Nitrogen nutrition diagnosis for cotton under mulched drip irrigation using unmanned aerial vehicle multispectral images

Remote sensing has been increasingly used for precision nitrogen management to assess the plant nitrogen status in a spatial and real-time manner.The nitrogen nutrition index(NNI)can quantitatively describe the nitrogen status of crops.Nevertheless,the NNI diagnosis for cotton with unmanned aerial vehicle(UAV)multispectral images has not been evaluated yet.This study aimed to evaluate the performance of three machine learning models,i.e.,support vector machine(SVM),back propagation neural network(BPNN),and extreme gradient boosting(XGB)for predicting canopy nitrogen weight and NNI of cotton over the whole growing season from UAV images.The results indicated that the models performed better when the top 15 vegetation indices were used as input variables based on their correlation ranking with nitrogen weight and NNI.The XGB model performed the best among the three models in predicting nitrogen weight.The prediction accuracy of nitrogen weight at the upper half-leaf level(R^(2)=0.89,RMSE=0.68 g m^(-2),RE=14.62%for calibration and R^(2)=0.83,RMSE=1.08 g m^(-2),RE=19.71%for validation)was much better than that at the all-leaf level(R^(2)=0.73,RMSE=2.20 g m^(-2),RE=26.70%for calibration and R^(2)=0.70,RMSE=2.48 g m^(-2),RE=31.49%for validation)and at the plant level(R^(2)=0.66,RMSE=4.46 g m^(-2),RE=30.96%for calibration and R^(2)=0.63,RMSE=3.69 g m^(-2),RE=24.81%for validation).Similarly,the XGB model(R^(2)=0.65,RMSE=0.09,RE=8.59%for calibration and R^(2)=0.63,RMSE=0.09,RE=8.87%for validation)also outperformed the SVM model(R^(2)=0.62,RMSE=0.10,RE=7.92%for calibration and R^(2)=0.60,RMSE=0.09,RE=8.03%for validation)and BPNN model(R^(2)=0.64,RMSE=0.09,RE=9.24%for calibration and R^(2)=0.62,RMSE=0.09,RE=8.38%for validation)in predicting NNI.The NNI predictive map generated from the optimal XGB model can intuitively diagnose the spatial distribution and dynamics of nitrogen nutrition in cotton fields,which can help farmers implement precise cotton nitrogen management in a timely and accurate manner.

Variation Dynamics of Total Nitrogen and Nicotine of Burley Tobacco at Various Growing Stages under Different Nitrogen Nutrition Levels

[Objective] This study aimed to investigate the variation dynamics of total nitrogen and nicotine of burtey tobacco at various growing stages under different ni- trogen nutrition levels to provide reference for optimizing fertilization technologies for burley tobacco. [Method] Fresh burley tobacco leaves were collected at various growing stages and dried to measure the content of total nitrogen, protein and nico- tine by using INTEGRAL automated chemical analyzer and analyze the correlation with nitrogen application level. [Result] Regardless of the nitrogen application level, the content of total nitrogen and protein showed a downward trend since root ex- tending stage and reached the minimum at mature stage; the content of nicotine showed an upward trend since early vigorous growing stage and increased to the maximum at mature stage; the content of total nitrogen, protein and nicotine all in- creased after air curing; the content of total nitrogen, protein and nicotine showed positive correlation with nitrogen application level, while total nitrogen/nicotine was negatively correlated. The results indicate that nitrogen level is closely related to the total nitrogen and nicotine of burley tobacco at growing period and post-air curing, rational application of nitrogen is an important measure to regulate the content of total nitrogen and nicotine of tobacco. [Conclusion] This study provides scientific ba- sis for rational fertilization of burley tobacco.

An optimized strategy of nitrogen-split application based on the leaf positional differences in chlorophyll meter readings

Modern rice production faces the dual challenges of increasing grain yields while reducing inputs of chemical fertilizer.However,the disequilibrium between the nitrogen(N)supplement from the soil and the demand for N of plants is a serious obstacle to achieving these goals.Plant-based diagnosis can help farmers make better choices regarding the timing and amount of topdressing N fertilizer.Our objective was to evaluate a non-destructive assessment of rice N demands based on the relative SPAD value(RSPAD)due to leaf positional differences.In this study,two field experiments were conducted,including a field experiment of different N rates(Exp.I)and an experiment to evaluate the new strategy of nitrogen-split application based on RSPAD(Exp.II).The results showed that higher N inputs significantly increased grain yield in modern high yielding super rice,but at the expense of lower nitrogen use efficiency(NUE).The N nutrition index(NNI)can adequately differentiate situations of excessive,optimal,and insufficient N nutrition in rice,and the optimal N rate for modern high yielding rice is higher than conventional cultivars.The RSPAD is calculated as the SPAD value of the top fully expanded leaf vs.the value of the third leaf,which takes into account the non-uniform N distribution within a canopy.The RSPAD can be used as an indicator for higher yield and NUE,and guide better management of N fertilizer application.Furthermore,we developed a new strategy of nitrogen-split application based on RSPAD,in which the N rate was reduced by 18.7%,yield was increased by 1.7%,and the agronomic N use efficiency was increased by 27.8%,when compared with standard farmers'practices.This strategy of N fertilization shows great potential for ensuring high yielding and improving NUE at lower N inputs.

Development of a novel critical nitrogen concentration-cumulative transpiration curve for optimizing nitrogen management under varying irrigation conditions in winter wheat

Accurate nitrogen(N)nutrition diagnosis is essential for improving N use efficiency in crop production.The widely used critical N(Nc)dilution curve traditionally depends solely on agronomic variables,neglecting crop water status.With three-year field experiments with winter wheat,encompassing two irrigation levels(rainfed and irrigation at jointing and anthesis)and three N levels(0,180,and 270 kg ha1),this study aims to establish a novel approach for determining the Nc dilution curve based on crop cumulative transpiration(T),providing a comprehensive analysis of the interaction between N and water availability.The Nc curves derived from both crop dry matter(DM)and T demonstrated N concentration dilution under different conditions with different parameters.The equation Nc=6.43T0.24 established a consistent relationship across varying irrigation regimes.Independent test results indicated that the nitrogen nutrition index(NNI),calculated from this curve,effectively identifies and quantifies the two sources of N deficiency:insufficient N supply in the soil and insufficient soil water concentration leading to decreased N availability for root absorption.Additionally,the NNI calculated from the Nc-DM and Nc-T curves exhibited a strong negative correlation with accumulated N deficit(Nand)and a positive correlation with relative grain yield(RGY).The NNI derived from the Nc-T curve outperformed the NNI derived from the Nc-DM curve concerning its relationship with Nand and RGY,as indicated by larger R2 values and smaller AIC.The novel Nc curve based on T serves as an effective diagnostic tool for assessing winter wheat N status,predicting grain yield,and optimizing N fertilizer management across varying irrigation conditions.These findings would provide new insights and methods to improve the simulations of water-N interaction relationship in crop growth models.

Nitrogen Nutrition Index and Its Relationship with N Use Efficiency, Tuber Yield, Radiation Use Effi ciency, and Leaf Parameters in Potatoes

Knowledge about crop growth processes in relation to N limitation is necessary to optimize N management in farming system. Plant-based diagnostic method, for instance nitrogen nutrition index （NNI） were used to determine the crop nitrogen status. This study determines the relationship of NNI with agronomic nitrogen use efficiency （AEN）, tuber yield, radiation use efficiency （RUE） and leaf parameters including leaf area index （LAI）, areal leaf N content （NJ and leaf N concentration （N0. Potatoes were grown in field at three N levels： no N （N 1）, 150 kg N ha^-1 （N2）, 300 kg N ha^-1 （N3）. N deficiency was quantified by NNI and RUE was generally calculated by estimating of the light absorbance on leaf area. NNI was used to evaluate the N effect on tuber yield, RUE, LAI, NAL, and NL. The results showed that NNI was negatively correlated with AEN, N deficiencies （NNI〈 1） which occurred for N 1 and N2 significantly reduced LAI, NL and tuber yield; whereas the N deficiencies had a relative small effect on NAL and RUE. To remove any effect other than N on these parameters, the actual ratio to maximum values were calculated for each developmental linear relationships were obtained between NNI and tuber RUE to NNI. stage of potatoes. When the NNI ranged from 0.4 to 1, positive yield, LAI, NL, while a nonlinear regression fitted the response of

An entirely new approach based on remote sensing data to calculate the nitrogen nutrition index of winter wheat

The nitrogen nutrition index(NNI)is a reliable indicator for diagnosing crop nitrogen(N)status.However,there is currently no specific vegetation index for the NNI inversion across multiple growth periods.To overcome the limitations of the traditional direct NNI inversion method(NNI_(T1))of the vegetation index and traditional indirect NNI inversion method(NNI_(T2))by inverting intermediate variables including the aboveground dry biomass(AGB)and plant N concentration(PNC),this study proposed a new NNI remote sensing index(NNI_(RS)).A remote-sensing-based critical N dilution curve(Nc_(_RS))was set up directly from two vegetation indices and then used to calculate NNI_(RS).Field data including AGB,PNC,and canopy hyperspectral data were collected over four growing seasons(2012–2013(Exp.1),2013–2014(Exp.2),2014–2015(Exp.3),2015–2016(Exp.4))in Beijing,China.All experimental datasets were cross-validated to each of the NNI models(NNI_(T1),NNI_(T2)and NNI_(RS)).The results showed that:(1)the NNI_(RS)models were represented by the standardized leaf area index determining index(sLAIDI)and the red-edge chlorophyll index(CI_(red edge))in the form of NNI_(RS)=CI_(red edge)/(a×sLAIDI~b),where"a"equals 2.06,2.10,2.08 and 2.02 and"b"equals 0.66,0.73,0.67 and 0.62 when the modeling set data came from Exp.1/2/4,Exp.1/2/3,Exp.1/3/4,and Exp.2/3/4,respectively;(2)the NNI_(RS)models achieved better performance than the other two NNI revised methods,and the ranges of R2 and RMSE were 0.50–0.82 and 0.12–0.14,respectively;(3)when the remaining data were used for verification,the NNI_(RS)models also showed good stability,with RMSE values of 0.09,0.18,0.13 and 0.10,respectively.Therefore,it is concluded that the NNI_(RS)method is promising for the remote assessment of crop N status.

Distribution of Leaf Color and Nitrogen Nutrition Diagnosis in Rice Plant

Greenness and nitrogen content of each leaf on main stem of different japonica and indica rice varieties under different nitrogen levels were investigated. Results showed that the fourth leaf from the top exhibited active changes with the change of plant nitrogen status. When the plant nitrogen content was low, its color and nitrogen content were obviously lower than those of the three top leaves. With the increase of plant nitrogen content, the color and nitrogen content of the fourth leaf increased quickly, and the differences of color and nitrogen content between the fourth leaf and the three top leaves decreased. So, the fourth leaf was an ideal indication of plant nutrition status. In addition, color difference between the fourth and the third leaf from the top was highly related to the plant nitrogen content regardless of the variety and development stage. Therefore, color difference between the fourth and the third leaf could be widely used for diagnosis of plant nutrition. Results also indicated that the minimized color difference between the fourth and the third leaf at the critical effective tillering, the emergence of the second leaf from the top, and the heading was the symbol of high yield. Plant nitrogen content of 27 g kg-1 DW for japonica rice and 25 g kg-1 DW for indica were the critical nitrogen concentrations.

Dynamics of nitrogen nutrition of coexisting dominant trees in mixed broad-leaved/Korean pine forest

Chemical analysis of ammonium, nitrate and total nitrogen in tree leaves and roots and anin-vivo bioassay for nitrate reductase activity (NRA) were used to monitor the seasonal variations in nitrogen assimilation among four coexisting dominant tree species, includingPinus koraiensis, Tilia amurensis, Fraxinus mandshurica andAcer mono, in a virgin mixed broad-leaved/Korean pine (Pinus koraiensis) forest. The soil study included individual horizons of L+F (0–5 cm), Ah (5–11 cm) and Aw (11–25 cm). All four species had nitrate and ammonium in their roots and leaves, and also NRA in leaves. This indicated that these coexisting species were adapted to ammonium + nitrate nutrition. A negative correlation existed between nitrate use and ammonium use. Ammonium concentration was higher than that of nitrate in tree leaves and roots, and also in soils, which indicated climax woody species had a relative preference for ammonium nutrition. There was a positive relationship between tree nitrogen nutrition use and soil nitrogen nutrient supply. Utilization of ammonium and nitrate as well as the seasonal patterns differed significantly between the species. Peaks of ammonium, nitrate, NRA and total nitrogen in one species were therefore not necessarily synchronous with peaks in other species, and which indicated a species-specific seasonal use of nitrogen. The species-specific temporal differentiation in nitrogen use might reduce the competition between co-existing species and may be an important mechanism promoting stability of virgin mixed broad-leaved//Korean pine forest.

Identification and evaluation of high nitrogen nutrition efficiency in rapeseed(Brassica napus L.)germplasm

To establish identification and evaluation methods of N(nitrogen)absorption and utilization of rapeseed(Brassica napus L.),difference of N nutrition efficiency(NNE)among rapeseed germplasms and relationship between NNE and plant traits under various N application rates were analyzed in this research.Pot cultivating experiments were conducted to investigate NNE with 3 N application rates in soil(0.05,0.2 and 0.3 g/kg).A total of 12 rapeseed germplasms were planted,nitrogen absorption efficiency(NAE)and nitrogen utilization efficiency(NUE)in seedling stage,bolting stage,initial flowering stage,final flowering stage,and maturity stage were obtained.Results showed that bolting stage was the best period for NAE identification and evaluation.Low N application rate in soil(0.05 g/kg)was the best for NAE,and the indirect indexes were basal stem diameter,plant root dry weight and above ground plant dry weight.Maturity stage was the best period for NUE identification and evaluation.High N application rate in soil(0.3 g/kg)was the best for NUE,and indirect indexes were above ground plant dry weight and basal stem diameter.N application rates of 0.05 g/kg in soil was the best for nitrogen harvest index at maturity stage,and indirect indexes was number of pods per plant.Plant traits of rapeseed germplasms affected NNE.Higher basal stem diameter,plant root dry weight and above ground plant dry weight at bolting stage under low N application rate were important characteristics of N absorption in rapeseed.Higher above ground plant dry weight and basal stem diameter at maturity stage under high N application rate were important characteristics of N utilization.Higher number of pods per plant at maturity stage under lowe N application rate was an important characteristic of N harvest index.These results provided a reliable index for N management and provided theoretical basis for guiding rapeseed breeding.

Effect of Intravital Staining on Leaf Surface Coloring and Plant Carbon and Nitrogen Nutrition in Chlorophytum comosum var. variegatum

Using potted seedlings of Chlorophytum comosum var. variegatum as the experimental materials, the effect of 2.0 mmol/L methyl orange （ Treatment T1 ）, 1.0 mmol/L methyl violet （ Treatment T2 ） and 1.0 mmol/L neutral red （ Treatment T3 ） on the biomass, root-shoot ratio, leaf color indices, plant carbon and nitrogen nutrition were studied. The results showed that the biomass of Treatment T3 was significantly greater than that of treatments T1 and CK. The root-shoot ratio decreased significantly in treatments T1, T2 and T3 , and the decrease in T3 was most obvious. In all the three treatments with coloring agent, a ^＊ , b ^＊ and L ^＊ values were increased gradually, C value were decreased, H0 and CIRG were increased, and the leaves were pink. In addition, the contents of chlorophyll a, chlorophyll b, chlorophyll a ＋ b and carotenoid were significantly decreased. The contents of soluble sugar and starch were also decreased, and the decrease in Treatment T2 was most significant. The contents of soluble protein and total nitrogen were increased, and the increase was most dramatic in Treatment T3. The carbon to nitrogen ratio was decreased. The results proved that staining can improve the ornamental value of indoor plants, despite its effects on plant carbon and nitrogen nutrition of C. comosum vat. variegatum, dyeing.

Remote Sensing Inversion of Nitrogen Nutrition Status of Apple Tree Leaves during Stopping Period of Spring Shoots

The nutrient inversion model of apple leaves was established by spectral analysis technology to provide technical support for the fine management of apple trees.In Shuangquan Town,Changqing District,Jinan City,Shandong Province,the Fuji apple trees with stopping period of spring shoots were taken as research objects.The spectral reflectance and nitrogen content of apple leaves were measured by ASD Field Spec 4 portable ground object spectrometer.Analyzed the correlation between leaf nitrogen content and spectral reflectance.The sensitive wavelengths with high correlation coefficient were select by fractional differential algorithm,and the optimal vegetation index was constructed and screened out.Partial Least Square Regression(PLSR),Support Vector Machine(SVM)and Random Forests(RF)method were used to construct an inversion model of leaf nitrogen content.The results show that the RF model based on fractional differential second-order treatment is the best inversion model for the nitrogen content of leaves during stopping period of spring shoots.The modeling accuracy determination coefficient R2 reached 0.891,RMSE was 0.0841,and RPD was 2.1396.The determination coefficient R2 of the fitting results of the verification set was 0.617,RMSE was 0.1251,and RPD was 1.7105.The inversion model established by RF method is effective in monitoring the nitrogen content in apple leaves,which provides a theoretical basis for monitoring the growth of apple by hyperspectral technology.

Influences of Nitrogen Level on Carbon Metabolism of Spring Maize

[Objective]To study the effect of supplies of nitrogen level on spring maize leaf blade carbon metabolism.[Method]In this experiment,field trail and biochemistry analysis were used to study the effect of the diference-nitrogen level on the content of chlorophyl and carboxylase activity of RuBP and PEP in the leaf of spring maize during main growing period.[Result]Applying proper amount of N could keep relative higher content of chlorophyl and higher activity of carboxylase of RuBP and PEP in the leaf of spring maize,insufficient or excessive（N 400 kg/hm^2） of nitrogenous fertilizer has the adverse effect.[Conclusion]In this experiment,applying 300 kg/hm^2 amount of N could keep relative higher content of chlorophyl and higher activity of carboxylase of RuBP and PEP in the leaf of spring maize during main growing period.It was important to strengthens the leaf blade photosynthesis ability,promote the yield formation and postpone the decline of leaf blade.

Responses of Halophyte Salicornia bigelovii to Different Forms of Nitrogen Source

Salt-affected soils are agricultural and environmental problems on a global scale. Plants suffer from saline stresses in these soils and show nitrogen （N） deficiency symptoms. However, halophytes grow soundly under saline conditions. In order to clarify the N nutrition of the halophyte Salicornia bigelovii, it was grown at several N levels （1, 2, 3, and 4 mmol L-1）, supplied in the form of NO3 or ammonium （NH4＋）, under high NaCl conditions （200 mmol L-l）. NH4^＋- fed plants showed better growth than NO3-fed plants at 1-3 mmol L-1N, and plants in both treatments showed the same growth at 4 mmol L-1 N. Nitrogen contents in NO3-fed plants increased with the N concentrations in solution; competitive inhibition of NO3- absorption by Cl- was observed under lower N conditions. In addition, shoot dry weight was significantly correlated only with shoot N content. Therefore, growth of NO3-fed plants was regulated by N absorption. In contrast, N contents of shoots in NH4＋-fed plants did not change with N concentration. Shoot Na content decreased with increasing N concentration, while K content increased. Dry weight was highly correlated only with K content in NH4＋-fed plants. These observations indicated that growth of NH4＋-fed plants was mainly regulated by K absorption.

Growth and Phosphorus Uptake of Oat (Avena nuda L.) as Affected by Mineral Nitrogen Forms Supplied in Hydroponics and Soil Culture

Plants show different growth responses to N sources supplied with either NH4^＋ or NO3^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavallability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat （Arena nuda L.） grown in hydroponics and in soil culture were investigated under supply with sole NH4^＋-N, sole NO3-N, or a combination. Sole NO^- -fed oat plants accumulated more biomass than sole NH4^＋ -fed ones. The highest biomass accumulation was observed when N was supplied with both NH^＋ -N and NO3^- -N. Growth of the plant root increased with the proportion of NO3^- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO3^- fed plants. However, root vigor was the highest when N was supplied with NO3^- ＋NH4^＋. NH4^＋ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg^-1. P uptake was increased when N was supplied partly or solely as NO3^--N, similarly as biomass accumulation. The results suggested that oat was an NO3-preferring plant, and NO3^- -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH4^＋ -N did not improve P nutrition, which was most likely due to the absence of P deficiency.

Ligation of Caeca Improves Nitrogen Utilization and Decreases Urinary Uric Acid Excretion in Chickens

This study was carried out to clarify role of ceca in nitrogen nutrition of the chicken. Exp. 1： The effect of cecal ligation on nitrogen utilization and excretion was investigated in chickens fed 5% to 14% protein diet. Irrespective of dietary protein level and different protein sources, the ligation of cecal decreased uric acid excretion and tended to increase nitrogen utilization and balance with the exception of urea-added 10% protein diet. Exp. 2： The effect of cecal ligation on nitrogen utilization and excretion was investigated in conventional and colostomized chickens fed a 5% protein diet or 5% protein diet plus urea. Total nitrogen excretion and uric acid excretion increased by colostomy were depressed by cecal ligation in chickens. Therefore, nitrogen utilization and balance decreased by colostomy were increased by cecal ligation. Urinary nitrogen excretion was significantly decreased by cecal ligation in colostomized chickens, but the cecal ligation did not change fecal nitrogen excretion in chickens fed either diet. Exp. 3： This experiment was carried out to examine the effects of removal of cecal contents on nitrogen utilization, balance and nitrogen excretion in cecally ligated chickens. Total nitrogen excretion was significantly decreased by washing out the cecal contents with saline or antibiotics. The cecal ligation and the removal of cecal contents significantly decreased uric acid excretion in the excreta. There was a highly inverse relationship between microbial counts in the ceca and an excretory amount of uric acid. Exp. 4： In order to examine effects of cecal ligation on microbial activity, microbes were counted and products of microbial fermentation were determined. The ligation of caeca decreased microbial counts, concentrations of acetic, propionic and butyric acids and ammonia concentration of cecal contents. These results suggest that nitrogen metabolism in chickens is affected by possible changes in cecal fermentation caused by preventing the substances from urine and digesta from entering into the ceca.

Stress Effects of Chlorate on Longan(Dimocarpus longan Lour.)Trees: Changes in Nitrogen and Carbon Nutrition

Three-year-old potted longan(Dimocarpus longan Lour.cv.Shixia)trees were treated with potassium chlorate and effects on nitrogen and carbon nutrition were examined.The results showed that potassium chlorate at 10 and 20 g per pot failed to induce flower but suppressed shoot growth and caused leaf chlorosis and drop.The treatment significantly inhibited nitrate reductase but increased nitrogen concentration in the leaves and buds.Concentration of soluble amino acids in the leaves of treated trees increased within 14 days and then declined to the control level,while it increased constantly in buds.In both organs,the amino acid increase was an all-round one,with all the tested 21 amino acids increased.However,soluble proteins in the leaves were slightly increased by chlorate,indicating that de novo synthesis of amino acids was activated.Chlorate reduced photosynthetic rate and stomatal conductance but slightly increased CO2 concentration in the mesophyll,suggesting that chlorate treatment damaged photosynthetic apparatus.The damage was reflected by the destruction of thylakoids and grana in the chloroplasts.Chlorate also caused depletion of starch with significant accumulation of soluble sugars in the leaves.Accumulation of sugars and soluble amino acids indicates osmotic adjustment in response to the stress caused by chlorate treatment.

Early diagnosis and monitoring of nitrogen nutrition stress in tomato leaves using electrical impedance spectroscopy

Nitrogen(N)is a life element for crop growth.In tomato growth and development,N stress often occurs and degrades crop yield and quality.Superfluous N can noticeably increase the nitrate content,which can be degraded into strong carcinogenic substance-nitrite.An accurate and timely monitoring and diagnosis of nutrition during crop growth is premise to realize a precise nutrient management.Crop N monitoring methods have been developed to improve N fertilizer management,and most of them are based on leaf or canopy optical property measurements.Although many optical/spectral plant N sensors have already commercialized for production use,low accuracy for phosphorus(P)and potassium(K)detection and diagnosis remains an important drawback of these methods.To explore the potential of N diagnosis by electrical impedance and perform study for nutrition status of plant NPK meanwhile by the electrical impedance,it is necessary that evaluate the N nutrition level by leaf impedance spectroscopy.Electrical impedance was applied to determine the physiological and nutritional status of plant tissues,but few studies related to plant N contents have been reported.The objective of this study was to evaluate the N nutrition level by leaf impedance spectroscopy and realize the early diagnosis and monitoring of N nutrition stress in tomato.Five sets of tomato plant samples with different N contents were cultivated in a Venlo greenhouse.N content of leaves was determined,and electrical impedance data were recorded in a frequency range of 1 Hz to 1 MHz.The obtained impedance data were analyzed using an equivalent circuit model for cellular tissues.The variation of equivalent parameters along with N content was analyzed,and the sensitive impedance spectroscopy characteristics of N nutrition level were extracted.Furthermore,the effect of moisture content on impedance measurement was discussed and the prediction model for N content was developed.Results showed that electrical impedance can be conveniently applied to early diagnosis and monitoring for tomato N nutrition stress.

A New Critical Nitrogen Dilution Curve for Rice Nitrogen Status Diagnosis in Northeast China

In-season diagnosis of crop nitrogen(N) status is crucial for precision N management. Critical N(N_c) dilution curve and N nutrition index(NNI) have been proposed as effective methods to diagnose N status of different crops. The N_c dilution curves have been developed for indica rice in the tropical and temperate zones and japonica rice in the subtropical-temperate zone, but they have not been evaluated for short-season japonica rice in Northeast China. The objectives of this study were to evaluate the previously developed N_c dilution curves for rice in Northeast China and to develop a more suitable N_c dilution curve in this region. A total of17 N rate experiments were conducted in Sanjiang Plain, Heilongjiang Province in Northeast China from 2008 to 2013. The results indicated that none of the two previously developed N_c dilution curves was suitable to diagnose N status of the short-season japonica rice in Northeast China. A new N_c dilution curve was developed and can be described by the equation N_c = 27.7 W^(-0.34) if W ≥ 1 Mg dry matter(DM) ha^(-1) or N_c = 27.7 g kg^(-1) DM if W < 1 Mg DM ha^(-1), where W is the aboveground biomass. This new curve was lower than the previous curves. It was validated using a separate dataset, and it could discriminate non-N-limiting and N-limiting nutritional conditions. Additional studies are needed to further evaluate it for diagnosing N status of different rice cultivars in Northeast China and develop efficient non-destructive methods to estimate NNI for practical applications.

Key variable for simulating critical nitrogen dilution curve of wheat:Leaf area ratio-driven approach

Nitrogen(N)dilution curves,a pivotal tool for N nutrition diagnosis,have been developed using different winter wheat(Triticum aestivum L.)tissues.However,few studies have attempted to establish critical nitrogen(N_(c))dilution curves based on the leaf area ratio(LAR)to improve the monitoring accuracy of N status.In this study,three field experiments using eight N treatments and four wheat varieties were conducted in Jiangsu Province of China from 2013 to 2016.The empirical relationship of LAR with shoot biomass(expressed as dry matter)was developed under different N conditions.The results showed that LAR was a reliable index,which reduced the effects of wheat varieties and years compared with the traditional indicators.The N nutrition index(NNI)based on the LAR approach(NNI-LAR)produced equivalent results to that based on shoot biomass.Moreover,the NNI-LAR better predicted accumulated N deficit and best estimated the relative yield compared with the other two indicator-based NNI models.Therefore,the LAR-based approach improved the prediction accuracy of N_(c),accumulated N deficit,and relative yield,and it would be an optimal choice to conveniently diagnose the N status of winter wheat under field conditions.