Little has been reported on the effects of long-term fertilization on rhizosphere soil microbial diversity. Here, we investigated the effects of long-term continuous nitrogen (N) fertilization on the diversity and composition of soil bacteria using data from a 10-year field experiment with five N application rates (0, 120, 180, 240, and 360 kg N hm^–2). The results revealed varying degrees of reduction in the numbers of bacterial operational taxonomic units (OTUs) in response to the different N application rates. The highest wheat yield and number of proprietary bacterial OTUs were found in the N input of 180 kg N hm^–2. In terms of average relative richness, the top seven phyla of soil bacteria in the rhizosphere of wheat after long-term nitrogen application were Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Gemmatimonadetes, and Patescibacteria. Among these, Proteobacteria and Gemmatimonadetes were found to be unaffected by the nitrogen fertilizer and soil environmental factors (pH, C/N ratio, and NO₃^– concentration), whereas Acidobacteria and Actinobacteria showed significant positive and negative correlations, respectively, with soil pH. The richness of Actinobacteria significantly increased in the N₁₈₀ treatment. Patescibacteria and Bacteroidetes showed significant positive correlations with soil NO₃^– and wheat yield, and the average relative richness of these two phyla was high under long-term application of the N₁₈₀ treatment. These findings indicate that the relative richness of Patescibacteria and Bacteroidetes can affect wheat yield. In conclusion, the results of our 10-year field experiments clearly show that long-term N fertilization can significantly affect most of the dominant soil bacterial species via changing the soil pH. The richness of Actinobacteria can serve as an indicator of a decreased soil pH caused by long-term N fertilization.

The contributions of the different leaf layers to maize yields identified as middle leaf > lower leaf > upper leaf, where the vertical photosynthetically active radiation (PAR) in the canopy gradually decreases. We hypothesized that the allocation of more PAR and nitrogen (N) to the highest contributing leaves will would be beneficial for higher yields and N use efficiencies. The N application rate and plant density effectively regulated the canopy light and N distribution. We evaluated the interactive effects of N rate and plant density on the agronomic and ecophysiological characteristics of leaves at different orientations in a 2019/2020 field experiment. In this study, an N application rate of 180 kg ha^–1 coupled with a plant density of 82,500 plants ha^–1 achieved the highest yield and N recovery efficiency (NRE). In contrast to the traditional farming practices in northern China, the density was increased and N rate was reduced. Densification from 52,500 to 82,500 plants ha^–1 increased the population leaf area index (LAI) by 37.1% and total photosynthetically active radiation (TPAR) by 29.2%; however, excessive density (from 82,500 to 97,500 plants ha^–1) drastically reduced the proportion of TPAR by 28.0% in the lower leaves. With increased density, the leaf areas and angles of the upper leaves decreased much more than those of the other leaves, which allowed the middle and lower leaves to access more light, which manifested a smaller extinction coefficient for light (K_L). A high yield (>1,000 kg ha^–1) of maize could be achieved simultaneously with higher NRE; however, it was negatively correlated with internal N use efficiency (IE_N). Higher N concentrations and lower total performance index (PI_total) in the lower leaves may be an important rationale for the reduction of IE_N in high-yielding maize. Additionally, decreased N rate without yield reduction under higher densities was primarily attributed to the more uniform vertical N distribution [a smaller extinction coefficient for N (K_N)]. These results suggest that the N fertilizer rate can be moderately reduced without a reduction in maize yield under high plant densities in northern China.

The performance of fertilizers may differ significantly in different soils. Here, we quantify effects of various phosphorus (P) fertilizers on maize yield and P uptake in soils with different pH values, using a pot experiment. Five P fertilizers were used; monoammonium phosphate (MAP), diammonium phosphate (DAP), calcium superphosphate (CSP), calcium magnesium phosphate (CMP) and, ammonium polyphosphate (APP). Two soils were neutral fluvo-aquic soil (pH 7.2) and acidic yellow cinnamon soil (pH 5.0). Generally, acidic soil restricted the root activity, dry matter accumulation, P uptake, and yield of maize. The effects of P fertilizers were inconsistent in the different soils. In neutral soil, the effects were the highest for DAP and lowest for CMP. However, in acidic soil they were highest for CMP, followed by DAP, and lowest for MAP. In neutral soil, DAP treatment showed higher P uptake efficiency (PUpE) and partial factor productivity (PPFP), while CMP treatment showed higher P harvest index (PHI) and utilization efficiency PUtE. In acidic soil, the PUpE and PPFP of CMP and DAP treatments were higher than in other treatments. Therefore, choosing the right P fertilizer based on soil acidity can significantly improve maize yield, P uptake, and P utilization to optimize P management.

Inadequate water and nitrogen (N) supplies can limit the productivity of maize. Climate change will likely increase drought in many regions on a global scale. The determination of N fertilizer rates under field drought conditions will be critical toward the reduction of agricultural risk. For this study, drought-resistant/sensitive cultivars were selected as experimental samples. Our results revealed that drought stress reduced the relative water content (RWC) of leaves, which resulted in leaf curling, while decreasing photosynthesis levels and N accumulation. In contrast to those without N treatments, the application of N significantly increased grain yields by 26.8% during the wet year but increased only by 5.4% during the dry year. Under the same N levels, the reduction in yield caused by drought increased with the increased application of N. This was because the application of the N fertilizer translated to increase the leaf area and transpiration, exacerbated the soil water loss and induced a leaf curling state in maize, which had deleterious effects on photosynthesis and N absorption. During the dry year, the yields of drought-sensitive cultivars were even less than those without the application of N. Compared with those of drought-sensitive cultivars, the RWCs of drought-resistant cultivars decreased more rapidly, and they entered the state of leaf curling earlier. Thus, N fertilizer inputs should be reduced, and the extent of N fertilization for drought-sensitive cultivars should be reduced even further.

The stay-green leaf phenotype is typically associated with increased yields and improved stress resistance in maize breeding, due to higher nitrogen (N) nutrient levels that prolong greenness. The application of N fertilizer can regulate the N status of plants, and furthermore, impact the photosynthetic rates of leaves at the productive stage; however, N deficiencies and N excesses will reduce maize yields. Consequently, it is necessary to develop N fertilizer management strategies for different types of stay-green maize. For this study, the senescent cultivar Lianchuang 808 (LC808), moderate-stay-green cultivar Zhengdan 958 (ZD958), and over stay-green cultivar Denghai 685 (DH685) were selected as experimental models. Our results revealed that yields of ZD958 were slightly higher than DH685 and notably improved over than LC808. Compared with a non-stay-green cultivar LC808, ZD958 and DH685 still maintained higher chlorophyll contents and cell activities following the silking stage, while efficiently slowing the senescence rate. The supply of N fertilizer significantly prolonged leaf greenness and delayed senescence for ZD958 and DH685; however, the effect was not obvious for LC808. The stem remobilization efficiency of N was higher in the moderate-stay-green cultivar ZD958, in contrast to LC808, while the transfer of leaf N was lower than LC808, which guaranteed high leaf N levels, and that sufficient N was transferred to grains in ZD958. To obtain the highest yields, the optimal N fertilizer rates were 228.1 kg hm⁻² for LC0808, 180 kg hm⁻² for ZD958, and 203.8 kg hm⁻² for DH685. In future, the selection of stay-green type crops might serve as an important agricultural strategy to reduce the quantity of N fertilizer and increase N efficiency.

Background: Lodging is a major factor contributing to yield loss and constraining the mechanical harvesting of wheat crops. Genetic improvement through breeding effectively reduced the lodging and improved the grain yield, however, the physiological mechanisms involved in providing resistance to lodging are different in the breeding stage and are not clearly understood. The purpose of this study was to compare the differences in the lodging resistance (LR) of the wheat varieties released during the different decades and to explore the effect of the application of nitrogen (N) fertilizer on the plasticity of LR. Results: A field study was conducted during the cultivation seasons of 2019–2020 and 2020–2021, in soil supplemented with three N levels: N₀ (0 kg ha^–1), N₁₈₀ (200 kg ha^–1), and N₃₆₀ (360 kg ha^–1) using eight varieties of wheat released for commercial cultivation from 1950 to date. The results obtained showed that genetic improvement had significantly enhanced the LR and grain yield in wheat. In the first breeding stage (from 1950 to 1980s) the lodging resistant index increased by 15.0%, which was primarily attributed to a reduced plant height and increased contents of cellulose, Si, and Zn. In the second breeding stage (the 1990s–2020s) it increased by 172.8%, which was mainly attributed to an increase in the stem diameter, wall thickness, and the contents of K, Ca, Fe, Mn, and Cu. The application of N fertilizer improved the grain yield but reduced the LR in wheat. This was mainly due to an increase in plant height resulting in an elevation of the plant center of gravity, a decrease in the contents of cellulose, and a reduction in the area of large-sized vascular bundles in the stems, even if N supplementation increased the concentrations of K, Ca, and Si. Conclusion: Although breeding strategies improved the stem strength, the trade-off between the grain yield and LR was more significantly influenced by the addition of N. Overcoming this peculiar situation will serve as a breakthrough in improving the seed yield in wheat crops in the future.