This study examined the planting density tolerance, grain yield improvement potential, and mechanisms of high-yielding spring maize varieties under increasing planting density and subsoiling. We planted two high-yielding spring maize varieties with a high or low tolerance to high planting densities (LM33 and XD20, respectively) at five different densities (D1: 60,000 plants ha⁻¹, D2: 75,000 plants ha⁻¹, D3: 90,000 plants ha⁻¹, D4: 105,000 plants ha⁻¹, and D5: 120,000 plants ha⁻¹) using two tillage methods (35-cm subsoiling and 15-cm traditional rotary tillage). The response characteristics used to compare the performance of the two maize varieties under different planting densities and tillage methods included root characteristics, canopy physiology, yield, and yield components. The results show that: (1) Under rotary tillage, with the increase of planting density from 75,000 plants ha⁻¹ to 90,000 plants ha⁻¹, yields of high-yielding spring maize varieties improved. However, when the planting densities were beyond 90,000 plants ha⁻¹, the yields stopped increase, or even decrease. Subsoiling increased the planting density by 15,000 plants ha⁻¹, enhanced the highest yield by 1080 kg ha⁻¹–1940 kg ha⁻¹, and raised the yield gain by 11.17–30.72%. (2) Under rotary tillage, the functional indexes of the roots and canopy of high-yielding spring maize decreased as planting density increased, and the largest reductions of root dry weight, leaf area index (LAI) of post-anthesis, light transmission percentage (LTP) of ear leaves, bottom leaves LTP, and dry matter accumulation all occurred between D2 and D4. The largest decline of high tolerance variety emerged between D3 and D5, and the extent was smaller than the low tolerance variety. (3) Compared with rotary tillage, subsoiling reduced the extent declines in root dry weight, root length, and root surface area; delayed the attenuation of LAI and the relative chlorophyll content (SPAD) determined in leaves; and improved the LTP of ear layers and bottom layer during the late growth stage. The post-anthesis populations dry matter accumulation of XD20 and LM33 increased by 7.07% and 13.18%, respectively. In addition, subsoiling significantly increased the number of kernels/spike and 1000-grain weight as the planting density increased. Meanwhile, the planting densities at which dry root weight, population LAI, ear leaf LTP, bottom leaf LTP, and dry matter accumulation arose the largest reductions was raised to 15,000 plants ha⁻¹. The effects of subsoiling in the high density-tolerant variety were more pronounced than the low density-tolerant variety.

Compound microbial agents are an important means to optimize soil quality and maintain soil microbial activity. When supplemented with microbial agents, straw returned to a field shows improved degradation efficiency and hence better nutrient release. However, due to the low temperature in the northern winter climate and the complex chemical composition of corn straw, the resultant low decomposition efficiency of straw returning to the field hinders the application of this process. In this study, the low-temperature-degradation microbial agent M44 of corn straw was used as the test material, and the effects of adding the pro-rot microbial agent on straw decomposition, nutrient release, enzyme activity, and the regulation of soil microorganisms were analyzed through an indoor pot straw degradation test. After 16 weeks of degradation under indoor pot conditions, the application of the microbial agent M44 promoted the shedding of the waxy layer on the surface of the straw, the average degradation efficiency of the straw increased by 8.9%, and the average nutrient-release rate of the straw carbon, nitrogen, phosphorus, and potassium increased by 6.7%, 12.8%, 7.4%, and 9.6%, respectively. The average enzyme activities of soil β-glucosidase (BG), β-xylosidase (BX), laccase (EC), acetyl glucosaminidase (NAG), and leucine aminopeptidase (LAP) increased by9.82, 4.13, 9.46, 2.73, and 5.55 [nmol/(g·h)], respectively, which promoted the degradation of methoxyl carbon and alkoxy carbon, increased the relative content of alkyl carbon, anomeric carbon, aromatic carbon, and carbonyl carbon, and decreased the O-alkyl C/alkyl C value by 2.52; the composition and structure of soil bacterial and fungal communities were significantly changed, and Pseudomonas, Stenotrophomonas, Microbacterium, Penicillium, and Gibberella were significantly enriched, which increased the overall microbial activity through the production of degrading enzymes such as cellulase, thereby promoting the rapid degradation of straw. The present results thus provide theoretical support for the efficient decomposition of corn stalks in cold and arid regions.

The increasing salinization of cultivated soil worldwide has led to a significant reduction in maize production. Using saline–alkaline-tolerant growth-promoting bacteria (PGPR) in the rhizosphere can significantly improve the saline tolerance of maize and ensure the stability of maize yields, which has become a global research hotspot. This study screened salt-tolerant microorganisms Klebsiella sp. (GF2) and Pseudomonas sp. (GF7) from saline soil to clarify the mechanism in improving the saline tolerance of maize. In this study, different application treatments (GF2, GF7, and GF2 + GF7) and no application (CK) were set up to explore the potential ecological relationships between the saline tolerance of maize seedlings, soil characteristics, and microorganisms. The results showed that co-occurrence network and Zi-Pi analysis identified Klebsiella and Pseudomonas as core microbial communities in the rhizosphere soil of maize seedlings grown in saline soil. The deterministic process of microbial assembly mainly controlled the bacterial community, whereas bacteria and fungi were governed by random processes. The application of saline–alkaline-resistant PGPR under saline stress significantly promoted maize seedling growth, increased the activity of soil growth-promoting enzymes, and enhanced total nitrogen, soil organic carbon, and microbial carbon and nitrogen contents. Additionally, it reduced soil salt and alkali ion concentrations [electrical conductivity (EC) and exchangeable Na⁺]. Among them, GF2 + GF7 treatment had the best effect, indicating that saline–alkaline-tolerant PGPR could directly or indirectly improve the saline tolerance of maize seedlings by improving the rhizosphere soil ecological environment. EC was the determining factor to promote maize seedling growth under saline–alkaline stress (5.56%; p < 0.01). The results provided an important theoretical reference that deciphers the role of soil factors and microecology in enhancing the saline tolerance of maize.

Introduction: Straw return has gained attention for its potential to improve soil quality and crop yields, particularly in semi-arid regions like the Tumu Chuan Plain Irrigation Area. Soil bacteria play a crucial role in regulating soil biological processes, and understanding how straw return affects bacterial populations can guide better agricultural management practices.Methods: We investigated the impact of continuous straw return on soil bacterial communities using 16S rRNA gene sequencing. Four treatments were applied: Farmers’ shallow rotation (CK), straw incorporated with deep tillage (DPR), straw incorporated with subsoiling (SSR), and no-tillage mulching straw return (NTR). Bacterial community structure, metabolic pathways, and assembly mechanisms were analyzed using Bugbase and PICRUSt2 for phenotypic and metabolic pathway predictions.Results: The study found that straw return practices significantly altered the relative abundance and life history strategies of bacterial phyla, mainly influenced by soil organic matter (SOM) and enzyme activity. The K-strategist to r-strategist ratio was highest in CK (2.06) and lowest in SSR (1.89). DPR and NTR treatments significantly changed bacterial community structure compared to CK (p < 0.05), resembling SSR. Predictions showed that DPR and NTR enhanced carbohydrate and amino acid metabolism and promoted more stable bacterial networks, with homogenous selection and drift effects. Bacterial aggregation in all treatments was driven by random processes, with varying aggregation levels: CK (20%), DPR (38.6%), SSR (16.5%), and NTR (30.7%).Discussion: The study demonstrates that continuous straw return practices significantly impact soil bacterial communities. DPR and NTR notably improved microbial diversity, bacterial cooperation, and ecosystem stability. These findings provide valuable insights for sustainable agricultural practices in semi-arid regions, enhancing soil microbial ecology and soil health through strategic straw return.

To address the bottleneck problem of slow decomposition of returned maize straw under low-temperature constraints in the cold and arid regions of northern China, this study systematically explored the microbial decomposition-promoting mechanism of microbial inoculant M44 combined with three straw returning methods: deep plowing (DPR), deep scarification and mixing (SSR), and no-tillage mulching (NTR), by integrating field tillage and in-situ micro-zone degradation experiments. The results showed that different straw returning methods combined with inoculant M44 could effectively overcome low-temperature limitations, significantly increasing the straw degradation rate by 2.33–9.81 percentage points and shortening the half-life by 20.7–62.8 d. The core mechanism was that the “tillage-inoculant” interaction regulated the soil microenvironment, directionally shaped and enriched key functional microbial taxa with degradation ability (such as Pseudoxanthomonas , Devosia , Streptomyces , Pseudomonas , etc.) and their key ASVs (such as ASV6, ASV12, ASV412, ASV1546, etc.), reshaped the soil bacterial community structure, and synergistically activated the soil extracellular enzyme system (such as β-glucosidase, β-xylosidase, etc., with the comprehensive enzyme index increased by 0.74–1.06), thereby synergistically driving the rapid degradation of returned straw. The PLS-PM model further clarified that there were differences in the pathways driven by inoculant M44 for straw degradation under different returning methods. In the DPR and SSR treatments, bacterial community composition was the most important direct driving force for degradation, and key ASVs indirectly affected the degradation process by regulating bacterial composition and enzyme activity, while in the NTR treatment, extracellular enzyme activity became the core driving force for degradation, whose activity was directly driven by bacterial composition and diversity. This study revealed the hierarchical interaction driving mechanism of “key microorganisms—bacterial community structure—extracellular enzyme activity—straw degradation” at the field scale, providing an important scientific basis for optimizing the “tillage-inoculant” synergistic technology for straw resource utilization in cold and arid regions.