Environmental dynamics of nitrogen and phosphorus release from river sediments of arid areas

Human activities lead to the accumulation of a large amount of nitrogen and phosphorus in sediments in rivers.Simultaneously,nitrogen and phosphorus can be affected by environment and re-enter the upper water body,causing secondary pollution of the river water.In this study,laboratory simulation experiments were conducted initially to investigate the release of nitrogen and phosphorus from river sediments in Urumqi City and the surrounding areas in Xinjiang Uygur Autonomous Region of China and determine the factors that influence their release.The results of this study showed significant short-term differences in nitrogen and phosphorus release characteristics from sediments at different sampling points.The proposed secondary kinetics model(i.e.,pseudo-second-order kinetics model)better fitted the release process of sediment nitrogen and phosphorus.The release of nitrogen and phosphorus from sediments is a complex process driven by multiple factors,therefore,we tested the influence of three factors(pH,temperature,and disturbance intensity)on the release of nitrogen and phosphorus from sediments in this study.The most amount of nitrate nitrogen(NO_(3)^(–)-N)was released under neutral conditions,while the most significant release of ammonia nitrogen(NH_(4)^(+)-N)occurred under acidic and alkaline conditions.The release of nitrite nitrogen(NO_(2)^(-)-N)was less affected by pH.The dissolved total phosphorus(DTP)released significantly in the alkaline water environment,while the release of dissolved organic phosphorus(DOP)was more significant in acidic water.The release amount of soluble reactive phosphorus(SRP)increased with an increase in pH.The sediments released nitrogen and phosphorus at higher temperatures,particularly NH_(4)^(+)-N,NO_(3)^(–)-N,and SRP.The highest amount of DOP was released at 15.0℃.An increase in disturbance intensity exacerbated the release of nitrogen and phosphorus from sediments.NH_(4)^(+)-N,DTP,and SRP levels increased linearly with the intensity of disturbance,while NO_(3)^(–)-N and NO_(2)^(–)-N were more stable.This study provides valuable information for protecting and restoring the water environment in arid areas and has significant practical reference value.

Drip fertigation and plant hedgerows significantly reduce nitrogen and phosphorus losses and maintain high fruit yields in intensive orchards

A field experiment was carried out to evaluate the effects of drip fertigation combined with plant hedgerows on nitrogen and phosphorus runoff losses in intensive pear orchards in the Tai Lake Basin.Nitrogen and phosphorus runoff over a whole year were measured by using successional runoff water collection devices.The four experimental treatments were conventional fertilization(CK),drip fertigation(DF),conventional fertilization combined with plant hedgerows(C+H),and drip fertigation combined with plant hedgerows(D+H).The results from one year of continuous monitoring showed a significant positive correlation between precipitation and surface runoff discharge.Surface runoff discharge under the treatments without plant hedgerows totaled 15.86%of precipitation,while surface runoff discharge under the treatments with plant hedgerows totaled 12.82%of precipitation.Plant hedgerows reduced the number of runoff events and the amount of surface runoff.Precipitation is the main driving force for the loss of nitrogen and phosphorus in surface runoff,and fertilization is an important factor affecting the losses of nitrogen and phosphorus.In CK,approximately 7.36%of nitrogen and 2.63%of phosphorus from fertilization entered the surface water through runoff.Drip fertigation reduced the accumulation of nitrogen and phosphorus in the surface soil and lowered the runoff loss concentrations of total nitrogen(TN)and total phosphorus(TP).Drip fertigation combined with plant hedgerows significantly reduced the overall TN and TP losses by 45.38 and 36.81%,respectively,in comparison to the CK totals.Drip fertigation increased the vertical migration depth of nitrogen and phosphorus nutrients and reduced the accumulation of nitrogen and phosphorus in the surface soil,which increased the pear yield.The promotion of drip fertigation combined with plant hedgerows will greatly reduce the losses of nitrogen and phosphorus to runoff and maintain the high fruit yields in the intensive orchards of the Tai Lake Basin.

Effects of nitrogen and phosphorus additions on soil microbial community structure and ecological processes in the farmland of Chinese Loess Plateau

Microorganisms regulate the responses of terrestrial ecosystems to anthropogenic nutrient inputs.The escalation of anthropogenic activities has resulted in a rise in the primary terrestrial constraining elements,namely nitrogen(N)and phosphorus(P).Nevertheless,the specific mechanisms governing the influence of soil microbial community structure and ecological processes in ecologically vulnerable and delicate semi-arid loess agroecosystems remain inadequately understood.Therefore,we explored the effects of different N and P additions on soil microbial community structure and its associated ecological processes in the farmland of Chinese Loess Plateau based on a 36-a long-term experiment.Nine fertilization treatments with complete interactions of high,medium,and low N and P gradients were set up.Soil physical and chemical properties,along with the microbial community structure were measured in this study.Additionally,relevant ecological processes such as microbial biomass,respiration,N mineralization,and enzyme activity were quantified.To elucidate the relationships between these variables,we examined correlation-mediated processes using statistical techniques,including redundancy analysis(RDA)and structural equation modeling(SEM).The results showed that the addition of N alone had a detrimental effect on soil microbial biomass,mineralized N accumulation,andβ-1,4-glucosidase activity.Conversely,the addition of P exhibited an opposing effect,leading to positive influences on these soil parameters.The interactive addition of N and P significantly changed the microbial community structure,increasing microbial activity(microbial biomass and soil respiration),but decreasing the accumulation of mineralized N.Among them,N24P12 treatment showed the greatest increase in the soil nutrient content and respiration.N12P12 treatment increased the overall enzyme activity and total phospholipid fatty acid(PLFA)content by 70.93%.N and P nutrient contents of the soil dominate the microbial community structure and the corresponding changes in hydrolytic enzymes.Soil microbial biomass,respiration,and overall enzyme activity are driven by mineralized N.Our study provides a theoretical basis for exploring energy conversion processes of soil microbial community and environmental sustainability under long-term N and P additions in semi-arid loess areas.

Effects of Different Nitrogen and Phosphorus Synergistic Fertilizer on Enzymes and Genes Related to Nitrogen Metabolism in Wheat

In recent years,in order to improve nutrient use efficiency,especially nitrogen use efficiency,fertilizer valueadded technology has been developed rapidly.However,the mechanism of the effect of synergistic fertilizer on plant nitrogen utilization is not clear.A study was,therefore,conducted to explore the activities and gene expression of key enzymes for nitrogen assimilation and the gene expression of nitrogen transporters in wheat after the application of synergistic fertilizer.Soil column experiment was set up in Qingdao Agricultural University experimental base from October 2018 to June 2019.Maleic acid and itaconic acid were copolymerized with acrylic acid as cross-linking monomer to make a fluid gel,which was sprayed on the fertilizer surface to make nitrogen and phosphorus synergistic fertilizer.A total of 6 treatments was set according to different nitrogen and phosphorus fertilizer ratios:(1)100%common nitrogen fertilizer+100%common phosphate fertilizer(2)70%nitrogen synergistic fertilizer+100%phosphorus synergistic fertilizer;(3)100%nitrogen synergistic fertilizer+70%phosphorus synergistic fertilizer;(4)100%nitrogen synergistic fertilizer+100%phosphorus synergistic fertilizer;(5)70%nitrogen synergistic fertilizer+70%phosphorus synergistic fertilizer;(6)100%commercial nitrogen synergistic fertilizer+100%commercial phosphorus synergistic fertilizer.The results are as follows:(1)the enzyme activities of wheat plants under synergistic fertilizer condition were higher than those under ordinary fertilizer,except under the treatment that nitrogen and phosphorus synergistic fertilizer were both reduced;(2)the expression level of the genes under the treatment“100%nitrogen synergistic fertilizer+100%phosphorus synergistic fertilizer”was significantly higher than those in other treatments.Combined with the higher performance of nitrogen concentration in various parts of the plant under the condition of applying synergistic fertilizer,this study indicated that the application of synergistic fertilizer can improve the nitrogen metabolism of the plant by increasing the nitrogen level in the rhizosphere soil,inducing the expression of nitrogen transporter genes and key assimilation enzymes genes.

Characteristics of Nitrogen and Phosphorus Losses in Different Crop Rotation Systems in the North of Erhai Lake Basin

[Objective] Nitrogen and phosphorus losses of surface runoff in various crop rotation systems in the north of Erhai Lake basin were studied with the objective to provide references for risk evaluation of environmental pollution and formulating countermeasures to control the nonpoint source pollution from agriculture.[Method] Water samples collected in four typical crop rotation systems distributed in seven towns（townships） in the north of Erhai Lake basin were investigated,as well as the fertilizer input,to explore the dynamic change of nitrogen and phosphorus content in surface water of farmland and ditch water,and the correlation between fertilizer input and the concentrations of nitrogen and phosphorus in the surface water of farmland and in the ditch water.[Result] The results showed that nitrogen loss in surface water of farmland in different crop rotation systems differed greatly,and the risk of nitrogen loss was 38% lower in broad bean-rice crop rotation than that in garlic-rice crop rotation.The water soluble nitrogen was the primary form of nitrogen loss.The content of water soluble nitrogen was significantly higher in garlic-rice crop rotation than that in the other rotation systems,and the concentrations of nitrogen in the surface water of farmland in different crop rotation systems followed the sequence below：garlic-rice crop rotationryegrass-rice crop rotationbroad bean-rice crop rotationrape-rice crop rotation.The loss of phosphorus in the surface water of farmland was relatively low and phosphorus combined with silt was the primary form for phosphorus loss.There was no significant difference of the loss of various forms of phosphorus in different crop rotation systems.The contents of total nitrogen and total phosphorus in the surface water of farmland were higher than that in ditch water,with increasing rates of total nitrogen and total phosphorus in ditch water of 72% and 82%,respectively.Topdressing was the critical reason for the high concentrations of nitrogen and phosphorus in the surface water,which also caused the increasing load to the ditch water.[Conclusion] Both the nitrogen and phosphorus loss were the highest in garlic-rice crop rotation.Reasonable crop rotation systems should be established based on both the environmental and economic benefits.This study provided references for controlling the nonpoint source pollution of farmland and improving the water quality of Erhai Lake.

Effects of Controlled Release Fertilizer on Loss of Nitrogen and Phosphorus from Farmland

[Objective] The aim was to study on effects of controlled release fertilizer on loss of nitrogen and phosphorus from farmland. [Method] Experiment was conducted in fields planted with rice and corn around Chao Lake and effects of compound fertilizer, controlled release fertilizer and controlled release fertilizer （reduced by 20%） on loss of nitrogen and phosphorus through runoff and leaching were analyzed. [Result] Loss of nitrogen and phosphorus mainly occurred in early stage of fertilizing; loss caused by runoff accounted for over 98% and caused by leaching was lower than 2%, indicating that nutrients of rice and corn mainly lost through runoff. As for controlled release fertilizers with 20% reduced, total loss of N and P decreased by 60% and 63% in rice field and reduced by 27.8% and 34% in corn field, respectively, indicating that controlled release fertilizer would maintain nutrients in soils high in later period of plant growth, improve use efficiency of N and P, reduce N and P loss in rice and corn fields in rainy season, and decrease non-point pollution. [Conclusion] The research suggested that controlled release fertilizer would slow down the loss of nutrients in farmlands, providing scientific references and technological support for extension of controlled release fertilizer and reduction of agricultural non-point pollution.

Non-Point-Source Nitrogen and Phosphorus Loadings from a Small Watershed in the Three Gorges Reservoir Area

Non-point-source pollution has become a major threat to the water quality of the Three Gorges Reservoir(TGR);however,nutrient loadings from terrestrial sources are unclear due to a lack of in situ monitoring.A representative small watershed in the central part of the TGR area was selected to monitor the loss of nitrogen(N) and phosphorous(P) continuously along with the runoff from 2007 through 2009 to understand the exact sources and loadings.Results show that the non-point-source nitrogen and phosphorus comes mainly from the storm runoff from residential areas,citrus orchards and sloping croplands,which contributes up to 76% of the loadings in this watershed.Thus,a crucial measure for controlling non-point-source pollution is to intercept storm runoff from the three sources.Paddy fields provide a sink for non-point-source N and P by intercepting the runoff and sediment along with their different forms of nitrogen and phosphorus.The N and P removal efficiency by paddy fields from residential areas is within the range of 56% to 98%.Paddy fields are an important land-use option for reducing the non-point-source loading of N and P in the TGR area.

Studies on the Characteristics of Nitrogen and Phosphorus Pollution of Natural Outcrop Springs in Wudalianchi

Objective] The research aimed to study the characteristics of nitrogen and phosphorus pollution of 30 natural outcrop springs in Wudalianchi, which provides a theoretical basis for the sustainable development and utilization and protection of Wudalianchi natural mineral resources. [Method] Choosing the 30 natural outcrop spring representatives in different regions, samples were collected in low water period, normal water period, wet period respectively, and the content of nitrogen, phosphorus and other contaminants in the samples were determined. Besides, the pollution characteristics of nitrogen and phosphorus in Wudalianchi natural outcrop spring were analyzed. [Result] The 30 natural outcrop spring in Wudalianchi area were seriously polluted by nitrogen. Total nitrogen and nitrate nitrogen were the main forms of nitrogen pollution. The content of total phosphorus and ammonia nitrogen were low. [Conclusion] The natural outcrop spring is mainly caused by agricultural non-point source pollution.

Changes in nitrogen and phosphorus and their effects on phytoplankton in the Bohai Sea

Systematic studies of the changes in dissolved inorganic nitrogen(DIN) and dissolved inorganic phosphorus(DIP) and their effects on phytoplankton over the last 30 years in the Bohai Sea are presented.The amount of sewage disposal,use of fertilizer and the Huanghe River runoff were found to have a significant influence on the DIN or DIP concentrations in the Bohai Sea over the last 30 years.Moreover,the changes in DIN and DIP resulted in changes in the limiting nutrients of phytoplankton in the Bohai Sea from nitrogen in the early 1980s to nitrogen-phosphorus in the late 1980s,and then to phosphorus after the 1990s.In addition,changes in nitrogen and phosphorus had a significant effect on the phytoplankton community structure.The half saturation constant(Ks) was used to evaluate the effect of nutrients on the phytoplankton community structure in the Bohai Sea over the last 30 years.Cell abundance percentages of dominant phytoplankton species with high Ks values for phosphorus and low Ks values for nitrogen have decreased since the 1980s,while those of dominant phytoplankton species with low Ks values for phosphorus and high Ks values for nitrogen increased during this period.

Carbon,nitrogen and phosphorus stoichiometry in Pinus tabulaeformis forest ecosystems in warm temperate Shanxi Province,north China

Although carbon(C), nitrogen(N), and phosphorous(P) stoichiometric ratios are considered good indicators of nutrient excess/limitation and thus of ecosystem health, few reports have discussed the trends and the reciprocal effects of C:N:P stoichiometry in plant–litter–soil systems. The present study analyzed C:N:P ratios in four age groups of Chinese pine, Pinus tabulaeformis Carr., forests in Shanxi Province, China: plantation young forests(AY,<20 year-old); plantation middle-aged forests(AM, 21–30 year-old); natural young forests(NY,<30 year-old); and natural middle-aged forests(NM,31–50 year-old). The average C:N:P ratios calculated for tree, shrub, and herbaceous leaves, litter, and soil(0–100 cm) were generally higher in NY followed by NM,AM, and AY. C:N and C:P ratios were higher in litter than in leaves and soils, and reached higher values in the litter and leaves of young forests than in middle-aged forests;however, C:N and C:P ratios were higher in soils of middle-aged forests than in young forests. N:P ratios were higher in leaves than in litter and soils regardless of stand age; the consistent N:P<14 values found in all forests indicated N limitations. With plant leaves, C:P ratios were highest in trees, followed by herbs and shrubs, indicating a higher efficiency in tree leaf formation. C:N ratios decreased with increasing soil depth, whereas there was no trend for C:P and N:P ratios. C:N:P stoichiometry of forest foliage did not exhibit a consistent variation according to stand age. Research on the relationships between N:P, and P, N nutrient limits and the characteristics of vegetation nutrient adaptation need to be continued.

Modelling Nitrogen and Phosphorus Dynamics in a Mesocosm Pelagic Ecosystem in Laizhou Bay in China

A model of nitrogen and phosphorus dynamics in mesocosm experiments was established on the basis of a summary and synthesis of the existing models. The established model comprised seven state variables(DIN,PO4-P,DON,DOP,phytoplankton,zooplankton and detritus) and five modules - phytoplankton,zooplankton,dissolved inorganic nutrients,dissolved organic nutrients and detritus. Comparison with the in situ experimental data in Laizhou Bay at the end of August 2002 showed that this model could properly simulate the variations of DIN,PO4-P,and phytoplankton biomass in a mesocosm pelagic ecosystem. It was found that not only the model structure but also the parameters adopted were fit for simulation. The sensitivity of the main state variables to the parameter change was assessed by sensitivity analysis. All these results are useful for studying the control mechanism of biogeochemical cycling of nutrients in Laizhou Bay and other Chinese coastal waters.

A nitrogen and phosphorus dynamic model of mesocosm pelagic ecosystem in the Jiaozhou Bay in China

A nitrogen and phosphorus dynamic model of mesocosm pelagic ecosystem was established according to the summary and synthesis of the models available, in which seven state variables （DIN, PO4-P, DON, DOP, phytoplankton, zooplankton and detritus） were included. Logically it had five modules--phytoplankton, zooplankton, dissolved inorganic nutrients, dissolved organic nutrients and detritus. The results showed that this model could simulate the variations of DIN, PO4-P, DON, DOP, POC and phytoplankton biomass in pelagic ecosystem in mesocosm properly, based on the site experiment data in the Jiaozhou Bay in the autumn of 1999 and the summer of 2000. Not only the logical structure but also the model parameters were feasible, and about 20 parameters were made to fit for the Jiaozhou Bay during the simulation. All of these are necessary to study the control mechanism of nutrients biogeochemical cycling in the Jiaozhou Bay and other China＇ s coastal waters.

Simultaneous removal of nitrogen and phosphorus from swine wastewater in a sequencing batch biofilm reactor

In this study, the performance of a sequencing batch biofilm reactor(SBBR) for removal of nitrogen and phosphorus from swine wastewater was evaluated. The replacement rate of wastewater was set at 12.5% throughout the experiment. The anaerobic and aerobic times were 3 h and 7 h, respectively, and the dissolved oxygen concentration of the aerobic phase was about 3.95 mg·L-1. The SBBR process demonstrated good performance in treating swine wastewater. The percentage removal of total chemical oxygen demand(COD), ammonia nitrogen(NH4+-N), total nitrogen(TN), and total phosphorus(TP) was 98.2%, 95.7%, 95.6%, and 96.2% at effluent concentrations of COD85.6 mg·L-1, NH4+-N 35.22 mg·L-1, TN 44.64 mg·L-1, and TP 1.13 mg·L-1, respectively. Simultaneous nitrification and denitrification phenomenon was observed. Further improvement in removal efficiency of NH4+-N and TN occurred at COD/TN ratio of 11:1, with effluent concentrations at NH4+-N 18.5 mg·L-1and TN 34 mg·L-1, while no such improvement in COD and TP removal was found. Microbial electron microscopy analysis showed that the filler surface was covered with a thick biofilm, forming an anaerobic–aerobic microenvironment and facilitating the removal of nitrogen, phosphorus and organic matters. A long-term experiment(15 weeks) showed that stable removal efficiency for N and P could be achieved in the SBBR system.

Removal of nitrogen and phosphorus in a combined A^2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Characterization of the Growth,Chlorophyll Content and Lipid Accumulation in a Marine Microalgae Dunaliella tertiolecta under Different Nitrogen to Phosphorus Ratios

Microalgal lipids are regarded as main future feedstock of biofuels for its higher efficiency of accumulation and sus- tainable production. In order to investigate the effect of various nitrogen to phosphorus ratios on cells growth, chlorophyll content and accumulation of lipids in Dunaliella tertiolecta, experiments were carried out in modified microalgal medium with inorganic nitrogen （nitrate-nitrogen） or organic nitrogen （urea-nitrogen） as the sole nitrogen source at initial N：P ratios ranging from 1：1 to 32：1. The favorable N：P of 16：1 in the nitrate-N or urea-N medium yielded the maximum cell density and specific growth rate. Decrease in chlorophyll content were observed at the N：P of 4：1 in both nitrate-N and urea-N cultures. It was also observed that the maximum lipids concentration was obtained at the N：P of 4：1 in both nitrate and urea nutrient medium. The lipid productivity and lipid content of cultures in the urea-N medium at the N：P of 4： lwere markedly higher than those from cultures with other N：P ratios （p〈 0.05）. The results of this work illustrate the possibility that higher ratios of nitrogen to phosphorus have enhancing effect on cells growth of D. tertiolecta. Conversely, higher lipid accumulation is associated with a decrease in chlorophyll content under lower ratios of nitro- gen to phosphorus. The results confirm the hypothesis of this study that a larger metabolic flux has been channeled to lipid accumu- lation in D. tertiolecta cells when the ratios of nitrogen to phosphorus drop below a critical level.

Cu_(3)P nanoparticles confined in nitrogen/phosphorus dual-doped porous carbon nanosheets for efficient potassium storage

Immobilizing primary electroactive nanomaterials in porous carbon matrix is an effective approach for boosting the electrochemical performance of potassium-ion batteries (PIBs) because of the synergy among functional components. Herein, an integrated hybrid architecture composed of ultrathin Cu_(3)P nanoparticles (~20 nm) confined in porous carbon nanosheets (Cu_(3)P⊂NPCSs) as a new anode material for PIBs is synthesized through a rational self-designed self-templating strategy. Benefiting from the unique structural advantages including more active heterointerfacial sites, intimate and stable electrical contact, effectively relieved volume change, and rapid K^(+) ion migration, the Cu_(3)P⊂NPCSs indicate excellent potassium-storage performance involving high reversible capacity, exceptional rate capability, and cycling stability. Moreover, the strong adsorption of K^(+) ions and fast potassium-ion reaction kinetics in Cu_(3)P⊂NPCSs is verified by the theoretical calculation investigation. Noted, the intercalation mechanism of Cu_(3)P to store potassium ions is, for the first time, clearly confirmed during the electrochemical process by a series of advanced characterization techniques.

Influence of the concentration ratio of nitrogen to phosphorus on the growth and interspecies competition of two red tide algae

The growth and interspecies competition of two red tide algal species Thalassiosira pseudonana Hasle et Heimdal and Gymnodinium sp. were studied under different concentration ratios of nitrogen to phosphorus, and the algal hatch culture experiments were conducted. The physiological and biochemical indexes were measured periodically, including the maximum comparing growth rate, relative growth rate, average double time and chlorophyll a concentration. The results showed that when the concentration ratio of nitrogen to phosphorus was 16： 1, the maximum comparing growth rate, relative growth rate and chlorophyll a concentration of Thalassiosira pseudonana all reached the highest,and average double time was the shortest. This implied that the optimal concentration ratio of nitrogen to phosphorus of Thalassiosira pseudonana is 16： 1. When the concentration ratio of nitrogen to phosphorus was 6：1, the maximum comparing growth rate, relative growth rate and the chlorophyll a concentration of Gymnodinium sp. reached the highest, and average double time was the shortest, so the optimal concentration ratio of nitrogen to phosphorus of Gymnodinium sp. is 6： 1. From the growth curves as indicated both in the cell density and the chlorophyll a concentration, it is suggested that the influence of concentration ratio of nitrogen to phosphorus on the chlorophyll a concentration and the cell density are almost the same. Different concentration ratios of nitrogen to phosphorus had weak influence on community succession and the competition between the two algae. Gymnodinium sp. may use the phosphorus in vivo for growth, so it is important to pay attention to the concealment of phosphorus, in order to avoid the outbreak of red tide. On the basis of the importance of nitrogen and phosphorus and the ratio of their concentration, the possible outbreak mechanism of red tide of the two algae was also discussed.

Yield performance and optimal nitrogen and phosphorus application rates in wheat and faba bean intercropping

Yield performance in cereal and legume intercropping is related to nutrient management,however,the yield response of companion crops to nitrogen(N)input is inconclusive and only limited efforts have focused on rationed phosphorous(P)fertilization.In this study,two multi-year field experiments were implemented from 2014-2019 under identical conditions.Two factors in a randomized complete block design were adopted in both experiments.In field experiment 1,the two factors included three planting patterns(mono-cropped wheat(MW),mono-cropped faba bean(MF),and wheat and faba bean intercropping(W//F))and four N application rates(N0,0 kg N ha^(-1);N1,90 and 45 kg N ha^(-1) for wheat and faba beans,respectively;N2,180 and 90 kg N ha^(-1) for wheat and faba beans,respectively;and N3,270 and 135 kg N ha^(-1) for wheat and faba beans,respectively).In field experiment 2,the two factors included three P application rates(P0,0 kg P_(2)O_(5) ha^(-1);P1,45 kg P_(2)O_(5) ha^(-1);and P2,90 kg P_(2)O_(5) ha^(-1))and the same three planting patterns(MW,MF,and W//F).The yield performances of inter-and mono-cropped wheat and faba beans under different N and P application rates were analyzed and the optimal N and P rates for intercropped wheat(IW)and MW were estimated.The results revealed that intercropping favored wheat yield and was adverse to faba bean yield.Wheat yield increased by 18-26%,but faba bean yield decreased by 5-21% in W//F compared to MW and MF,respectively.The stimulated IW yield drove the yield advantage in W//F with an average land equivalent ratio(LER)of 1.12.N and P fertilization benefited IW yield,but reduced intercropped faba bean(IF)yield.Nevertheless,the partial LER of wheat(pLER_(wheat))decreased with increasing N application rates,and the partial LER of faba bean(pLER_(faba bean))decreased with increasing P application rates.Thus,LER decreased as N input increased and tended to decline as P rates increased.IW maintained a similar yield as MW,even under reduced 40-50% N fertilizer and 30-40% P fertilizer conditions.The estimated optimum N application rates for IW and MW were 150 and 168 kg ha^(-1),respectively,and 63 and 62 kg ha^(-1) for P_(2)O_(5),respectively.In conclusion,W//F exhibited yield advantages due to stimulated IW yield,but the intercropping yield benefit decreased as N and P inputs increased.Thus,it was concluded that modulated N and P rates could maximize the economic and ecological functions of intercropping.Based on the results,rates of 150 kg N ha^(-1) and 60 kg P_(2)O_(5) ha^(-1) are recommended for IW production in southwestern China and places with similar conditions.

Changes in Phosphorus Fractions and Nitrogen Forms During Composting of Pig Manure with Rice Straw

The study was conducted to reveal P fractions and N forms changing characters during composting of pig manure with rice straw.During composting,the NH 4 ＋-N concentration decreased and reached at a relatively low value（〈400 mg kg-1） in the final compost,while the NO 3--N concentration increased.Total N losses mainly occurred during thermophilic phase due to the high temperature,the high NH 4 ＋-N concentration and the increase of pH value.Labile inorganic P was dominated in the pig manure and initial compost mixture.During composting,the proportion of labile inorganic P of total extracted P decreased,while the proportion of Fe＋Al-bound P,Ca＋Mg-bound P and residual P increased.The evolutions of the proportion of labile inorganic P,Fe＋Al-bound P and Ca＋Mg-bound P were well correlated with the changes of pH value,organic matter and C/N ratio.Therefore,composting could increase the concentration of N and P and decrease the presence of NH 4 ＋-N and labile P fractions which might cause environmental issues following land application.

Nitrogen and Phosphorus Diffusive Fluxes Across the Sediment-Water Interface in Estuarine and Coastal Tidal Flats

Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082-2.56, 0.03-0.58, 0.69-5.38 and 0.035-0.53 mg/L, respectively, while 0.0025 - 1.35 mg /L for NH^-N, 0. 0055 ~0.20mg/L for NO2-N, 0.61-1.14 mg/L for NO3-N and 0.11~0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusionfluxes across the sediment-water interface are between -0.024~0.99, -0.39~ -0.0019, -3.09--0.12 and -0.48- 0.12 ug/ (cm.d ) respectively, showing that the sediment in tidal flats is the source of phosphorus and an important sink for nitrogen in the waters.