| Rice straw is a major biomass that can be utilized as lignocellulosic materials and renewable energy.Rapid assessment of the compositional,mechanical,and near-infrared reflectance spectroscopy(NIRS)characteristics of rice straw would help to decipher its growth mechanisms and thereby improve its sustainable usages.A wide variety of rice straw featuring different subspecies(indica and japonica),growing seasons(early,middle,and late seasons),growing locations(paddy land and upland),and growing environments(paddy land and upland)were collected from Yacheng and Sanya of Hainan Province in South China and examined in this study.The main innovation achievements and conclusions were obtained as follows.1.Chemical analysis including 3 lignocellulosic compositions,5 ultimate compositions,4 proximate compositions,14 mineral elements,and 2 thermochemical characteristics was conducted.Results showed that the compositional characteristics of rice straw were significantly different among the diversified varieties with a significant difference level(P)<0.05.The lignocellulosic contents of rice straw were ranked as cellulose(39.96%±3.19%)>lignin(15.39%±1.57%)>hemicellulose(14.68%±1.96%).The contents of the ultimate compositions were ranked as oxygen(O)(40.83%±1.38%)>carbon(C)(39.78%±1.03%)>hydrogen(H)(4.93%±0.31%±nitrogen(N)(1.51%±0.25%)>sulfur(S)(0.38%± 0.07%).The contents of the proximate compositions were:moisture(5.62%± 0.41%),volatile matter(VM)(71.77%± 1.60%),ash(12.58%± 1.92%),and fixed carbon(FC)(10.04%± 0.83%).The mineral elements were ranked as potassium(K)(16.42 ? 3.27 g kg-1)>Calcium(Ca)(3.72±0.76 g kg-1)>phosphorus(P)(2.30 ± 0.68 g kg-1)>magnesium(Mg)(1.24±0.36 g kg-1)>manganese(Mn)(770.67 ± 173.28 mgkg-1)>sodium(Na)(0.28 ± 0.16 g kg-1)>iron(Fe)(0.28±0.12 g kg-1)>zinc(Zn)(25.36±10.38 mg kg-1)>arsenic(As)(12.00± 4.94 mg kg-1)>boron(B)(5.53±1.03 mg kg-1)>copper(Cu)(3.46 ± 1.15 mg kg-1),chromium(Cr)(0.66 ±0.45 mg kg-1),nickel(Ni)(0.38 ± 0.18 mg kg-1)>cadmium(Cd).The higher heating value(HHV)and lower heating value(LHV)of rice straw ranged from 14.35 to 17.24 MJ kg-1 and 13.18 to 16.14 MJ kg-1,respectively.Noteworthy correlations with a correlation coefficient(R)>0.50 among the 28 compositions(P<0.01)can be summarized as C,VM,HHV,and LHV were positively correlated to each other and negatively correlated with ash;O,VM,HHV,and LHV were positively correlated to each other and negatively correlated with ash;VM,HHV,and LHV were positively correlated to each other and negatively with ash and K.2.Phenotypic(diameter,thickness,and area)and mechanical characteristics(shear,bending,and tensile)of a wide variety of rice straw were determined.Results showed that the phenotypic and mechanical characteristics were inversely related to each other.There were almost no significant differences in the phenotypic characteristics among different rice straw varieties.The large diameter was 3.64 ? 0.54 mm of rice straw and small diameter was 2.31 ± 0.38 mm.Thickness was 0.37 ± 0.06 mm and area was 3.00 ± 0.77 mm2 of rice straw.The rank of force rice straw loaded was a maximum tensile force(11.53-133.27 N)>maximum shear force(4.34-54.56 N)>bending force(0.43-4.93 N).The rank of strength in rice straw was tensile strength(56.47±22.67 MPa)>bending strength(22.44±6.60 MPa)>shear strength(2.94±1.10 MPa).Tensile modulus(6.87 ± 1.95 MPa)was bigger than bending modulus(2.82 ±1.10 MPa).The samples with superior mechanical characteristics were selected based on their interquartile ranges and their genetic differences need to be further investigated.3.NIRS models for predicting the lignocellulosic and ultimate compositions of rice straw were developed based on two algorithms including partial least squares(PLS)and competitive adaptive reweighted sampling-partial least squares(CARS-PLS).Modeling results showed that most CARS-PLS models were of higher accuracy than the PLS models,possibly because the CARS-PLS models selected optimal combinations of wavenumbers,which might have enhanced the signal of chemical bonds and thereby improved the predictive efficiency.As a major contributor to the applications of rice straw,the N content was predicted precisely by the CARS-PLS model.Generally,the CARS-PLS models efficiently quantified the lignocelulose and ultimate compositions of a wide variety of rice straw.The acceptable accuracy of the models allowed their practical applications. |
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