Soil, which exhibits difference in nutrient contents and aggregate sizes, provides spatially distinct habitats for biota. Cover crops influence the compositions of soil organism communities, playing an indispensable role in regulation of underground food webs and ecosystem functions. However, the effect of cover crops on soil microbes and nematodes distribution within different aggregate sizes remains unknown. Thus, a field experiment in a kiwifruit orchard with cover crops was conducted to estimate the distribution of soil nematodes and bacteria with different soil aggregate sizes (mega-aggregate (>2 mm, LMA), macro-aggregate (0.25–2 mm, SMA), and micro-aggregate (<0.25 mm, MA)) and cover crop treatments (four cover crop species (CC) and no cover crop as control (CK)). The results showed that bacterial compositions varied with both aggregate sizes and cover crop treatments. The composition of bacterial community was significantly different between mega-aggregate and micro-aggregate, and bacterial community diversity was significantly higher in micro-aggregate compared with mega-aggregate. Moreover, cover crop treatment dramatically changed the compositions of bacterial communities. However, the nematode communities were mainly impacted by soil aggregate sizes. Larger aggregates (mega- and macro-aggregates) contained higher abundance of omnivores/predators and lower abundance of fungivores. In contrast to bacterial community, the richness of nematode community was lower in micro-aggregates compared with larger aggregates (mega- and macro-aggregates). Redundancy analysis (RDA) and structural equation model (SEM) showed soil organic carbon (SOC) was the main soil factor that directly and indirectly affected both bacterial and nematode communities. The investigations of both bacterial and nematode communities could provide a better understanding on carbon and nutrient cycling across aggregate size fractions.

Nitrogen is the principal mineral nutrient limiting maize yield formation and effective nitrogen management is thus key for maximizing yield. However, conventional urea releases nutrients rapidly and the supply of nutrients is often mismatched with crop demand, leading to early-stage nutrient loss and late-stage nitrogen deficiency. Therefore, reasonable nitrogen management is a key measure for increasing maize yield. This study aimed to evaluate the effects of different ratios of controlled-release fertilizer (CRF) and urea on changes in the accumulation, distribution, and translocation of dry matter across the entire growth period of maize to optimize nitrogen management, yield, and maize production efficiency. A two-year field experiment (2023–2024) was performed to test the effects of different CRF-N to urea-N ratios [1:0 (N10, controlled-release fertilizer), 3:7 (N37), 5:5 (N55), 7:3 (N73), and 0:1 (N01, conventional urea), no N (N0) as control] on dry matter accumulation, distribution, translocation and yield. The results showed that dry matter accumulation followed a typical sigmoidal (“S-shaped”) trajectory. The dry matter accumulation advantage of N73 (70% CRF) treatment was most significant after the V6 stage, and dry matter accumulation at R6 increased by 14.58% and 10.33% compared with that in N10 treatment in 2023 and 2024, respectively. With the progress of growth period, the distribution of dry matter among organs was changed, and N73 treatment effectively promoted dry matter allocation to the ear. Logistic equation fitting indicated that N73 treatment moderately delayed the time of the maximum dry matter accumulation rate ( T m a x ), sustained a relatively high maximum dry matter accumulation rate ( V m a x ), and extended the active growth period ( P ). In addition, N73 treatment increased both pre-anthesis dry matter remobilization (DMR) and post-anthesis assimilation (DMA), enhanced the contribution of dry matter accumulation to grain at post-anthesis (DMAC) and maize yield. In summary, a 7:3 CRF:urea application ratio optimizes maize dry matter accumulation and partitioning and coordinates pre-anthesis reserve remobilization with post-anthesis photosynthetic assimilation, and ultimately increased maize yield. Our findings have implications for optimizing nitrogen management, enhancing maize yield, and improving the efficiency of maize production. These results indicate that in the black soil region of Northeast China, a mixture of 70% controlled-release fertilizer and 30% urea is an effective strategy for promoting dry matter accumulation and transport, and for increasing yield of maize.