Yalin Gao

Biochar has been widely investigated as an amendment for mitigating soil desiccation cracking. However, variation in its effects across soil textures, application rates, and long-term drying–wetting (DW) cycles remains insufficiently resolved. Based on a global dataset comprising 278 paired observations from 44 peer-reviewed articles, this study employed a random-effects meta-analysis with article-clustered robust variance estimation to quantify the impacts of biochar on soil crack intensity factor (CIF), crack length density, and mean crack width. The pooled estimates indicated average reductions of 39.12%, 35.17%, and 22.20% in CIF, crack width, and crack length density, respectively; however, substantial heterogeneity (>98%) and prediction intervals crossing zero indicated considerable variation in both the magnitude and direction of responses among experimental conditions. Subgroup analyses revealed the following: (1) Soil-group differences were statistically supported for CIF, while the 14.20% increase in crack length density and 25.86% reduction in mean width observed in non-clay soils were not statistically significant. (2) Application-rate groups differed significantly across all three indices. The 5% group showed the largest average reductions. However, application rate explained only 12.60–15.80% of the observed variation. (3) Mean crack suppression was generally greater during the early DW cycles, but evidence beyond 6 cycles was too limited to determine whether the effect persisted under prolonged cycling. Overall, the evidence supported average reductions in CIF and mean crack width, whereas the effect on crack length density and the persistence of crack suppression under prolonged drying–wetting exposure remained uncertain. Field application should balance crack mitigation with agronomic feasibility, soil quality, and long-term performance under repeated drying–wetting conditions.

Improper irrigation and fertilization can easily lead to soil nutrient imbalance, inhibit microbial reproduction, and thereby reduce soil quality and crop yield. This study conducted winter wheat planting experiments in 2023–2025, setting three muddy water (sediment-laden irrigation water) treatments of different sediment concentrations (3, 6 and 9 kg·m⁻³), irrigation levels (0.50–0.65, 0.65–0.80 and 0.80–0.95 FC), and nitrogen application rates (100, 160 and 220 kg·ha⁻¹). An L9(3³) orthogonal experimental design was applied to evaluate the influence of water and nitrogen regulation on soil properties, microbial community structure, and wheat productivity. The results showed the following: Among these treatments, the T5 treatment (6 kg·m⁻³, 0.65–0.80 FC, 160 kg·ha⁻¹) significantly improved the root zone environment, and the total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), and soil organic carbon (SOC) content also increased significantly. T5 also enhanced the diversity and network complexity of bacterial and fungal communities. Notably, genera such as Lysobacter, Lasiobolidium, and Ascobolus became central to nitrogen transformation and nutrient cycling. Structural equation modeling revealed the interdependent mechanism between soil quality, microorganisms, and wheat yield: NO₃⁻-N and SOC drive improvements in soil quality, while microbial community structure and network complexity are key to yield increases, with fungal communities making the largest direct contribution to yield (R² = 0.93). The T5 treatment increased two-year yields by 21.34–24.96% compared to conventional irrigation and fertilization (CK2), improved irrigation water use efficiency by 56.40–57.51% and peak nitrogen agronomic efficiency. The synergistic effect of “soil quality optimization–enhanced microbial activity–efficient utilization of water and nitrogen–high wheat yield” has been achieved, providing a theoretical basis and practical reference for scientific water and nitrogen management and sustainable yield increase in winter wheat in the Yellow River Basin and similar areas.