Increasing maize planting density is considered as a potential strategy for enhancing grain yield in Northeast China; however, its yield-enhancing effects and underlying regulatory mechanisms remain inadequately characterized. Based on 508 paired observations from 42 publications, this meta-analysis quantified the effects of increased planting density on yield components and elucidated the regulatory roles of environmental and agronomic factors. Results demonstrated that increased density intensified plant competition, raising grains per ear by 43.7% and 100-kernel weight by 6.7%. The optimal regional planting density was determined to be 89,622.6 plants ha⁻¹, achieving a peak yield of 12,143 kg ha⁻¹—significantly exceeding current conventional densities (49,000–65,000 plants ha⁻¹) and highlighting substantial yield potential. Although nitrogen (N) management did not alter peak yield levels, it significantly increased the optimal density threshold (reaching 99,600 plants ha⁻¹ under high N). Among environmental factors, mean annual precipitation (MAP) was the primary constraint: yield responses to increased density were negligible in arid regions (20 g kg⁻¹) and optimal bulk density (BD) (1.25–1.40 g cm⁻³) synergistically enhanced optimal density and peak yield. This study confirms the substantial, yet context-dependent, yield potential of increasing planting density in Northeast China, providing a science-based framework for region-specific optimization.

Water and fertilizer are the two indispensable elements in agriculture. The rational use of soil water and fertilizer can not only improve crop yield and quality rate, but also alleviate land pollution and water shortage. Water and fertilizer management in Chinese cabbage (Brassica rapa spp. pekinensis) involves in improper irrigation and fertilization. This experiment was conducted to explore he shoot growth, root traits, nutrient contents, soil microbial population and soil enzyme activities of Chinese cabbage in response to different irrigation and organic fertilizer application rates. The experiment consisted of three irrigation levels (A1-A3: 90%-70% ± 5% of field water holding capacity), five organic fertilizer application rates (B1-B5: 10%-50% cattle manure with nitrogen replacement) and CK treatments (CK1: regular fertilizer, CK2: 100% cattle manure with nitrogen replacement). The results showed that irrigation rate A2 was the better irrigation rate. At this irrigation rate B2 treatment significantly increased shoot fresh weight by 22.65% and 31.09% compared to CK1 and CK2, respectively. Organic fertilizer application increased the SPAD value of Chinese cabbage, but the trend was not consistent under different irrigation and organic fertilizer levels. All irrigation levels showed more soil available K content in CK2. Compared to other treatments, CK2 was enhanced by 20.70%-317.42% under A1, 7.34%-235.68% under A2, and 28.16%-188.42% under A3 irrigation. Adequate irrigation is prerequisite to enhance root fresh weight, while lower irrigation and organic fertilizer helps to promote root length and root surface area. Soil enzyme activity and bacteria were significantly higher in A1 and A2 treatments than A3, while irrigation had no significant differences on soil actinomycetes and fungi. Under A1 irrigation, the B4 treatment had higher acid phosphatase and sucrase activities, 11.31%-22.46% and 4.30%-63.50%, respectively, compared to other treatments. In conclusion, the effect of organic fertilizer on soil enzyme activity and soil microbial population varied according to the irrigation levels, but generally organic fertilizer were beneficial to boost up the soil enzyme activity and soil microbial population.

Phosphorus (P) is vital for the growth of crops, and its absorption efficiency is closely linked to the traits of the plants. Further research is needed to understand how vegetable crops adjust to changes in P availability and how their root morphology and physiology are affected by high P levels in the shoots. In this study, eight Chinese cabbage (Brassica rapa pekinensis) genotypes were grown in a culture room under 0, 25, 50, 100, 150, 300, 600, 900, and 1200 mg kg⁻¹ concentrations of P to evaluate root responses in order to define various adaptive strategies in relation to P acquisition. We selected high-PE and low-PE Chinese cabbage in order to identify how different P efficiency groups responded to P supply and shoot P concentration. P supply level and shoot P concentration significantly affected growth. With the increase in the P supply level, the growth variable characteristics of Chinese cabbage first increased and then decreased or increased first and then stabilized. But it was found that P300 was the most suitable level for Chinese cabbage growth. At the same P supply level, high-PE cabbages had higher shoot dry weight and P absorption capacity, stronger root traits, and higher plasticity as compared to low-PE cabbages. The optimal shoot P concentration is 2.1 mg g⁻¹ and 1.7 mg g⁻¹ for low- and high-PE cabbages, respectively. The root morphological traits performed greatly when the shoot P concentration was at the optimal concentration. The low-PE cabbages had greater shoot growth traits, and high-PE cabbages had higher root dry weight and P absorption. This study offers valuable insights to improve P management by analyzing the relationships between soil P dynamics and root processes in the cultivation of Chinese cabbage.

The Huang-Huai-Hai Plain, one of China’s most important grain-producing regions dominated by winter wheat–summer maize rotation systems, has ex