Exogenous addition of nitrate nitrogen regulates the uptake and translocation of lead (Pb) by Iris lacteal Pall. var. chinensis (Fisch.) Koidz.

Since Pb is a non-biodegradable inorganic pollutant and a non-essential metal,its long-term presence in soil poses a great threat to the environment.Iris lactea Pall.var.chinensis(Fisch.)Koidz.,a perennial dense bush herb with high resistance of Pb and wide adaptability,was used in pot experiments to study the effects of exogenous nitrate N(NO_(3)^(–)-N)on the absorption and transportation of Pb and plant growth under different Pb concentrations.Then,the mechanism of NO_(3)^(-)-N affecting Pb and nutrient uptake and transport was explored.The concentration of Pb in the experiment ranged from 0 to 1600 mg/kg,and the added concentration of NO_(3)^(-)-N was 0.0–0.3 g/kg.The results showed that I.lactea was highly tolerant to Pb,and the shoot fraction was more sensitive to varied Pb concentrations in the soil than the root fraction.This protective function became more pronounced under the condition of raised Pb concentration in the soil.When the concentration of Pb in the soil reached 800 mg/kg,the highest Pb content of I.lactea was found under the condition of 0.1 g/kg of NO–3-N addition.When Pb concentration in the soil increased to 1600 mg/kg,the increase in NO_(3)^(-)-N addition promoted Pb uptake by the root.To ensure the well growth of I.lactea and the effect of remediation of Pb-contaminated soil,the recommended concentration of NO–3-N in the soil is 0.1 g/kg.This result provides a theoretical basis for exogenous N regulation of phytoremediation of Pb-contaminated soil.

Effects of autumn plowing on the movement and correlation of moisture,heat and nitrate nitrogen in seasonal freeze-thaw soil

A two-year experiment was established in northern Xinjiang to investigate the effects of autumn plowing methods on nitrate nitrogen accumulation,spring-sown soil conditions and cotton emergence rate,and to explore the response relationship between soil water,heat and nitrate nitrogen.The experiment included five autumn plowing treatments,namely,plough tillage(FG),no-tillage(MG),ridge and furrow alternation(LG),plough tillage with straw mulch(FJ)and plough tillage with activated charcoal mulch(FH).The results showed that both FH and FJ treatments were beneficial to promote the nitrate-nitrogen accumulation in topsoil,while FG,MG and LG treatments aggravated the nitrate nitrogen leaching in topsoil.During the freezing period,FH and FJ treatments were beneficial to reduce soil heat loss and facilitate the coordinated upward migration of soil water and nitrate nitrogen.In the thawing period,FH and FJ treatments favored suppressing the synergistic downward transport of soil water and nitrate-nitrogen and motivated the synergistic upward migration of heat and nitrate nitrogen in deep soil.Binary regression analysis suggested that the interaction between water,heat and nitrate nitrogen under FH and FJ treatments showed a highly significant correlation.FH and FJ treatments showed obvious advantages in regulating soil conditions and optimizing soil water,heat and nitrate nitrogen co-transport mechanism.During the spring sowing period,the FH and FJ treatments increased the average soil temperature by 0.99℃and 1.29℃,and the average soil moisture content by 6.01%and 8.70%,and the average soil nitrate content by 10.20 mg/kg and 10.47 mg/kg,in the 0-25 cm soil layer,respectively.FH and FJ treatments significantly grew the emergence rate of cotton,which can be used as the main autumn tillage strategies in arid areas of northern Xinjiang.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Nitrogen and phosphorus changes and optimal drainage time of flooded paddy field based on environmental factors

While many controlled irrigation and drainage techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study was conducted to examine the changes of nitrogen and phosphorus of a flooded paddy water system after fertilizer application and at each growth stage so as to obtain the optimal drainage time at each growth stage. Four treatments with different water level management methods at each growth stage were conducted under the condition of ten-day continuous flooding. Results show that the ammonia nitrogen （ NH4-N ） concentration reached the peak value once the fertilizer was applied, and then decreased to a relatively low level seven to ten days later, and that the nitrate nitrogen （NO^-N） concentration gradually rose to its peak value, which appeared later in subsurface water than in surface water. Continuous flooding could effectively reduce the concentrations of NH^-N , NO3-N, and total phosphorus （TP） in surface water. However, the paddy water disturbance, in the process of soil surface adsorption and nitrification, caused NH]-N to be released and increased the concentrations of NH4-N and NO^-N in surface water. A multi-objective controlled drainage model based on environmental factors was established in order to obtain the optimal drainage time at each growth stage and better guide the drainage practices of farmers. The optimal times for surface drainage are the fourth, sixth, fifth, and sixth days after flooding at the tillering, jointing-booting, heading-flowering, and milking stages, respectively.

Genome-wide identification and expression analysis of NIN-like Protein(NLP)genes reveals their potential roles in the response to nitrate signaling in watermelon

To balance the relationship between high yield and low nitrogen supply,the nitrogen utilization efficiency of watermelon needs to be improved urgently.Nodule inception-like Protein(NLP)transcription factors play a key node role in nitrate response and growth and development of plant,however,comprehensive analysis of the NLP gene family in watermelon is unclear.This study explored the functional classification,evolutionary characteristics,and expression profile of the ClNLP gene family.Three ClNLPs were categorized into three groups according to their gene structure and phylogeny.All of them contained the conserved RWP-RK and PB1 domains.Evolutionary analysis of ClNLPs revealed that ClNLP1 and ClNLP3 underwent strong purified selection.In addition,cis-acting elements related to plant hormones and abiotic stresses were present in the ClNLP promoter.According to tissue-specific analysis ClNLP was widely expressed in roots,stems,leaves,flowers and fruits,and ClNLP1 was significantly induced in the roots of different nitrogen utilization varieties under different nitrate nitrogen supply.The SRTING functional protein association network suggested that ClNLP1 is associated with most genes,such as NRT1.1,NRT2.1,NIA1,and NIR1,and the dual-luciferase reporter assay found that ClNLP1 positively regulates the expression of ClNRT2.1.We speculated that ClNLP1 might play a central role in regulating the response of watermelon to nitrate nitrogen.

Identification of Differentially Expressed Genes Induced by Ammonium Nitrogen in Rice Using mRNA Differential Display

RNAs isolated from ammonium- and nitrate-treated rice leaves were used to screen differentially expressed genes through mRNA differential display. A total of 72 bands appeared significant differences and some of them were further confirmed by reverse Northern and Northern blot. The results showed that two genes, A-02 （Oryza sativa drought stress related mRNA） and A-03 （Zea mays partial mRNA for TFIIB-related protein） were highly up-regulated in the ammonium-fed rice leaves. The enzyme assays showed that the activities of the two anti-oxidative enzymes, catalase and peroxidase, and the content of a non-enzymic antioxidant, glutathione, were significantly higher in the ammonium-fed rice leaves than those in the nitrate-fed ones, indicating that the ammonium nutrition might be beneficial for rice plants to improve the stress resistance during growth and development.

The Effect of Different Nitrogen Form on Key Enzyme Activity of Sugarbeet(Vulgaris L.) Carbon and Nitrogen Metabolism

This article analyses the effect of the proportion of the different nitrogen forms on key enzyme activity of carbon and nitrogen metabolism under the condition of nutritional water while Tian Yan-7 was used as experimental material.The result showed that nitrate reductase(NR) activity in the leaves gradually enhanced with the increase of NO - 3.No matter in root or leaves,glutamina synthetase(GS) activity first enhanced with increasing NH + 4 when NH + 4 was lower than that of NO - 3,and GS activity was the highest when NH + 4and NO - 3 was equal,then GS activity declined with NH + 4 increasing further.In the anaphase of growth,synthetic activity in root of sucrose synthetase(SS) in the mixed NH + 4 and NO - 3 was obviously highr than or NO - 3 alone.Both of the root and sugar yields were the highest when the proportion of NH + 4 and NO - 3 was 1:1.

Nitrate leaching of winter wheat grown in lysimeters as affected by fertilizers and irrigation on the North China Plain

Proper application of nitrogen（N） fertilizers and irrigation management are important production practices that can reduce nitrate leaching into groundwater and improve the N use efficiency（NUE）. A lysimeter/rain shelter facility was used to study effects of the rate of N fertilization, type of N fertilizer, and irrigation level on key aspects of winter wheat production over three growing seasons（response variables were nitrate transport, N leaching, and NUE）. Results indicated that nitrate concentration in the soil profile and N leaching increased with the rate of N fertilization. At the end of the third season, nitrate concentration in the top 0–75 cm layer of soil was higher with manure treatment while urea treatments resulted in higher concentrations in the 100–200 cm layer. With normal irrigation, 3.4 to 15.3% of N from applied fertilizer was leached from the soil, yet no leaching occurred under a stress irrigation treatment. The manure treatment experienced less N leaching than the urea treatment in all cases except for the 180 kg N ha^-1 rate in 2011–2012（season 3）. In terms of grain yield（GY）, dry matter（DM） or NUE parameters, values for the manure treatment were lower than for the urea treatment in 2009–2010（season 1）, yet were otherwise higher for urea treatment in season 3. GY and crop nitrogen uptake（NU） were elevated when the rate of N fertilizer increased, while the NUE decreased; GY, DM, and NU increased with the amount of irrigation. Data indicated that reduced rates of N fertilization combined with increased manure application and proper irrigation management can lower nitrate levels in the subsoil and reduce potential N leaching into groundwater.

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

Nitrogen (N) plays a key role in crop growth and production;however,data are lacking especially regarding the interaction of biochar,grass cover,and irrigation on N leaching in saturated soil profiles.Eighteen soil columns with 20-cm diameter and 60-cm height were designed to characterize the effects of different grass cover and biochar combinations,i.e.,bare soil+0%biochar (control,CK),perennial ryegrass+0%biochar (C1),Festuca arundinacea+0%biochar (C2),perennial ryegrass+1%biochar (C3),perennial ryegrass+2%biochar (C4),perennial ryegrass+3%biochar (C5),F.arundinacea+1%biochar (C6),F.arundinacea+2% biochar (C7),and F.arundinacea+3%biochar (C8),on periodic irrigation infiltration and N leaching in homogeneous loess soils from July to December 2020.Leachates in CK were 10.2%–35.3%higher than those in C1 and C2.Both perennial ryegrass and F.arundinacea decreased the volumes of leachates and delayed the leaching process in the 1%,2%,and 3%biochar treatments,and the vertical leaching rate decreased with biochar addition.The N leaching losses were concentrated in the first few leaching tests,and both total N (TN) and nitrate (NO_(3)^(-))-N concentrations in CK and C1–C8 decreased with increasing leaching test times.Biochar addition (1%,2%,and 3%) could further reduce the leaching risk of NO_(3)^(-)-N and the NO_(3)^(-)-N loss decreased with biochar addition.However,compared to 1%biochar,2% biochar promoted the leaching of TN under both grass cover types.The N leaching losses in CK,C1,C2,C3,C4,C6,and C7 were primarily in the form of NO_(3)^(-)-N.Among these treatments,CK,C1,and C2had the highest cumulative leaching fractions NO_(3)^(-)-N (>90%),followed by those in C3,C4,C6,and C7 (>80%).The cumulative leaching fraction of NO_(3)^(-)-N decreased with increasing leaching test times and biochar addition,and 3%biochar addition (i.e.,C5 and C8) reduced it to approximately 50%.The one-dimensional advective-dispersive-reactive transport equation can be used as an effective numerical approach to simulate and predict NO_(3)^(-)-N leaching in saturated homogeneous soils.Understanding the effects of different biochar and grass combinations on N leaching can help us design environmentally friendly interventions to manage irrigated farming ecosystems and reduce N leaching into groundwater.

Rice Grain Chalkiness Is Negatively Correlated with Root Activity During Grain Filling

Field and pot experiments were conducted using indica rice varieties with differential chalkiness. There were significant differences in root activity among the varieties. The percentages of chalky grains and chalky area were both negatively correlated with root activity expressed as α-naphthylamine oxidation ability （RA） per gram of fresh root （RAfw） , RA per spikelet （RAgrn）, or RA per sink capacity （RAsink）. The RAsink was more closely related to chalkiness than RAt, and RAgrn when varieties differed greatly in panicle size and grain weight. Application of NO3^--N fertilizer at heading resulted in higher root activity and reduced chalkiness. Application of 30 mg/L NaN3 （respiration inhibitor） resulted in reduced root activity and increased chalkiness for one variety ＇GD9501＇, but for the other variety ＇Qinluai＇ was in reverse. The percentages of chalky grains and chalky area were negatively correlated with root activity at 10 days after heading under different chemical treatments （r=-0.8567^＊ and r=-0.9211^＊＊, respectively）.

A putative 6-transmembrane nitrate transporter OsNRT1.1b plays a key role in rice under low nitrogen

OsNRT1.1a is a low-affinity nitrate（NO_3^-） transporter gene. In this study, another mRNA splicing product, OsNRT1.1b,putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a-expressing oocytes accumulated ^（15）N levels to about half as compared to OsNRT1.1bexpressing oocytes. The electrophysiological recording of OsNRT1.1b-expressing oocytes treated with 0.25 mM NO_3^- confirmed ^（15）N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen（N） deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild-type（WT）. The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25 mM NH_4NO_3 and 2.5 mM NO_3^- or NH_4~＋ treatments, but not in 0.125 mM NH_4NO_3.However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125 m M NH_4NO_3,suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.

Experimental Study on the Distribution of Soil Nitrate and Ammonium Nitrogen under Controlled Drainage

A field experimental project was set up to assess the effects of controlled drainage on the distribution and concentration of nitrogen in the soil at the Irrigation and Drainage Experimental Station under Four-Lake Engineering Administration of Jingzhou City, Hubei Province. Two plots drain runoff by controlled drainage system, with an area of 0.1 hm^2 （20 m×50 m） each. The third one with an area of 0.04 hm^2 （8 m×50 m） has a conventional subsurface drainage system. Under this experimental condition, the study draws the following conclusions： ① The controlled drainage system has a remarkable effect on the diminishing ratios of nitrate nitrogen between neighboring layers. It is presented that the diminishing ratio increases with the raising height of drain outlet. Controlled drainage system also reduces the transference of nitrate nitrogen in topsoil.② Different from nitrate nitrogen, the concentration of ammonium nitrogen is stable along the longitudinal section of soil, which is little affected by the controlled drainage system. It indicates that the concentration of ammonium nitrogen decreases according to the lowering of controlling height of the drain outlet.

Effects of Aeration on Nitrification Process in a Polluted Urban River

[Objective] The study aimed to discuss the effects of aeration on nitrification process in a polluted urban river, [Metbod] Through indoor simulation experiments, the effects of different aeration conditions （aerating water named Ew, aerating sediment named Es ） on nitrification process in a polluted urban river were studied.[ Result]The nitrification of the control group named Ec proceeded slowly, while two kinds of aeration promo- ted the process of nitrification, that is, the peak values of nitrate nitrogen of Ew and Es group were respectively 5.15 and 3.83 times that of Ec group. During aeration, NO2 --N accumulation in the overlying water of Ew and Es group lasted for 10 and 14 days separately, and the maximum concentrations reached 11.41 and 7.41 mg/L respectively. Nitrification process was not consistent during the two aeration conditions, that is, the rate of nitrite oxidation in Ew group was faster than that in Es group. Denitrification process was significant after aeration, and the concentration of nitrate nitrogen in Ew and Es group was 1.26 and 2.82 mg/L respectively at the end of the experiment. [ Conclusion]The research could provide scientific references for the restoration of polluted urban rivers.

Soil acidification of alfisols influenced by nitrate and ammonium nitrogen level in tea plantation

Nitrogen is an important fertilizer in tea production,but it is also an important factor in tea garden soil acidification.The relationship between absorption and transport of different forms of nitrogen in the tea plant and soil acidification is still unknown.In order to explore the different characteristics of absorption,utilization and distribution of nitrogen,stable isotope 15N tracer technique was used to measure the absorption,utilization and allocation of nitrate nitrogen(NO_(3-)15N)and ammonium nitrogen(NH4-15N)under the same nitrogen application amount of tea tree seedlings as experimental materials.The results showed that the tea seedlings had the same pattern of nitrogen application:tissue nitrogen content increased after fertilization,remarkable rising at 7 d and the absorption speed increased quickly after 28 d,finally reached its maximum at 56 d.The nitrogen use efficiency of two nitrogen sources in two kinds of soil varied not significantly.The maximum NUE of NO_(3-)^(15)N reached 12.66%,and at the same time NH_(4)-^(15)N utilization rose up to 11.54%.According to the absorption of soil nitrogen and nitrogen fertilizer in the two kinds of soil,it is concluded that the soil nitrogen cannot meet the growth needs of tea tree and extra nitrogen supply was required.The declined soil pH indicated that fertilizer should be used in moderation,which can not only satisfy the growth of tea tree but also to restrict soil acidification.

The Growth Effect of Enhanced Ammonium Nutrition on Maize

The two maize varieties,Yuanzheng 808(astrictive type) and Sidan 19(explanate type),were cultured in pots.There were six treatments which the proportion of NO 3 - N and NH 4 + N were 1∶0 (treatment 1),2∶1(treatment 2),1∶1(treatment 3),1∶2(treatment 4),0∶1(treatment 5) and CK(no nitrogen) respectively.After emergence of seedings,the samples were picked up per 20 days in the growth period and measured chlorophyll contents,nitrate reductase(NR) activity,the weight of dry matter and single plant seed yield respectively.The result showed that enhanced ammonium nutrition (EAN) may increase chlorophyll content,dry matter weight and single plant seed yield.But there was a difference between varieties.To Yuanzheng 808,treatment 2 was the highest yield in all treatments;but treatment 4 was the highest yield to Sidan 19.

Improving Nitrogen Use Efficiency in Rice through Enhancing Root Nitrate Uptake Mediated by a Nitrate Transporter, NRT1.1B

Nitrogen （N） is one of most important nutrients for crop production, which makes up 1%-5% of total plant dry matter （Marschner, 2012）. Due to the limited availability of N in soil, application of N fertilizers has been an important agronomic practice to increase crop yield. However, over-application of N fertilizers has caused pollution of N in soil, water and air. It was estimated that the nitrogen use efficiency （NUE, the total biomass or grain yield produced per unit of applied fertilizer N） in cereal crops is as low as 33% （Raun and Johnson, 1999）. Therefore, improving NUE together with reducing application of N fertilizers is an important issue for environment and sustainable production of crops. This is especially important for rice, which is a staple food for half population in the world.

Distribution characteristics of soil organic carbon and nitrogen in farmland and adjacent natural grassland in Tibet

Land-use significantly affects soil organic carbon(SOC)and nitrogen cycling,eventually leading to global climate change.The cold and arid climate conditions in Tibet are not conducive to transformation of SOC and nitrogen.Hence,research on SOC and nitrogen distribution under different land-use patterns in Tibet is an important basis to assess the soil carbon and nitrogen potential in the land ecosystem of this area.This study aims to explain the effects of two land-use patterns,namely,farmland and grassland,on SOC and nitrogen contents in the cold regions of Tibet.This study also seeks to provide a scientific basis for the agricultural and grass production system.To achieve these goals,the changing features of total nitrogen(TN),mineralized nitrogen(nitrate nitrogen(NN)and ammonium nitrogen(AN)),and SOC were analyzed in different soil depths(0-5,5-10,10-20,20-30,30-40,and 40-50 cm)in farmland and adjacent natural grassland.The differences in carbon and nitrogen contents between the farmland and grassland of the main agricultural area of Tibet were determined through combined field survey and lab analysis.Results showed that the contents of SOC,TN and mineralized nitrogen in the grassland and farmland decreased with increasing soil depth mainly in the surface with depth of 0-20 cm.The effects of the different land-use patterns on the contents of SOC and TN were primarily evident in the 0-10 cm surface layer.The contents of SOC and TN in the farmland were significantly lower than those in the grassland,with mean reduction by 28.36%for SOC and 20.76%for TN.When the soil layer is deeper than 10 cm,the contents of SOC and TN in the farmland were greater than those in the grassland.This finding indicated that the transformation from grassland to farmland in Tibet mainly influenced the SOC and TN in the 0-10 cm surface layer.Moreover,the results showed that the increment of carbon in the deep soil layers of the farmland partially offsets the SOC loss from the surface because of cultivation.The ratio of mineralized nitrogen to TN in the farmland was significantly higher than that in the grassland(p<0.001).Mineralized nitrogen in the farmland mainly existed in the form of NN,with a mean content of 2.7%in the 0-50 cm surface layer.By contrast,the difference in the ratio of AN to TN between the grassland and farmland was not significant.The results revealed that the land-use pattern in extremely cold agricultural areas mainly affects the contents of SOC and nitrogen in the 0-10 cm surface layer,and agricultural management is beneficial in increasing the SOC content in the deeper layers.

Statistical modeling of nitrogen-dependent modulation of root system architecture in Arabidopsis thaliana

Plant root development is strongly affected by nutrient availability. Despite the importance of structure and function of roots in nutrient acquisition,statistical modeling approaches to evaluate dynamic and temporal modulations of root system architecture in response to nutrient availability have remained as widely open and exploratory areas in root biology. In this study,we developed a statistical modeling approach to investigate modulations of root system architecture in response to nitrogen availability. Mathematical models were designed for quantitative assessment of root growth and root branching phenotypes and their dynamic relationships based on hierarchical con figuration of primary and lateral roots formulating the fishbone-shaped root system architecture in Arabidopsis thaliana. Time-series datasets reporting dynamic changes in root developmental traits on different nitrate or ammonium concentrations were generated for statistical analyses. Regression analyses unraveled key parameters associated with：（i） inhibition of primary root growth under nitrogen limitation or on ammonium;（ii） rapid progression of lateral root emergence in response to ammonium; and（iii） inhibition of lateral root elongation in the presence of excess nitrate or ammonium. This study provides a statistical framework for interpreting dynamic modulation of root system architecture,supported by metaanalysis of datasets displaying morphological responses of roots to diverse nitrogen supplies.

Earthworm biomass and population structure are negatively associated with changes in organic residue nitrogen concentration during vermicomposting

Vermicomposting is an efficient and environmentally friendly technology to dispose of agricultural organic residues.The efficiency of organic residue decomposition during vermicomposting is directly affected by the biomass and population structure of earthworms.In this study,we investigated how the earthworm biomass and population structure responded to changes in the physicochemical properties of six types of organic residue(cattle dung,herbal waste,rice straw,soybean straw,garden waste,and tea residues)during vermicomposting.Each type of organic residues was placed in a pot with earthworms Eisenia fetida,and the physicochemical properties of the organic residues and earthworm growth dynamics were recorded at 0,30,60,and 90 d of vermicomposting.The biomass and population structure of earthworms were stable or increased in rice straw,garden waste,and cattle dung within 60 d of vermicomposting,whereas in tea residues and herb waste,very little earthworm activity(3 adults and 2 cocoons)was recorded on day 30.Among the physicochemical parameters,the substrate C/N ratio was negatively correlated with earthworm growth dynamics.Decomposing organic residues showed higher NH_(4)^(+)-N and NH_(3)^(-)-N concentrations but a lower total organic carbon content,which negatively affected earthworm growth and reproduction.We recommend that chemical properties of vermicomposting systems should be monitored regularly.At the threshold levels of decomposing organic residue NH_(4)^(+)-N and NH_(3)^(-)-N concentrations,earthworms should be removed and the vermicompost can be harvested.Small-and large-scale farmers thus need to monitor the physicochemical properties of vermicompost to sustain active earthworm populations.

Effects of irrigation regimes on soil NO_(3)^(-)-N, electrical conductivity and crop yield in plastic greenhouse

Developing water-saving irrigation regimes has important practical significance not only in alleviating the crucial water shortage,but also in controlling soil salinization for the protected cultivation in eastern China.A field study with six treatments was conducted to evaluate the effects of different irrigation regimes with subdrainage systems on the soil nitrate nitrogen,salinity and moisture,also evaluate the effects on tomato growth,fruit yield and irrigation water use efficiency(IWUE).The treatments were distinguished by three different irrigation amounts of 310 mm,360 mm and 410 mm,and two irrigation frequencies of 7 and 11 times.Results showed that the irrigation amount had significant effects on the soil NO_(3)^(-)-N and electric conductivity(EC).A positive correlation was detected between soil NO_(3)^(-)-N(x)and EC(y)at 0-20 m depth after harvest,with a linear equation of y=0.063x-0.670.Soil volumetric moisture at 0.10 m and 0.20 m depth was increased as the irrigation amount increased.Moreover,a higher amount of irrigation increased the fruit yield but reduced the IWUE of tomato.It was also found that smaller irrigation amounts combined with frequent intervals could increase fruit yield and IWUE.However,the fruit quality of tomato had a significant(p<0.05)negative correlation with irrigation amount.Therefore,the parameters of irrigation regime including the irrigation amount and intervals should be considered comprehensively in order to find a compromise between salinity control and irrigation water use efficiency improvement.