Evaluation Method Of In-situ Lodging Resistance Of Maize In The Field

Increasing planting density is one of the main way to achieve high yield in maize.However,a part of maize cultivars are prone to stem lodging under high density planting conditions.In addition to causing varying degrees of yield loss,lodging can result in mold growth on grains and lead to a negative impact on grain quality and mechanical operations.Most methods for evaluating maize lodging resistance rely on testing and analyzing detached plants as so far,which may not accurately reflect actual lodging conditions in the field.By simulating wind damage to corn and predicting the maximum lodging resistance with lower destruction on plant growth,it is possible to evaluate the in-situ lodging resistance of maize in the field.Aiming to solve the problems existing in the research of maize lodging resistance,this study conducted experiments involving different maize varieties and planting densities.A lodging resistance tester was used to measure the lodging resistance of maize at various growth stages and an evaluation criteria for maize lodging resistance was established subsequently.The study also identified biological indicators of lodging resistance in maize and provided a theoretical foundation for breeding lodging-resistant maize varieties.The main research results are as follows:1.In-situ lodging resistance tester was used to determine the relationship between displacement and force of maize stalk at different inclination angles in the field.The evaluation method of nondestructive lodging resistance of maize in the field had the ability to determine the lodging resistance simply,quickly and accurately.The results show that the values of force on maize plants at 45°inclination angles(F₄₅)can be used to characterize the maize lodging resistance in situ by nondestructive testing in the field.The maximum lodging resistance(F_max)can be calculated by the equation F_max=1.1354·F₄₅–0.3358.2.The lodging resistance ability in maize was classified into 4 levels by its difference in F_maxvalues.The 4 levels were:（1）Inferior lodging resistance:F_max≤11.8 N;（2）Medium lodging resistance:11.8 N<F_max≤17.5 N;（3）High lodging resistance:17.5 N<F_max≤25.8 N;and（4）Strong lodging resistance:F_max>25.8 N.3.Based on the principle of moment balance and the law of conservation of energy,the proportion of wind and gravity in the maize lodging process was quantified and the role of the ear in the maize lodging process was further elucidated.The lodging of maize was caused by the combined force of wind and gravity,and the elastic potential energy of plants was converted from both wind and gravity potential energy.When the maximum elastic potential energy was constant,the more gravity potential energy was converted,lower ability of maize to resist wind.Maize with higher ear position can convert more gravitational potential energy into elastic potential energy of stalk compared to maize with lower ear height.The conversion efficiency of ear gravity potential energy was higher than that of stem,and the conversion efficiency of ear gravity potential energy per unit mass to elastic potential energy was 1.8 times that of the former.Reducing the ear position can greatly improve the lodging resistance of maize and a reduction of the ear height by 20 cm could improve F_max by more than 30%.4.Correlation analysis between maximum lodging resistance and traits of the stem from the3^rd to the 6^th internodes indicates the strong relationships of F_max with stem traits of the 4th internode.The composition of dry matter accumulation,lignin content,crusty thickness and other materials per unit length were positively correlated with lodging resistance.Mechanical variables of maize internodes,such as internode cross-sectional shape and bending cross-section coefficient,were positively correlated with lodging resistance,especially at the 3rd and 4th internodes.However,maximum lodging resistance was negatively correlated with internode length.and it is suggested that the 4th internode could be used as the key part for the determination of lodging resistance of maize.5.The irregular cross-sectional shape of internodes under ear leads to various lodging resistance of maize among different directions.Optimizing the length-to-short diameter ratio（LSR）of the internode cross-section could improve the lodging resistance of maize.The lodging of maize stems is followed by the principle of minimum resistance.The cross-sectional area and short diameter of internodes had decisive effect on the lodging resistance of stems.The lodging resistance will be promoted with the decrease in the LSR of internode under maize ear under the condition of the same cross-sectional area.The LSR of the 4th internode can be used as a key index to evaluate the lodging resistance of maize.The lodging resistance of maize could be improved by LSR times if the elliptical section was optimized into a circular section with the same area without changing the cross-sectional area of internodes.To sum up,the lodging of maize stems followed the law of conservation of energy and the principle of minimum resistance.The lodging resistance of maize will get weaker along with the higher the proportion of gravity potential energy transformation in the maximum elastic potential energy of the stalk.In addition,the contribution of ear to the lodging resistance of maize was greater than that of the stalk.The LSR of cross section in the 4th internode was the key index to evaluate the lodging resistance of different maize cultivars.The lodging resistance could be effectively improved by the reductions in both LSR of the 4th internode and the ear height.