The stalk lodging caused by stalk rot after physiological maturity (PM) is a major factor restricting further development of mechanical grain harvesting in China. The physiological mechanism of stalk rot on maize stalk lodging after PM is not clear. This study, based on investigating stalk rot under natural field conditions, demonstrated the relation between stalk rot caused by Fusarium spp. and lodging of 35 maize cultivars after PM. In addition, three widely-planted maize cultivars were inoculated with Fusarium spp. at PM to analyze the pathogen of stalk rot causing lodging, by measuring the infection process, carbohydrate contents, and mechanical strength of stalks. Stalk lodging increased by 0.11–0.32% for each 1% incidence of stalk rot. The stalk rot pathogen infected stalks from the pith to the rind. At the level of longitudinal section, the stalk rot pathogen spread from the inoculation internode upwardly and downwardly. These infections gradually increased with the days after PM. Inoculated plants had decreased soluble sugar content; however, cellulose and lignin contained in the inoculated plants were both higher than that in the non-inoculated treatment. Crushing strength was significantly and positively correlated with percentage of soluble sugar. This indicated that the reduction of soluble sugar content during the natural senescence of maize stalk after PM was an important factor for the decrease of stalk strength and the increase of stalk lodging. The occurrence of stalk rot accelerated the decomposition of soluble sugar, which accelerated the decrease of stalk strength and greatly increased risk of stalk lodging.

Applications of unmanned aerial vehicle (UAV) spectral systems in precision agriculture require raw image data to be converted to reflectance to produce time-consistent, atmosphere-independent images. Complex light environments, such as those caused by varying weather conditions, affect the accuracy of reflectance conversion. An experiment was conducted here to compare the accuracy of several target radiance correction methods, namely pre-calibration reference panel (pre-CRP), downwelling light sensor (DLS), and a novel method, real-time reflectance calibration reference panel (real-time CRP), in monitoring crop reflectance under variable weather conditions. Real-time CRP used simultaneous acquisition of target and CRP images and immediate correction of each image. These methods were validated with manually collected maize indictors. The results showed that real-time CRP had more robust stability and accuracy than DLS and pre-CRP under various conditions. Validation with maize data showed that the correlation between aboveground biomass and vegetation indices had the least variation under different light conditions (correlation all around 0.74), whereas leaf area index (correlation from 0.89 in sunny conditions to 0.82 in cloudy days) and canopy chlorophyll content (correlation from 0.74 in sunny conditions to 0.67 in cloudy days) had higher variation. The values of vegetation indices TVI and EVI varied little, and the model slopes of NDVI, OSAVI, MSR, RVI, NDRE, and CI with manually measured maize indicators were essentially constant under different weather conditions. These results serve as a reference for the application of UAV remote sensing technology in precision agriculture and accurate acquisition of crop phenotype data.

Evaluation of grain breakage sensitivity of maize varieties mechanically-harvested by combine harvester

Improving crop yield and resource utilization efficiency is essential for agricultural productivity. In the Huang-Huai-Hai maize region of China, optimizing planting density, nitrogen (N) application, and fertilization methods are key strategies for enhancing maize yield and N use efficiency. However, traditional approaches have often hindered these improvements. To address this issue, we conducted a study in Baoding, Hebei, from 2022 to 2023, focusing on planting density, the N application rate, and the fertilization method on grain yield, N use efficiency, water use efficiency (WUE), and economic benefits. The trial involved two planting densities: 6.0 × 10⁴ plants ha⁻¹ (D1, typical local density) and 9.0 × 10⁴ plants ha⁻¹ (D2). Five N application rates were tested: 0 (N0), 120 kg ha⁻¹ (N1), 180 kg ha⁻¹ (N2), 240 kg ha⁻¹ (N3), and 300 kg ha⁻¹ (N4). The control treatment (D1N4) utilized the local planting density and traditional fertilization methods. Our findings revealed a positive correlation between the maize yield and N application rate, with the maximum yields (13.78–13.88 t ha⁻¹), high WUE (24.42–29.85 kg m⁻³), agronomic efficiency of N (AE_N) (18.11–19.00 kg kg⁻¹), and economic benefits (2.44 × 10⁴–2.47 × 10⁴ CNY ha⁻¹) observed with D2N3 and surface drip fertilization. This was significantly higher than the yield and resource efficiency of traditional fertilization methods and saved fertilizer and production costs. Therefore, adopting surface drip fertilization, adjusting planting density, and optimizing N application rates proved effective in enhancing maize yield and resource utilization efficiency in the Huang-Huai-Hai maize region.

Grain size and shape are important factors for yield and quality. The difference in grain phenotypic characteristics in the same maize hybrid is related to its position in the ear. This study aimed to clarify the distribution characteristics of grain morphological characteristics in the ear and to provide guidance for research of grain phenotype and kernel position effects. Three maize hybrids were used in the experiment, namely, Denghai 618 (DH618), KX3564, and Xianyu 335 (XY335), and the kernel number per row were 40, 40, and 36, respectively. The X-ray μCT was applied to obtain five kernel morphological indicators, including grain length, width, thickness, volume, surface area. Grain sphericity, length-width ratio, specific surface area, and volume coefficient were further calculated. The results showed that there were three types of maize ear morphological indicators trends: grain length, width, volume, and surface area were parabolic; thickness and sphericity were inverted parabolic; length-to-width ratio and specific surface area were irregular. The volume coefficient of grain at different parts of the ear, namely the relation coefficient between grain volume and grain length, width, and thickness, was determined. The average value of the middle grains morphological indicators of the ear was taken to select kernels representing stable characteristics of the variety. Within the range of 5% deviation from the morphological mean value of the middle grains of the ear, the grains in the middle part accounted for 26.39% of the total ear, about 10 grains extending from the 14th grain at the base of the ear to the top. Within the range of 10% deviation, the middle accounted for 47.22%, about 18 grains extending from the 12th grain at the base of the ear to the top. This study found that grain morphological indicators were greatly different at different positions of the maize ear, and showed different change rules as extend from the base to the top of the ear. Therefore, there were different grain volume coefficients at different positions of maize ear. And the representative sampling range on maize ear was determined based on the comprehensive analysis of different morphological indexes variation of grain. Keywords: grain morphology, X-ray μCT, kernel position effects, maize (Zea Mays L.) DOI: 10.25165/j.ijabe.20211402.6039 Citation: Yin X B, Hou J F, Ming B, Zhang Y, Guo X Y, Gao S, et al. Kernel position effects of grain morphological characteristics by X-ray micro-computed tomography (μCT). Int J Agric & Biol Eng, 2021; 14(2): 159–166.