Estimation of carbon and nitrogen contents in citrus canopy by low-altitude remote sensing

The study aimed to investigate the fast and nondestructive method for detecting carbon and nitrogen content in citrus canopy.The multispectral imagery of Tarocco blood orange(Citrus sinensis L.Osbeck)plant canopy was obtained by a multispectral camera array mounted at an eight-rotor unmanned aerial vehicle(UAV)flying at an altitude of 100 m above the canopy in Wanzhou District of Chongqing Municipality,China.Average spectral reflectance data of the whole canopy,mature leaf areas and young leaves areas were extracted from the imagery.Two spectral pre-processing methods,multiplicative scatter correction(MSC)and standard normal variable(SNV),and two modeling methods,the partial least squares(PLS)and the least squares support vector machine(LS-SVM),were adopted and compared for their prediction accuracy of total content of nitrogen,soluble sugar and starch in the leaves.The results showed that,based on the spectral data extracted from the mature leaves in the multispectral imagery,the PLS model based on the original spectrum obtained a Rp(correlation coefficient)of 0.6469 and RMSEP(root mean squares error of prediction)of 0.1296,suggested that it was the best for the prediction of total nitrogen content;the PLS model based on MSC(multiplicative scatter correction)spectrum pre-processing was the best for predicting total soluble sugar content(Rp=0.6398 and RMSEP=8.8891);and the LS-SVM model based on MSC was the best for the starch content prediction(Rp=0.6822 and RMSEP=14.9303).The prediction accuracy for carbon and nitrogen contents based on the spectral data extracted from the whole canopy and the young leaves were lower than that from the mature leaves.The results indicate that it is feasible to estimate the carbon and nitrogen contents by low-altitude airborne multispectral images.

The Vertical Distribution Law of Underground Biomass of Reed

[Objective]The aim of this study was to reveal the relationship between the reed and salinity in severely salinized area,so as to making clear the vertical distribution of underground biomass of reed.[Method]Field investigation and sampling method were used to get the mass accurate data of underground biomass of reed.further its vertical distribution was analyzed using combined statistical and ecological method.Moreover,the C/N ratio was obtained by measuring the contents of organic carbon and nitrogen in reed wetland soil.The correlation model among organic carbon,nitrogen of reed wetlands and C/N were finally analyzed.[Result]Total underground biomass of reed population is concentrated at 10 to 40 cm underground soil layer.Thick root plays crucial role in the composition of reed total biomass,Overall change of organic carbon and total nitrogen shows a declining trend.The content of organic carbon and nitrogen in soils becpmes stable below 50 cm from the surface.The content of organic carbon in soil is positively correlated with total nitrogen in soil at significant level.[Conclusion]These results provided theoretical basis for revealing underground biomass of reed in salinized area of arid region.