| Rapeseed is one of the main oil crops in China,however,the lodging problem has become the main limiting factor of its yield and mechanized harvesting with the planting area expanding rapidly in the past few years.The lodging resistance of the rape stem was found to be closely related to its mechanical properties,as a result,exploring the influence of cultivation factors on the mechanical properties of it could provide a theoretical basis for the regulation of high yield and lodging resistance measures in rapeseed cultivation.Firstly in order to explore the effects of cultivation factors on mechanical properties of rapeseed stem,bend and shear test of rape stems of"Huaza 62"and"Jinyouza 158"was conducted under different sowing date,sowing density and nitrogen fertilizer rate.Secondly the contents of the chemical compositions and parameters of cross-section structure were detected,which were used to analyze the impact mechanism of the cultivation factors on the biomechanical properties.Finally,the influence of the cultivation factors on the lodging resistance of the rape was studied and the correlation model of the mechanical properties and lodging index was established,which were employed to verify the feasibility of evaluating the lodging resistance of rapeseeds by using mechanical properties of their stems.The main contents and conclusions were described as follows:?1?In order to explore the effects of sowing date,sowing density and nitrogen fertilizer rate on the elastic modulus?EM?,bending strength?BS?and shear strength?SS?of rape stems,“Huaza62”and“Jinyouza158”rape stems were used as test materials in bend and shear test by TMS-Pro texture analyzer.As a result,sowing date,sowing density and nitrogen fertilizer rate had significant influence on the mechanical properties of rape stem?P<0.05?;Both increase of nitrogen fertilizer rate and delay of sowing date decreased EM,BS and SS of stems;While EM,BS and SS were increased firstly with the increase of sowing density,got to their peak when the sowing density was 60×104 plant ha-1,and then decreased.The strengths of mechanical properties of rape stems both in full bloom and pod stage were better than those in final bloom stage.?2?The chemical compositions of“Huaza62”under different sowing date,sowing density and nitrogen fertilizer rate was detected,and grey relation theory was used to analyze the correlation between the contents of chemical compositions of the stems and their mechanical parameters.The results showed that the contents of cellulose,hemicellulose,lignin and pectin decreased with the delay of sowing.The contents of cellulose and pectin were increased firstly and then decreased with the increase of sowing density,whereas the contents of lignin and hemicellulose had slight changes.With the increase of nitrogen fertilizer rate,the contents of cellulose,hemicellulose,lignin and pectin decreased.The results of correlation analysis showed that the contents of cellulose and lignin had significant influence on EM as both their relevance were greater than 0.70,the content of cellulose had the greatest influence on BS as the relevance were 0.75 and 0.68,respectively,in flowering and mature period,and the content of lignin had the most obvious effect on culm SS,as the relevance were 0.79 and 0.76,respectively,in flowering and mature period.?3?The image processing technique was used to extract the cross-section structural parameters of thick-wall tissue,thin-wall tissue and medullary substance of the stems of“Huaza 62”,which was used to analyze the correlation between individual parameters and different mechanical properties.The results showed that,in comparison to S1,the area of thick-wall tissue and thin-wall tissue of S3 decreased by 1.80%and 2.97%,respectively,while the area of medullary substance increased by 4.77%with the delay of sowing date.The total cross-section area,thick-wall tissue and thin-wall tissue increased firstly with the increase of sowing density,got to their peak when the sowing density was 60×104 plant ha-1,and then decreased.With the increase of nitrogen fertilizer rate,the area of thick-wall tissue and thin-wall tissue of 360 kg ha-1 decreased by 4.61%and 5.18%,respectively,while the area of medullary substance increased by 7.48%,compared to those of 120kg ha-1.The area of thick-wall tissue and thin-wall tissue has a significantly positive correlation with the mechanical properties of rape stems,while the area of medullary substance tissue was negatively correlated with them.?4?In order to verify the feasibility of evaluating the lodging resistance of rape stems with biomechanical properties,the changing rules of the lodging resistant of rape stems of“Huaza 62”and“Jinyouza 158”with different cultivation factors were explored and a prediction model of the lodging resistant of their stems was established.The results showed that sowing date,sowing density and nitrogen fertilizer rate had significant influences on the lodging resistance of rape stems?P<0.05?.The lodging resistance had a significantly negative correlation with the mechanical properties of rape stems.The fitted values that evaluated the lodging resistance with biomechanical properties was around 90%,as a result,the lodging resistance of rape stems could be evaluated by their EM,BS and SS. |
PDF Full Text Request