Environmental loss is primarily caused by soil, water, and nutrient loss, and runoff is associated with nutrient transport and sediment loss. Most existing studies have focused on one influencing factor, namely slope gradient or rainfall intensity, for slope erosion and nutrient loss, but the joint effects of the two factors have rarely been researched. In this context, the impact of slope gradients (0°, 5°, 10°, and 15°) and rainfall intensities (30, 40, 50, 60, 70, and 80 mm/h) on soil erosion and nutrient loss on the sloping fields of Miyun Reservoir were explored using the indoor artificial rainfall simulation testing system. Based on the results of the study, the variation of runoff coefficient with slope gradient was not noticeable for rainfall intensities 40 mm/h, the increased range of runoff coefficient doubled, and the increase was the fastest under 0° among the four slope gradients. The slope surface runoff depth and runoff rate showed positive correlations with the rainfall intensity (r = 0.875, p < 0.01) and a negative correlation with the slope gradient. In addition, the cumulative sediment yield was positively related to the slope gradient and rainfall intensity (r > 0.464, p < 0.05). Moreover, the slope surface runoff-associated and sediment-associated loss rates of total nitrogen (TN) rose as the rainfall intensity or slope gradient increased, and significant linear positive correlations were found between the runoff-associated TN loss rate (NLr) and the runoff intensity and between the sediment-associated NLr and the erosion intensity. In addition, there were positive linear correlations between slope runoff-associated or sediment-associated TN loss volumes and rainfall intensity, surface runoff, and sediment loss volumes, which were highly remarkable. The slope gradient had a significant positive correlation with the slope surface runoff-associated TN loss at 0.05 (r = 0.452) and a significant positive correlation with the sediment-associated TN loss at the level of 0.01 (r = 0.591). The rainfall intensity exhibited extremely positive correlations with the slope surface runoff-associated and sediment-associated TN loss at 0.01 (r = 0.717 and 0.629) Slope gradients have less effect on nitrogen loss on sloped fields than rainfall intensity, mainly because rainfall intensity affects runoff depth. Based on the findings of this study, Miyun Reservoir may be able to improve nitrogen loss prevention and control.

The purpose of this study was to clarify the effects of biochar on the diversity of bacteria and fungi in the rice root zone and to reveal the changes in soil microbial community structure in the root zone after biochar application to provide a scientific basis for the improvement of albic soil. Rice and corn stalk biochar were mixed with albic soil in a pot experiment. Soil samples were collected at the rice maturity stage, soil nutrients were determined, and genomic DNA was extracted. The library was established using polymerase chain reaction (PCR) amplification. The abundance, diversity index, and community structure of the soil bacterial 16SrRNA gene V3 + V4 region and the fungal internal transcribed spacer-1 (ITS1) region were analyzed using Illumina second-generation high-throughput sequencing technology on the MiSeq platform with related bioinformatics. The results revealed that the biochar increased the soil nutrient content of albic soil. The bacteria ACE indexes of treatments of rice straw biochar (SD) and corn straw biochar (SY) were increased by 3.10% and 2.06%, respectively, and the fungi ACE and Chao indices of SD were increased by 7.86% and 14.16%, respectively, compared to conventional control treatment with no biochar (SBCK). The numbers of bacterial and fungal operational taxonomic units (OUT) in SD and SY were increased, respectively, compared to that of SBCK. The relationship between soil bacteria and fungi in the biochar-treated groups was stronger than that in the SBCK. The bacterial and fungal populations were correlated with soil nutrients, which suggested that the impacts of biochar on the soil bacteria and fungi community were indirectly driven by alternation of soil nutrient characteristics. The addition of two types of biochar altered the soil microbial community structure and the effect of rice straw biochar treatment on SD was more pronounced. This study aimed to provide a reference and basic understanding for albic soil improvement by biochar, with good application prospects.

Biochar has demonstrated to have ability to improve soil properties and boost plant productivity. However, the underlying mechanisms by which dissolved organic matter (DOM) fluorescent components and microbial communities in black soil regions contribute to plant productivity remain uncertain. To address this gap, a long-term field experiment was conducted in Northeastern China’s black soil region, investigating how varying biochar application rates (0, 15.75, 31.50, and 47.25 t ha⁻¹) influence DOM fluorescence properties and the composition of soil microbial communities. Employing fluorescence excitation–emission matrix-parallel factor analysis (EEM-PARAFAC) and high-throughput sequencing, the research systematically analyzed how biochar amendments influence DOM composition, fluorescence properties, microbial diversity, and their interrelations. The findings demonstrated that biochar significantly modified DOM composition, increasing the proportions of protein-like and humic substances while enhancing its aromaticity and stability. A medium application rate (31.5 t ha⁻¹) notably improved alpha- and beta-diversity within the soil microbial community, optimized a co-occurrence network dominated by Proteobacteria and Acidobacteria, and facilitated key DOM transformations and nutrient cycling. In contrast, a high biochar application rate (47.25 t ha⁻¹) negatively impacted the stability of microbial communities. Structural equation modeling (SEM) revealed that biochar indirectly boosted crop yields by modulating DOM fluorescence and microbial community dynamics. The insights gained from this study provide practical guidance for optimizing biochar application rates, maximizing its benefits, and mitigating potential ecological risks in black soil systems. Graphical Abstract

Long-term application of nitrogen (N) fertilizer adversely degrades soil and decreases crop yield. Biochar amendment with N fertilizer not only can increase yield but also can improve the soil. A 3-year field experiment was conducted to determine the effect of biochar doses with N fertilizer on maize yield and soil N and water dynamics under border irrigation (BI) and drip irrigation (DI) methods. Treatments were 260 kg N ha⁻¹ without biochar addition and combined with low, medium, and high doses of biochar, namely, 15.5 t ha⁻¹, 30.7 t ha⁻¹, and 45.3 t ha⁻¹ (NB₀, NB₁, NB₂, and NB₃), respectively. The biochar doses and irrigation methods significantly (p < 0.05) increased maize growth and yield characteristics, irrigation water use efficiency (IWUE), and fertilizer N use efficiency (FNUE) and enhanced the soil properties. In the BI and DI method, the NB₁, NB₂, and NB₃ treatments increased yield by 4.96%–6.10%, 8.36%–9.85%, and 9.65%–11.41%, respectively, compared to NB₀. In terms of IWUE and FNUE, the non-biochar treatment had lower IWUE and FNUE compared to biochar combined with N fertilizer treatments under both BI and DI methods. In the BI method, the IWUE in NB₂ and NB₃ ranged from 3.36 to 3.43 kg kg⁻¹, and in DI, it was maximum, ranging from 5.70 to 5.94 kg kg⁻¹. Similarly, these medium and high doses of biochar increased the FNUE of maize. The FNUEs in NB₂ and NB₃ under BI ranged from 38.72 to 38.95 kg kg⁻¹ and from 38.89 to 39.58 kg kg⁻¹, while FNUEs of these same treatments under DI ranged from 48.26 to 49.58 kg kg⁻¹ and from 48.92 to 50.28 kg kg⁻¹. The effect of biochar was more obvious in DI as compared to the BI method because soil water content (SWC) and soil N concentrations (SNCs) were higher at rhizosphere soil layers under DI. Biochar improved SWC and SNC at 0–20 cm and 20–40 cm soil layers and decreased below 60-cm soil layers. In contrast, despite biochar-controlled SWC and SNCs, still, values of these parameters were higher in deeper soil layers. In the BI method, the SNCs were higher at 60–80 cm and 80–100 cm compared to the top and middle soil layers. Depth-wise results of SNC demonstrated that the biochar’s ability to store SNC was further enhanced in the DI method. Moreover, biochar increased soil organic matter (OM) and soil aggregate stability and maintained pH. The NB₀ treatment increased soil OM by 11.11%–14.60%, NB₂ by 14.29%–19.42%, and NB₃ by 21.98%–23.78% in both irrigation methods. This increased OM resulted in improved average soil aggregates stability by 2.45%–11.71% and 4.52%–14.66% in the BI and DI method, respectively. The results of our study revealed that combined application of N fertilizer with a medium dose of biochar under the DI method would be the best management practice, which will significantly increase crop yield, improve SWC, enrich SNC and OM, improve soil structure, and maintain pH.

Excessive, long-term chemical fertilizer application adversely affects soil quality and maize yield. The combined application of biochar with chemical fertilizer can increase maize yield and improve soil fertility. A four-year field experiment was conducted to determine soil physio-biochemical properties and maize yield under a soybean–maize rotation in the black soils of Northeast China. There were five treatments, including no fertilization (CK), fertilizer (NPK), fertilizer + biochar (15.75 t·hm⁻², BC₁), fertilizer + biochar (31.50 t·hm⁻², BC₂), and fertilizer + biochar (47.25 t·hm⁻², BC₃). Compared with CK, the number of macroaggregates and the average weight diameter of soil aggregates in BC₂ treatment increased significantly by 10.3% and 24.5%, respectively. The soil pH in the study area was 7.03, and it increased in all treatments except for BC₁. The highest pH of 7.17 was recorded in NPK and BC₂ treatments, which was around the optimal soil pH. In contrast to the CK and NPK treatments, the biochar application increased soil organic carbon (SOC) and total nitrogen (TN) content. The BC₂ treatment improved soil C/N and increased the copy number of soil bacteria by 25.6% compared to CK. The combined application of chemical fertilizer and biochar was better than NPK treatment alone, and improved soil mechanical composition and fine soil particle contents (powder and clay). Mixed biochar with chemical fertilizer application also significantly increased maize yield and the weight of 100 grains increased from 9.5% to 10.9% compared to CK. The maize yield of the three fertilizer and biochar treatments was higher than treatments with applied chemical fertilizer alone, in the order of BC₂ > BC₃ > BC₁ > NPK > CK (BC₂ treatment increased by 34.8%). Additionally, the maize yield was significantly and positively correlated with soil aggregates, organic carbon and total nitrogen (p < 0.05) as well as the 100-grain weight (p < 0.01). The application of 31.50 t·hm⁻² (BC₂ treatment) of biochar can enhance soil physicochemical properties and improve maize yield.

Biochar-based fertilizers are used to improve soil’s physiochemical and biological properties and increase fertilizer utilization rate. Therefore, a technological model of biochar-based fertilizers is essential for the reduced application. This study was conducted to determine the effects of the different levels of biochar-based fertilizer applications on soil and plant nutrient content, as well as maize yield. Biochar-based fertilizer increased the total N content of maize stem and kernel and the total P content of maize axis and kernel. Biochar-based fertilizer increased the total P but decreased the total K of maize plants while increasing the fertilizer’s partial productivity. Treatment B1 (600.00 kg hm⁻² of biochar-based fertilizer) increased the dry-matter weight of the maize at silking and filling stages by 1.60 and 15.83%. Treatment B1 increased the ear length, diameter, and plant height. Compared with BCK (600.00 kg hm⁻² of conventional fertilizer), the yield of B1 was increased by 9.23%, and the difference was significant (p < 0.05). Biochar-based fertilizer treatments B2–B5 (biochar-based fertilizer reduced by 5–20%) reduced maize yield, but there was no significant difference between their yield and BCK. This study aimed to provide a basic understanding and reference for maize fertilizer reduction with good application prospects.