[Effect of Biochar on NO3--N Transport in Loessial Soil and Its Simulation]

The objective of this study was to explore the effects of different amounts of biochar on the migration process and characteristics of NO3--N in loessial soil. In this study, six groups of mixed soil samples with biochar and loessial soil mass ratios of 0% (T0), 1% (T1), 2% (T2), 3% (T3), 4% (T4), and 5% (T5) were used as research objects. NO3--N was used as the tracer. Through the indoor soil column solute transport simulation tests, the effects of different biochar application amounts on the NO3--N transport process in loessial soil were simulated and studied. The results showed that the breakthrough curve of NO3--N in loessial soil shifted to the right with the increasing of biochar application, and the peak value gradually decreased. The initial penetration time, complete penetration time, and total penetration time increased with the increasing of biochar application amount. The total penetration time of NO3- in the T1, T2, T3, T4, and T5 treatments was 1.26, 2.31, 2.72, 3.22, and 3.57 times that of T0, respectively. The R2 was > 0.997 and RMSE was < 2.083 of the two-zone model (TRM). Compared with the convection-dispersion equation (CDE), the TRM model had higher fitting accuracy and could better simulate the NO3--N migration process in loessial soil after the application of different contents of biochar. The analysis of the fitting parameters of the TRM model showed that the average pore velocity, hydrodynamic dispersion coefficient, and water content ratio in the movable zone gradually decreased with the increasing of biochar application, whereas the dispersion and mass exchange coefficient showed an increasing trend. The results showed that biochar application could effectively enhance the ability of loessial soil to fix NO3--N, reduce the leakage of NO3--N to groundwater, and play an important role in maintaining soil fertility and preventing groundwater pollution.

Effect of Calcium and Phosphorus on Ammonium and Nitrate Nitrogen Adsorption onto Iron (Hydr)oxides Surfaces: CD-MUSIC Model and DFT Computation

Calcium (Ca2+) and phosphorous (PO43-) significantly influence the form and effectiveness of nitrogen (N), however, the precise mechanisms governing the adsorption of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) are still lacking. This study employed batch adsorption experiments, charge distribution and multi-site complexation (CD-MUSIC) models and density functional theory (DFT) calculations to elucidate the mechanism by which Ca2+ and PO43- affect the adsorption of NH4+-N and NO3--N on the goethite (GT) surface. The results showed that the adsorption of NH4+-N on the GT exhibited an initial increase followed by a decrease as pH increased, peaking at a pH of 8.5. Conversely, the adsorption of NO3--N decreased with rising pH. According to the CD-MUSIC model, Ca2+ minimally affected the NH4+-N adsorption on the GT but enhanced NO3--N adsorption via electrostatic interaction, promoting the adsorption of ≡FeOH-NO3- and ≡Fe3O-NO3- species. Similarly, PO43- inhibited the adsorption of ≡FeOH-NO3- and ≡Fe3O-NO3- species. However, PO43- boosted NH4+-N adsorption by facilitating the formation of ≡Fe3O-NH4+ via electrostatic interaction and site competition. DFT calculations indicates that although bidentate phosphate (BP) was beneficial to stabilize NH4+-N than monodentate phosphate (SP), SP-NH4+ was the main adsorption configuration at pH 5.5-9.5 owing the prevalence of SP on the GT surface under site competition of NH4+-N. The results of CD-MUSIC model and DFT calculation were verified mutually, and provide novel insights into the mechanisms underlying N fixation and migration in soil.

[Effects of Straw Returning and Biochar Addition on Greenhouse Gas Emissions from High Nitrate Nitrogen Soil After Flooding in Rice-vegetable Rotation System in Tropical China]

In rice-vegetable rotation systems in tropical areas, a large amount of nitrate nitrogen accumulates after fertilization in the melon and vegetable season, which leads to the leaching of nitrate nitrogen and a large amount of N2O emission after the seasonal flooding of rice, which leads to nitrogen loss and intensification of the greenhouse effect. How to improve the utilization rate of nitrate nitrogen and reduce N2O emissions has become an urgent problem to be solved. Six treatments were set up [200 mg·kg-1 KNO3 (CK); 200 mg·kg-1 KNO3 + 2% biochar addition (B); 200 mg·kg-1 KNO3+1% peanut straw addition (P); 200 mg·kg-1 KNO3 + 2% biochar + 1% peanut straw addition (P+B); 200 mg·kg-1 KNO3 + 1% rice straw addition (R); 200 mg·kg-1 KNO3 + 2% biochar+1% rice straw addition (R+B)] and cultured at 25℃ for 114 d to explore the effects of organic material addition on greenhouse gas emissions and nitrogen use after flooding in high nitrate nitrogen soil. The results showed that compared with that in CK, adding straw or combining straw with biochar significantly increased soil pH (P<0.05). The B and P treatments significantly increased the cumulative N2O emissions by 41.6% and 28.5% (P<0.05), and the P+B, R, and R+B treatments significantly decreased the cumulative N2O emissions by 14.1%, 24.7%, and 36.7% (P<0.05), respectively. The addition of straw increased the net warming potential of greenhouse gases (NGWP). The addition of coir biochar significantly reduced the effect of straw on NGWP (P<0.05). The combined application of straw and biochar decreased NGWP, and P+B significantly decreased NGWP, but that with R+B was not significant (P>0.05). Adding straw or biochar significantly increased soil microbial biomass carbon (MBC) (P<0.05), and that of P+B was the highest (502.26 mg·kg-1). The combined application of straw and biochar increased soil microbial biomass nitrogen (MBN), and that of P+B was the highest. The N2O emission flux was negatively correlated with pH (P<0.01) and positively correlated with NH4+-N and NO3--N (P<0.01). The cumulative emission of N2O was negatively correlated with MBN (P<0.05). There was a significant negative correlation between NO3--N and MBN (P<0.01), indicating that the reduction in NO3--N was likely to be held by microorganisms, and the increase in the microbial hold of NO3--N also reduced N2O emission. In conclusion, the combined application of peanut straw and coconut shell biochar could significantly inhibit N2O emission and increase soil MBC and MBN, which is a reasonable measure to make full use of nitrogen fertilizer, reduce nitrogen loss, and slow down N2O emission after the season of Hainan vegetables.

Development of a Simultaneous Quantification Method for Multiple Modes of Nitrogen in Leaf Models Using Near-Infrared Spectroscopic Measurement

By focusing our attention on nitrogen components in plants, which are important for cultivation management in data-driven agriculture, we developed a simple, rapid, non-chemical and simultaneous quantification method for proteinic and nitrate nitrogen in a leaf model based on near-infrared (NIR) spectroscopic information obtained using a compact Fourier Transform NIR (FT-NIR) spectrometer. The NIR spectra of wet leaf models impregnated with a protein-nitric acid mixed solution and a dry leaf model obtained by drying filter paper were acquired. For spectral acquisition, a compact MEMS (Micro Electro Mechanical Systems) FT-NIR spectrometer equipped with a diffuse reflectance probe accessory was used. Partial least square regression analysis was performed using the spectral information of the extracted absorption bands based on the determination coefficients between the spectral absorption intensities and the contents of the two-dimensional spectral analysis between NIR and mid-infrared spectral information. Proteinic nitrogen content in the dry leaf model was well predicted using the MEMS FT-NIR spectroscopic method. Additionally, nitrate nitrogen in the dry leaf model was also determined by the provided method, but the necessity of adding the data for a wider range of nitric acid concentrations was experimentally indicated for the prediction of nitrate nitrogen content in the wet leaf model. Consequently, these results experimentally suggest the possibility of the application of the compact MEMS FT-NIR for obtaining the bioinformation of crops at agricultural on-sites.

[Effects of Microplastics on the Leaching of Nutrients and Cadmium from Soil]

The environmental effects of microplastics, which are considered a type of emerging contaminants, have attracted increasing concern due to their small size, large specific surface area, strong adsorption capacity, and low degradability. Microplastics can change soil properties and affect the migration ability of nutrients and pollutants in soil, but their effects on the leaching of soil nutrients and heavy metals have not been sufficiently studied. A soil column leaching experiment was conducted to explore the effects of polystyrene (PS) and polylactic acid (PLA) microplastics at different mass fractions (0%, 0.2%, and 2%) on the leaching of nutrients and cadmium under simulated rainfall scenarios. The results showed that increasing rainfall intensity enhanced the leaching of nutrients and cadmium from soil. During downpour conditions, 2% PS significantly increased the leaching of total nitrogen and the content of available phosphorus in soil and reduced the leaching of inorganic phosphorus and the content of ammonium nitrogen in the soil, whereas it increased the content of available potassium during heavy rain. By comparison, 2% PLA reduced the leaching of nitrate nitrogen during heavy rain and intense rainfall and decreased the content of ammonium nitrogen in soil during intense rainfall and downpour conditions and the content of total nitrogen in soil during downpours. In addition, 0.2% PLA significantly increased cadmium leaching during downpours. To conclude, the effects of microplastics on the leaching of nutrients and cadmium were dependent on the type and concentration of microplastics, as well as the rainfall level. Our findings showed that the microplastics derived from both nondegradable PS and biodegradable PLA could affect the leaching of nutrients and heavy metals from soil.

Performance and microbial response to nitrate nitrogen removal from simulated groundwater by electrode biofilm reactor with Ti/CNT/Cu5-Pd5 catalytic cathode

To enhance the removal of nitrate nitrogen (NO3 - -N) in groundwater with a low C/N ratio, electrocatalytic reduction of NO3 - -N has received extensive attention since its electrons can be directly produced in situ while simultaneously providing a clean electronic donor of hydrogen for denitrifying bacteria. In this study, Ti/CNT/CuPd bimetallic catalytic electrodes with different copper-palladium (CuPd) ratios were prepared by electrodeposition onto carbon nanotube (CNT) using titanium (Ti) plates. The results showed that the NO3 - -N conversion rate by Ti/CNT/Cu5-Pd5 electrode was the highest (53.60%) compared with other CuPd electrode ratios because of the combined role of the copper's high NO3 - -N catalytic activity and the palladium's high N2 selectivity. A new type of electrode biofilm reactor (EBR) with Ti/CNT/Cu5-Pd5 cathode, biochar substrate was constructed to explore the removal ability of NO3 - -N in simulated low C/N groundwater. When the influent NO3 - -N concentration was 30 mg/L, under the condition of a 30 mA electronic current and hydraulic retention time (HRT) of 12 h, the removal rate of NO3 - -N could reach as high as 78.1 ± 1.2%, and the N2 conversion rate was 99.7%. The horizontal distribution of microbial communities in EBR showed that the denitrification capacity was significantly improved through the electrochemical catalytic reduction of the Ti/CNT/Cu5-Pd5 cathode and the supply of the hydrogen electron donor to autotrophic denitrogenerating microbes such as Anaerobacillus, Thauera, and Hydrophaga. This study provides a new bimetallic catalytic cathode to enhance the removal of NO3 - -N in groundwater with a low C/N ratio. PRACTITIONER POINTS: The Cu5Pd5/CNTs/Ti electrode is beneficial to the adsorption and reduction of NO3 - -N to N2 . The production of hydrogen electron donors by cathode promoted nitrogen degradation. Activated electrodes together with denitrifying microorganisms contributed to the improved N removal rate.

Controlled-Release Nitrogen Mixed with Common Nitrogen Fertilizer Can Maintain High Yield of Rapeseed and Improve Nitrogen Utilization Efficiency

Field experiments were conducted to study the effects of different proportions of controlled-release nitrogen fertilizer mixed with quick-acting nitrogen fertilizer on the yield and nitrogen utilization efficiency of direct-seeding rapeseed. Using a conventional nitrogen application rate of 180 kg ha-1 as a control, a total of 5 types of available nitrogen fertilizers and different proportions of controlled-release nitrogen fertilizers were mixed for fertilizer treatment. The proportion of available nitrogen fertilizer used was 135 kg ha-1, and the addition ratios of the five types of controlled-release nitrogen fertilizers were 0%, 30%, 50%, 70%, and 100%, respectively (i.e., the proportion of controlled-release nitrogen to the total nitrogen application amount). These ratios were represented as N135R0, N135R1, N135R2, N135R3, and N135R4, respectively. The results showed that there was no significant difference in the number of pods per plant, the number of seeds per pod, or the grain yield under the treatment of controlled-release nitrogen fertilizer mixed with quick-acting nitrogen fertilizer for proportions of 30-50% (N135R1~R3) when compared with the control, and a stable yield was achieved. Mixing controlled-release nitrogen fertilizer under reduced nitrogen application can significantly improve the apparent utilization rate of rapeseed nitrogen fertilizer, but it first increases and then decreases with the increase of the controlled-release nitrogen mixing ratio, reaching its highest under the N135R2 treatment. The agronomic utilization efficiency and partial productivity of nitrogen fertilizer first increased and then decreased with the increased proportion of controlled-release nitrogen, and both reached their highest utilization with the N135R2 treatment. The mixed treatment of controlled-release nitrogen did not affect soil urease activity, but significantly increased soil sucrase activity. The mixed treatment of controlled-release nitrogen also increased soil microbial biomass nitrogen and carbon content. Especially in the flowering stage, the soil microbial biomass nitrogen and carbon content was significantly higher under a controlled-release nitrogen mixing ratio of 30-50%. At the same time, it had a similar effect on soil inorganic nitrogen content. Therefore, a controlled-release nitrogen mixing treatment provided sufficient nitrogen for the key growth period of rapeseed. Under the condition of reducing the amount of nitrogen fertilizer by 25% based on the amount of nitrogen fertilizer applied to conventional rapeseed, the application of controlled-release urea mixed with common nitrogen fertilizer mixed at a ratio of 30-50% can be an effective way to maintain grain yield levels and improve nitrogen utilization efficiency.

Effects of Valine and Urea on Carbon and Nitrogen Accumulation and Lignin Content in Peach Trees

Nitrogen availability and uptake levels can affect nutrient accumulation in plants. In this study, the effects of valine and urea supplementation on the growth of new shoots, lignin content, and carbon and the nitrogen metabolism of 'Ruiguang 39/peach' were investigated. Relative to fertilization with urea, the application of valine inhibited shoot longitudinal growth, reduced the number of secondary shoots in autumn, and increased the degree of shoot lignification. The application of valine also increased the protein level of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in plant leaves, phloem, and xylem, thereby increasing the soluble sugar and starch content. It also resulted in an increase in nitrate reductase (NR), glutamine synthase (GS), and glutamate synthase (GOGAT) protein levels, with an increase in plant contents of ammonium nitrogen, nitrate nitrogen, and soluble proteins. Although urea application increased the protein level of carbon- and nitrogen-metabolizing enzymes, the increase in plant growth reduced the overall nutrient accumulation and lignin content per unit tree mass. In conclusion, the application of valine has a positive effect on increasing the accumulation of carbon and nitrogen nutrients in peach trees and increasing the lignin content.

Application of Natural and Calcined Oyster Shell Powders to Improve Latosol and Manage Nitrogen Leaching

Excessive N fertilizer application has aggravated soil acidification and loss of N. Although oyster shell powder (OSP) can improve acidic soil, few studies have investigated its ability to retain soil N. Here, the physicochemical properties of latosol after adding OSP and calcined OSP (COSP) and the dynamic leaching patterns of ammonium N (NH₄⁺-N), nitrate N (NO₃^--N), and Ca in seepage, were examined through indoor culture and intermittent soil column simulation experiments. Various types of N fertilizer were optimized through the application of 200 mg/kg of N, urea (N 200 mg/kg) was the control treatment (CK), and OSP and COSPs prepared at four calcination temperatures-500, 600, 700, and 800 °C-were added to the latosol for cultivation and leaching experiments. Under various N application conditions, the total leached N from the soil followed ammonium nitrate > ammonium chloride > urea. The OSP and COSPs had a urea adsorption rate of 81.09-91.29%, and the maximum reduction in cumulative soil inorganic N leached was 18.17%. The ability of COSPs to inhibit and control N leaching improved with increasing calcination temperature. Applying OSP and COSPs increased soil pH, soil organic matter, total N, NO₃^--N, exchangeable Ca content, and cation exchange capacity. Although all soil enzyme activities related to N transformation decreased, the soil NH₄⁺-N content remained unchanged. The strong adsorption capacities for NH₄⁺-N by OSP and COSPs reduced the inorganic N leaching, mitigating the risk of groundwater contamination.

[Characteristics of Soil Erosion and Nitrogen Loss in Vegetable Field Under Natural Rainfall]

The effects of vegetable planting on soil loss and nutrient loss, runoff, soil erosion, and nitrogen (ammonium nitrogen and nitrate nitrogen) losses under individual rainfalls of fruit- and leaf-vegetable fields between April to October in 2021 were observed using in-situ observation testing. The results showed that: ① the runoff, erosion, and nitrogen loss of the fruit-vegetable pattern (eggplant-chili) were 1.27-2.00 times those under the leaf-vegetable pattern (leaf lettuce-sweet potato leaves), especially under the second season vegetable period. Those losses under the second season vegetable accounted for 50.86%-68.83% of the total losses under different vegetable patterns, which were approximately 1.03-2.04 times those under the first season vegetable. The runoff, erosion, and nutrient loss of vegetable fields under different treatments were both concentrated in June and July, and the nitrogen loss was mainly in the form of nitrate nitrogen with surface runoff. ② The runoff, erosion, and nutrient losses under individual rainfalls of vegetable fields under different treatments fluctuated among the vegetable growing season, and the losses were mainly concentrated in several typical rainfall events. On the whole, the loss and concentration of nitrate and ammonium nitrogen in runoff and erosion sediment of vegetables in the first season were lower than those in the second season. The runoff, erosion, and loss of ammonium nitrogen and nitrate nitrogen of fruit-vegetable were higher than those of leaf-vegetable. ③ Both rainfall amount and maximum 30 min rainfall intensity had significantly positive effects on runoff, soil loss, and nitrogen loss. Runoff, erosion, and nutrient losses under different vegetable patterns were mainly generated by moderate rain, heavy rain, and heavy rainstorms, which accounted for 29.58%-46.68%, 24.54%-36.79%, and 24.01%-39.13% of the total losses, respectively. The results also showed that soil erosion and nutrient losses generated by different rainfall grades were obviously different for the fruit- and leaf-vegetable treatments. The results indicated that the vegetable pattern had significant impacts on soil loss and nutrient loss, and the leaf-vegetable pattern could reduce soil erosion and nutrient loss compared with the fruit-vegetable pattern. Furthermore, for different vegetable patterns and vegetable growing seasons, the effects of rainfall on soil loss and nutrient loss were quite different. The results of this study were helpful in clarifying the soil erosion and nutrient loss characteristics of vegetable fields in South China.

Effects of the nitrogen form ratios on photosynthetic productivity of poplar under condition of phenolic acids

Phenolic acids can reduce nitrogen utilization rate of poplar, which seriously restrict the productivity of poplar plantation. In this study, three phenolic acid concentrations (T0, T1, and T2) and three ratios of nitrogen forms (NH₄⁺-N to NO₃^--were 1:3, 1:7, and 1:14) were chosen for orthogonal experiment on poplar (Populus × euramericana "Neva") seedlings to study the effects of the nitrogen form ratios on photosynthetic productivity of poplar under environment of phenolic acids. Results showed that photosynthetic physiology parameters were influenced by both phenolic acid concentration and nitrogen form ratio. The order of net photosynthetic rate (P_N) values obtained from 9 treatments were T1-1:3, T0-1:3, T2-1:3, T0-1:7, T1-1:7, T0-1:14, T2-1:7, T1-1:14, and T2-1:14 (from high to low). Under environment of phenolic acids, when poplar were treated with NH₄⁺-N to NO₃^--N ratio of 1:14, the major limitation factor of photosynthesis was non stomatal factor. When poplar were treated with NH₄⁺-N to NO₃-N ratio of 1:3, the major limitation factor of photosynthesis changed to stomatal factor. The leaf nitrogen content and total biomass were obviously positively related with P_N (p < 0.05). Phenolic acid inhibited photosynthetic productivity of poplar in a major way and this effect decreased with increase of the content of NH₄⁺-N.

Influence of the carbon source concentration on the nitrate removal rate in groundwater

At present, groundwater nitrate pollution in China is serious. The use of microorganisms for biological denitrification has been widely applied, and it is a universal and efficient in situ groundwater remediation technique, but this approach is influenced by many factors. In this study, glucose was adopted as the carbon source, four different concentrations of 0, 2, 5 and 10 g/L were considered, and natural groundwater with a nitrate concentration of 300.8 mg/L was employed as the experimental solution. The effect of the carbon source concentration on the nitrate removal rate in groundwater was examined through heterotrophic anaerobic denitrification experiments. The results showed that the nitrate removal rate could be improved by the addition of an external carbon source in the process of biological denitrification, and an optimal concentration was observed. At a glucose concentration of 2 g/L, the denitrification effect was the best.

Nitrogen Regulates the Distribution of Antibiotic Resistance Genes in the Soil-Vegetable System

The increasing antibiotic resistance genes (ARGs) in fertilizer-amended soils can potentially enter food chains through their transfer in a soil-vegetable system, thus, posing threats to human health. As nitrogen is an essential nutrient in agricultural production, the effect of nitrogen (in the forms NH₄ ⁺-N and NO₃ ^--N) on the distribution of ARGs (blaTEM-1, sul1, cmlA, str, and tetO) and a mobile genetic element (MGE; tnpA-4) in a soil-Chinese cabbage system was investigated. Not all the tested genes could transfer from soil to vegetable. For transferable ones (blaTEM-1, sul1, and tnpA-4), nitrogen application influenced their abundances in soil and vegetable but did not impact their distribution patterns (i.e., preference to either leaf or root tissues). For ARGs in soil, effects of nitrogen on their abundances varied over time, and the positive effect of NH₄ ⁺-N was more significant than that of NO₃ ^--N. The ARG accumulation to vegetables was affected by nitrogen application, and the nitrogen form was no longer a key influencing factor. In most cases, ARGs were found to prefer being enriched in roots, and nitrogen application may slightly affect their migration from root to leaf. The calculated estimated human intake values indicated that both children and adults could intake 10⁶-10⁷ copies of ARGs per day from Chinese cabbage consumption, and nitrogen application affected ARG intake to varying degrees. These results provided a new understanding of ARG distribution in vegetables under the agronomic measures such as nitrogen application, which may offer knowledge for healthy vegetable cultivation in future.

Rapid Detection of Different Types of Soil Nitrogen Using Near-Infrared Hyperspectral Imaging

Rapid and accurate determination of soil nitrogen supply capacity by detecting nitrogen content plays an important role in guiding agricultural production activities. In this study, near-infrared hyperspectral imaging (NIR-HSI) combined with two spectral preprocessing algorithms, two characteristic wavelength selection algorithms and two machine learning algorithms were applied to determine the content of soil nitrogen. Two types of soils (laterite and loess, collected in 2020) and three types of nitrogen fertilizers, namely, ammonium bicarbonate (ammonium nitrogen, NH₄-N), sodium nitrate (nitrate nitrogen, NO₃-N) and urea (urea nitrogen, urea-N), were studied. The NIR characteristic peaks of three types of nitrogen were assigned and regression models were established. By comparing the model average performance indexes after 100 runs, the best model suitable for the detection of nitrogen in different types was obtained. For NH₄-N, R²_p = 0.92, RMSE_P = 0.77% and RPD = 3.63; for NO₃-N, R²_p = 0.92, RMSE_P = 0.74% and RPD = 4.17; for urea-N, R²_p = 0.96, RMSE_P = 0.57% and RPD = 5.24. It can therefore be concluded that HSI spectroscopy combined with multivariate models is suitable for the high-precision detection of various soil N in soils. This study provided a research basis for the development of precision agriculture in the future.

[Effects of manure substituting chemical nitrogen fertilizer on rubber seedling growth and soil environment.]

The substitution of manure for chemical nitrogen fertilizers has great impacts on the growth of rubber seedlings and soil environment, with implications for rubber cultivation and transplantation and soil environment improvement. In this study, rubber seedlings of thermal research '7-33-97' strain were cultivated under four treatments: No fertilizer application (CK), only application of chemical fertilizer (N), manure replacing 50% chemical fertilizer (M+N), and manure replacing 100% chemical fertilizer (M). Plants parameters (including plant height, basal diameter, biomass, and chlorophyll), soil physicochemical properties (including pH, soil organic carbon and nitrogen, soil enzyme activities), and their relationships were investigated. The results showed that plant height, basal diameter, biomass, and chlorophyll content in the M+N and M treatments were significantly higher, while underground biomass and root-shoot ratio were significantly lower than those of in N treatment. Compared with CK, soil pH was significantly increased in the M treatment, decreased in the N treatment, and was not changed in the M+N treatment. Soil ammonium and nitrate content in the M+N and M treatments were significantly lower, while soil organic carbon content, the activity of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG) and leucine aminopeptidase (LAP) were significantly higher than those of in N treatment. Results of correlation analysis showed that soil pH was negatively correlated with soil ammonium and nitrate content, but positively correlated with BG and NAG activities. The structural equation model analysis showed that soil pH had significant positive effects on seedling quality index, while nitrate content had significant negative effects, and soil enzyme activities had no significant effect. Those results indicated that soil pH and nitrate content were the important driving factors on the growth of rubber seedlings. The manure replacing of 50% and 100% chemical nitrogen fertilizer could promote rubber seedlings growth, improve soil environment, and promote sustainable development of rubber production in Danzhou City, Hainan Province.

Minimalizing Non-point Source Pollution Using a Cooperative Ion-Selective Electrode System for Estimating Nitrate Nitrogen in Soil

Nitrate nitrogen ( NO 3 - -N) in the soil is one of the important nutrients for growing crops. During the period of precipitation or irrigation, an excessive NO 3 - -N readily causes its leaching or runoff from the soil surface to rivers due to inaccurate fertilization and water management, leading to non-point source pollution. In general, the measurement of the NO 3 - -N relies upon the laboratory-based absorbance, which is often time-consuming, therefore not suitable for the rapid measurements in the field directly. Ion-selective electrodes (ISEs) support the possibility of NO 3 - -N measurement by measuring the nitrate ( NO 3 - ) ions in soil quickly and accurately due to the high water solubility and mobility of NO 3 - ions. However, such a method suffers from a complicated calibration to remove the influences caused by both temperature and other ions in the measured solution, thus limiting field use. In this study, a kind of all-solid ISE system combined with a temperature sensor and a pH electrode is proposed to automatically measure the concentrations of the NO 3 - -N. In this study, a soil water content calibration function was established, which significantly reduces a relative error (RE) by 13.09%. The experimental results showed that the stabilization time of this electrode system was less than 15 s with a slope of -51.63 mV/decade in the linear range of 10^-5-10^-2.2 mol/L. Both the limit of detection of 0.5 ppm of the NO 3 - -N and a relative SD of less than 3% were obtained together with the recovery rate of 90-110%. Compared with the UV-Vis spectroscopy method, a correlation coefficient (R ²) of 0.9952 was obtained. The performances of this all-solid ISE system are satisfied for measuring the NO 3 - -N in the field.

[Effects of short-term combined application of ammonium nitrogen and nitrate nitrogen on the growth and leaf traits of Machilus pauhoi seedlings]

Trees are characterized with selective absorption of different forms of nitrogen. Ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) are the main forms of nitrogen for plant absorption. We examined the differences of absorption between NH₄⁺-N and NO₃^--N for 1-year-old Machilus pauhoi seedlings planted in local hilly red soil in a pot experiment. A controlled experiment with 7 different NH₄⁺-N/NO₃^--N treatments was conducted, to study the effects of nitrogen forms and different NH₄⁺-N/NO₃^--N ratios on the growth and leaf traits of M. pauhoi seedlings. The results showed that there were no significant differences in the relative growth rate of ground diameter (GD), plant height (TH), and biomass (RGR) of M. pauhoi seedlings with different NH₄⁺-N/NO₃^--N ratios for four months, but these parameters were relatively high under the treatment of NH₄⁺-N:NO₃^--N=5:5. The seedlings of M. pauhoi didn't show obvious preference for NH₄⁺-N and NO₃^--N in short term. The extremely low NH₄⁺-N/NO₃^--N ratio application was unsuitable for their growth. Different NH₄⁺-N/NO₃^--N application had significant effects on leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf relative water content (LRWC), net photosynthetic rate (P_n), intercellular CO₂ concentration (C_i), water use efficiency (WUE), and photosynthetic nitrogen use efficiency (PNUE). M. pauhoi seedlings under the treatment of NH₄⁺-N:NO₃^--N=1:9 had the highest LA, SLA, P_n, WUE and PNUE. However, the seedlings under the treatment of NH₄⁺-N:NO₃^--N=9:1 had the lowest LDMC, leaf tissue density (LTD), LRWC and C_i. Different NH₄⁺-N/NO₃^--N combined application did not affect leaf nitrogen content (LN) and leaf phosphorus content (LP), which were highest under the treatment of NH₄⁺-N:NO₃^--N=5:5. Across different NH₄⁺-N/NO₃^--N combined treatments, GD, TH, and RGR were significantly negatively correlated with SLA, while both GD and RGR were significantly negatively correlated with PNUE. Our results could provide theoretical basis for precise nutrient management and high-efficiency cultivation techniques during the seedling stage of the M. pauhoi.

[Application effect of high efficiency and stability urea added with biochemical inhibitors and humic acid in loess]

We carried out pot experiment to investigate nitrogen transformation characteristics, yield increasing effect, and apparent utilization rate of nitrogen fertilizer in loess soils by combining chemi-cal inhibitor and biostimulant humic acid to investigate the application effect and provide a theoretical basis for new type highly efficient and stable urea in loess soil. In this study, blank (CK) and urea (N) were set as controls, and humic acid alone (F), N-butyl thiophosphate-triamine (NBPT), 3,4-dimethyl-pyrazolate phosphate (DMPP), 2-chloro-6-trimethyl-pyridine (CP) and humic acid were respectively combined with three biochemical inhibitors to urea. The results showed that compared with N treatment, F, NBPT+F, DMPP+F, CP+F treatments significantly increased maize yield, chlorophyll content, leaf area index and nitrogen uptake, and had obvious effects on soil available nitrogen contents. The addition of humic acid increased chlorophyll content of maize leaves in all cases compared to the application of biochemical inhibitors alone. Compared with CP treatment, CP+F treatment could significantly increase nitrogen uptake, chlorophyll content, and nitrogen adsorption efficiency of maize. Addition of humic acid with NBPT increased nitrification inhibition rate by 10.7% compared with NBPT alone, but decreased yield, leaf area index, nitrogen uptake, nitrogen use efficiency. Compared with DMPP treatment, DMPP+F treatment significantly reduced maize yield, leaf area index, nitrogen uptake, nitrogen use efficiency and nitrification inhibition rate. Considering maize yield, plant N uptake, N fertilizer uptake rate and soil ammonium N and nitrate N contents, the addition of humic acid and CP is recommended for urea application in loess areas to enhance urea performance, yield, and fertilizer utilization.

[Soil denitrifying enzyme activity and its influencing factors in a bamboo forest riparian zone in the upper reaches of the Taihu Lake Basin, China]

Soil denitrifying enzyme activity (DEA) was measured by acetylene inhibition technique, along with exploration of factors influencing DEA in a bamboo forest riparian zone in the upper reaches of the Taihu Lake Basin during summer. Our aim was to provide important insights into the assessment of ecological functions of bamboo forest riparian zone on reducing nitrogen pollution in rivers. The results showed that the riparian soil DEA ranged from 6.32 to 23.22 μg N·kg^-1·h^-1, with a mean value of 14.65 μg N·kg^-1·h^-1. The vertical distribution (0-40 cm soil profile) of DEA was affected by several factors, such as soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO₃^--N), soil water content, and activity of carbon and nitrogen hydrolase, which resulted in decreased DEA with increasing soil depth. The horizontal changes in DEA (at the same soil depth but at different distances from river) was mainly governed by the variation in SOC concentration. In this area, the concentration of soil dissolved organic carbon was relatively low, which might inhibit the soil DEA during summer.

[Effects of warming on soil inorganic nitrogen in the young and mature Cunninghamia lanceolata plantations in humid subtropical region, China]

Soil nitrogen cycling in forests may be accelerated or inhibited by global warming, with consequences on forest productivity. Such an impact will be more complicated with extending period of warming. We examined the effects of warming on soil inorganic nitrogen content in the young and mature Cunninghamia lanceolata plantations. Warming was simulated by means of soil cable warming, simulating a future climate change scenario of 4 ℃ warming. The results showed that after three years warming, both total soil inorganic nitrogen and ammonium contents in the young and mature plantations were significantly reduced. The sharp decline occurred in the young plantation, with soil ammonium content in 0-10, 10-20, 20-40, 40-60 cm soil layers decreased by 32.1%, 37.1%, 20.8% and 19.9%, respectively. Dissolved organic nitrogen was reduced and N₂O emission was accelerated in the both plantations. The main reasons for the reduction of soil inorganic nitrogen concentration were lower input of organic nitrogen substrate and higher gaseous nitrogen loss. The decrease in soil organic nitrogen substrate and increase in gaseous nitrogen emissions in the young plantation were larger than those in the mature plantation, indicating that soils in the young plantation were more sensitive to increasing temperature. The 3-year warming decreased soil inorganic nitrogen contents in the two C. lanceolata plantations, which might negatively affect productivity of the C. lanceolata plantations in subtropic China.

[Effects of reduced nitrogen application on yield, nitrogen utilization of spring maize and soil nitrate content in Weibei dryland, Northwest China]

To get a scientific pattern for nitrogen-reducing and efficiency-increasing production of spring maize in Weibei dryland, we conducted an in-situ field experiment of spring maize (Zhengdan 958 and Shaandan 8806) under dryland farming from 2016 to 2019 in Heyang County, located in Weibei dryland of Shaanxi. There were five nitrogen (N) treatments, including 360 kg·hm^-2(N₃₆₀, a rate commonly adopted by local farm households), 270 kg·hm^-2(N₂₇₀), 150-180 kg·hm^-2(N_150-180), 75-90 kg·hm^-2(N_75-90) and 0 kg·hm^-2(N₀). We investigated the effects of reduced nitrogen application on maize yield, nitrogen uptake and utilization of spring maize and soil nitrate residue. The results showed that: 1) Maize yield of both varieties at N_150-180 was increased by 0.9%-7.1% and nitrogen uptake was decreased by 4.1%-4.6%, while average reco-very efficiency, partial-factor productivity and agronomic efficiency of N at N_150-180 were increased by 79.3%-83.6%, 105.9%-157.7%, and 101.9%-114.1% compared with those at N₃₆₀, respectively. 2) The contents of residual nitrate increased significantly when nitrogen application rate was more than 180 kg·hm^-2, while nitrogen uptake was significantly reduced under rainfall shortage, and thus resulted in increasing soil residual nitrogen. After four-year treatments, the residual nitrate was up to 504.7-620.8 kg·hm^-2 in 0-200 cm soil layer, with a peak in 80-140 cm soil layer. There was a risk of nitrate leaching. According to the comprehensive evaluation for annual yield, nitrogen use efficiency and soil nitrate residue, the optimum N application rate was recommended to be 150-180 kg N·hm^-2 for spring maize in Weibei dryland.

The Eco-Friendly Biochar and Valuable Bio-Oil from Caragana korshinskii: Pyrolysis Preparation, Characterization, and Adsorption Applications

Carbonization of biomass can prepare carbon materials with excellent properties. In order to explore the comprehensive utilization and recycling of Caragana korshinskii biomass, 15 kinds of Caragana korshinskii biochar (CB) were prepared by controlling the oxygen-limited pyrolysis process. Moreover, we pay attention to the dynamic changes of microstructure of CB and the by-products. The physicochemical properties of CB were characterized by Scanning Electron Microscope (SEM), BET-specific surface area (BET-SSA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), and Gas chromatography-mass spectrometry (GC-MS). The optimal preparation technology was evaluated by batch adsorption application experiment of NO3-, and the pyrolysis mechanism was explored. The results showed that the pyrolysis temperature is the most important factor in the properties of CB. With the increase of temperature, the content of C, pH, mesoporous structure, BET-SSA of CB increased, the cation exchange capacity (CEC) decreased and then increased, but the yield and the content of O and N decreased. The CEC, pH, and BET-SSA of CB under each pyrolysis process were 16.64-81.4 cmol·kg-1, 6.65-8.99, and 13.52-133.49 m2·g-1, respectively. CB contains abundant functional groups and mesoporous structure. As the pyrolysis temperature and time increases, the bond valence structure of C 1s, Ca 2p, and O 1s is more stable, and the phase structure of CaCO3 is more obvious, where the aromaticity increases, and the polarity decreases. The CB prepared at 650 °C for 3 h presented the best adsorption performance, and the maximum theoretical adsorption capacity for NO3- reached 120.65 mg·g-1. The Langmuir model and pseudo-second-order model can well describe the isothermal and kinetics adsorption process of NO3-, respectively. Compared with other cellulose and lignin-based biomass materials, CB showed efficient adsorption performance of NO3- without complicated modification condition. The by-products contain bio-soil and tail gas, which are potential source of liquid fuel and chemical raw materials. Especially, the bio-oil of CB contains α-d-glucopyranose, which can be used in medical tests and medicines.

[Atmospheric Nitrogen Dioxide, Nitric Acid, Nitrate Nitrogen Concentrations, and Wet and Dry Deposition Rates in a Double Rice Region in Subtropical China]

Nitrogen dioxide (NO₂) and nitric acid (HNO₃) are nitrogen-containing acidic gases in the atmosphere, and they are important precursors of nitrate in aerosol and rainwater. The emission intensity of atmospheric nitrogen oxides is high in the subtropical region of China, but the concentrations and deposition rates of atmospheric nitrogen dioxide, nitric acid, particulate nitrate-nitrogen (NO₃^--N_p), and rainwater nitrate-nitrogen (NO₃^--N_r) in a double rice region in subtropical China are still unclear,. In this study, the atmosphere concentrations of NO₂-N, HNO₃-N, NO₃^--N_p in PM₁₀, and NO₃^--N_r and related meteorological parameters were simultaneously monitored in a typical double rice region within a subtropical hilly region of China, with the aim of determining the characteristics and influencing factors of NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r concentrations and quantifying the wet and dry deposition rates. The results showed that the annual mean concentrations of NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r were 4.2 μg·m^-3, 0.7 μg·m^-3, 4.0 μg·m^-3, and 1.0 mg·L^-1, respectively, and the deposition rates were 1.5, 3.2, 2.3, and 6.1 kg·hm^-2, respectively. The NO₂-N concentrations were negatively correlated with air temperatures, and the HNO₃-N concentrations were negatively correlated with wind speeds. TheNO₃^--N_p concentrations were negatively correlated with air temperatures, positively correlated with NO₂-N concentrations, but not significantly correlated with HNO₃-N concentrations, thus indicating that NO₂-N concentrations were an important limiting factor forNO₃^--N_p pollution in this study area. The NO₃^--N_r concentrations were negatively correlated with rainfall, as well as the concentrations of HNO₃-N and NO₃^--N_p. The annual total dry and wet depositions of the atmospheric NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r were 13.0 kg·hm^-2, which indicates that these compounds are important sources of nitrogen in paddy fields and may have significant impacts on paddy fields and surrounding ecosystems.

[Regulation effects of irrigation methods and nitrogen application on soil water, nitrate, and wheat growth and development]

Field experiments were conducted to examine the effects of flooding irrigation (FI), micro-sprinkler irrigation (SI), drip irrigation (DI), combined with nitrogen application (N₁:157.5 kg·hm^-2 as basal, 67.5 kg·hm^-2 top dressed at jointing stage; N₂:157.5 kg·hm^-2 as ba-sal, 45 kg·hm^-2 and 22.5 kg·hm^-2 top dressed at jointing stage and filling stage, respectively) on soil moisture, nitrate (NO₃^--N) content, and wheat growth and development, under maize straw returning to field. Results showed that irrigation methods and nitrogen application modes affected soil water content and soil water storage (SWS). Irrigation methods had limited effect on soil water content in the 0-60 cm soil depth at the wintering and re-greening stages, 0-160 cm soil depth at the booting and filling stages, 100-160 cm soil depth at the mature stage, but had substantial effect on water content in the 80-160 cm soil depth at the wintering and re-greening stages, 0-80 cm soil depth at the mature stage. The effects of irrigation methods on water content and SWS were in the order of FI>DI>SI. Under SI and DI, water content, SWS of soil layers, and their changes increased with increasing irrigation rate. Nitrogen application had obvious effect on NO₃^--N content in the 0-20 cm soil depth. In the SI, variation of NO₃^--N content among different growth stages was evident. In the DI, changes of NO₃^--N content were non-evident during wintering and booting stages, and were evident after booting stage, with opposite change treand in the FI. In general, NO₃^--N content was influenced by irrigation rate at early and middle stages of wheat growth, but was mainly affected by N application at late stage. In the SI and DI, NO₃^--N content changed larger by irrigation rate before winter. Total stem number and tillers per plant during overwintering period, panicle number rate, panicle number, yield, WUE and nitrogen use efficiency (NUE) were in the order of SI>DI>FI. In the SI and DI, total stem number and panicle number were higher in the N₁ than that in the N₂, but grain number per panicle, 1000-grain mass, yield, WUE and NUE were lower. Sowing wheat after maize straw returning to the field, replacing FI with micro-sprinkler irrigation four times during the wheat growth period, applying sufficient basal fertilizer and then topdressing at jointing and filling stages, are the high-efficiency and water-saving cultivation strategies of wheat in wheat-maize double cropping area in southern Shanxi.

[Effects of straw returning amount and type on soil nitrogen and its composition]

Straw returning to soil can supplement soil nutrients required for crop growth, fertilize soil, and improve soil quality. To explore the long-term effect of straw returning on soil total nitrogen and its composition, herein, five treatments including no rice straw + no wheat straw returning (NRW), no rice straw + all wheat straw returning (W), all rice straw + no wheat straw returning (R), half rice straw + half wheat straw returning (HRW), and all rice straw + all wheat straw returning (ARW) were conducted in triplicate in Taihu Lake region, China. The effects of both straw amount and type were examined. Compared with the results obtained in 2007, the results herein obtained in 2017 showed that after 10 years of straw returning, soil total nitrogen and heavy fraction nitrogen increased, while light fraction organic matter decreased. Among the five treatments, ARW had the largest decrease in light fraction nitrogen of 8.09 g·kg^-1; the R treatment had the highest contents of both total and heavy fraction nitrogen, and also the highest contents of ammonium and nitrate. There was no significant difference in alkali-hydrolyzable nitrogen among the five treatments. These results indicated that crop straw was the critical material source for soil nitrogen, and that the effects of straw returning on soil nitrogen depended on the type and amount of crop straw returned to soil. The changes of light fraction nitrogen were more sensitive to straw returning, while the heavy fraction nitrogen was relatively stable, which was the key fraction sustaining soil fertility. With the prolonging of straw returning, the relationship between the total nitrogen and diffe-rent nitrogen components changed. The processing manner of all rice straw returning + no wheat straw returning was the way that could most significantly enhance soil nitrogen content.

A High-Performance Optoelectronic Sensor Device for Nitrate Nitrogen in Recirculating Aquaculture Systems

The determination of nitrate nitrogen (NO₃-N) in recirculating aquaculture systems is of great significance for the health assessment of the living environment of aquatic animals. Unfortunately, the commonly used spectrophotometric methods often yield unstable results, especially when the ambient temperature varies greatly in the field measurement. Here, we have developed a novel handheld absorbance measurement sensor based on the thymol-NO₃-N chromogenic rearrangement reaction. In terms of hardware, the sensor adopts a dual channel/dual wavelength colorimeter structure that features a modulated light source transmitter and a synchronous detector receiver. The circuit measures the ratio of light absorbed by the sample and reference containers at two LEDs with peak wavelengths at 420 nm and 450 nm. Using the modulated source and synchronous detector rather than a constant (DC) source eliminates measurement errors due to ambient light and low frequency noise and provides higher accuracy. In terms of software, we design a new quantitative analysis algorithm for absorbance by studying colloid absorbing behavior. The application of a buffer operator embedded in the algorithm makes the sensor get the environmental correction function. The results have shown that the sensitivity, repeatability, precision and environmental stability are higher than that by ordinary spectrophotometry. Lastly, we have a brief overview of future work.

Effects of different mulching modes on soil nitrate concentration and grain yield of Linum usitatissimum in dry land

To investigate soil NO₃^--N dynamics and yield increasing effect of mulching planting for Linum usitatissimum (oil flax) in semi-arid Loess Plateau, we examined the effects of three mul-ching modes (whole field plastic mulching and micro ridges with soil cover and bunch-seeding; whole field plastic mulching with soil cover and bunch-seeding; and straw mulching with strips) on seed yield and distribution of soil NO₃^--N during the main growth periods of oil flax, with the conventional planting model as control (CK) in 2015 and 2016. Results showed that the average yield under mulching modes was increased by 56.1% (2015) and 22.7% (2016). The treatment of whole field plastic mulching with soil cover and bunch-seeding had the highest grain yield. Mulching treatments significantly increased soil water content. Soil water content was increased first and then reduced in the whole growth stage of oil flax. The soil NO₃^--N content was gradually decreased during the oil flax growth process. In both years, NO₃^--N content in 0-40 cm soil depth under mul-ching treatments were increased by 3.1%-18.6% (2015) and 5.1%-16.4% (2016) at budding stage of oil flax, respectively. The whole field plastic mulching with soil cover and bunch-seeding treatment showed the larges increases across all treatments. In 2015, NO₃^--N accumulation in 0-100 cm soil depth between the flowering and maturity stages of oil flax were increased by 10.2%-22.2% and 8.6%-21.4%, respectively. Especially during the more rainfall period of maturity stage, NO₃^--N accumulation in 0-40 cm soil depth was significantly enhanced by 3.3%-4.9% than that in 40-100 cm soil depth. It indicated that more rainfall could slow down the migration of NO₃^--N to the lower layer under the mulching modes in the maturity stage. In 2016, high temperature and drought at late growth stages had a great influence on oil flax growth. The NO₃^--N accumulation in 0-100 cm soil depth at the maturity stage was increased by 6.6%-18.0%. There was significant correlation between NO₃^--N content and grain yield during the main growth stages of oil flax. In conclusion, the whole field plastic mulching with soil cover and bunch-seeding treatment was the most appropriate way of oil flax production in arid and semi-arid area.

[Characteristics of soil nitrate accumulation and leaching under different long-term nitrogen application rates in winter wheat and summer maize rotation system.]

Winter wheat and summer maize were the main crops in the North China Plain. While intensive farming system could generally achieve high yield, the perennial large amounts of nitrogen (N) fertilization application cause environmental problems including NO₃^--N accumulation and leaching at deep soil layer. Here, the effects of different N application rates on soil NO₃^--N accumulation and leaching in winter wheat-summer maize cropping system were investigated from 2010 to 2016 at Qingyuan County, Hebei Province, China. There were five treatments with N application rates at 0 (N₀), 100 (N₁₀₀), 180 (N₁₈₀), 255 (N₂₅₅) and 330 (N₃₃₀) kg·hm^-2. Results showed that crop yield and soil N status significantly varied among treatments for both wheat and maize after each harvest, respectively. Soil NO₃^--N were accumulated during winter wheat growing season and leached to deeper soil during summer maize growing season. Moreover, the soil NO₃^--N accumulation amount in the 90 to 180 cm soil profile decreased with the decreases of N inputs (N₃₃₀ > N₂₅₅ > N₁₈₀ > N₁₀₀ > N₀). Soil NO₃^--N could be leached to 990 cm soil depth. There were six NO₃^--N accumulation peaks in the soil profile, with the peaks presenting at deeper soil profile with higher N fertilization rate. The deepest peak appeared at 840 cm soil depth with the N application rate of 330 kg·hm^-2. From the distribution of NO₃^--N accumulation in the soil profile, only around 10% of total NO₃^--N was accumulated between 0-90 cm soil depth, while the rest accumulated below 90 cm, which could not be largely absorbed by plants. Therefore, NO₃^--N leaching during summer maize growing season was serious and it was greater with higher N fertilization rate which might lead to increased risk of underground water contamination. In terms of balanced crop yield and soil NO₃^--N accumulation, the rate of 180 kg·hm^-2 would be the optimum one in areas with similar cultivation and environmental conditions to the present study.

[Characteristics of Biochar-mediated N2O Emissions from Soils of Different Surface Conditions]

It was aimed to investigate the response to biochar addition on N₂O gas production and emission in different surface conditions. To study the dynamic changes of soil N₂O release, soil nitrate(NO₃^--N) and ammonium(NH₄⁺-N), a field trials experiment was conducted from 2014 to 2015 in wheat and corn season, which contained three treatments[the blank control group (CK), biochar applied at 5 t·(hm²·a)^-1(BC5) and 45 t·(hm²·a)^-1(BC45), respectively] under crop cultivation(+) and non-cultivation(-) condition. The results indicated that:1 During the season of wheat growth, the soil N₂O emissions of CK+, BC5+, BC45+ were 21.70-88.91, 21.42-130.09, 64.44-179.58 μg·(m²·h)^-1 respectively, and that of BC45+ possessed a higher value than those of the other treatments(P<0.05). Compared with wheat winter period, the soil N₂O emissions of the three treatments decreased evidently in wheat peak stage(returning green and jointing stage, booting and heading stage) (P<0.05), and the amplification of BC45+ reduced by 18.43% and 14.62% in comparison with CK+ and BC5+ in wheat booting and heading stages. In the early stage of maize growth, the soil N₂O emissions of BC45+ were significantly increased compared with CK+ and BC5+(P<0.05). However, there were no significant differences among treatments of maize heading stage and mature stage. It showed that the biochar-mediated promotion effect of soil N₂O emissions was effectively inhibited by crop growth and the increase of surface mulch. Besides, the result of soil N₂O release in the same treatment had also confirmed this conclusion in bare land. 2 Under the conditions of wheat cultivation and homochronous non-cultivation, the soil NO₃^--N and NH₄⁺-N contents of BC5+ and BC45+ treatments were raised with respect to CK+, but the values dropped significantly in wheat peak stage, especially for BC45+ treatment, with 96.44% and 69.40% decrease respectively. The soil inorganic nitrogen content of maize growth season had a similar trend in wheat season. Parallel to this result of the apparently falling soil NO₃^--N and NH₄⁺-N concentrations, the soil N₂O emissions of BC45+ also declined remarkably in peak stage. The decline in respiratory substrate caused by the increase of nitrogen uptake by crop growth, may be one of the reasons for the decrease of N₂O emission. 3 In wheat growth season, the soil pH values of the biochar treatments were improved from 4.62 to 5.18. In maize season, the soil pH values ranged from 4.42 to 5.02. When the soil pH value was relatively low, the soil N₂O emission was high, and vice versa. The soil N₂O emission was partly influenced by the soil pH value.

[Effect of Wastewater Nitrogen Concentrations on Nitrogen Removal Ability of Myriophyllum aquaticum]

Myriophyllum aquaticum, which is an important plant for constructed wetlands, has powerful purification ability for wastewater, however, the relationship between nitrogen removal ability of Myriophyllum aquaticum and wastewater nitrogen concentrations is still unclear. In this study, pot culture experiment was conducted to investigate the effect of wastewater nitrogen levels on nitrogen removal ability of Myriophyllum aquaticum. 7 nitrogen levels were set up as following:2, 5, 10, 20, 100, 200, 400 mg·L^-1. The results showed that when the wastewater nitrogen concentration was not higher than 20 mg·L^-1, Myriophyllum aquaticum with 20 mg·L^-1 of nitrogen concentration grew best in the first 3 weeks; the removal rates of total and ammonia nitrogen were nearly 100% after one week, while the nitrate nitrogen concentrations were very low and varied little; the nitrogen contents of Myriophyllum aquaticum had no significant change, the upper part nitrogen content was higher than the underneath, Myriophyllum aquaticum could also remove nitrogen from the sediment. When wastewater nitrogen concentrations were 100-400 mg·L^-1, Myriophyllum aquaticum with 200 mg·L^-1 of nitrogen concentration grew best from 4th to 5th week; the removal rates of total nitrogen were 76.5%, 71.5% and 48.1% in the three treatments, and the removal rates of ammonia nitrogen were 99.6%, 99.3% and 60.2% respectively, while the removal rates of nitrate nitrogen were all about 50% and there was no significant difference among treatments; the nitrogen contents of Myriophyllum aquaticum increased with nitrogen levels, but the difference between upper part and underneath was not remarkable, showing uniform distribution; nitrogen accumulations by Myriophyllum aquaticum and sediment accounted for 27.9%-48.4% and 12.2%-24.4% of total nitrogen loss in wastewater. Therefore, the nitrogen removal ability of Myriophyllum aquaticum should be inhibited by higher wastewater nitrogen level, the ammonia nitrogen removal rate was significantly higher than nitrate, the mechanism of Myriophyllum aquaticum nitrogen accumulation and distribution should also be affected by wastewater nitrogen level, and further research is needed.

[Effects of different cultivation patterns on yield, nitrate accumulation and nitrogen balance in winter wheat and summer maize rotation system.]

This study investigated the impacts of four cultivation patterns including farmer practice, high yield and high efficiency practice, super high yield practice, and super high yield and high efficiency practice on yields, soil nitrate and nitrogen (N) balances in 3 winter wheat-summer maize rotations with straw returning in Hebei Province. Results showed that the super high yield practice was identified with greatest winter wheat and summer maize yields, followed by high yield and high efficiency practice, and super high yield and high efficiency practice, which were all greater than that of farmer practice. The N use efficiency of high yield and high efficiency practice was significantly greater than the other cultivation patterns. The total nitrate accumulation in 0-400 cm soil of these cultivation patterns reached 768.4-1133.3 kg·hm^-2, where 80%-85% of the accumulated nitrate were in 90-400 cm soil. Meanwhile, the nitrate leaching was observed in all cultivation patterns and nitrate accumulation peaks at 120-150 cm and 270-330 cm were found. Soil nitrate content of high yield and high efficiency practice was less than 30 mg·kg^-1 and generally lower than other cultivation patterns, which to some extent reduced the environmental risk. In addition, nitrate surplus in 0-90 cm soil during winter wheat season was lower than that during summer maize season, and the high yield and high efficiency practice had the lowest apparent nitrogen loss. Overall, the high yield and high efficiency practice was evaluated to be the best cultivation pattern in consi-deration of yield, nitrogen use efficiency and nitrate accumulation in soil, but there was still certain achievable improvement potential.

Influence of different organic waste materials on the transformation of nitrogen in soils

Organic waste materials like crop residues, well-decomposed cow dung, composts, and other rural and urban wastes are considered highly useful resources in enhancing soil fertility and also in build-up of soil organic matter. Organic matter decomposition provides plant nutrients in soil, which in turn increases crop productivity. Availability of nutrients and nitrogen (N) and phosphorus from organic waste materials is dependent upon the nature of organic residues, climatic conditions, and soil moisture activity. Keeping these factors in view, the present investigation was undertaken to study the transformation of N from different organic waste materials in two contrasting soils from an eastern India, subtropical region. The results showed that the amounts of ammoniacal-N (NH4-N), nitrate-N (NO3-N), hydrolysable N (HL-N), and nonhydrolysable (NHL-N) were increased for up to 60 days of soil submergence and increased further with the increase (1% by weight of soil) of organic residue application. Considering the effect of various organic waste materials, it was found that the amounts of NH4-N, NO3-N, HL-N, and NHL-N were higher with the application of groundnut hull as compared to wheat straw and potato skin, which may be due to relatively narrow carbon:N ratio of groundnut (22:43) than that of wheat straw (62:84) and potato skin (71:32); however, the results showed that the release of NH4-N, NO3-N, HL-N, and NHL-N was in the order of groundnut hull > wheat straw > potato skin.

Nitrogen use and carbon sequestered by corn rotations in the northern corn belt, U.S

Diversified crop rotation may improve production efficiency, reduce fertilizer nitrogen (N) requirements for corn (Zea mays L.), and increase soil carbon (C) storage. Objectives were to determine effect of rotation and fertilizer N on soil C sequestration and N use. An experiment was started in 1990 on a Barnes clay loam (U.S. soil taxonomy: fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, SD. Tillage systems for corn-soybean ( Glycine max [L.] Merr.) rotations were conventional tillage (CS) and ridge tillage (CSr). Rotations under conventional tillage were continuous corn (CC), and a 4-year rotation of corn-soybean-wheat ( Triticum aestivum L.) companion-seeded with alfalfa ( Medicago sativa L.)-alfalfa hay (CSWA). Additional treatments included plots of perennial warm season, cool season, and mixtures of warm and cool season grasses. N treatments for corn were corn fertilized for a grain yield of 8.5 Mg ha(-1) (highN), of 5.3 Mg ha(-1) (midN), and with no N fertilizer (noN). Total (1990-2000) corn grain yield was not different among rotations at 80.8 Mg ha(-1) under highN. Corn yield differences among rotations increased with decreased fertilizer N. Total (1990-2000) corn yields with noN fertilizer were 69 Mg ha-1 under CSWA, 53 Mg ha(-1) under CS, and 35 Mg ha(-1) under CC. Total N attributed to rotations (noN treatments) was 0.68 Mg ha(-1) under CSWA, 0.61 Mg ha(-1) under CS, and 0.28 Mg ha(-1) under CC. Plant carbon return depended on rotation and N. In the past 10 years, total C returned from above- ground biomass was 29.8 Mg ha(-1) under CC with highN, and 12.8 Mg ha(-1) under CSWA with noN. Soil C in the top 15 cm significantly increased (0.7 g kg(-1)) with perennial grass cover, remained unchanged under CSr, and decreased (1.7 g kg(-1)) under CC, CS, and CSWA. C to N ratio significantly narrowed (-0.75) with CSWA and widened (0.72) under grass. Diversified rotations have potential to increase N use efficiency and reduce fertilizer N input for corn. However, within a corn production system using conventional tillage and producing (averaged across rotation and N treatment) about 6.2-Mg ha(-1) corn grain per year, we found no gain in soil C after 10 years regardless of rotation.