Excessive nitrogen (N) application rates and serious over-exploitation of groundwater under farmer practice threatens the sustainable use of resources in the North China Plain (NCP). Crop canopy structure affects light distribution between leaves, which is important to determine crop growth. A field experiment conducted from October 2016 to June 2019 in the NCP was designed to examine whether optimum water and nitrogen management could optimize canopy characteristics to improve yield and resource use efficiency. Field treatments included: (1) an example of local farming practices, which include the addition of 330 kg N ha⁻¹ and irrigated twice (FP), (2) a reduced N rate of 270 kg N ha⁻¹ and irrigated twice (T1), (3) a reduced rate of N rate of 210 kg N ha⁻¹ and irrigated once (T2), and (4) no N applied (0 kg N ha⁻¹) and irrigated once (T3). Results showed that the highest yield was in T1 treatment during 3 years’ winter wheat growing seasons. Water use efficiency (WUE), N use efficiency (NUtE), and N partial factor productivity (PFP_N) were significantly higher in T2 treatment than in FP, and the three-year average yield was 9.4% higher than that at FP. Optimum crop management practice (T1 and T2) improved canopy structure characteristics, with less relative photosynthetically active photon flux density (PPFD) penetrated of canopy and higher population uniformity as well as leaf area index, to coordinate the distribution of light within the canopy and maximize canopy light interception, resulting in higher yield and resource use efficiency. Leaf area index (LAI) and specific leaf area (SLA) were closely correlated with grain yield and WUE, while PPFD penetrated of canopy was negatively and significantly correlated with grain yield and WUE. The results indicate that canopy structure characteristics, especially PPFD and population uniformity are good indicators of yield and resource use efficiency.

Sugar beet production is threatened by beetroot rot, which can be triggered by consecutive monoculture. Previous studies have shown the beneficial function of microbes affiliated with different plant compartments in inhibiting various plant pathogens. However, whether sugar beet root can recruit particular microbes at the risk of beet rot is still unclear. Therefore, this study explored the composition and community structure of bacteria and fungi of the different compartments (endosphere root, rhizosphere, bulk soil) under two farming modes (monoculture and rotation). Our result showed that the farming mode significantly affected the community structure of bacteria and fungi in bulk soil. In the rhizosphere, the community structures of bacteria between the two varieties were similar under rotation mode, and markedly different under monoculture mode. The bacterial and fungal diversity in the rhizosphere and endophytic root of the rot-suppressive variety was higher than in the rot-conducive variety. Under monoculture mode, the beneficial microbes as biomarkers were enriched in the rot-resistant variety, e.g., operational taxonomic units (OTUs) affiliated to the genus of Sordariomycetes, Cordycipitaceae, Lecanicillium, Plectosphaerellaceae, S085, Pedosphaeraceae in the rhizosphere and the genus of Actinobacteria, and Pseudonocardia, Exobasidiomycetes in the endophytic root, while for the rot-conducive variety, OTUs affiliated to the genus of Chitinophagaceae, Flavisolibacter in the rhizosphere and the Novosphingobium, Sphingobacterium, Tilletiopsis_washingtonensis, and Flavobacterium in the endophytic root. The network analysis showed that OTUs affiliated to the order of Saccharimonadales, Anaerolineae, the family of Saprospiraceae, the genus of Subgroup_10 (belonging to the family of Thermoanaerobaculaceae), Lysobacter, and AKYG587 were the keystone taxa in the rot-suppressive variety, while both beneficial and harmful microbes in the rot-conducive variety, such as Pedobacter, Ferruginibacter, and P3OB-42, were present. The variation in soil pH was shown to be the critical contributor to the microbial difference. In summary, the farming mode is critical in shaping bulk soil microbial structure by changing soil pH. Under monoculture mode, the rot-suppressive variety has more microbial diversity in both the rhizosphere and endophytic root, and enriched different beneficial microbes relative to the rot-conducive variety; the underlying mechanisms and associations of critical microbes are worth further investigation.

The application of compost to soil is a common fertilization practice for improving soil quality and crop growth. The isotopic labeling technique is mostly used to investigate the contribution of compost N to crop uptake. However, compost N includes various N fractions and labeling dissimilarity, which may cause bias when calculating the compost N contribution to plants. Therefore, the labeling dynamics of different N fractions in compost and the homogenous labeling time point should be clarified. Given the ¹⁵N-labeling in chemical fertilizer and the carbon source, i.e., glucose, the compost N pools were divided into active N (mineral N, soluble organic N [SON], microbial biomass N [MBN]), stable N (hot-water extractable organic N [HWDON]), and recalcitrant N. The atom percentage excess (APE) of different N in compost notably varied at the beginning of incubation, ranging from 0–3.7%. After the addition of glucose, biological N immobilization was promoted (13.7% and 28.8% for MBN and HWDON, respectively) and promoted the transformation among available N pools. Adding distinct doses of glucose at three stages to ¹⁵N-labeled compost resulted in diverse microbial responses, thereby redistributing exogenous N in each fraction (¹⁵NH₄⁺-N went into SO¹⁵N from day 15 to day 30 and increased by 5.1%; SO¹⁵N entered MB¹⁵N and HWDO¹⁵N during day 30 to day 45 and increased by 5.7% and 5.2%, respectively). On day 45, homogeneous ¹⁵N-labeled compost was achieved, which was 2.4% for ¹⁵N APE for all N fractions. Overall, the quantitative data for the transformation of N fractions in compost at distinct stages provides a scientific basis for compost labeling trials, in order to identify the time point at which compost N-labeling is homogeneous, which is necessary and meaningful to reduce the bias of the contribution rate of compost-N to plants.