Southwestern China is receiving excessive chemical fertilizers to meet the challenges of continuous cropping. These practices are deteriorating the soil environment and affecting tobacco (Nicotiana tabacum L.) yield and quality adversely. A novel microbially enriched biochar-based fertilizer was synthesized using effective microorganisms, tobacco stalk biochar and basal fertilizer. A field-scale study was conducted to evaluate the yield response of tobacco grown on degraded soil amended with our novel biochar-based microbial fertilizer (BF). Four treatments of BF (0%, 1.5%, 2.5% and 5%) were applied in the contaminated field to grow tobacco. The application of BF_1.5, BF_2.5 and BF_5.0 increased the available water contents by 9.47%, 1.18% and 2.19% compared to that with BF₀ respectively. Maximum growth of tobacco in terms of plant height and leaf area was recorded for BF_1.5 compared to BF₀. BF_1.5, BF_2.5 and BF_5.0 increased SPAD by 13.18–40.53%, net photosynthetic rate by 5.44–60.42%, stomatal conductance by 8.33–44.44%, instantaneous water use efficiency by 55.41–93.24% and intrinsic water use efficiency by 0.09–24.11%, while they decreased the intercellular CO₂ concentration and transpiration rate by 3.85–6.84% and 0.29–47.18% relative to BF₀, respectively (p < 0.05). The maximum increase in tobacco yield was recorded with BF_1.5 (23.81%) compared to that with BF₀. The present study concludes that the application of BF_1.5 improves and restores the degraded soil by improving the hydraulic conductivity and by increasing the tobacco yield.

Continuous cropping causes soil degradation and decreases crop yield in the karst region of southwestern China. However, the relationship between continuous cropping systems and soil hydraulic and physicochemical properties remains incompletely elucidated. In this study, we performed a comparative investigation on the soil physicochemical properties and soil-water-characteristic-curve-derived parameters from sites subjected to 3, 5, or 7 years of continuous cropping (CC3, CC5, and CC7) and cropping rotation (CC0). Soil organic matter content, clay content, and pH were significantly greater in soils under CC0 and short-term cropping (CC3) than in soils under long-term cropping (CC5 and CC7). This finding illustrated that continuous cropping reduced soil organic matter content, clay content, and pH. Across all continuous cropping durations, soil water holding capacity at 40~60 cm was greater than the 20~40 cm and 0~20 cm layers. The significantly greater soil water characteristics (except saturated moisture) in CC0 and CC3 soils than in CC5 or CC7 soils at all soil depths demonstrated that soil water characteristics deteriorated with the prolongation of cropping duration. The same soil water characteristics were positively correlated with soil organic matter content, clay content, and pH. These correlations, when viewed within the context of continuous cropping, can inform the development of more sustainable cropping systems in similar karst regions.

Plastic film mulching in the field changes the soil structure and the normal distribution of soil water. Residual plastic film (RPF) in the soil causes serious environmental problems to the agricultural ecosystem. In order to determine the role of biochar in mitigating the negative effects of RPF pollution in the soil on agricultural production, in this work, we conducted a pot experiment without biochar and RPF as the control treatment. Four levels were set for biochar: no biochar ($0\mathrm{t}/{\mathrm{hm}}^2$ ), low biochar ($2.5\mathrm{t}/{\mathrm{hm}}^2$ ), medium biochar ($7.5\mathrm{t}/{\mathrm{hm}}^2$ ), and high biochar ($15\mathrm{t}/{\mathrm{hm}}^2$ ). Besides, four levels were set for the RPF: 0, 80, 320, and $720\mathrm{kg}/{\mathrm{hm}}^2$ . The results showed that medium biochar could improve the soil environment of the RPF, the saturation water content in the soil was increased by 4.5%–11.4%, and the root activity was increased by 6.3%–13.4%. In addition, the root density of flue-cured tobacco was also significantly increased. Medium and high biochar had a significant effect on higher residual plastic film (320 and $720\mathrm{kg}/{\mathrm{hm}}^2$ ). It can alleviate soil tillage obstacles caused by plastic film residue, improve soil water-holding and water-releasing capacity, and optimize tobacco plant growth environment. This study provides evidence for the application of biochar as a soil ameliorant in residual film soil. This suggests that we should do more research on the environmental impact of RPF pollution on agroecosystems.