Abstract:

[Objective] Maize leaf biomass is a key trait that reflects plant morphology, growth vigor, and physiological processes including photosynthetic production. Its dynamic changes can effectively characterize the growth status of maize. Accurate estimation of maize leaf biomass is crucial for accurately predicting maize yield and informing production management decisions. Extensive research on crop biomass estimation indicates that 3D point cloud data characterizing crop morphological structure, along with features derived therefrom, exhibit an extremely high correlation with crop biomass. However, traditional biomass prediction studies focus primarily on the population canopy scale, and lack effective prediction methods for biomass at the plant and organ scales. Research on non-destructive measurement methods for maize leaf biomass, based on 3D point clouds and machine learning, is conducted to address the demand for rapid acquisition of organ-level biomass information in maize cultivation and management research. [Methods] Maize leaf point cloud data were acquired using three techniques: multi-view stereo (MVS), LiDAR scanning, and 3D digitalization (DT). The leaf point clouds underwent preprocessing steps that included plant segmentation, denoising, mesh refinement, and uniform subsampling. Subsequently, morphological traits were extracted from the processed data, including leaf length, leaf area, bounding box dimensions, and the number of points contained within the leaf point clouds. Three machine learning methods—random forest (RF), gradient boosting regression tree (GBRT), and support vector regression (SVR)—as well as two deep learning methods—convolutional neural network (CNN) and fully connected neural network (FCNN)—were employed for predicting maize leaf dry weight. A point cloud-based maize leaf biomass prediction model was subsequently developed. This study utilized the mean squared error reduction method inherent to RF and the cumulative improvement method based on decision tree splits in GBRT to rank and visualize feature importance for optimal models. The resulting rankings were then visualized. Simultaneously, Pearson correlation analysis was used to analyze the correlations of the features from the fused dataset (integrating data from the three devices) as well as those from the DT data with maize leaf biomass. [Results and Discussions] The results demonstrated that, among the biomass prediction models developed in this study, the model based on Laser point cloud data and the FCNN method achieved the highest accuracy, with a mean absolute error (MAE) of 0.08 g, a mean absolute percentage error (MAPE) of 4.60%, a root mean square error (RMSE) of 0.10 g, and a coefficient of determination (R²) of 0.98. In the correlation analysis, the leaf area exhibited the strongest correlation with biomass (r = 0.92), followed by the number of points (r = 0.88), leaf width (r = 0.86), and leaf length (r = 0.77). In the feature importance ranking, the leaf area trait consistently ranked within the top two positions, whereas the number of points traits ranked among the top three in most cases. However, features such as the height of the leaf base from the ground, the horizontal distances from the leaf tip and apex to the stem, and the azimuth angle demonstrated low correlations with biomass and low feature importance. [Conclusions] Among all the maize leaf features investigated in this study, size-related traits (such as leaf area, point count, leaf length, and leaf width) had the greatest impact on the accuracy of biomass estimation. The utilization of high-resolution 3D point clouds of maize leaves, combined with machine learning methods, enabled a high-accuracy estimation of leaf dry weight and provided a novel approach for the non-destructive measurement of biomass in crop organs.

Key words: maize leaves, 3D point cloud, machine learning, biomass, prediction