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.

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.

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.

Effects of Different Nitrogen Application Strategies on Yield and Forage Nutritive Quality of Zea mexicana

A pool experiment was carried out to study the effects of different nitrogen applicationstrategies (rates and stages of nitrogen application) on yield and forage nutritivequality of Zea mexicana cultivated in summer, 2002. In the whole growing stage, its stemwas clipped three times at the height of 25cm when it was 110cm high (H1, H2 and H3 standfor the first, second and third harvest stage, respectively). Six indexes includingcrude protein (CP), ether extract (EE), nitrogen free extract (NFE), acid detergentfiber (ADF), crude ash (CA), and general energy (GE) were employed to evaluate the foragenutritive value. The results showed that the content of CP and EE increased but thecontent of CA and ADF decreased under the two nitrogen rates (High-rate N, 600kgha-1;Mid-rate N, 300kgha-1). The fresh and dry harvest biomass of the whole plants on H1 andthose of the leaves on H2 were also improved. But the stalks on H2 and the whole plantson H3 were affected mainly by dressing nitrogen fertilizer. The yield of CP and EE, CA,NFE, and GE was mainly affected by nitrogen rates. The ADF yield increased was due to theincrement of the fresh and dry harvest biomass. Nitrogen applied as base fertilizer forsummer Zea mexicana can be harvested a higher biomass and improve the forage nutritivequality.

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.

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.