Appropriate Supply of Ammonium Nitrogen and Ammonium Nitrate Reduces Cadmium Content in Rice Seedlings by Inhibiting Cadmium Uptake and Transport

Reasonable nitrogen(N) application is a promising strategy for reducing crop cadmium(Cd) toxicity. However, the specific form of N and the required amount that affect Cd tolerance and accumulation in rice remain unclear. This study explored the influence of different N-fertilizer forms(NH_(4)NO_(3), NH_4Cl, and KNO_(3)) and dosages on Cd tolerance and uptake in Cd-stressed N-sensitive and N-insensitive indica rice accessions. The results indicated that the Cd tolerance of N-sensitive indica accessions is more robust than that of N-insensitive ones. Furthermore, the shoot Cd content and Cd translocation rate in both N-sensitive and N-insensitive indica accessions decreased with an appropriate supply of NH_(4)NO_(3) and NH_4Cl, whereas they were comparable or slightly increased with increased KNO_(3). Unfortunately, we did not find significant and regular differences in Cd accumulation or translocation between N-sensitive and N-insensitive rice accessions. Consistent with the reduction of shoot Cd content, the addition of NH_(4)NO_(3) and NH_4Cl also inhibited the instantaneous root Cd^(2+) uptake. The expression changes of Cd transport-related genes under different N forms and dosages suggested that the decreased shoot Cd content, caused by the increased supply of NH_(4)NO_(3) and NH_4Cl, is likely achieved by reducing the transcription of OsNRAMP1 and OsIRT1. In summary, our findings reveal that an appropriate supply of NH_(4)NO_(3) and NH_4Cl could reduce Cd uptake and transport in rice seedlings, suggesting that rational N management could reduce the Cd risk in rice production.

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.

Plant Nitrogen Metabolism: Balancing Resilience to Nutritional Stress andAbiotic Challenges

Plant growth and resilience to abiotic stresses,such as soil salinity and drought,depend intricately on nitrogen metabolism.This review explores nitrogen’s regulatory role in plant responses to these challenges,unveiling a dynamic interplay between nitrogen availability and abiotic stress.In the context of soil salinity,a nuanced rela-tionship emerges,featuring both antagonistic and synergistic interactions between salinity and nitrogen levels.Salinity-induced chlorophyll depletion in plants can be alleviated by optimal nitrogen supplementation;however,excessive nitrogen can exacerbate salinity stress.We delve into the complexities of this interaction and its agri-cultural implications.Nitrogen,a vital element within essential plant structures like chloroplasts,elicits diverse responses based on its availability.This review comprehensively examines manifestations of nitrogen deficiency and toxicity across various crop types,including cereals,vegetables,legumes,and fruits.Furthermore,we explore the broader consequences of nitrogen products,such as N_(2)O,NO_(2),and ammonia,on human health.Understand-ing the intricate relationship between nitrogen and salinity,especially chloride accumulation in nitrate-fed plants and sodium buildup in ammonium-fed plants,is pivotal for optimizing crop nitrogen management.However,prudent nitrogen use is essential,as overapplication can exacerbate nitrogen-related issues.Nitrogen Use Effi-ciency(NUE)is of paramount importance in addressing salinity challenges and enhancing sustainable crop productivity.Achieving this goal requires advancements in crop varieties with efficient nitrogen utilization,pre-cise timing and placement of nitrogen fertilizer application,and thoughtful nitrogen source selection to mitigate losses,particularly urea-based fertilizer volatilization.This review article delves into the multifaceted world of plant nitrogen metabolism and its pivotal role in enabling plant resilience to nutritional stress and abiotic challenges.It offers insights into future directions for sustainable agriculture.

New Insights into the Nitrogen Form Effect on Photosynthesis and Photorespiration

Under high light conditions, ammonium nutrition has a negative effect on plant growth. This suggests that the adverse effects of ammonium nutrition on plant growth may be related to carbon gain, photosynthesis, and photorespiration. However, there is no consistent evidence of a specific mechanism that could explain the plant growth reduction under ammonium supply. It is generally accepted that during the light reaction, a surplus of nicotinamide adenine dinucleotide hydrogen phosphate （NADPH） is produced, which is not completely used during the assimilation of CO2, Nitrate reduc- tion in the leaf represents an additional sink for NADPH that is not available to ammonium-grown plants. Nitrate and ammonium nutrition may use different pathways for NADPH consumption, which leads to differences in photosynthesis and photorespiration. The morphological （i.e., cell size, mesophyll thickness, and chloroplast volume） and enzymic （i.e., ribulose-1,5-bisphosphate carboxylase/oxygenase （Rubisco）, phosphoenolpyruvate carboxylase （PEPCase）, and glutamine synthetase/glutamate synthetase （GS/GOGAT）） differences that develop when plants are treated with either nitrate or ammonium nitrogen forms are related to photosynthesis and photorespiration. The differences in photorespiration rate for plants treated with nitrate or ammonium are related to the conversion of citrate to 2-oxoglutarate （2-OG） and photorespiratory CO2 refixation.

Mechanisms of Enhanced Rice Growth and Nitrogen Uptake by Nitrate

Rice is being increasingly cultivated in intermittently irrigated regions and also in aerobic soil in which Nitrate （NO3^- ） plays important role in nutrition of plant. However, there is no information regarding the influence of nitrate on the overall growth and uptake of nitrogen （N） in rice plant. Solution culture experiments were carried out to study the effects of NO^3- on the plant growth, uptake of N, and uptake kinetics of NH4^＋ in four typical rice （Oryza sativa L.） cultivars （conventional indica, conventional japonica, hybrid indica, and hybrid japonica）, and on plasma membrane potential in roots of two conventional rice cultivars （indica and japonica） at the seedling stage. The results obtained indicated that a ratio of 50/50 NH4^＋-N/NO3^--N increased the average biomass of rice shoots and roots by 20% when compared with that of 100/0 NH4^＋-N/NO3^--N. In case of the 50/50 ratio, as compared with the 100/0 ratio, total N accumulated in shoots and roots of rice increased on an average by 42% and 57%, respectively. Conventional indica responds to NO3^- more than any other cultivars that were tested. The NO^3- supply increased the maximum uptake rate （Vmax） of NH4^＋ by rice but did not show any effect on the apparent Michaelis-Menten constant （Km） value, with the average value of Vmax for NH4^＋ among the four cultivars being increased by 31.5% in comparison with those in the absence of NO3^-. This suggested that NO3^- significantly increased the numbers of the ammonium transporters. However, the lack of effect on the Km value also suggested that the presence of NO3^- had no effect on the affinity of the transporters for NH4^＋. The plasma membrane potential in the roots of conventional indica and japonica were greatly increased by the addition of NO3^- , suggesting that NO3^- could improve the uptake of N by roots of the rice plant. In conclusion, the mechanisms by which NO3^- enhances the growth and N uptake of rice plant was found by the increased value of Vmax of NH4^＋ and increased plasma membrane potential. Thus promotion of nitrification in paddy soil is of great significance for improving the production of rice.

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.

Physiological Responses of Two Wheat Cultivars to Nitrogen Starvation

Plants need to be efficient in nutrient management, especially when they face the temporal nutrient defficiencies. Understanding how crops respond to nitrogen （N） starvation would help in the selection of crop cultivars more tolerant to N deficiency. In the present work, the physiological responses of two wheat cultivars, Yannong 19 （YN） and Qinmai 11 （QM）, to N starvation conditions were investigated. The two cultivars differed in biomass and N rearrangement between shoots and roots during N starvation. QM allocated more N to roots and exhibited higher root/shoot biomass ratio than YN. However, tissue measurement indicated that both cultivars had similar nitrate content in leaves and roots and similar remobilization rate in roots. Microelectrode measurement showed that vacuolar nitrate activity （concentration） in roots of QM was lower than that in roots of YN, especially in epidermal cells. Nitrate remobilization rates from root vacuoles of two cultivars were also identical. Moreover, vacuolar nitrate remobilization rate was proportional to vacuolar nitrate activity. During N starvation, nitrate reductase activity （NRA） was decreased but there were no significant differences between the two cultivars. Nitrate efflux from roots reduced after external N removal and QM seemed to have higher nitrate efflux rate.

Nitrogen Fertilization as Ammonium or Nitrate-N on <i>Hippeastrum hybridum</i>Bulb Growth

Hippeastrum (Hippeastrum hybridum), a native of Central and South America, is a bulbous ornamental flowering plant in the Amaryllidaceae family. However, the correct balance of NH4 to NO3-nitrogen in a fertilizer mix for Hippeastrum plants is largely unknown. Nitrogen was applied 2x weekly following irrigation at either 0.6 g (high), 0.3 g (medium) or 0.15 g (low) total N every four months. Nitrogen was supplied in different combinations of NO3 and/or NH4. Nitrate:NH4-N ratios were either 100% NO3:0% NH4 (100NO3), 70% NO3:30% NH4 (70NO3), 50% NO3:50% NH4 (50NO3) (second group only), 30%NO3:70%NH4 (30NO3), or 0% NO3/100% NH4 (100NH4). Growth in bulb diameter after one year of fertilizer treatments not only increased from 0.15 to 0.6 g N (low to high level), but also differed with the form of N supplied to the plant. The largest diameter bulbs were produced in the 70NO3 and 50NO3 high N treatments. Within any NO3/NH4-N ratio grouping, fertilization at the high N rate resulted in larger diameter bulbs. No significant differences existed between treatments in the number of bulbs produced. Bulb growth was greater with a portion of N supplied as NO3 than with NH4-N alone. These results indicate that application of N as a mixture of NH4 and NO3 at 0.6 g per 4 months produces the largest increase in bulb diameter.

Effects of Growing of Different Types of Crops on Constitution of Soil Available Nitrogen and Conversion and Utilization of Nitrogen Fertilizer

The soybean, cotton, maize and sorghum were planted in pot under low nitrogen, high nitrogen treatments, the soil available nitrogen constitution and con- version and utilization of nitrogen fertilizer were determined, so as to provide techni- cal guidance for reasonable use and improving use efficiency of nitrogen fertilizer for different types of crops. Compared with the control with nitrogen but unplanted crop, growing soybean, cotton, maize, sorghum significantly decreased the soil available N contents by 53. 48%, 51.54%, 33.10%, 55.03%,and influenced the constitution of soil available N. Thereinto, growing soybean, cotton, maize and sorghum significantly decreased soil inorganic N contents by 85.41%, 83.09%, 70.89% and 83.35%,but increased soil hydrolysable organic N contents by 1.41, 1.53, 2.11 and 1.28 times, respectively; growing soybean, cotton, maize and sorghum significantly decreased the rate of soil inorganic N to available N by 68.61%, 65.09%, 56.47% and 63.00%, but increased the rate of soil hydrolysable organic N to available N by 4.18, 4.21, 3.66 and 4.08 times, respectively. Compared with the control, growing soybean, cotton, maize and sorghum significantly increased the transform rate of ammonium nitrogen fertilizer by 93.66%, 38.19%, 32.58% and 38.31% respectively, and growing soybean treatment had the highest increasing range; the nitrification rates of ammo- nium nitrogen fertilizer of growing soybean, cotton, maize and sorghum treatments were negative values, and growing soybean treatment had the highest decreasing amplitude. The ammonium nitrogen fertilizer use efficiency of growing soybean, cot- ton, maize and sorghum treatments were 52.01%, 28.31%, 24.16% and 28.40% re- spectively and growing soybean treatment had the highest value. In conclusion, growing crops suppressed the soil nitrification and accelerated the development of soil hydrolysable organic nitrogen by the utilization of soil available nitrogen and the alteration of soil environment, and hence impacted the constitution of soil available nitrogen and the transform and use of ammonium nitrogen applied in soil. Legumi- nous crops had stronger ability of suppressing nitrification, making use of ammonium compared with non-Leguminous crops.

Effects of Nitrogen Application on Plant Growth and Soil Inorganic Nitrogen Content in Alpine Grasslands

In order to further determine the nitrogen demand of plants in alpine grassland ecosystem,different nitrogen levels( 0,1,2,4,8,16,24,32 g/m2)were designed through field control to study the responses of different plant functional groups( grass,sedge and weed) to different nitrogen application levels in the aboveground biomass and soil inorganic nitrogen( nitrate nitrogen and ammonium nitrogen).The results showed that with the increase of nitrogen application rate,the aboveground biomass of different functional groups increased linearly,and the soil inorganic nitrogen content increased with the increase of nitrogen application rate,among which treatments N16,N24 and N32 increased significantly in soil nitrate nitrogen content( P < 0.05).The results showed that the optimal nitrogen content in alpine grasslands was 8 g/m^2,which could not only promote plant growth,but also effectively control soil nitrate nitrogen content.

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.

Morphological and kinetic parameters of the absorption of nitrogen forms for selection of Eucalyptus clones

Eucalyptus clones are selected according to productivity,wood quality,rooting capacity,and resistance to drought,frost and diseases.However,kinetic and morphological parameters that determine the absorption efficiency of nutrients such as nitrate(NO_(3)^(-)) and ammonium(NH_(4)^(+))are often not considered in breeding programs.The objective of this study was to evaluate the morphological,physiological and kinetic parameters of nitrogen uptake by clones of Eucalyptus saligna(32,864) and Eucalyptus grandis(GPC23).Morphological parameters in shoot and root systems,biomass and N concentrations in different organs,photosynthetic pigment concentrations,parameters of chlorophyll a fluorescence and photosynthetic rates were evaluated.Kinetic parameters,maximum absorption velocity(V_(max)),Michaelis-Menten constant(K_(m)),minimum concentration(C_(min)) and influx(I) were calculated for NO_(3)^(-)and NH_(4)^(+) in the two clones.E.granais clone was more efficient in the uptake of NO_(3)^(-)and NH_(4)^(+),and showed lower K_(m) and C_(min)values,allowing for the absorption of nitrogen at low concentrations due to the high affinity of the absorption sites of clone roots to NO_(3)^(-)and NH_(4)^(+).Higher root lengths,area and volume helped the E.grandis clone in absorption efficiency and consequently,resulted in higher root and shoot biomass.The E.saligna clone had higher K_(m) and Cmin for NO_(3)^(-)and NH_(4)^(+),indicating adaptation to environments with higher N availability.The results of NO_(3)^(-)and NH_(4)^(+) kinetic parameters indicate that they can be used in Eucalyptus clone selection and breeding programs as they can predict the ability of clones to absorb NO_(3)^(-)and NH_(4)^(+) at different concentrations.

Effect of NH_4^+-N/NO_3^--N Ratios on Growth and Some Physiological Parameters of Chinese Cabbage Cultivars

The responses of three cultivars of Chinese cabbage (Brassica chmensis L.), one of the main vegetable crops in China, to different ratios of NH4+-N/NO3--N was investigated to find the optimal ratio of ammonium to nitrate for maximal growth and to explore ways of decreasing the nitrate content, increasing nitrogen use efficiency of Chinese cabbage, and determining distributions of nitrogen and carbon. Three cultivars of Chinese cabbage were hydroponically grown with three different NH4+-N/NO3--N ratios (0:10…

Pelagic Nitrogen Cycling in Jiaozhou Bay, a Model Study I: the Conceptual Model

A zero dimensional box model (PNCMjzb) with six state variables (ammonium, nitrate, dissolved organic nitrogen, phytoplankton, zooplankton and detritus) was developed to study nitrogen cycling in the Jiaozhou Bay pelagic ecosystem. The dominant processes within these compartments are considered with nitrogen as flow currency. Phytoplankton and zooplankton are treated as separate state variables, assuming that the species composition was dominated by two or three species the dynamic constants of which are similar and that they represent the entire plankton community. The microbial loop has not been integrated explicitly in the model. The turnover of bacteria is included implicitly in processes such as detritus decomposition, DON remineralization, pelagic nitrification and denitrification. The model is driven by two forcing variables, viz. water temperature and light intensity. Historical data from the1980s and 1990s were compiled and used for model calibration. In this paper (part I), the consideration of every main compartment in the model is interpreted in detail. And the applied equations and parameters are presented. The main results from the simulations together with discussion about phytoplankton dynamics and primary production in Jiaozhou Bay are presented in the next paper (part II).

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.

Nitrogen Leaching from Saybrook Soil Amended with Biosolid and Polyacrylamide

In this study, Nitrogen leaching following surface application of biosolid with and without polyacrylamide (PAM) coating was investigated using soil column experiments. Three treatments including bare soil (C), a commercially available biosolid (BS) and PAM coated biosolid (PAM + BS), were applied to manually packed (bulk density: 1.3 g·cm-3) growth chamber soil columns (GC columns: 5 cm diameter by 40 cm long) and greenhouse soil columns (GH columns: 15 cm diameter by 40 cm long). The application rates for BS and PAM + BS were 729 and 740 kg/ha, respectively. The GC columns were incubated for 60 days in a dark chamber at 25℃ and no crop was grown in the columns. The GH columns were incubated for 60 days in a greenhouse and Ryegrass (seed rate: 252 kg/ha) was grown in these columns under 16 h daylight and at about 25℃. The columns were irrigated weekly using 270 mL DI-water for GC columns and 850 mL for GH columns and leachate was analyzed for Ammonium (NH4-N), Nitrate (NO3-N) and total Nitrogen (TN). The GH column experiments were repeated with three times greater biosolid application rate (2187 kg/ha) while keeping the PAM and Ryegrass seed rate constant. The leachate volume and NH4-N, NO3-N and TN concentration/load were not significantly different among the treatments for the GH columns but were significantly different during the incubation period. The same was true for GC columns with the exception of NO3-N and TN concentration/load which, overall, were higher for the BS and PAM + BS treatments than for the C treatment. In the beginning of the incubation, the leachate from all treatments (GC and GH) contained the highest NH4-N concentrations (>USEPA target level: 0.1 mg/L) and decreased, in some cases rapidly, to near zero. The NO3-N concentrations were highest in the middle of the incubation and greater than the USEPA target level (10 mg/L). The NO3-N concentrations were lower for cropped GH columns compared to GC columns due to NO3-N uptake by plants. The three fold increase in biosolid application rate did not increase NH4-N concentrations in leachate but did increase NO3-N and TN concentrations/loads in leachate on average 2.5 to 2.7 times. The non-significant differences among treatment means for NH4-N, NO3-N and TN concentrations/loads for the GH columns suggest that land application of biosolid (with or without PAM) to cropped silt loam landscapes at the rates considered may be safe within the context of groundwater pollution.

Enzyme Activities and Microbial Communities in Subtropical Forest Soil Aggregates to Ammonium and Nitrate-Nitrogen Additions

A laboratory incubation experiment was established to examine the impacts of nitrate and ammonium nitrogen additions on soil microbial attributes of a subtropical Pinus elliottii forest ecosystem in southern China. Soils were subjected to three different treatments： the control with no nitrogen addition （CK）, the ammonium nitrogen addition （NH4^＋-N）, and the nitrate nitrogen addition （NO23^-N）. Samples from bulk and two different size fractions （macroaggregate （〉250 pm） and microaggregate （53-250 μm）） were analyzed for soil properties, enzyme activities and microbial communities on day 7 and 15 of the incubation. Our study demonstrated that NH4^＋-N had a 9rearer influence on soil microbial activities than NO3-N. NH4^＋-N additions resulted in significant increases in 13-1,4-glucosidase （βG） and β-1,4-N-acetyl glucosaminidase （NAG） enzyme activities in bulk, macroaggregate and microag- gregate soils after 7 and 15 days incubation. NO3^-N additions only significantly increased in βG and NAG enzyme activities in bulk, macroaggregate soils after 7 and 15 days incubation, but not in microaggregate. All NH4^＋-N and NO3-N additions resulted in significant increases in gram-positive bacterial PLFAs in microaggregates. Only a significant correlation between soil nutrient contents and enzyme activities in macroaggregates was founded, which suggests that the soil aggregation structure played an important role in the determining enzyme activities.

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.

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.