Accumulation Of Nitrate Nitrogen Research Articles

Effects of Basic Soil Treatment Techniques on the Nitrate Nitrogen Accumulation Dynamics in Soil

This paper addresses the effects that basic soil treatment techniques that place crop residues on the field surface in different ways have on the nitrate nitrogen content in the soil. The study was carried out in 2018–2019 in Saratov oblast in the framework of a stationary experiment conducted by the Agricultural Research Institute for the Southeastern Region in a sloping–hollow agrolandscape represented by a landscape strip on a south-facing slope with an inclination of 1°–3°. The nitrate nitrogen dynamics was monitored in the course of cultivation of soft spring wheat, variety Saratovskaya 70. The purpose of this study was to identify the accumulation dynamics patterns of nitrate nitrogen in soils treated by sweep cultivation that leaves crop residues on the soil surface and by a cultivation technique that places crop residues locally in coulisses divided by mineralized soil strips. It is established that surface placement of crop residues as a result of sweep loosening and their local placement in coulisses reduce the nitrate nitrogen content iRUBRICSn the arable layer. By contrast, the mineralized strips formed between the coulisses provide optimal conditions for nitrification processes.

Quantitative trait loci analysis of nitrate-nitrogen content in Italian ryegrass (Lolium multiflorum Lam.)

Italian ryegrass (Lolium multiflorum Lam.) is widely cultivated in temperate regions owing to its excellent producibility and digestibility. Nitrogen is an essential nutrient for plant growth; however, the overuse of nitrogen fertilizers can lead to excessive accumulation of nitrate-nitrogen in Italian ryegrass, which can prove to be lethal for ruminants. To study the genetic control of the nitrate-nitrogen content in Italian ryegrass, an Italian ryegrass line LNG8 (with low 0.12% dry matter (DM) of nitrate-nitrogen) and a second line JFIR12 (with a “normal” 0.20% DM of nitrate-nitrogen) were pair-crossed and 190 F2 individuals derived from these were used to construct an SSR-based linkage map for conducting QTL analysis. A linkage map was constructed based on 212 Lolium SSR markers. The female parental map consisted of seven linkage groups (LGs) and had a total length of 714.1 cM with 178 loci and an average map density of 4.0 cM. The male parental map consisted of 7 LGs and had a total length of 737.4 cM with 199 loci and an average map density of 3.7 cM. We measured the nitrate-nitrogen content of the mapping population in three replicates (including the main stem and two tillers separated from the main stem) at the six-leaf stage. The nitrate-nitrogen content of the mapping population followed a normal distribution with a marginal skewness toward the lower parent. Our analysis revealed the presence of six QTLs on three LGs. A major QTL on LG1 was detected in all three replicates in both two-parental maps, which could explain 19.4%–29.9% of the phenotypic variation. Furthermore, based on the information of model plant species such as rice and Arabidopsis, we cloned six nitrogen metabolism-related genes and attempted to locate these on our linkage maps; however, none of these six genes were located in the demarcated QTL regions. These results will be useful for understanding the genetic bases of nitrate-nitrogen content in Italian ryegrass and the molecular cloning of QTLs for determination of nitrate-nitrogen content. The flanking markers of the QTLs will be helpful for breeding Italian ryegrass with low nitrate-nitrogen content.

Minimizing Soil Nitrogen Leaching by Changing Furrow Irrigation into Sprinkler Fertigation in Potato Fields in the Northwestern China Plain

Irrigation water is limiting for crop production in arid areas and application rates of fertilizers often exceed crop requirements, resulting in high accumulation of nitrate nitrogen (NO3−-N) in the soil. Management practices play a significant role in the leaching of NO3−-N. This experiment compares the effects of traditional furrow irrigation and sprinkler fertigation on the soil NO3−-N concentration trend throughout the cropping season in potato fields in China. Two irrigation systems that were fertilized, namely by furrow (NF-FI) and sprinkler fertigation (NF-SI), and two controlling without any fertilizer (C-FI and C-SI) were tested in the same experimental site for three consecutive years. Both the NF-FI soils and NF-SI soils with three replications and fertilizer applications of 273 kg N ha−1 exhibited a different trend of NO3−-N accumulation at different depths of soil profile. However, the magnitude of NO3−-N accumulation was low in the NF-SI soil profile. In NF-SI treatments, higher NO3−-N was observed at 20–40 cm soil layer. In the NF-FI, the concentration of the highest nitrate was observed at the 40–120 cm soil layer. The concentrations of NO3−-N in the fertilized soil were higher than those of the control soil for each irrigation system. Residual levels of NO3−-N in the soil depth of 40–120 cm from NF-FI were 1.54, 3.45 and 5.28 times higher than NF-SI after harvesting potatoes from 2015 to 2017. In NF-FI treatments, apparent nitrogen loss was 234.7, 237.5 and 276.7 kg ha−1 after harvesting potatoes in 2015, 2016 and 2017. Meanwhile, apparent nitrogen loss from NF-SI treatments was only 161.9, 132.1 and 148.9 kg ha−1, which was 31.0%, 44.4% and 46.2% lower than that of NF-FI in 2015, 2016 and 2017, respectively. The risk of NO3−-N leaching below the root zone from NF-FI was higher than that from NF-SI. It has been demonstrated that sprinkler fertigation can also be used as a tool for mitigating NO3−-N accumulation and apparent nitrogen loss.

Identification of Critical Diffuse Pollution Sources in an Ungauged Catchment by Using the Swat Model- A Case Study of Kolleru Lake, East Coast of India

Freshwater ecosystems are facing severe threats from human activities. As a consequence of this, they can get disturbed. In developing countries, like India, freshwater lakes are endangered primarily by agricultural activities, which often accelerate erosion and the runoff. The massive application of pesticides and chemical fertilizers to agricultural lands is one of the reasons for eutrophication in Kolleru Lake. The different natural and anthropogenic influences increase the highly complex ecosystem of the lake. Therefore, the objectives of this study are to ascertain the priority control areas, aiming at socio-economic development for the protection of the lake water quality by applying the Best Management Practices (BMPs). 
 For this purpose, the Soil and Water Assessment Tool (SWAT) was used to identify the critical areas of the lake's catchment in terms of pollution from agricultural runoff into the tributaries of the Kolleru Lake and the lake itself. The results demonstrated that the diffuse pollution load in the western and downstream watersheds the highest and that agricultural land was the primary pollutant source besides the accumulation of nutrients in the downstream areas. The differences in the sub-basin loads were observed in the catchment mainly depends on the topographic features, soil properties, land use, vegetation, and drainage patterns. From where the major outlet sub-basin has the highest accumulation of nitrate-nitrogen (NO3_N), and total phosphorus (TP) emissions were quantified. The temporal distribution of runoff and diffuse sources were estimated from 2008 – 2014. The runoff mainly governed diffuse pollution was found to be a significant contributing factor to the lake. Further, suggestions were provided for the implementation of agricultural management practices to minimize pollution levels.
 
 Graphical Abstract:
 
 
 (Own Source: Diagrammatic representation showing the interrelationship of the SWAT run model)

Main elements of nutrition content in the soil for maize crops, depending on the predecessors and methods of soil treatment

The article presents data on the study of the main nutrition elements in the soil under maize crops, depending on the predecessors and methods of soil treatment in the conditions of ordinary Chernozem. The object of research is aKrasnodarsky 194MVhybrid of maize. Variants: 1. Fallow arable land (control); 2. Lupine as green manure; 3. Peas as green manure; 4. Binary sowing of lupine and peas as green manure; 5. Soy as green manure. The experiment was repeated three times, field placement was randomized, and area of each was 120 m². Agrotechnics of maize cultivation in the experiment corresponded to the recommendations for this zone. Green manure was plowed in during its reproduction phase. In the variants with green mass plowing to a depth of 23–25 cm, the largest amount of nitrate nitrogen was in the soil layer 0–20 cm. In the specified soil horizon, before sowing maize, the content of nitrate nitrogen ranged, depending on the variant, from 24.7 mg/kg to 42.8 mg/kg. In the soil layer 20–40 cm, the amount of nitrogen was lower, just 19.4–29.5 mg/kg. Similar dependence was observed for maize during its flowering phase. Tillage methods had almost no effect on the accumulation of nitrate nitrogen in the upper soil layer (0–20 cm). As in all the variants, the differences in this indicator were within the experimental error. However, the content of nitrate nitrogen during the growing season was different. The greatest amount of it was observed during the spring period, both in versions with plowing to a depth of 25–28 cm and in versions with blade loosening to a depth of 10–12 cm. The smallest amount of available phosphorus, regardless of the method of soil preparation, in the layer 0–20 cm was on fallow arable land – 122 mg/kg during the sowing period and 104 mg/kg during the flowering period. In variants with cultivation of legumes as green manure, the content of available phosphorus in the specified horizon was significantly chigher, being 147–171 mg/kg. The highest content of exchangeable potassium was provided by lupine – 209–213 mg/kg in the 0–20 cm soil layer, and lupine sown together with peas – 196–207 mg/kg. The minimum amount of exchangeable potassium was 143–146 mg/kg in fallow arable land, depending on the method of soil treatment.

Application of an innovative front aeration and internal recirculation strategy to improve the removal of pollutants in subsurface flow constructed wetlands

The pollutant removal performance of traditional horizontal subsurface flow (HSSF) constructed wetlands (CWs) is limited because of the dissolved oxygen (DO) supply is insufficient. The aeration of HSSF CWs usually improves their pollutant removal performance, but a high DO induces the accumulation of nitrate-nitrogen (NO3−-N) and suppresses the improvement of total nitrogen (TN) removal. In this study, an integrated solution that involved in-tank front aeration and internal recirculation (FAIR) was used to improve the pollutant removal performance of HSSF CWs. Based on the experimental results, the FAIR system significantly increased the removal efficiencies of biochemical oxygen demand (BOD) from 53.8–76.0% to 82.0–91.7% and reduced the BOD concentration in the effluent to below 10 mg L−1. The removal efficiency of ammonia-nitrogen (NH3–N) increased from 15.1–78.3% to 98.5–98.6% while the removal efficiencies of the total Kjeldahl nitrogen (TKN) of the control and FAIR HSSF CWs were 18.2–77.1% and 93.5–94.3%, respectively. HSSF CWs with FAIR outperformed aerated HSSF CWs in the removal of NH3–N and TKN. The effects of two recirculation flow ratios (Rr = recirculation flow rate/influent flow rate), 14.3 and 3.0, on the improvement of pollutant removal performance were investigated. The lower Rr did not significantly affect the improvement of BOD, NH3–N, and TKN, but a higher Rr resulted in more severe accumulation of NO3−-N. The removal efficiency of TN in control HSSF CWs ranged from 20.4% to 75.5%, and in the FAIR HSSF CW was 71.6% for Rr = 14.3 and 81.3% for Rr = 3.0. However, the FAIR system did not enhance the removal performance of total phosphorus, suggesting that the DO level and internal recirculation were not dominant mechanisms for the removal of phosphorous. The easy maintenance of the FAIR system made it a superior modification for improving the pollutant removal performance of HSSF CWs.

Effects of dopamine on growth, carbon metabolism, and nitrogen metabolism in cucumber under nitrate stress

Dopamine, which is a catecholamine neurotransmitter, is widely present in plant organs. The accumulation of soil nitrate limits the growth of plants. We investigated the role of dopamine in regulating the growth, carbon metabolism, and nitrogen metabolism in cucumber (Cucumis sativus L. “Jin You No. 1”) under nitrate stress. Under nitrate stress, plants showed significant reductions in growth, chlorophyll concentrations, chlorophyll fluorescence and gas exchange parameters. However, dopamine markedly alleviated such reductions. Excess nitrate led to an increase in sucrose phosphate synthase, acid invertase, and neutral invertase activity, but decreased sucrose synthase activity. Similarly, the expression of the CsSPS4 gene was also up-regulated and the expression of the CsSUS3 gene was down-regulated under nitrate stress. Dopamine significantly increased the activity and gene expression of these enzymes. The CsNRT1.1 gene was up-regulated under nitrate conditions. Dopamine significantly alleviated the accumulation of nitrate nitrogen and ammonium nitrogen under nitrate conditions. Nitrate reductase activity and the expression of the CsNR1 gene were significantly inhibited due to exposure to excess nitrate. We found that glutamine synthetase activity decreased and glutamate dehydrogenase activity increased after nitrate induction, which indicated that ammonium assimilation relied mainly on glutamate dehydrogenase pathway rather than glutamine synthetase/glutamate synthase cycle under nitrate stress. Dopamine significantly enhanced the activity of enzymes and gene expression of nitrogen metabolism. Our results indicated that dopamine plays an important role in mediating plant growth, carbon metabolism, and nitrogen metabolism.

Effects of mulching measures on soil moisture and N leaching potential in a spring maize planting system in the southern Loess Plateau

A field experiment was conducted in the southern gully region of the Loess Plateau to study the effects of mulching measures on spring maize yield and nitrate accumulation in dryland areas under traditional tillage conditions. The study was performed to provide a scientific basis for spring maize planting and environmental protection in this area. The four treatments were non–mulching (CK), plastic film–mulching during the growth period (PM1), plastic film–mulching during the fallow period (PM2), and straw–mulching (JM). After 13 years of continuous application, the yield of spring maize, the nitrogen uptake by plants, and the nitrate nitrogen content at the harvest stage were measured. The results revealed that soil moisture content and water storage capacity of the three soil–mulching treatments were all higher than those of the non–mulching treatment. Soil water storage at a depth of 0–300 cm in the JM, PM1 and PM2 treatments was increased by 11.8%, 10.6% and 8.8%, respectively, compared with the CK treatment. Compared with the CK treatment, the mulching treatments significantly increased the aboveground biomass and grain yield of spring maize. The yield enhancement effect of the PM1 treatment was the most significant, with a yield of 1.1 Mg ha-1 and an increase of 26.72%. In addition to the JM treatment, the accumulation of soil nitrate at a depth of 0–300 cm in the PM1 and PM2 treatments was less than that of the CK treatment, but the largest increase in soil nitrate (80.20% in the JM treatment) was observed at a depth of 0–100 cm. The results suggest that in the rainfed agriculture in the southern Loess Plateau, mulching cultivation can effectively increase the soil moisture content and water storage capacity. PM1, and PM2 treatments could significantly reduce the content and accumulation of nitrate nitrogen in the deeper soil profile, and the three mulching measures could slow down the deep accumulation of soil nitrate nitrogen to a certain extent.

Effect of different mulching measures on nitrate nitrogen leaching in spring maize planting system in south of Loess Plateau

Field experiment was conducted in the southern gully region of the Loess Plateau to study the effects of different mulching measures on spring maize yield and nitrate leaching in dryland under the traditional tillage conditions, so as to provide a scientific basis for spring maize planting and environmental protection in this area. The four treatments included non-mulching (CK), plastic film-mulching (PM1), plastic film-mulching in fallow (PM2) and straw-mulching (JM). After 13 years of continuous application, the yield of spring maize, the nitrogen uptake by plants and the nitrate nitrogen content at the harvest stage were measured. The results showed that the soil moisture content and water storage capacity of three kinds of soil mulching treatments were all higher than those of non-mulching ones. Soil water storage in the range of 0 ∼ 300 cm of JM, PM1 and PM2 increased by 11.8%, 10.6% and 8.8% respectively compared with CK. Compared with CK, the mulching treatments significantly increased the aboveground biomass and grain yield of spring maize. The yield enhancement effect of PM1 was the most significant, with a yield of 11,314.42 kg / ha and an increase of 26.72%. In addition to the JM treatment, the accumulation of soil nitrate nitrogen in the range of 0 ∼ 300 cm of PM1 and PM2 was less than that of CK, but the increase of nitrate nitrogen of 80.20% of JM treatment was in the range of 0 ∼100 cm. Therefore, in the rain-fed agriculture in the south of Loess Plateau, mulching cultivation can effectively increase the soil moisture content and water storage, improve crop growth. The yield enhancement effect of plastic mulching-film was the best. PM1, PM2 could significantly reduce the content and accumulation of nitrate nitrogen in soil profile, and the three mulching measures could slow the deep leaching of soil nitrate nitrogen to a certain extent.

Effect of Aeration Modes and COD/N Ratios on Organic Matter and Nitrogen Removal in Horizontal Subsurface Flow Constructed Wetland Mesocosms

A series of mesocosm-scale horizontal subsurface flow constructed wetlands (HSSF-CWs) were established. In Experiment 1, four artificial aeration (AA) modes, including pre-aeration at 24 h before the input of influent water (PA), aeration at 6 h (6AA) and 12 h (12AA) after the input of influent water and non-aeration (NA), were tested to obtain an optimal aeration mode for chemical oxygen demand (CODCr) and nitrogen removal. The results showed that aeration after the input of influent water could improve the removal efficiencies of CODCr and ammonia-nitrogen (NH4⁺-N), but lead to an accumulation of nitrate-nitrogen (NO3−-N). The above observation demonstrated that a single aeration cannot create an ideal alternation of aerobic and anaerobic conditions for simultaneous nitrification and denitrification. Therefore, HSSF-CWs with intermittent aeration (IA), after the input of influent water and NA were established to evaluate the combined effects of IA and influent COD/N ratios on pollutant removal in Experiment 2. The HSSF-CW with IA exhibited a better performance in CODCr and nitrogen removal compared to HSSF-CW with NA. The highest removal percentages of CODCr (90.1%), NH4+-N (99.8%) and total nitrogen (TN, 99.5%) were achieved at a COD/N ratio of 9.3 in HSSF-CW with IA.

Effects of long-term medieval agriculture on soil properties: A case study from the Kislovodsk basin, Northern Caucasus, Russia

The chemical properties and biological activities of soils were studied in the vicinity of the medieval settlement Podkumskoe-3 in the Kislovodsk basin (Northern Caucasus, Russia). Between the 5th and 8th centuries this area was ploughed regularly, but it was then abandoned up to the present day. It has been established that past human activity leads to soil undergoing significant transformations in terms of microbial communities and enzyme activity, and that such changes are maintained over long periods. Long-term manuring in the middle of the first millennium AD led to an increase in organic carbon content and the accumulation of nitrate nitrogen. Soils of ancient abandoned fields are associated with increases in microbial biomass, number of saprotrophic bacteria, urease activity, and fungal mycelium biomass. The observed changes in the microbiological and biochemical properties of soil were conditioned by secondary anthropogenically induced succession after the abandonment of arable lands.

Irrigation and Nitrogen Regimes Promote the Use of Soil Water and Nitrate Nitrogen from Deep Soil Layers by Regulating Root Growth in Wheat.

Unreasonably high irrigation levels and excessive nitrogen (N) supplementation are common occurrences in the North China Plain that affect winter wheat production. Therefore, a 6-yr-long stationary field experiment was conducted to investigate the effects of irrigation and N regimes on root development and their relationship with soil water and N use in different soil layers. Compared to the non-irrigated treatment (W0), a single irrigation at jointing (W1) significantly increased yield by 3.6–45.6%. With increases in water (W2, a second irrigation at flowering), grain yield was significantly improved by 14.1–45.3% compared to the W1 treatments during the drier growing seasons (2010–2011, 2012–2013, and 2015–2016). However, under sufficient pre-sowing soil moisture conditions, grain yield was not increased, and water use efficiency (WUE) decreased significantly in the W2 treatments during normal precipitation seasons (2011–2012, 2013–2014, and 2014–2015). Irrigating the soil twice inhibited root growth into the deeper soil depth profiles and thus weakened the utilization of soil water and NO3-N from the deep soil layers. N applications increased yield by 19.1–64.5%, with a corresponding increase in WUE of 66.9–83.9% compared to the no-N treatment (N0). However, there was no further increase in grain yield and the WUE response when N rates exceeded 240 and 180 kg N ha−1, respectively. A N application rate of 240 kg ha−1 facilitated root growth in the deep soil layers, which was conducive to utilization of soil water and NO3-N and also in reducing the residual NO3-N. Correlation analysis indicated that the grain yield was significantly positively correlated with soil water storage (SWS) and nitrate nitrogen accumulation (SNA) prior to sowing. Therefore, N rates of 180–240 kg ha−1 with two irrigations can reduce the risk of yield loss that occurs due to reduced precipitation during the wheat growing seasons, while under better soil moisture conditions, a single irrigation at jointing was effective and more economical.

Effects of nitrogen and irrigation water application on yield, water and nitrogen utilization and soil nitrate nitrogen accumulation in summer cotton

A field experiment was carried out to study the effects of nitrogen and irrigation water application on growth, yield, and water and nitrogen use efficiency of summer cotton, and to develop the optimal water and nitrogen management model for suitable yield and less nitrogen loss in summer cotton field in the Huang-Huai region. Two experimental factors were arranged in a split plot design. The main plots were used for arranging nitrogen factor which consisted of five nitrogen fertilizer le-vels(0, 60, 120, 180, 240 kg·hm-2, referred as N0, N1, N2, N3, N4), and the subplots for irrigation factor which consisted of three irrigation quota levels (30, 22.5, 15 mm, referred as I1, I2, I3). There were 15 treatments with three replications. Water was applied with drip irrigation system. Experimental results showed that both irrigation and nitrogen fertilization promoted cotton growth and yield obviously, but nitrogen fertilizer showed more important effects than irrigation and was the main factor of regulating growth and yield of summer cotton in the experimental region. With the increase of nitrogen fertilization rate and irrigation amount, the dry mater accumulation of reproductive organs, the above-ground biomass at the flowering-bolling stage and seed cotton yield increased gradually, reached peak values at nitrogen fertilization rate of 180 kg·hm-2 and decreased slowly with the nitrogen fertilization rate further increased. The maximum yield of 4016 kg·hm-2 was observed in the treatment of N3I1. Increasing nitrogen fertilizer amount would improve significantly total N absorption of shoots and N content of stem and leaf, but decrease nitrogen partial factor productivity. The maximum irrigation-water use efficiency of 5.40 kg·m-3 and field water use efficiency of 1.24 kg·m-3 were found in the treatments of N3I3 and N3I1, respectively. With increasing nitrogen fertilization amount, soil NO3--N content increased and the main soil NO3--N accumulation layer moved downward. By comprehensively considering above-ground biomass, seed cotton yield, water and nitrogen uptake and utilization, and soil NO3--N accumulation in the soil profile, the treatment N3I1 could be recommended as the optimal water and nitrogen application pattern for summer cotton production in the experimental region.

市販ホウレンソウ,コマツナの硝酸態窒素含有率と全窒素,カリウム含有率との関係

市販ホウレンソウ,コマツナの硝酸態窒素含有率と全窒素,カリウム含有率との関係

Impact of Groundwater Level on Nitrate Nitrogen Accumulation in the Vadose Zone Beneath a Cotton Field

In this study, the impacts of groundwater level on nitrate nitrogen accumulation in the vadose zone of a cotton field were investigated. Experiments were conducted in a cotton field at the CAS Ecological Agricultural Experiment Station in Nanpi from 2008 to 2010. A vertical observation well was drilled, and time-domain reflectometry probes and soil solution extractors were installed every 50 cm in the walls of the well to a depth of 5 m. The soil water content was monitored, and soil solution samples were obtained and analyzed every six days throughout the growing seasons during the three studied years. Additionally, a water consumption experiment was conducted, and the topsoil water content and leaf area index were measured in the cotton field. The resulting data were used to estimate parameters for use in a soil hydraulic and nitrate nitrogen movement model, and cotton evapotranspiration was calculated using the Penman–Monteith method. Groundwater level increases and decreases of ±4 m were simulated during a ten-year period using HYDRUS-1D. The results showed significant nitrate nitrogen accumulation in the vadose zone when the groundwater level remained unchanged or decreased, with increased accumulation as the groundwater depth increased. Additionally, increased precipitation and a deeper groundwater level resulted in greater nitrate nitrogen leaching in the cotton root zone. Therefore, irrigation and fertilization strategies should be adjusted based on precipitation conditions and groundwater depth.

Influence of Soybean Residue Management on Nitrate Nitrogen Accumulation and Subsequent Sorghum Yield in Kanhaplic Haplustults of Western Kenya

Influence of Soybean Residue Management on Nitrate Nitrogen Accumulation and Subsequent Sorghum Yield in Kanhaplic Haplustults of Western Kenya

Effect of different fertilization managements on nitrate accumulation in a Mollisol of Northeast China

In a continuous spring maize system in Northeast China, the accumulation and succession characteristics of nitrate in Mollisol with four fertilization treatments, including no fertilization (CK), farmers’ conventional fertilization (FC), recommendation fertilization (RF), and controlled release fertilizer application (CRF), were compared over a 6-year field plot trial. On average, the RF and CRF treatments decreased nitrate nitrogen by 16.6 and 39.5 % in the 0–90 cm soil layer, respectively, and maintained a relatively high maize grain yield, as compared to the FC treatment. The accumulation of nitrate nitrogen was more obvious in the CRF treatment compared with the other fertilizer treatments under the arid climate. However, the high precipitation resulted in the leaching of nitrate nitrogen into the deeper soil layer in all the fertilizer treatments. The maximum of nitrate nitrogen in the 0–90 cm soil layer was 81.4 kg N/ha at a nitrogen fertilizer rate of 250 kg N/ha in the long-term trial, which was within the rational and safe level for groundwater. The best fertilization strategy to decrease nitrate accumulation in soil should consider both soil characteristics and precipitation.

Nitritation via heat shock using immobilized active sludge aggregates

The nitritation process is considered to be one of the most energy-saving and efficient methods for treating polluted water. In this study, active sludge was immobilized with waterborne polyurethane (WPU), and a heat-shock method was employed to treat the immobilized aggregates. When environmental factors that adversely affect nitritation (pH, dissolved oxygen, temperature, etc.) were controlled, steady nitrite nitrogen accumulation was also successfully achieved. We investigated the effect of temperature and timing of the heat-shock method on the activity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Subsequently, temperatures of 60 and 70°C were selected to evaluate the nitritation stability of the heat-shocked immobilized aggregates, and continuous-flow experiments were conducted. The results of preliminary experiments indicated that NOB can be completely deactivated at temperatures above 60°C after 10 min, whereas AOB continued to exhibit some activity. In addition, the effect of temperature was more significant than the effect of heating time for NOB. The results of the nitritation stability assay indicated that the heat-shocked immobilized aggregates that formed at two temperatures remained in stable nitritation; however, the performance of the AOB was decreased at the highest temperature tested. A high temperature and long duration were required for stable nitritation. In the continuous-flow experiments, we discovered that nitrate nitrogen accumulation occurred after 65 d of operation. Therefore, the immobilized aggregates were heat shocked again, and nitrite nitrogen accumulation recurred in the reactor (results not shown). Heat shock is an effective method for stabilizing the nitritation of immobilized nitrifying sludge; this method also provides new ideas for a nitritation-based nitrogen removal process. Key innovations are: (1) a new nitration method based on heat shock has been proposed to generate steady nitritation using immobilized bacterial aggregates; (2) polymerase chain reaction (PCR) has been applied to analyze variations in the AOB and NOB populations of immobilized aggregates before and after heat shock; (3) optimal heat-shock conditions (including duration and temperature) have been identified.

Nitrate nitrogen accumulation and leaching pattern at a winter wheat: summer maize cropping field in the North China Plain

Excess application of nitrogen has proved to be one of the detrimental impact factors on soil and groundwater quality in the North China Plain (NCP). A 4-year (from October 2008 to September 2012) field experiment was carried out to investigate the impact of N application rate on NO3–N dynamics in soils, its leaching pattern, and movement in deep soils under different nitrogen (N) application rates in a sprinkler irrigated winter wheat (Triticum aestivum L.)- summer maize (Zea mays L.) field in the NCP. The N application rates were 0, 110, 220, and 330 kg N ha−1 per wheat or maize planting season, referred to as CK, N1, N2, and N3 treatments, respectively. The results indicate that in winter wheat season, the applied water and fertilizer N mostly accumulated in the 0–60 cm soil layer and NO3–N leaching out of the root zone (0–100 cm) was negligible under the sprinkler irrigation scheduling, while water and NO3–N leached out of the root zone during summer maize season mainly due to high rainfall event. A relatively constant NO3–N concentration in soil profile was maintained and NO3–N leaching was negligible when N application rate was 110 kg N ha−1 per crop season. While about 70 % of the applied N accumulated in 0–500 cm soil layer and about 50 % of the applied N leached out of the root zone when N application rate lager than 110 kg N ha−1 per crop season, and the NO3–N downward movement was observed to the depth of 300 cm at the end of the 4-year experiment with an average migration rate of about 50 cm year−1. Considering the potential risk of groundwater pollution, an N application rate of 110 kg ha−1 per crop season was recommend for winter wheat and summer maize under the conditions of sprinkler irrigation in the NCP and those areas with similar conditions.

Impact of tillage practices on nitrogen accumulation and translocation in wheat and soil nitrate-nitrogen leaching in drylands

Although the effects of tillage practices on soil properties and root growth is well studied, how they affect nitrogen accumulation and translocation in wheat in dryland regions is poorly understood. Here, the impact of different tillage practices, namely, strip rotary tillage (SR), strip rotary tillage after subsoiling (SRS), rotary tillage (R), and rotary tillage after subsoiling (RS), on nitrogen accumulation and translocation, grain yield, and economic benefit in wheat and soil nitrate-nitrogen leaching in drylands was studied over three wheat growing seasons from 2009 to 2012. The results showed that compared with R, nitrogen accumulation amount under SRS increased by 36.8% from jointing to maturity in 2009–2011 and by 12.9 and 16.4% from sowing to maturity in 2009–2010 and 2010–2011, respectively. Post-anthesis nitrogen accumulation, its contribution rate to grain and nitrogen accumulation in grains at maturity under SRS were 48.3, 31.3 and 12.7% higher, respectively, compared to that under R in 2009–2010. On the other hand, nitrate-nitrogen accumulation under SRS in 0–60cm soil layers was lower in comparison to that under SR and R, which suggested that SRS promoted absorption of nitrate-nitrogen in soil layers by wheat. However, no significant difference in nitrate-nitrogen accumulation in the 60–200cm soil layers was observed between SR and R. Average grain yield, nitrogen production efficiency and economic benefit were all the highest under SRS at 598.78gm−2, 39.9kgkg−1 and 8350.8 RMB¥ha−1, respectively, over the study period. Therefore, we propose that SRS is the optimal tillage practice for wheat production in this region.