To investigate the interactions between genotype, nitrogen application rate and planting density on the regulation of wheat lodging resistance and grain yield, so as to identify the optimal combination of nitrogen-density that matches the biological characteristics of varieties. The results provide theoretical basis and technical support for stable and abundant winter wheat yield and resistant strain cultivation.

A split-split plot field experiment was conducted in Jiaozuo, Henan Province, China, for two consecutive years from 2020 to 2022. Two wheat varieties Xinhuamai 818 and Xinmai 26 with different lodging resistance were selected in the main plots. The nitrogen fertilizer application rates were used as split-plots, and five levels were set: no N application (N0), 180 kg·hm^-2 (N1), 240 kg·hm^-2 (N2), 300 kg·hm^-2 (N3) and 360 kg·hm^-2 (N4), the planting densities were used as split-split plots, and three levels were set: 2.25 million plants/hm² (D1), 3.75 million plants/hm² (D2) and 5.25 million plants/hm² (D3). The study focused on analyzing the effects of the three-factor combination of variety, nitrogen application and planting density on the anatomical structure of wheat culms, field lodging rate and yield.

The results showed that nitrogen application rate and planting density significantly regulated the vascular bundle structure of both wheat varieties. The number and area of big vascular bundles and the ratio of number and area of big and small vascular bundles were significantly and positively correlated with culm wall thickness and culm breaking strength, while the area of small vascular bundles was significantly and negatively correlated with culm wall thickness. Compared with Xinmai 26, Xinhuamai 818 had more big vascular bundles and larger area, while the number of small vascular bundles was equal and the area was smaller. This may be the anatomical basis for the superiority of Xinhua 818 over Xinmai 26 in terms of lodging resistance. Under the same planting density, the number and area of big vascular bundles of both wheat varieties showed a trend of increasing and then decreasing with the increase of nitrogen application rate, with the largest number and area of big vascular bundles in N3 treatment. The average increase of number and area of big vascular bundles of Xinhuamai 818 and Xinmai 26 under N3 treatment compared with the minimum treatment were 14.61%, 15.80% and 16.18%, 20.10% respectively. The number and area of small vascular bundles showed similar changes. Under the same level of nitrogen application rate, the number and area of big vascular bundles of both varieties were the largest in the low density D1 treatment. Compared with the minimum value of high density D3, the average increase in the number and area of big vascular bundles of Xinhuamai 818 and Xinmai 26 under D1 treatment were 6.14%, 5.20% and 8.95%, 11.42%, respectively.

Nitrogen-density control combination D1N2 with 240 kg·hm^-2 and planting density of 2.25 million plants/hm² can optimize the vascular bundle structure, coordinate the development of big and small vascular bundles. Specifically, the number and area of big vascular bundles and the number ratio and area ratio of two vascular bundles were increased in this treatment. The combination can also increase the thickness of the culm wall between the basal nodes and improve the breaking strength of the plant. These changes realize the synchronous improvement of lodging resistance and yield of wheat. We think this treatment can be used as a suitable nitrogen-density combination pattern for high-yielding and efficient cultivation of winter wheat in high-yielding irrigation areas in northern Henan.

The passivation effect of passivator and compound microbial fertilizer on cadmium (Cd) activity in slightly Cd-polluted weak alkaline farmland soil in northern Henan Province was studied, and their effects on Cd accumulation and translocation in different organs and yield of winter wheat were investigated too. The purpose of this study was to explore soil remediation materials for efficient remediation of Cd-contaminated soil, to reduce Cd content in winter wheat grains, and to screen wheat varieties with low Cd accumulation, so as to provide the technical support for the safe and efficient production of wheat in lightly polluted weak alkaline farmland in northern Henan Province.

In two consecutive winter wheat growing seasons of 2020-2022, two-factor split field comparison experiments of four different soil remediation materials (CK, no soil remediation treatment; CMF, single application of compound microbial fertilizer; GP, single application of soil passivator; CMF+GP, combination of compound microbial fertilizer and soil passivator) and six winter wheat varieties (Xinhuamai818, Luomai 163, Zhengmai 9023, Xinmai 296, Zhengmai 136, and Zhengmai 7698) in northern Henan Province were set up and used in the weakly Cd-polluted alkaline farmland. The changes of available Cd in soil, Cd contents in aboveground organs of wheat plants, enrichment coefficient (BCF), transport coefficient (TF), their correlations, and winter wheat yields and its components were analyzed.

(1) In two winter wheat growing seasons (2020-2021 and 2021-2022), compared with CK, single application and equal combination application of passivation agent and compound microbial fertilizer could remarkably reduce the content of available Cd in soil. CMF+GP treatment had the best effect, which significantly and effectively reduced the available Cd content by 17.6%-22.4% in the surface soil of the roots among the six varieties. The decreased available Cd in soil was related to the changes of Cd content in the aboveground organs of winter wheat plants, and there were also some differences between the same organs of different varieties. (2) Single application of soil passivator and compound microbial fertilizer, as well as equal combined application of soil passivator and compound microbial fertilizer, could make Xinhuamai 818, Luomai 163 and Zhengmai 9023 decrease TF_{Stem sheath-leaf}, TF_{Stem sheath-grain}, increase TF_{Stem sheath-(Spike shaft+chaff)}, TF_{Leaf-(Spike shaft+chaff)}, reduce BCF_{Stem sheath} and BCF_Leaf, and make wheat body in order to reduce BCF _Grain, the content of Cd in it shifted to panicle axis + glume. In contrast, they did not reduce TF_{Stem sheath-Leaf} and BCF _{Stem sheath} of Xinmai 296, whereas increased BCF _{Stem sheath} of Zhengmai 136 and Zhengmai 7698. (3) Application of passivating agents and compound microbial fertilizers in soil could comprehensively regulate the number of ears, grains per ear and 1000-kernel weight of winter wheat plants, and improve the grain yields of winter wheat. However, variance analysis on soil remediation treatment and varieties showed that the increased grain yields in their interactions was mainly due to the increased ear numbers. Under CMF+GP treatment, the grain yield of Zhengmai 136 variety was the highest among all treatments, which was 7 317.17 kg·hm^-2 and 10 485.32 kg·hm^-2 in two consecutive 2020-2021 and 2021-2022 winter wheat growing seasons, respectively.

The application of compound microbial fertilizer and soil passivator could effectively reduce the available Cd content in the rhizosphere soil with weak alkaline and mild Cd pollution in northern Henan Province, and regulate the enrichment coefficient and transport coefficient of soil Cd in various organs of winter wheat plants. The combination treatment of compound microbial fertilizer and soil passivator with the same applied amounts was better than single treatment, which could also reduce the Cd content of winter wheat grains to the maximum extent, and significantly improve the yield of winter wheat varieties. In addition, the combination of planting modes combined with the low Cd accumulation and high yield variety Zhengmai 136 screened out, could achieve the high grain yields and safe production of winter wheat in the farmland with weak alkaline Cd pollution in northern Henan Province.