江苏沿海地区棉花氮肥最佳用量研究

为提高江苏沿海地区棉花施氮水平,在江苏省如东县进行了不同氮肥用量对棉花生长发育和产量、效益的影响试验。结果表明,在满足磷、钾、锌、硼等其他养分供应的条件下,以每667m2施纯氮22～25kg为宜。

Estimation of Biological Nitrogen Fixation Capacity by Sugarcane Using 15N

[ Objective] The study aimed to reveal the biological nitrogen fixation capacity by sugarcane from Brazil under the ecological conditions of Guangxi, and to provide reference for study on the biological nitrogen fixation capacity by sugarcane and related generalization and application. [ Method] The ^15N isotopic fertilizer was solely applied on plants of three sugarcane cultivars planted in greenhouse with no other fertilizer forms applied, meanwhile virus-free stem seedling was regarded as control, to measure their biological nitrogen fixation capacity using ^15N isotope. [ Result ] The nitrogen fixation rate of B8 from Brazil reached 26.91%, while Guitang 11 and RIC16 presented no or poor nitrogen fixation capacity. [ Conclusion] The sugarcane eultivar B8 from Brazil showed some nitrogen fixation capacity under the ecological conditions of Guangxi.

Effects of a New Long-term Controlled-release Fertilizer on Growth and Development and Yield of Summer Maize

[Objective] The aim was to select the optimal amount of controlled-release fertilizer and provide theoretical references for controlled-release fertilizers use in summer maize. [Method] Long-term controlled-release fertilizers were applied once at sowing summer maize to explore effects on maize growth, yield, economic profits and environment. [Result] Maize yield reduced a little in the treatment group with 60% CRF, and increased in varying degrees in the rest groups in the range of 1.1%-7.4%, and some showed significant differences. [Conclusion] Controlled-release fertilizers can be applied once at the amount of 80% common fertilizer＇s, with con- sideration of maize yield, nitrogen use rate and economic profits, which is beneficial for summer maize application and promotion in North China.

Effects of Controlled-Release Nitrogen on Yield and Nitrogen Use Efficiency of Summer Maize

The field experiments were conducted in Anhui during 2016 to investigate the effects of controlled-release nitrogen （CRN） rates and mixture of controlled-re- lease nitrogen and conventional nitrogen （CN） on the yield and nitrogen efficiency of summer maize. Six treatments included CK （with no application of N）, CNIO0% splits （CN）, CRFIO0% （CRN1）, CRN60%＋CN40% （CRN2）, CRN85% （CRN3） and CRN70% （CRN4）. The results showed proper CRN increased yields and output val- ue. Compared with CN, CRN2 significantly increased by 13.74%, CRN1 increased by 4.84%, and CRN3 was equal to CN. CRN increased yield by grain number per spike of yield components. CRN2 had the highest apparent nitrogen fertilizer recov- ery efficiency and CRN1 was the second, which were significantly higher than CN. Nitrogen agronomic efficiency of CRN2 was significantly higher than CN. Nitrogen physiological efficiency of CRN2 was higher than CN. The partial productivity of CRN1 was higher than that with CN. And the effect of nitrogen fertilizer of CRN2 was the highest, which was increased 758 yuan/hm2. Considering yield, nitrogen use efficiency and economic benefit, applying the mixture of CRN and CN was the most beneficial treatment. CRN1 was the second treatment, and CRN3 didn＇t reduce yield.

Effects of Nitrogen,Phosphorus and Potassium Application on Growth and Dry Matter Accumulation in Mulberry

In this paper, the effect of different fertilizer treatments on the main indexes of growth and development and dry matter accumulation of perennial mulberry, which is cut and pruned in summer, were studied with ‘3414’ field experiment design. The results showed that N, P, and K at proper amounts could promote mulberry growth and development, improve its dry matter content, increase its dry matter accumulation. The effects of N, P, K on leaf yield per plant were respectively expressed as follows： N2 N3 N1 N0 , P2 P1 P3 P0 , K2 K1 K3 K0 . It can be concluded that the recommended fertilizer amounts of dry matter accumulations in mulberry leaf were 694.36 kg/hm2 of N, 198.15 kg/hm2 of P, and 274.26 kg/hm2 of K and the dry matter achieved the maximum at 8 045.04 kg/hm2 . The recommended fertilizer amounts of accumulated dry matter in branch were 1 000.05 kg/hm2 of N, 242.04 kg/hm2 of P, and 218.01 kg/hm 2 of K, and the dry matter achieved the maximum at 5 969.05 kg/hm2 . The recommended fertilizer amount in young shoots were 883.76 kg/hm2 of N, 204.48 kg/hm2 of P and 426.59 kg/hm2 of K and dry matter achieved the maximum at 1 410.24 kg/hm2 . This paper could provide reference for the construction of highly-qualified mulberry field in Sichuan hilly area.

Effects of Green Manure Rotation on Rice Growth Dynamics and Nitrogen Uptake and Utilization

This study aimed to comprehensive evaluation of different winter green manure on characterization of nitrogen uptake and utilization, to provide the basis for N fertilizer reasonable operation and characteristics improvement of nitrogen nutrition in rice high-yield cultivation. This experiment was set to compare milk vetch, rapeseed,ryegrass and mixed of green manure on rice yield, rice growth dynamics and nitrogen uptake and utilization in rice. The results showed that among 4 different winter green manure, the treatment of MV-R-R（milk vetch-rice-rice） for the early rice yield was the most than others treatments. Compared with RG-R-R（ryegrass-rice-rice）, RPR-R（rapeseed-rice-rice）, MS-R-R（mixed green manure-rice-rice）, the treatment of MVR-R inceased by 6.61%, 3.29%, 0.78%, respectively. The treatment of MV-R-R in N content in plant of rice was maximized in the tillering, booting, heading and maturity periods, respectively higher than the average of other treatments 9.68%, 19.72%,6.23% and 8.66%. At tillering, booting, heading and maturity, the treatment of MV-R-R were the highest in N uptake, RP-R-R minimum. The N periodic accumulation for MV-R-R were higher than other treatments in the tillering to booting, booting to heading and heading to maturity periods. The rates respectively were 21.81%, 68.73% and286.5%. In addition, N periodic accumulation and its ratio to total in the heading to maturity was minimum, maximum before tillering under green manure rotation system.So the cropping system of milk vetch-rice-rice could increase nitrogen use efficiency and improve N cycling.

Comparions of Required Nitrogen Fertilizers by Hybrid Cultivar and Conventional Cultivar of Rapeseed(Brassica napus L.)

[Objective] The aim of this study was to understand the difference of N fertilizer requirement between hybrid rapeseed and conventional rapeseed. [Method] Two hybrid cultivars, ZY5628 and ZY7819, and the conventional cultivar ZS10, were compared through two field experiments. In Experiment 1, seed yield and optimum N application rate were assessed in the field with five N application treatments. In Expedment 2, N was applied uniformly at 180 kg/hm2, and plant biomass and N accumulation were measured at several developmental stages, while N use efficien- cy was calculated for rape at maturity. [Results] The experiment 1 results showed that seed yields of ZY5628 and ZY7819 were both significantly higher than that of ZS10, and compared to ZS10, optimum yield （plateau yield） was higher by 18.7% and 20.2%, while the recommended N application rate was lower by 9.5% and 9.6% for ZY5628 and ZY7819, respectively. The experiment 2 results showed that during vegetative development, all three cultivars exhibited similar accumulations of plant biomass and N, but through flowering and maturity ZY5628 and ZY7819 pro- duced more biomass, acquired more N, and utilized acquired N more efficiently to- wards seed production than ZS10. [Conclusion] With equivalent inputs, the hybrid rapeseed cultivars ZY5628 and ZY7819 tested herein yield more seed with higher N use efficiency than the conventional rapeseed ZS10. This information will be valu- able for growers seeking to improve efficiency while reducing costs of rape production in China.

Effects of Main Cultivation Factors on Rapeseed Oil Yield

[Objective] This study aimed to analyze the influence of six cultivation fac- tors： sowing date, plant density, nitrogen fertilizer amount, phosphate fertilizer amount, potash fertilizer amount and boron fertilizer amount on seed oil yield of Brassica napus. [Method] Statistical analysis was carried out based on the data from previous studies and our work. [Result] Oil yield shared a negative correlation with sowing date, a parabolic relationship with plant density mostly, parabolic rela- tionships with amount of applied nitrogen fertilizer and amount of applied boron fer- tilizer, straight-line relationships with amount of applied phosphate fertilizer and amount of applied potash fertilizer. The average amount of applied nitrogen fertilizer required to obtain the highest oil yield was 185.18 kg/hm2 for high-oil rape varieties （with oil content above 44.00%）, and under this condition, the average oil yield of low-oil rape varieties （with oil content below 42.00%） was 1 247.84 kg/hm2, while that of high-oil rape varieties was 1 442.60 kg/hm2, which was 15.61% more than the former. The average amount of applied nitrogen fertilizer required to obtain the highest oil yield for lower-oil rape varieties was 286.28 kg/hm2, and under this con- dition, the average oil yield of the low-oil rape varieties was 1 350.57 kg/hm2, while that of the high-oil varieties was 6.81% higher than it. There was a significant neg- ative correlation between rapeseed oil yield and the amount of applied nitrogen fer- tilizer to obtain the highest oil yield （0.980 0）. The optimum amount of applied ni- trogen, phosphate, potash and boron fertilizer were 187.5-195, 187.5-195, 105-120, 135-150 and 15-22.5 kg/hm2 for high-oil B. napus varieties. [Conclusion] This study determined the influence of sowing date, plant density and amount of applied nitro- gen fertilizer on oil yield of B. napus, and proposed an optimum cultivation pattern for high-oil varieties.

Effects of Continuous Nitrogen Application on Grain Yield and Nitrogen Uptake and Utilization in Winter Wheat-Summer Maize Rotation System

[Objective] This study aimed to achieve high yield and stable yield of win- ter wheat-summer maize rotation system and provide basis for rational application of nitrogen fertilizer. [Method] Effects of continuous nitrogen application on grain yield, economic profit, nitrogen uptake and utilization efficiency, and soil inorganic nitrogen accumulation in winter wheat-summer maize rotation system were investigated. [Re- sult] Nitrogen application could significantly increase the y（eld of the winter wheat- summer maize rotation system, which increased by 17.76%-30.32% and 22.24%- 46.63% in two rotation cycles, respectively. The yield of the winter wheat-summer maize rotation system was the maximum in two rotation cycles with nitrogen appli- cation amount of 660.0 kg/hm2, which reached respectively 23 391.19 and 23 444.35 kg/hm2, the yield and economic benefit were the highest, the nitrogen fertilizer use efficiency was 22.2% and 30.7%, the agronomic efficiency was 8.3 and 11.3 kg/kg. However, the nitrogen fertilizer use efficiency and agronomic efficiency between ni- trogen application amount of 540.0 and 660.0 kg/hm2 showed no significant differ- ence. After two rotation cycles, inorganic nitrogen accumulation in 0-40 cm soil with nitrogen application amount of 540.0 kg/hm2 was almost equal to that before experi- ment. [Conclusion] Under the experimental conditions, comprehensively considering the grain yield, economic profit, nitrogen fertilizer efficiency and soil inorganic nitro- gen balance, the optimal nitrogen application amount was 625.3-660.0 kg/hm2 in high-yield winter wheat-summer maize rotation system.

Release Characteristics of Release-controlled Nitrogen Fertilizer in Winter Wheat on Dry Land

[Objective] The aim was to study the release characteristics of different release-controlled fertilizers, as well as their effects on wheat growth and develop- ment under water stress. [method] With phosphorus-potassium fertilization and opti- mized fertilization （OPT） as the control, the release characteristics of 4 kinds of re- lease-controlled nitrogen fertilizers （A, B, C and D） coated with different materials were studied. [Result] Under the same phosphorus and potassium levels, the re- lease-controlled nitrogen fertilizers A and B significantly improved the yield of wheat. Spike number is the main reason leading to the difference in yield. The fertilizers A and B were released by 44.4% and 46.3% before winter, released by 72.1% and 69.8% at the jointing stage, and related by 88.0% and 91.5% in the harvest period, meeting the nitrogen requirement of dryland wheat across the growth period. Com- pared with OPT, the nitrogen accumulation amounts in treatments A and B were increased by 1.39 and 2.09 kg/667 m2, the nitrogen use efficiencies were increased by 8.66% and 13.04%, and the nitrogen partial factor productivities were increased by 9.00 and 7.22 kg/kg, respectively. [Conclusion] Among the 4 kinds of fertilizers, A and B were considered as the optimum release-controlled nitrogen fertilizers for winter wheat on dry land.

Effect of Continuous Application of Controlled Release Nitrogen Fertilizer in Various Types of Soil in Dong-Ting Lake Region under Double Rice Cropping System

[Objective] This study aimed to explore the effects of continuous application of controlled release nitrogen fertilizer under double rice cropping system. [Method] By modeling three types of paddy soils in Dong-Ting Lake area, four treatments as no fertilizer （CK）, urea, controlled release nitrogen fertilizer （CRNF） and 70% controlled release nitrogen fertilizer （70% CRNF） were designed in the micro-plot trials from 2005 to 2008. [Result] The rice yield in treatment CRNF at N 150 kg/hm2 was increased by 10.3%, 8.0% and 2.4% compared with treatment of urea, in alluvial sandy loamy paddy soil （ALS）, purple calcareous clayey paddy soil （PCS）, and reddish yellow loamy paddy soil （RYS）, respectively; and the yield in treatment of 70% CRNF was increased by 6.1%, 2.6% and -0.8%, respectively. The ranking order of nitrogen uptake amount by plant in early rice and late rice was CRNF 70% CRNF urea CK in all three types of soil. Nitrogen utilization efficiency of CRNF in above three types of soil was 60.7%, 59.6% and 56.3%, increased by 23.8%, 19.4% and 16.3% compared with that in treatment of urea, respectively. Nitrogen utilization efficiency of CRNF in early rice was increased year by year, and was higher than that of 70% CRNF during the whole experiment stage, while that in late rice was increased first and then decreased from the 3rd year. [Conclusion] Continuous application CRNF could alleviate the decreasing of soil nitrogen fertility and organic carbon especially in ALS, increase rice yield and nitrogen utilization efficiency in double-rice cropping system.

Effect of Different Fertilization Methods on Grain Yield and Nitrogen Agronomy Efficiency of TwoLine Super Hybrid Rice

ln order to explore the effect of broadcast application of urea （BR-U） and surface concentrated-fertilization on grain yield and nitrogen agronomy efficiency of two-line super hybrid rice, this experiment was conducted with super hybrid rice Y-Liangyou 1 and Liangyou 0293 to determine til ering dynamics, SPAD, LAl and dry matter accumulation. lts total N application was 180 kg/hm2 and different application rate and topdressing methods were set respectively. The results showed that grain yield and nitrogen agronomy efficiency were significantly improved with the T3 and T4 nitrogenous fertilizer application model. The improving of grain yield and nitrogen agronomy efficiency was benefited from rational postponing N application. However, neither single application of base fertilizer （T2） nor single application of topdressing fertilizer （T5 and T6） can coordinate the relationship between source and sink. Both grain yield and nitrogen agronomy efficiency were insignificantly under the broadcast application of urea and surface concentrated fertilization.

Genotypic Differences in Grain Yield and Physiological Nitrogen Use Efficiency Among Rice Cultivars

Efficient use of N in agricultural practice can increase yield, decrease production costs and reduce the risk of environmental pollution. Effects of N fertilizer application rates on grain yield and physiological N use efficiency (PE) in relation to the accumulation and redistribution of biomass and N in rice (Oryza sativa L.) cultivars were studied at two experimental farms of Nanjing Agricultural University, Nanjing, China in 2004. Three high N use efficiency (NUE) rice cultivars (Wuyunjing 7, Nanguang and 4007) and one low NUE rice cultivar (Elio) with similar growth patterns were studied under seven N rates (0, 60, 120, 180, 240, 300 and 360 kg ha -1 ). Grain yield increased with the N application rate and attained plateau at 180 kg N ha -1 for rice cultivars at each site. Increasing N rate decreased PE for biomass and grain yield. Grain yield and PE of Elio were about 20% and 18% lower than those of high NUE cultivars. Differences in biomass, N accumulation and N redistribution were observed at the post-heading stage among rice cultivars with differing NUEs. The less reproductive tillers of Elio resulted in less demand for C and N during grain filling, thus leading to lower PE of Elio compared with the high NUE rice cultivars.

Feasibility of Field Evaluation of Rice Nitrogen Status From Reflectance Spectra of Canopy *1

Techniques for measurement of the N status of rice can be an aid to making management decisions with economic and environmental implications. A field experiment was conducted to identify spectral variables most sensitive to N deficiency detection in rice canopy with the possibility for their use as a management tool. Spectral and agronomic measurements were collected in the evaluation experiment of N status from rice canopy under five N treatments in a silt loam soil. Nitrogen fertilization effects were seen across the entire wavelength measured. Red reflectance decreased and near infrared reflectance increased with increasing N fertilizer application. Spectral differences between treatments were seen throughout the test period. The near infrared reflectance/red reflectance ratio (RVI) differed more between treatments than between single bands. Variations in canopy reflectances due to other environmental factors were reduced by the use of RVI. In the spectral variables examined, the RVI separated the treatments most effectively, and three or four treatments can be separated. Differences in spectral responses between the treatments were attributable to leaf area index, leaf chlorophyll concentration and phytomass, which all changed with N fertilization.

Effects of Nitrogen Fertilizer on Yield, Nitrogen Absorption and Utilization on Four Summer Maize Species

[Objective] The aim was to explore scientific application of N fertilizer for summer maize species.[Method] A test was designed to research effects of N quantities on Zhengdan No.958,Xundan No.20,Nonghua No.101 and Xianyu No.335 in terms of yield,economic benefits,accumulated nitrogen and use efficiency of N fertilizer.[Result] The increase of N fertilizer improved yields of summer maize dramatically.Specifically,with low N quantity,yield and net revenue of Zhengdan No.958 reached 18.19% and 3 158 yuan/hm^2,respectively,and yields and net revenues of Jundan No.20,Nonghua No.101 and Xianyu No.335 were 17.31% and 2 642 yuan/hm^2,25.03% and 3 726 yuan/hm^2,17.41% and 3 182 yuan/hm^2,accordingly.With N quantity increased,agricultural efficiency of Zhengdan No.958 reduced significantly and the agricultural efficiencies showed little differences among Xundan No.20,Nonghua No.101 and Xianyu No.335.[Conclusion] In practice,Zhengdan No.958 is suitable to be applied with N at low quantity,and Xundan No.20,Nonghua No.101 and Xianyu No.335 are suitable to be applied with N at high quantity.

Effects of urea-N fertilizer dosage supplemented with Ipil-Ipil tree litter on yield of rice and insect prevalence

The present study was undertaken to determine the effects of different levels of urea-N fertilizer in addition to ipil-ipil tree litter on yield of rice and insect prevalence. The field study was conducted at the Agroforestry Field Laboratory, Bangladesh Agricultural University, Mymensingh during July-December 2004. The treatments included 0, 90, 180, and 270 kg urea per hectare. All four treatments received five tons ipil-ipil tree litter per hectare. The experiment was laid out in a randomized complete block design （RCBD） with four replications. The results showed that the different treatments significantly influenced the yield and yield component viz. total tillers/hill, effective tillers/hill, filled grains and unfilled grains/panicle. The highest yield of 4.62 t·h^m-2 with an increase of 21.57% over the control was recorded in treatment 180 kg urea·h^m-2, which was statistically similar to treatment 90 kg urea·h^m-2. The prevalence of insects viz. green leafhopper, brown plant hopper, rice bugs, leaf folder and stem borers were mostly correlated with N-levels. The prevalence of insects in general gradu- ally increased with the increase of N. Therefore, this study suggests that the combined application of organic materials （tree litter of ipil-ipil） and N-fertilizer of 90 kg·h^m-2 may oroduce good yield while minimizine insect arevalence in the rice field.

Direct Estimation of Nitrogen Gases Emitted from Flooded Soils During Denitrification of Applied Nitrogen

Denitrification losses measured by direct method (measuring the evolution of (N2+N2O)-15N) were compared with the apparent denitrification losses (calculated from the difference between the total N loss and ammonia loss), for fertilizers applied to flooded soils. The direct measured denitrification losses from potassium nitrate were 23.0%, 40.0%, and 63.1-79.7% of applied N in rice field, and in incubations of 7 cm deep layer of soil and 2 cm deep layer of soil, respectively; while the corresponding apparent denitrification losses were 96.0%, 98.4%, and 97.7-97.9%, respectively. In field experiments with urea, the direct measured denitrification losses ranged from 0.1-1.8%, which were much less than the apparent denitrification losses (41.3-45.7%). Such discrepancies were primarily due to the entrapment of the gaseous products of denitrification in the soil as revealed by the facts: (1) stirring the floodwater and the surface soil markedly increased the fluxes of (N2+N2O)-15N from urea or potassium nitrate applied to the flooded rice field, and (2) reducing the pressure in the headspace of the incubation bottle with the 7 cm soil layer during gas sampling decreased the discrepancy between the direct measured and apparent denitrifecation losses from 58.4% to 21.2%. The advantage of reducing the pressure in the headspace is that there is minimal disturbance of the soil. Further testing of this technique in rice field is needed to determine its effectiveness in releasing the entrapped gaseous products of denitrification so that denitrification losses can be quantified directly.

^(15)N Isotope Techniques for Estimating Effects of Urea-N Fertilizer Application Rate on Yields and Nutrient Contents of Pakchoi Cabbage and Asparagus Lettuce and Nitrogen Utilization Efficiency

A pot experiment combined with15N isotope techniques was conducted to evaluate effects of the varying rates of urea-N fertilizer application on yields,quality,and nitrogen use efficiency (NUE) of pakchoi cabbage (Brassica chinensis L.) and asparagus lettuce (Lactuca saiva L.).15N-labbled urea (5.3515N atom %) was added to pots with 6.5 kg soil of 0.14,0.18,0.21,0.25,and 0.29 g N/kg soil,and applied in two splits:60 percent as basal dressing in the mixture and 40 percent as topdressing.The fresh yields of two vegetable species increased with the increasing input of urea-N,but there was a significant quadratic relationship between the dose of urea-N fertilizer application and the fresh yields.When the dosage of urea-N fertilizer reached a certain value,nitrate readily accumulated in the two kinds of plants due to the decrease in NR activity; furthermore,there was a linear negative correlation between nitrate content and NR activity.With the increasing input of urea-N,ascorbic acid and soluble sugar initially increased,declined after a while,and crude fiber rapidly decreased too.Total absorbed N (TAN),N derived from fertilizer (Ndff),and N derived from soil (Ndfs) increased,and the ratio of Ndff and TAN also increased,but the ratio of Ndfs and TAN as well as NUE of urea-N fertilizer decreased with the increasing input of urea-N.These results suggested that the increasing application of labeled N fertilizer led to the increase in unlabeled N (namely,Ndfs) presumably due to "added nitrogen interaction" (ANI),the decease in NUE of urea-N fertilizer may be due to excess fertilization beyond the levels of plant requirements and the ANI,and the decrease in the two vegetable yields with the increasing addition of urea-N possibly because the excess accumulation of nitrate reached a toxic level.

Effects of Increased Planting Density with ReducedNitrogen Application on Yield Formation and NitrogenUtilization of Autumn Maize

With the change of cropping system in the middle reaches of the Yangtze River,the planting area of autumn maize is gradually increasing.However,the cultivation techniques are still under improvement for higher yield and nitrogen efficiency of autumn maize.Increase in planting density with reduced nitrogen fertilizer application is one of the important paths to achieve high yield and high nitrogen utilization efficiency.Meanwhile,the effect needs to be verified for autumn maize.The semi-compact autumn maize variety Qinyu 58 was planted under different planting densities and nitrogen fertilizer amounts with the split plot design.Different nitrogen application rates were arranged in the main plots,including the conventional nitrogen application(N300,300 kg/hm^2),30%reduction from the conventional treatment(N210,210 kg/hm^2)and no nitrogen application(N0).Different planting densities were arranged in the sub-split plots,including the conventional planting density(D60,60000 plants/hm2),medium density(D78,78000 plants/hm^2)and high density(D93,93000 plants/hm2).The effects of nitrogen fertilizer,planting density and their interaction effects on canopy structure,dry matter accumulation,yield and nitrogen use efficiency of autumn maize were studied.The nitrogen application rate and planting density had obvious interaction effects on the yield formation of autumn maize.Compared with the conventional cultivation(N300D60),increasing the planting density with 30%reduction in nitrogen application(N210)can obviously increase the canopy light interception rate,LAI,dry matter accumulation and yield.However,there was no significant change in canopy light interception rate,LAI,dry matter accumulation,grain weight and yield between D93 and D78.Compared with N300D60,nitrogen translocation efficiency and nitrogen contribution proportion to grain nitrogen did not change significantly in autumn maize grown under N210 and D78 treatments,whereas nitrogen partial productivity,nitrogen agronomic efficiency and recovery and utilization efficiency of nitrogen fertilizer increased significantly.Moreover,high density(D93)planting at N210 plots significantly improved nitrogen transport efficiency and utilization efficiency in autumn maize.Therefore,the suitable planting density of the autumn maize variety Qinyu 58 in Hubei Province is recommended a value of 78000 plants/hm^2,with the nitrogen application rate of 210 kg/hm2,which can achieve the target of higher yield by increasing density and reducing nitrogen.

Effect of Nitrogen Fertilization on Growth and Photosynthetic Nitrogen use Efficiency in Tobacco （Nicotiana tabacum L.）

Soil pot experiments were conducted in a greenhouse to examine the effects of different nitrogen （N） supply （low, 0.15 g N/kg; middle, 0.3 g N/kg; and high, 0.6 g N/kg dry soil） on the growth, photosynthetic characteristics and photosynthetic nitrogen use efficiency （PNUE） of tobacco seedlings （Nicotiana tabacum L. Yunyan 87）. The results showed middle and high N significantly enhanced seedling growth including plant stem and leaf dry weight comparing with low N. High N supply could lead to a dramatic increase in the photosynthetic capacity of tobacco seedlings under low N conditions. There were significant differences in leaf N content between nitrogen treatments. About a 76% increase in leafN content in plants fed by high N resulted in about 43% increase in Rubisco content and 27% in net photosynthetic rate. The non-corresponding increases in photosynthetic rate in tobacco seedlings fed by high N relative to low N resulted from Rubisco activity and/or carboxylation efficiency （CE）. These results indicated that tobacco seedlings under high N application can maintain high net photosynthetic rate （Pn） but lower PNUE, will finally result in a decline in N use efficiency.