Foxtail millet is an important cereal crop in the North China Plain. However, excessive nitrogen fertilizer application over the years has led to declining yield and soil quality. This study investigated nutrient management strategies for foxtail millet based on crop yield levels and soil nutrient availability. In a field where targeted fertilization was conducted over six seasons, nitrogen fertilization effects and the dynamics of soil-available nitrogen were monitored continuously for two consecutive years (2022–2023) across five different foxtail millet varieties with varying yield levels. The study aimed to determine the optimal nitrogen application rate for achieving a high yield of foxtail millet, the minimum soil nitrate threshold required to maintain soil fertility, and the effective nitrogen application rate range for sustaining soil-available nitrate levels. Results showed that fertilization significantly affected dry matter weight during flowering, while variety affected dry matter weight at maturity. The average nitrogen application rate for achieving high yield across all five millet varieties was 141.3 kg·ha⁻¹. Specifically, the average nitrogen application rate of nitrogen-efficient varieties achieving high yield (5607.32–5637.19 kg·ha⁻¹) was 151.5 kg·ha⁻¹, while the average nitrogen application rate of nitrogen-inefficient varieties achieving high yield (4749.77–4847.74 kg·ha⁻¹) was 134.5 kg·ha⁻¹. Soil NH₄⁺-N and NO₃⁻-N content increased when nitrogen application rate exceeded 360 kg·ha⁻¹, posing environmental risks. To achieve high yield, soil nitrate levels would be maintained at an average of 17.23 mg·kg⁻¹ (before sowing) and 9.75 mg·kg⁻¹ (at maturity). A relationship between soil nitrate and nitrogen application rate was established: y = 867.5 − 50z (where y represents the optimal nitrogen application rate for high yield (kg·ha⁻¹), and z represents soil NO₃⁻-N content in the 0–20 cm layer before sowing, ranging from 10.0 to 17.35 mg·kg⁻¹), which provided a practical method for nitrogen fertilization to achieve high yield of foxtail millet. In this study, the fertilization strategy was optimized according to soil nutrient level and yield targets, and the nitrogen application rate was controlled within 360 kg·ha⁻¹ based on the soil nitrate nitrogen content, which will be instructive for reducing fertilizer use, maximizing fertilizer efficiency, and increasing yield.

The millet, an important coarse grain crop, exhibits drought resistance, water conservation efficiency, and adaptability to poor soil conditions. Although

Background: Drought is one of the most severe and prevalent abiotic stresses affecting crop production. Foxtail millet ( Setaria italica ), an important cereal crop in the Poaceae family, is considered an ideal crop for future sustainable agriculture due to its remarkable drought tolerance, water-use efficiency (WUE), and strong adaptability to poor soils. The booting stage is widely acknowledged as a pivotal developmental phase in foxtail millet, and this consensus has been well established in existing research. However, the molecular mechanisms underlying the drought response of foxtail millet during this critical stage remain poorly elucidated. In the present study, we employed an integrated approach combining transcriptomic and metabolomic sequencing to identify the core regulatory mechanisms and key genes governing the drought stress response in foxtail millet at the booting stage. Results: In this study, phenotypic variations, gene expression profiles, and metabolite accumulation patterns in foxtail millet were determined following drought treatments at different growth stages. Among these stages, drought stress imposed at the booting stage resulted in the most severe yield reduction of 34.94%, accompanied by the identification of 566 differentially expressed genes (DEGs) — the highest number across all tested stages. These findings indicated that the booting stage was the most vulnerable period to drought stress during foxtail millet growth. Furthermore, analyses of photosynthetic parameters and yield-related traits revealed that drought stress at the booting stage significantly inhibited photosynthetic capacity, which may represent a critical factor contributing to the yield decline observed in foxtail millet subjected to drought stress during the booting stage. Multi-omics integration analysis identified three core responsive pathways: phenylpropanoid biosynthesis, photosynthetic carbon fixation, and glyoxylate and dicarboxylate metabolism. Based on these findings, we constructed a drought resistance regulatory network model for the booting stage, revealing significant expression changes GAPA , ALDO , tktA , glpx , PRK , RPE , rbcS , maeB , GLUL , and gcvT . At the metabolic level, we observed significant accumulation of metabolites such as sinapyl alcohol, aconitic acid, citric acid, isocitric acid, and mesaconic acid, while the contents of methyl isoeugenol, eugenol, p -coumaric acid, chlorogenic acid, sedoheptulose, aspartic acid, and malic acid were markedly reduced. Most notably, this study revealed that downregulation of gcvT expression may restrict ammonia (NH ₃ ) supply, thereby activating the methanesulfonate synthesis pathway as an alternative nitrogen (N) source. This discovery provided novel insights into N metabolic remodeling under drought stress in plants. Conclusions: This study laid the foundation for preliminary exploration of the molecular mechanisms underlying drought stress response during the booting stage in foxtail millet. Furthermore, these findings had identified valuable key candidate genes that may contribute to the breeding of high-yield and drought-resistant foxtail millet varieties.

Foxtail millet (Setaria italica (L.) P. Beauv.) is an important traditional cereal crop in dryland ecological agriculture in China and is widely grown in India, the United States, and Nigeria. It is of significance to understand the variety–location–fertilizer (V–L–F) interaction for highly efficient production. Therefore, a two-year field experiment was conducted with six varieties in five locations, and data were analyzed by combined ANOVA analysis, redundancy analysis (RDA), and additive main multiplicative interaction (AMMI). The results showed that the mean sum of squares was significantly different among years, locations, varieties, fertilizations, and their interactions, except for Y–V and V–F interactions. The contributions of various factors to yield variation varied, location was the largest contributor (38.7%), followed by year (33.6%), and variety and fertilizer contributed 7.1% and 3.2%, respectively. JI25 was widely adapted, and its yield was stable and higher than that of others over diverse environments in two years. The RDA results showed that two principal components explained more than 66.1% of the yield variance, while more than 63.0% of the variances were clustered in the first factor. Excessive single rainfall or total rainfall and air temperature (especially minimum temperature) were significantly associated with the millet yield. The results offered an important reference for variety layout, natural resource potential mining, and formulation of efficient green cultural practices.