We used the HYDRUS-2D model to simulate the dynamic changes of NO3-N in the 0–100 cm soil layer as well as NO3-N uptake by crops, leaching after irrigation and fertilization, and loss through subsurface pipes in 2020 (model calibration period) and 2021 (model validation period). The degree of agreement between the simulated and measured values was high, indicating a high simulation accuracy. CD increased the soil NO3-N content and crop NO3-N uptake, and decreased NO3-N leaching and loss. We observed significant differences in the soil NO3-N content after irrigation at the budding stage of oilseed sunflower between CD and FD, with the largest difference seen for the 0–40 cm soil layer. CD increased crop yield, and the average oilseed sunflower yield of the CWT1 and CWT2 treatments increased by 4.52% and 3.04% relative to the FD treatment (p &lt; 0.05). CD also enhanced nitrogen use efficiency. In moderately salinized soil, CD at 40 cm (CWT1) reduced the nutrient difference in vertical and horizontal directions while retaining water and fertilizer. CWT1 stabilized the groundwater depth, reduced the hydraulic gradient of groundwater runoff, and decreased the drainage flow rate. The NO3-N leaching and loss dropped, which promoted crop nitrogen uptake and utilization, improved nitrogen use efficiency, reduced nitrogen loss, and had a positive effect on protecting the soil and water environment. The results demonstrate that CD is a suitable drainage method for the experimental area.

Biochar and Its Potential to Deliver Negative Emissions and Better Soil Quality in Europe

AbstractNegative emissions are essential to limit global warming, but their large‐scale deployment rises sustainability concerns. At the same time, agricultural soils are under increasing threat of degradation, as measured by losses in soil organic matter, water holding capacity, and nutrient retention, with increasing negative effects on plant productivity. Biochar from biomass residues is a technically mature option that does not compete for land and can typically restore key functions of degraded soils while delivering negative emissions. However, quantitative estimates of its potentials in Europe and a detailed spatially‐explicit analysis of the co‐benefits and trade‐offs for agricultural land are unclear. Here, we estimate an annual negative emission potential of biochar from forest and crop residues available in Europe from 1.7% to 3.9% of 2021s European greenhouse gas emissions (15.2%–35% of the agricultural emissions), depending on residue potentials and biochar scenarios. At the same time, biochar application to cropland increases water holding capacity (+6.5%‐9%), crop production (+7.1%‐8.4%), NH3 volatilization (+21.7%‐24.2%), and reduces soil N2O emissions (−13.7%–34.7%) and nitrogen leaching (−17.5%–22.7%). There are spatially heterogeneous trade‐offs for some soil effects (ammonia volatilization and yields) and air pollution (mainly due to emissions from biochar systems). Biochar offers synergistic solutions that co‐deliver across different sustainability challenges, but its optimal deployment requires strategies tailored to local conditions.

Application fruit tree hole storage brick fertilizer is beneficial to increase the nitrogen utilization of grape under subsurface drip irrigation.

It is very important to promote plant growth and decrease the nitrogen leaching in soil, to improve nitrogen (N) utilization efficiency. In this experiment, we designed a new fertilization strategy, fruit tree hole storage brick (FTHSB) application under subsurface drip irrigation, to characterise the effects of FTHSB addition on N absorption and utilization in grapes. Three treatments were set in this study, including subsurface drip irrigation (CK) control, fruit tree hole storage brick A (T1) treatment, and fruit tree hole storage brick B (T2) treatment. Results showed that the pore number and size of FTHSB A were significantly higher than FTHSB B. Compared with CK, T1 and T2 treatments significantly increased the biomass of different organs of grape, N utilization and 15N content in the roots, stems and leaves, along with more prominent promotion at T1 treatment. When the soil depth was 15-30 cm, the FTHSB application significantly increased the soil 15N content. But when the soil depth was 30-45 cm, it reduced the soil 15N content greatly. T1 and T2 treatments obviously increased the activities of nitrite reductase (NR) and glutamine synthetase (GS) in grape leaves, also the urease activity(UR) in 30 cm of soil. Our findings suggest that FTHSB promoted plant N utilization by reducing N loss in soil and increasing the enzyme activity related to nitrogen metabolism. In addition, this study showed that FTHSB A application was more effective than FTHSB B in improving nitrogen utilization in grapes.

Molecular and Dual-Isotopic Profiling of the Microbial Controls on Nitrogen Leaching in Agricultural Soils under Managed Aquifer Recharge.

Nitrate (NO3-) leaching is a serious health and ecological concern in global agroecosystems, particularly those under the application of agricultural-managed aquifer recharge (Ag-MAR); however, there is an absence of information on microbial controls affecting NO3- leaching outcomes. We combine natural dual isotopes of NO3- (15N/14N and 18O/16O) with metagenomics, quantitative polymerase chain reaction (PCR), and a threshold indicator taxa analysis (TITAN) to investigate the activities, taxon profiles, and environmental controls of soil microbiome associated with NO3- leaching at different depths from Californian vineyards under Ag-MAR application. The isotopic signatures demonstrated a significant priming effect (P < 0.01) of Ag-MAR on denitrification activities in the topsoil (0-10 cm), with a 12-25-fold increase of 15N-NO3- and 18O-NO3- after the first 24 h of flooding, followed by a sharp decrease in the enrichment of both isotopes with ∼80% decline in denitrification activities thereafter. In contrast, deeper soils (60-100 cm) showed minimal or no denitrification activities over the course of Ag-MAR application, thus resulting in 10-20-fold of residual NO3- being leached. Metagenomic profiling and laboratory microcosm demonstrated that both nitrifying and denitrifying groups, responsible for controlling NO3- leaching, decreased in abundance and potential activity rates with soil depth. TITAN suggested that Nitrosocosmicus and Bradyrhizobium, as the major nitrifier and denitrifier, had the highest and lowest tipping points with regard to the NO3- changes (P < 0.05), respectively. Overall, our study provides new insight into specific depth limitations of microbial controls on soil NO3- leaching in agroecosystems.

Response of Forest Ecosystems to Decreasing Atmospheric Nitrogen Deposition

Nitrogen deposition has serious consequences to global change. Excessive nitrogen deposition leads to nitrogen saturation in forests, resulting in soil acidification, nitrate leaching, an increase in nitrous oxide emissions, and a decrease in plant species diversity and vegetation productivity. Under the reduction of atmospheric nitrogen deposition in Europe, North America, and China, summarizing the response of forests to decreasing nitrogen deposition can not only improve the knowledge framework of the impact of nitrogen deposition on forests, but also evaluate the effects of emission abatement actions, as well as provide scientific basis for future air pollution control. This study reviewed the response of soil, surface water, nitrogen cycle, and vegetation of temperate forests in Europe and North America and subtropical forests in southwest China to the reduction in atmospheric nitrogen pollution gases and thus nitrogen deposition. The soil water nitrogen concentration responded rapidly to the nitrogen deposition reduction, although the trend was inconsistent. The soil acidification and nitrogen cycles showed a delayed response of recovery from high nitrogen deposition. The nitrogen mineralization and immobilization, soil carbon retention, and net primary production might take decades to respond to the nitrogen deposition reduction. However, the soil inorganic nitrogen pool and nitrogen leaching decreased with the decline in nitrogen deposition, although a one-or two-year lag existed. The surface water nitrogen concentration was closely related to nitrogen status in forests. After the nitrogen deposition decreased, the nitrogen leaching and thus the surface water nitrogen concentration decreased in the areas with historically high nitrogen deposition. However, the low surface water nitrogen concentration in the nitrogen-limited forests was not significantly affected by the nitrogen deposition changes. The recovery of surface water acidification was affected by soil sulfur desorption/mineralization and nitrification/denitrification. The foliar nitrogen concentration decreased with the decline in nitrogen deposition. The nitrogen-saturated forests and regional surface water in southwest China showed a recovery trend from high nitrogen deposition, as a consequence of the implementation of the Total Emissions Control of Air Pollutants and later the Action Plan of Air Pollution Prevention and Control.

DNRA and ANRA-centered microbial mechanism of biogas slurry on soil nitrogen leaching: An indication from a laboratory study

Biogas slurry has ammonia (NH4+-N) abundance and is applied in a major production region, Southwest China. This study compared the consequent environmental risk of nitrogen (N) leaching in two major soils, yellow soil and calcareous soil, in Southwest China, and investigated underlying microbial mechanisms. Biogas slurry was applied to soil columns packed with yellow soil and calcareous soil at the rates of 0 to 240 kg N/hm2. Soil N leaching, N contents, and N-related bacteria gene abundances were measured, with their responses to slurry application analyzed through partial least squares-structural equation modeling (PLS-SEM). Nitrate (NO3−-N) dominated in N leaching as a result of soil NO3−-N accumulation and microbial regulation. Nitrification increased yellow soil NO3−-N contents and leaching, however, both were inhibited by dissimilatory nitrate reduction to ammonium (DNRA) and assimilatory nitrate reduction to ammonium (ANRA) in the two soils. Further, NO3−-N leaching was enhanced by biogas slurry in yellow soil by promoting nitrification and preventing DNRA and ANRA; but it was not affected in calcareous soil. Accordingly, yellow soil has higher NO3−-N leaching than calcareous soil. The leaching can be regulated by the DNRA and ANRA in both soils, which were overlooked relative to nitrification but probably reactive to slurry, warranting further exploration.

Laboratory and numerical modelling of irrigation infiltration and nitrogen leaching in homogeneous soils

Nitrogen (N) plays a key role in crop growth and production; however, data are lacking especially regarding the interaction of biochar, grass cover, and irrigation on N leaching in saturated soil profiles. Eighteen soil columns with 20-cm diameter and 60-cm height were designed to characterize the effects of different grass cover and biochar combinations, i.e., bare soil + 0% biochar (control, CK), perennial ryegrass + 0% biochar (C1), Festuca arundinacea + 0% biochar (C2), perennial ryegrass + 1% biochar (C3), perennial ryegrass + 2% biochar (C4), perennial ryegrass + 3% biochar (C5), F. arundinacea + 1% biochar (C6), F. arundinacea + 2% biochar (C7), and F. arundinacea + 3% biochar (C8), on periodic irrigation infiltration and N leaching in homogeneous loess soils from July to December 2020. Leachates in CK were 10.2%–35.3% higher than those in C1 and C2. Both perennial ryegrass and F. arundinacea decreased the volumes of leachates and delayed the leaching process in the 1%, 2%, and 3% biochar treatments, and the vertical leaching rate decreased with biochar addition. The N leaching losses were concentrated in the first few leaching tests, and both total N (TN) and nitrate (NO3-)-N concentrations in CK and C1–C8 decreased with increasing leaching test times. Biochar addition (1%, 2%, and 3%) could further reduce the leaching risk of NO3--N and the NO3--N loss decreased with biochar addition. However, compared to 1% biochar, 2% biochar promoted the leaching of TN under both grass cover types. The N leaching losses in CK, C1, C2, C3, C4, C6, and C7 were primarily in the form of NO3--N. Among these treatments, CK, C1, and C2 had the highest cumulative leaching fractions NO3--N (> 90%), followed by those in C3, C4, C6, and C7 (> 80%). The cumulative leaching fraction of NO3--N decreased with increasing leaching test times and biochar addition, and 3% biochar addition (i.e., C5 and C8) reduced it to approximately 50%. The one-dimensional advective-dispersive-reactive transport equation can be used as an effective numerical approach to simulate and predict NO3--N leaching in saturated homogeneous soils. Understanding the effects of different biochar and grass combinations on N leaching can help us design environmentally friendly interventions to manage irrigated farming ecosystems and reduce N leaching into groundwater.