To clarify the effects of co-application of rice-straw biochar and different chemical fertilizer doses on paddy soil properties and japonica rice production in Northeast China, a located-field experiment was adopted for 5 years. The treatments included fertilization (F, no biochar, control) and rice-straw biochar (7.5 t ha⁻¹) combined with different chemical fertilizer doses (100, 80, and 60% that of F) set as CF, CF1, and CF2, respectively. The results showed that the co-application of biochar and chemical fertilizers after 5 years reduced soil bulk density, increased soil total and capillary porosity, changed the soil solid–liquid–gas ratio (increased the liquid and air ratios and decreased the solid ratio), and increased soil macroaggregates (>0.25 mm) and aggregate stability, which enhanced the soil’s physical properties. Furthermore, the co-application improved soil pH and soil enzyme activity (urease, sucrase, and catalase) and had a significant effect on promoting SOM. The soil total N, P, and K of CF and CF1, were 23.48, %, 47.28%, and 26.59% and 9.47%, 43.98%, and 27.87% higher than those of the control, respectively. The soil available nutrients (N, P, and K) increased in the co-application treatment, shown as the nitrogen was promoted higher in the early growth of rice, while phosphorus and potassium were exhibited greater in the late growth. With the soil amendment, the co-application increased the rice plant height and dry matter accumulation, and the CF and CF1 increased yields by 5.78 and 2.41%, respectively, by increasing the rice effective panicles, grains per panicle, and seed-setting rate. The co-application of biochar and chemical fertilizers could significantly amend soil properties and reduce chemical fertilizer use to ensure rice–grain output, which has an important significance for enhancing sustainable soil and crop productivity.

Continuous cropping obstacles limit soybean production. Biochar is beneficial for soybean growth, but it is unclear whether biochar performs a sustainable role in continuous cropping. To further explore the effects of biochar on soil properties and soybean growth, a ceramic Wagner pot-simulated field experiment was conducted with biochar at different doses (12, 24, and 48 t·ha⁻¹) over a period of 3 years, no fertilizer, no biochar (CK) and fertilizer (F)treatments were used for comparison. The results showed that biochar significantly reduced soil bulk and improved the rhizosphere soil pH, available nutrients (N, K), and total nutrients (C, N, P, and K) compared with CK and F. Moreover, the soybean root length, surface area, volume, and exudates increased with biochar amendment. In particular, biochar significantly increased the nodule number, dry weight, and nitrogenase activity of soybean. Furthermore, biochar promoted soybean growth and increased soybean yield. In general, we found that the soybean yield increased with biochar and that biochar had a positive, sustainable effect on soil properties and soybean root growth, providing a new cultivation measure for soil health and soybean production in continuous cropping, which is very important for increasing soybean productivity to break the limitations of soybean traditional continuous cultivation.

Dissolved organic matter (DOM) is a key factor in soil carbon sequestration and greenhouse gas emissions (GHGs). However, the molecular-level change of soil DOM and the implications of GHGs under different long-term fertilization regimes (LFRs) remain elusive. Therefore, we conducted a long-term field experiment with an unfertilized control (CK) and fertilization regimes (chemical fertilizer (F), straw (ST), and biochar (BC)), We employed the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the molecular-level change of soil DOM. Our findings revealed that LFR, especially BC, increased the quantity, molecular weight, double bond equivalence, aromaticity index and molecular formula complexity of DOM. The F increased the molecular diversity and functional complexity of DOM and decreased the Gibbs free energy (ΔG Cox°), whereas BC and ST decreased the molecular diversity because of greater accumulation of lignin-like compounds and increased the ΔG Cox°. The specific molecular evolution and fractionation analysis indicated that LFR increased the aggregation of specific molecules: BC stimulated high O/C and molecularly stable lignin compounds accumulation, whereas ST promoted lignin and unsaturated hydrocarbon compound accumulation. Simultaneously, the F increased GHGs (CH₄ and N₂O), whereas the BC significantly decreased the CH₄ emissions and the global warming potential. Furthermore, the correlation analysis revealed that the quantity and quality of DOM were closely correlated with GHGs, the quantity of DOM and unstable compounds increased the CH₄ and N₂O emissions, and the relative abundance of persistent compounds decreased CH₄ emissions. These findings elucidate the potential mechanisms by which LFR, especially BC, regulates DOM characteristics and subsequently influences GHGs, which contributes to the development of more effective soil management strategies for mitigating GHGs while maintaining soil health and productivity. Graphical Abstract