Qian Wang

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.

To investigate the impact of sediment on water infiltration and soil structure under muddy water irrigation conditions, indoor muddy water film hole infiltration experiments were conducted. Four different muddy water sediment concentrations (3%, 6%, 9%, 12%) and four typical sediment particle size distributions (which were quantified by the physical clay content with a particle size of less than 0.01 mm, d_0.01: 9.13%, 16.46%, 27.34%, 44.02%) were employed to examine how muddy water properties affect infiltration law and the stratum compactum soil particle composition under film hole irrigation. The results showed that as the muddy water sediment concentration and physical clay content increased, the wetting front migration distance, cumulative infiltration amount, and soil water content gradually decreased simultaneously. The Kostiakov infiltration model effectively captured the changes in soil water infiltration during muddy water film hole irrigation, exhibiting a strong fit with a high coefficient of determination (R² > 0.9). With higher muddy water sediment concentration, the deposition layer thickness increases within the same infiltration time. Conversely, higher physical clay content leads to a decrease in deposition layer thickness. The characteristics of the muddy water have a significant impact on the particle composition of the soil in the stratum compactum caused by film hole irrigation. The deposition layer has a lower relative content of fine soil particles compared to muddy water, but this content increases with higher muddy water sediment concentration and physical clay content. In the stranded layer soil, fine particles have a higher relative content than the original soil. Fine particle content increases notably with higher muddy water sediment concentration and physical clay content. The stranded layer soil particles exhibit a higher fractal dimension than the original soil, and as the infiltrated soil layer depth increases, the soil fractal dimension decreases until it matches the original soil. The fractal dimension increased with the increase in muddy water sediment concentration and physical clay content in muddy water irrigation conditions under the same soil layer depth. This research findings could serve as a theoretical foundation for understanding soil water movement under muddy water irrigation conditions.

Soil amendments such as humic acid (HA), a biochar-based microbial agent (M), and vermicompost (V) can improve soil quality and promote crop growth. However, it remains unclear whether the co-application of the three soil amendments (HMV) has a synergistic effect on alleviating soil quality deterioration obstacles caused by dry sowing and wet emergence technology in Xinjiang cotton fields. A three-year field experiment was conducted in saline–alkali soils using plastic-film-mulched drip irrigation in Xinjiang, China. Through the orthogonal experiment method, the application amounts of HA, M and V were 75 kg ha⁻¹, 75 kg ha⁻¹ and 225 kg ha⁻¹ respectively in 2021. In 2022, three application amount gradients were used for HA, M and V: 60 kg ha⁻¹, 90 kg ha⁻¹ and 120 kg ha⁻¹ respectively. In 2023, the application amounts of HA, M, and V were 60 kg ha⁻¹, 120 kg ha⁻¹, and 120 kg ha⁻¹. It should be pointed out that V contains HA in the range of 20–35%. This study aimed to explore the improvement effect of a single or combined application of HA, M, and V on soil quality and cotton emergence rate using dry sowing and wet emergence technology in Xinjiang cotton fields. The results showed that the single and combined applications of HA, M, and V improved the soil quality and water–heat–salt environment of the cultivated layer. In the combined application, the cotton seedling emergence rate and yield increased by 1.9–22.8% and 7.0–54.1%. Therefore, it is recommended to jointly apply HA, M, and V to promote cotton seedling emergence and increase yield using dry sowing and wet emergence technology in Xinjiang cotton fields.