Digital mapping of pesticides bioconcentration by integrating remote sensing techniques and plant uptake model

Although pesticides have been widely used worldwide to enhance crop yield and product quality,most pesticides are harmful to the environment and human health.Plants absorb pesticides mainly from air and soil.Therefore,the soil-plant pathway is essential for pesticide absorption.Bioconcentration factor(BCF)has extensively been applied to evaluate potential plant contamination by pesticides from soil.Hence,this study developed a simplified plant transpiration-based plant uptake model(PT-model)to estimate plant pesticides’BCF from soil based on plant transpiration.Remote sensing techniques were employed to generate spatiotemporal continuous plant transpiration via evapotranspiration.Pesticide BCF mapping was achieved by integrating PT-model with Moderate Resolution Imaging Spectroradiometer(MODIS)remotely sensed data.The results were compared with a verified model driven by relative humidity and air temperature(RA-model),which has been confirmed byfindings from previous studies.The estimated BCF was within the boundaries of the RA-model,indicating the simulation’s overall acceptability.In this study,the BCF temporal trend estimated by the proposed method agreed with the RA-model assimilating meteorology datasets,while the spatial distribution was partially inconsistent.Overall,the proposed method generates the spatiotemporal patterns of pesticide BCF with relatively consistent results supported by previous records andfindings.

A New Method to Determine Central Wavelength and Optimal Bandwidth for Predicting Plant Nitrogen Uptake in Winter Wheat

Plant nitrogen （N） uptake is a good indicator of crop N status. In this study, a new method was designed to determine the central wavelength, optimal bandwidth and vegetation indices for predicting plant N uptake （g N m-2） in winter wheat （Triticum aestivum L.）. The data were collected from the ground-based hyperspectral reflectance measurements in eight field experiments on winter wheat of different years, eco-sites, varieties, N rates, sowing dates, and densities. The plant N uptake index （PNUI） based on NDVI of 807 nm combined with 736 nm was selected as the optimal vegetation index, and a linear model was developed with R2 of 0.870 and RMSE of 1.546 g N m-2 for calibration, and R2 of 0.834, RMSE of 1.316 g N m-2, slope of 0.934, and intercept of 0.001 for validation. Then, the effect of the bandwidth of central wavelengths on model performance was determined based on the interaction between central wavelength and bandwidth expansion. The results indicated that the optimal bandwidth varies with the changes of the central wavelength and with the interaction between the two bands in one vegetation index. These findings are important for prediction and diagnosis of plant N uptake more precise and accurate in crop management.

Patterns and drivers of seasonal water sources for artificial sand-fixing plants in the northeastern Mu Us sandy land,Northwest China

Understanding plant water-use patterns is important for improving water-use efficiency and for sustainable vegetation restoration in arid and semi-arid regions. However, seasonal variations in water sources and their control by different sand-fixing plants in water-limited desert ecosystems remain poorly understood. In this study, stable isotopic ratios of hydrogen(δ^(2)H) and oxygen(δ^(18)O) in precipitation, soil water, groundwater, and xylem water were determined to document seasonal changes in water uptake by three representative plant species(Pinus sylvestris var. mongolica Litv., Amygdalus pedunculata Pall., and Salix psammophila) in the northeastern Mu Us sandy land, Northwest China. Based on the depth distribution and temporal variation of measured gravimetric soil water content(SWC), the soil water profile of the three species stands was divided into active(0.01 g g^(-1)< SWC < 0.08 g g^(-1), 20%< coefficient of variation(CV) < 45%), stable(0.02 g g^(-1)< SWC < 0.05 g g^(-1), CV < 20%), and moist(0.08 g g^(-1)< SWC < 0.20 g g^(-1), CV >45%) layers. Annually, P. sylvestris, A. pedunculata, and S. psammophila obtained most water from deep(59.2%±9.7%, moist layer and groundwater),intermediate(57.4%±9.8%, stable and moist layers), and shallow(54.4%±10.5%, active and stable layers) sources, respectively. Seasonally, the three plant species absorbed more than 60% of their total water uptake from the moist layer and groundwater in the early(June) dry season;then, they switched to the active and stable layers in the rainy season(July–September) for water resources(50.1%–62.5%). In the late(October–November) dry season, P. sylvestris(54.5%–66.2%) and A. pedunculata(52.9%–63.6%) mainly used water from stable and moist layers, whereas S. psammophila(52.6%–70.7%) still extracted water predominantly from active and stable layers. Variations in the soil water profile induced by seasonal fluctuations in precipitation and groundwater levels and discrepancies in plant phenology, root distribution, and water demand are the main factors affecting the seasonal water-use patterns of artificial sand-fixing plants. Our study addresses the issue of plant water uptake with knowledge of proportional source-water use and reveals important implications for future vegetation restoration and water management in the Mu Us sandy land and similar desert regions around the world.

Effects of Microbial Inoculants on Nutrient Availability and Rice Yield

Under field conditions, an experiment was conducted to study the effects of ammonification bacteria, potassium bacteria and phosphorus bacteria on nutrient availability in soil and yield of rice in the cold region of China and compared to the conventional fertilization. Results showed that DF1P2 treatment （ammonifiers 1.5× 108 cfu· m2, phosphorus bacteria 1.5× 108 cfu. m2, and potassium bacteria 1.5× 108 cfu· m2） increased available nutrient concentrations in soil, increased the concentrations of N, P, and K in plant organs and increased the rice yield and was the most significantly among all the treatments. This treatment could be recommended as the best suitable biological fertilizer application rate for the rice production in the cold region of China.

Biochar-induced changes in metal mobility and uptake by perennial plants in a ferralsol of Brazil’s Atlantic forest

Despite an abundance of short-term studies focusing on biochar’s effects on annual plants,the long-term effects of biochar on perennial plants and the effects of the biochar on the mobility and speciation changes of metals/metalloids not limited to main plant nutrients in soils are poorly constrained.This study reports on the amelioration a sloped orthic ferralsol by biochar from Tibouchina wood and the resulting effects on perennial crops and microbiota,including a comprehensive analysis of metals/metalloids speciation changes.Fields were amended with biochar and urine-amended biochar(2 kg/m^(2))and were planted with papaya,banana,and manioc.Soil and plant materials were analyzed using acid digestions,sequential extractions,and 16S rRNA gene sequencing.Biochar applications led to decreased soil acidity,shifted the cation exchange capacity from being Al-influenced to being Mg/K/Ca-dominated,and elevated the concentrations of Mg,K,Ca,Zn,and Ba in soils.The exchangeable/acid-soluble fraction of Ca,P,and S notably increased.The soil microbial biome became more species rich and diverse in the biochar-amended fields.Manioc benefited from biochar applications,demonstrating increased growth,which resulted in generally decreased concentrations of trace elements in most plant parts,however,with an increased total elemental uptake.Urine amendment contributed to higher concentrations of P,S,and K in soils,but did not further increase plant growth.Biochar was shown to be a promising soil amendment for agricultural use of orthic ferralsols of the Brazil’s Atlantic forest region,but the accumulation of potentially harmful metals needs to be considered.

Predicting As,Cd and Pb uptake by rice and vegetables using field data from China

Plant uptake factor （PUF）, single-variable regression of natural log-transformed concentrations in rice grain/vegetables versus natural log-transformed concentrations in soil and multiple-variable regression with soil concentrations and pH, was derived, validated and compared based on the paired crop and soil data collected from studies regarding As, Cd and Pb contaminated croplands in China. Results showed that the median value of PUF did not present deterministic prediction. But after natural logarithm transformation, the PUF followed Gaussian distribution which could be useful in risk assessment. The single-variable regression models were significant for As, Cd and Pb uptake both by rice and vegetables; however, the standard errors of all the regressions were comparatively large. Soil pH as a variable was generally significant but it only contributed positively to model fit for Cd uptake. After model comparison and selection, the upper 95% prediction limits of the multiple regression model for Cd uptake by rice was recommended to calculate screening value of Cd for paddy soil based on the limit for Cd concentration in rice grain.

Dissipation of polycyclic aromatic hydrocarbons and microbial activity in a field soil planted with perennial ryegrass

Dissipation and plant uptake of polycyclic aromatic hydrocarbons （PAHs） in contaminated agricul- tural soil planted with perennial ryegrass were investigated in a field experiment. After two seasons of grass cultivation the mean concentration of 12 PAHs in soil decreased by 23.4% compared with the initial soil. The 3-, 4-, 5-, and 6- ring PAHs were dissipated by 30.9%, 25.5%, 21.2%, and 16.3% from the soil, respectively. Ryegrass shoots accumulated about 280 ug.kg1, shoot dry matter biomass reached 2.48 x 104kg-ha1, and plant uptake accounted for about 0.99% of the decrease in PAHs in the soil. Significantly higher soil enzyme activities and microbial community functional diversity were observed in planted soil than that in the unplanted control. The results suggest that planting ryegrass may promote the dissipation of PAHs in long-term contaminated agricultural soil, and plant-promoted microbial degradation may be a main mechanism of phytoremediation.

Modelling sulphate-enhanced cadmium uptake by Zea mays from nutrient solution under conditions of constant free Cd^(2+) ion activity

A controlled hydroponic experiment was undertaken to investigate Cd uptake in relation to the activity of Cd species in solution other than the free ion （Cd^2＋） by maintaining a constant Cd^2＋ activity under variable SO4^2- and Cl^- concentrations exposed to maize （Zea mays vat. Cameron） plants. The objectives of these experiments were： （1） to distinguish and quantify the different uptake rates of free and inorganic-complexed Cd from nutrient solution, and （2） to model the uptake of Cd by maize with a Biotic Ligand Model （BLM） in a system which facilitates the close examination of root characteristics. Results of the current experiments suggest that, in addition to the free ion, CdSO4^0 complexes are important factors in determining Cd uptake in nutrient solution by maize plants. Higher nominal SO4^2- concentrations in solution generally resulted in a greater Cd accumulation by maize plants than predicted by the Cd^2＋ activity. A better integration of the complete dataset for the 3 harvest times （6, 9 and 11 days after treatment） was achieved by including consideration of both the duration of Cd exposure and especially the root surface area to express Cd uptake. Similarly, the fit of the BLM was also improved when taking into account exposure time and expressing uptake in terms of root morphological parameters.

Effect of pyrolysis temperature on Si release of alkali-enhanced Si-rich biochar and plant response

Recent studies have shown that silicon(Si)dissolution from biochar may be influenced by the pyrolysis temperature.In addition,the enhancement of biochar by treatment with alkali has been proposed to produce a Si source that can be used for environmentally friendly plant disease control.In this study,biochars from rice straw and rice husk pretreated with KOH,CaO and K_(2)CO_(3)and then pyrolyzed at 350,450 and 550°C were prepared to evaluate the effects of pyrolysis temperature on Si release and plant uptake from alkali-enhanced Si-rich biochar.Extractable Si and dissolution Si from the prepared biochars were assessed by different short-term chemical methods and long-term(30-day)release in dilute acid and neu-tral salt solutions,respectively,along with a rice potting experiment in greenhouse.For both rice straw-and husk-derived alkali-enhanced biochars(RS-10KB and HS-10K2B,respectively),increasing the pyrolysis temperature from 350 to 550°C generally had the highest extractable Si and increased Si content extracted by 5-day sodium carbonate and ammonium nitrate(5dSCAN)designated for fertilizer Si by 61-142%,whereas non-enhanced biochars had more extractable Si at 350°C.The alkali-enhanced biochars produced at 550°C pyrolysis temperature also released 82-172%and 27-79%more Si than that of 350°C produced biochar in unbuffered weak acid and neutral salt solutions,respectively,over 30 days.In addition,alkali-enhanced biochars,especially that derived from rice husk at 550°C facilitated 6-21%greater Si uptake by rice and 44-101%higher rice grain yields than lower temperature biochars,non-enhanced biochars,or conventional Si fertilizers(wollastonite and silicate calcium slag).Overall,this study demonstrated that 550°C is more efficient than lower pyrolysis temperature for preparing alkali-enhanced biochar to improve Si release for plant growth.

Arbuscular mycorrhizal fungi reduce ammonia emissions under different land-use types in agro-pastoral areas

Ammonia(NH3)emissions,the most important nitrogen(N)loss form,always induce a series of environmental problems such as increased frequency of regional haze pollution,accelerated N deposition,and N eutrophication.Arbuscular mycorrhizal(AM)fungi play key roles in N cycling.However,it is still unclear whether AM fungi can alleviate N losses by reducing NH3emissions.The potential mechanisms by which AM fungi reduce NH_(3)emissions in five land-use types(grazed grassland,mowed grassland,fenced grassland,artificial alfalfa grassland,and cropland)were explored in this study.Results showed that AM fungal inoculation significantly reduced NH3emissions,and the mycorrhizal responses of NH3emissions were determined by land-use type.Structural equation modeling(SEM)showed that AM fungi and land-use type directly affected NH_(3)emissions.In addition,the reduction in NH_(3)emissions was largely driven by the decline in soil NH_(4)^(+)-N and pH and the increases in abundances of ammonia-oxidizing archaea(AOA)amoA and bacteria(AOB)amoB genes,urease activity,and plant N uptake induced by AM fungal inoculation and land-use type.The present results highlight that reducing the negative influence of agricultural intensification caused by land-use type changes on AM fungi should be considered to reduce N losses in agriculture and grassland ecosystems.

Lead stabilization in a polluted calcareous soil using cost-effective biochar and zeolite amendments after spinach cultivation

Biochar has been shown to be an effective organic soil amendment for the in-situ immobilization of lead(Pb).Little research has been done on the effects of biochar and zeolite interactions on Pb immobilization in contaminated calcareous soils.Therefore,the aim of this study was to investigate the effects of different levels of zeolite(2%and 4%,weight:weight)and biochars(3%,weight:weight)prepared from green compost(GB),poultry manure(PB),and municipal waste(MB)on the content of Pb in spinach shoots and Pb stabilization in a greenhouse experiment conducted using a Pb-contaminated calcareous soil.Application of GB and PB significantly decreased the Pb mobility factor(MF)from 2.8%to 4.6%and the cumulative Pb release(diethylenetriamine pentaacetate(DTPA)extraction)from 16.8%to 20.1%in the calcareous soil,which were further enhanced by the combined addition of zeolite,with Pb MF reduction from 4.4%to 8.4%and cumulative Pb release reduction from 24.8%to 28.6%.The enhancement of soil Pb immobilization was attributed to the properties of the amendments,such as high pH,ash content,and phosphorus content(10.5^(-1)1.0,390-435 g kg^(-1),and 2.5-4.3 g kg^(-1),respectively).Results of the soil Pb sequential extraction and Pb release kinetics were highly and significantly correlated with spinach shoot Pb content.Soil chemical data showed that the application of MB with 4%zeolite was the most effective treatment for immobilizing Pb(8.4%reduction in Pb MF and 28.6%reduction in cumulative DTPA-extractable Pb),which is in agreement with the results of the spinach shoot Pb(89.0%reduction in Pb uptake).

A Meta-Analysis on Phenotypic Variation in Cadmium Accumulation of Rice and Wheat:Implications for Food Cadmium Risk Control

In some densely-populated countries, farmland has been widely cadmium (Cd) contaminated, and the utilization of the contaminated farmland for crop production is currently unavoidable. This necessitates the use of low-Cd crops (i.e., pollution-safe cultivars, the crop varieties with the ability to accumulate a low level of Cd in their edible parts when grown on polluted soil) in these areas and highlights the importance of knowledge on phenotypic variation in crop Cd accumulation for food Cd risk control. Studies on phenotypic variation in heavy metal accumulation started decades ago for a wide range of crops, and synthesis of the scattered experimental results in the literature is in need. We built a Low-Cd Crops Database based on literature research, and relevant meta-analysis was performed to quantitatively explore the phenotypic variation in Cd uptake and translocation of rice and wheat. Considerable variability existed among rice (median grain Cd bioconce nt ration factor (BCF) of 0.10) and wheat (median grain Cd BCF of 0.21) phenotypes in grain Cd accumulation, and this variability was labile to soil pH and the level of Cd stress. Wheat statistically had a higher root-to-shoot Cd-translocating ability than rice, highlighting potential food Cd risks and the importance of growing low-Cd wheat in slightly Cd-contaminated regions. Meanwhile, no correlations were detected among soil-to-root, root-to-shoot, and shoot-to-grain translocation factors, implying that Cd uptake and internal translocation in crops were probably controlled by different underlying gene tic mechanisms. Root-to-shoot Cd transport could be a favorable target trait for selecting and breeding low-Cd rice and wheat. In all, this review provides a comprehensive low-Cd crop list for remediation practice and a systematic meta-analysis inferring food Cd risks based on plant capacity for Cd accumulation and desired traits for low-Cd crop breeding.

Accumulation and phytotoxicity of technical hexabromocyclododecane in maize

To investigate the accumulation and phytotoxicity of technical hexabromocyclododecane（HBCD）in maize,young seedlings were exposed to solutions of technical HBCD at different concentrations.The uptake kinetics showed that the HBCD concentration reached an apparent equilibrium within 96 hr,and the accumulation was much higher in roots than in shoots.HBCD accumulation in maize had a positive linear correlation with the exposure concentration.The accumulation of different diastereoisomers followed the orderγ-HBCD〉β-HBCD〉α-HBCD.Compared with their proportions in the technical HBCD exposure solution,the diastereoisomer contribution increased forβ-HBCD and decreased forγ-HBCD in both maize roots and shoots with exposure time,whereas the contribution ofα-HBCD increased in roots and decreased in shoots throughout the experimental period.These results suggest the diastereomer-specific accumulation and translocation of HBCD in maize.Inhibitory effects of HBCD on the early development of maize followed the order of germination rate〉root biomass≥root elongation〉shoot biomass≥shoot elongation.Hydroxyl radical（OH）and histone H2AX phosphorylation（γ-H2AX）were induced in maize by HBCD exposure,indicative of the generation of oxidative stress and DNA double-strand breaks in maize.An OH scavenger inhibited the expression ofγ-H2AX foci in both maize roots and shoots,which suggests the involvement of OH generation in the HBCD-induced DNA damage.The results of this study will offer useful information for a more comprehensive assessment of the environmental behavior and toxicity of technical HBCD.

Nitrogen mass balance in a constructed wetland treating piggery wastewater effluent

The nitrogen changes and the nitrogen mass balance in a free water surface flow constructed wetland （CW） using the four-year monitoring data from 2008 to 2012 were estimated. The CW was composed of six cells in series that include the first settling basin （Cell 1）, aeration pond （Cell 2）, deep marsh （Cell 3）, shallow marsh （Cell 4）, deep marsh （Cell 5） and final settling basin （Cell 6）. Analysis revealed that the NH4＋-N concentration decreased because of ammonification which was then followed by nitrification. The NO4＋-N and NO4＋-N were also further reduced by means of microbial activities and plant uptake during photosynthesis. The average nitrogen concentration at the influent was 37,819 kg/year and approximately 45% of that amount exited the CW in the effluent. The denitrification amounted to 34% of the net nitrogen input, whereas the accretion of sediment was only 7%. The biomass uptake of plants was able to retain only 1% of total nitrogen load. In order to improve the nutrient removal by plant uptake, plant coverage in four cells （i.e., Cells 1, 3, 4 and 5） could be increased.

Ractopamine up take by alfalfa (Medicago sativa) and wheat (Triticum aestivum) from soil

Ractopamine is a beta adrenergic agonist used as a growth promoter in swine, cattle and turkeys. To test whether ractopamine has the potential to accumulate in plants grown in contaminated soil, a greenhouse study was conducted with alfalfa（Medicago sativa） and wheat（Triticum aestivum） grown in two soils having different concentrations of organic matter（1.3% and 2.1%）, amended with 0, 0.5, and 10 μg/g of ractopamine. Plant growth ranged from 2.7 to 8.8 g dry weight（dw） for alfalfa, and 8.7 to 40 g dw for wheat and was generally greater in the higher organic matter content soil. The uptake of ractopamine in plant tissues ranged from non-detectable to 897 ng/g and was strongly dependent on soil ractopamine concentration across soil and plant tissue. When adjusted to the total fortified quantities, the amount of ractopamine taken up by the plant tissue was low, 〈 0.01% for either soil.

Efficiency of soil-applied ^(67)Zn-enriched fertiliser across three consecutive crops

A very small amount of applied zinc(Zn) is taken up by crops, resulting in low recovery by plants. Adding elemental sulphur to zinc oxide(ZnO) fertiliser could improve Zn solubilisation and exert a higher residual effect on crops than soluble Zn sources. We produced an isotopically labelled Zn-elemental sulphur fertiliser and evaluated its performance in comparison to traditional Zn sources during sequential crop cultivation. Three ^(67)Zn-labelled fertilisers,ZnO, zinc sulphate(ZnSO_(4)), and ZnO co-granulated with elemental sulphur(ZnOS^(0)), were soil applied, and their contributions to the uptake of Zn by three consecutive crops, wheat, ryegrass, and corn, were assessed in a 294-d pot experiment. The contributions of Zn fertilisers followed the order: ZnSO_(4) > ZnO= ZnOS^(0). The relative contributions of Zn fertilisers were lower in the first crop than in the subsequent crops. The overall recovery of applied Zn by the three crops was higher for ZnSO_(4) than for ZnO and ZnOS^(0), reaching 1.56%, 0.45%, and 0.33% of the applied Zn, respectively. Zinc recovery by plants was very low, regardless of the source of Zn. Adding elemental sulphur to ZnO did not increase its effectiveness up to 294 d after application. Fertiliser contribution was higher for the subsequent crops than for the initial crop, indicating the importance of assessing the residual effects of Zn fertilisers.

Contaminant removal from low-concentration polluted river water by the bio-rack wetlands

The bio-rack is a new approach for treating low-concentration polluted river water in wetland systems.A comparative study of the efficiency of contaminant removal between four plant species in bio-rack wetlands and between a bio-rack system and control system was conducted on a small-scale （500 mm length × 400 mm width × 400 mm height） to evaluate the decontamination effects of four different wetland plants.There was generally a significant difference in the removal of total nitrogen （TN）,ammonia nitrogen （NH 3-N） and total phosphorus （TP）,but no significant difference in the removal of permanganate index （COD Mn） between the bio-rack wetland and control system.Bio-rack wetland planted with Thalia dealbata had higher nutrient removal rates than wetlands planted with other species.Plant fine-root （root diameter 3 mm） biomass rather than total plant biomass was related to nutrient removal efficiency.The study suggested that the nutrient removal rates are influenced by plant species,and high fine-root biomass is an important factor in selecting highly effective wetland plants for a bio-rack system.According to the mass balance,the TN and TP removal were in the range of 61.03-73.27 g/m^2 and 4.14-5.20 g/m^2 in four bio-rack wetlands during the whole operational period.The N and P removal by plant uptake constituted 34.9%-43.81% of the mass N removal and 62.05%-74.81% of the mass P removal.The study showed that the nitrification/denitrification process and plant uptake process are major removal pathways for TN,while plant uptake is an effective removal pathway for TP.

Impacts of chicken manure and peat-derived biochars and inorganic P alone or in combination on phosphorus fractionation and maize growth in an acidic ultisol

The forms of phosphorus(P)in animal manure and peat are different from synthetic P fertilizers and will affect soil P fractions when they are used as P amendments.Effects of chicken manure(CMB)and peat(PB)derived biochars(CMB and PB)alone or in combination with P fertilizer(KH_(2)PO_(4))and rock phosphate(RP)on plant/soil health and soil P fractions in an acidic ultisol were examined with greenhouse pot experiments.The total P rate was constant at 120 mg kg^(−1) in all treatments.Soil P fractions,P uptake,and maize growth were determined after 56 days.Application of CMB combined with P fertilizer or alone significantly increased soil pH,water extractable and relatively labile P,dry matter yield of maize,chlorophyll contents in maize leaves,while decreasing the Fe and Al binding P.Moreover,sole application of CMB and PB showed greater effects than application of P fertilizer alone regarding plant growth and P fractionation.Integration of syn-thetic inorganic P sources with CMB or sole application of CMB is more beneficial than application of inorganic P sources to improve plant growth and P availability.

Nondestructive estimation of bok choy nitrogen status with an active canopy sensor in comparison to a chlorophyll meter

Precise estimation of vegetable nitrogen(N)status is critical in optimizing N fertilization management.However,nondestructive and accurate N diagnostic methods for vegetables are relatively scarce.In our two-year field experiment,we evaluated whether an active canopy sensor(GreenSeeker)could be used to nondestructively predict N status of bok choy(Brassica rapa subsp.chinensis)compared with a chlorophyll meter.Results showed that the normalized difference vegetation index(NDVI)and ratio vegetation index(RVI)generated by the active canopy sensor were well correlated with the aboveground biomass(AGB)(r=0.698–0.967),plant N uptake(PNU)(r=0.642–0.951),and root to shoot ratio(RTS)(r=-0.426 to-0.845).Compared with the chlorophyll meter,the active canopy sensor displayed much higher accuracy(5.0%–177.4%higher)in predicting AGB and PNU and equal or slightly worse(0.54–1.82 times that of the chlorophyll meter)for RTS.The sensor-based NDVI model performed equally well in estimating AGB(R2=0.63)and PNU(R2=0.61),but the meter-based model predicted RTS better(R2=0.50).Inclusion of the days after transplanting(DAT)significantly improved the accuracy of sensor-based AGB(19.0%–56.7%higher)and PNU(24.6%–84.6%higher)estimation models.These findings suggest that the active canopy sensor has a great potential for nondestructively estimating N status of bok choy accurately and thus for better N recommendations,especially with inclusion of DAT,and could be applied to more vegetables with some verification.