Effects of Combined Applications of Biogas Slurry and Biochar on Phosphorus Leaching and Fractionations in Lateritic Soil

Persistent effects of swine manure biochar and biogas slurry application on soil nitrogen content and quality of lotus root

Using swine manure biochar and biogas slurry in agriculture proves to be an effective strategy for soil improvement and fertilization. In this study, a pot trial on the growth of lotus root was conducted to investigate the persistent effects of applying 350°C swine manure biochar (1% and 2%) and biogas slurry (50% and 100%) on soil nitrogen nutrient and lotus root quality. The results showed that compared to chemical fertilizer alone (A0B0), swine manure biochar significantly increased soil nitrogen content after one year of application. The contents of total nitrogen (TN), alkali-hydrolyzed nitrogen (AHN), ammonium nitrogen (NH4 +-N), and nitrate nitrogen (N O 3 -   - N ) increased by 17.96% to 20.73%, 14.05% to 64.71%, 17.76% to 48.68% and 2.22% to 8.47%, respectively, during the rooting period. When swine manure biochar was present, the application of biogas slurry further elevated soil nitrogen content. The co-application of swine manure biochar and biogas slurry significantly increased soil nitrogen content, and the 100% nitrogen replacement with biogas slurry combined with 2% swine manure biochar (A2B2) treatment exhibited the most significant enhancement effect during whole plant growth periods. Soil enzyme activities, including soil protease (NPT), leucine aminopeptidase (LAP), b-glucosidase (β-GC) and dehydrogenase (DHA), showed a tendency to increase and then decrease with the prolongation of lotus root fertility period, reaching the maximum value during the rooting period. Compared to A0B0, the treatment with 2% swine manure biochar had the most significant effect on enzyme activities and increased the lotus root's protein, soluble sugar, and starch contents. Nitrate content decreased with the application of 2% swine manure biochar as the amount of biogas slurry increased. In conclusion, swine manure biochar effectively improved soil nitrogen content, enzyme activity, and lotus root quality. Even after one year of application, 2% swine manure biochar had the best enhancement effect.

Organic pulses and bacterial invasion alleviated by the resilience of soil microbial community

Biogas slurry is a nutrient-rich secondary product of livestock feces digestion which is recycled as a crop plantation fertilizer and provides exogenous microbes to the soil. However, the effects of biogas slurry microbes on the soil resident community remain unknown. In this study, we examined the ecological consequences of long-term biogas slurry pulse on the soil resident community and found that it promoted crop yield and altered soil characteristics. The soil microbial ecosystem was altered as a result of organic amendments due to the exogenous input of microbes and nutrients. Nevertheless, the soil resident communities were highly resilient to long-term organic pulses, as evidenced by community diversity and composition. The two dominant bacterial species in biogas slurry were Sterolibacterium and Clostridium. Notably, the abundance of Clostridium in biogas slurry increased following long-term amendments, while other species such as GP1 and Subdivision3_genera_incertae_sedis decreased; which was consistent with the results of module-eigengene analysis. Long-term organic pulses shifted the balance of microbial community assembly from stochastic to deterministic processes. Overall, our findings indicated that organic pulses accompanied with bacterial invasion could be alleviated by the resilience of soil microbial communities, thereby emphasizing the importance of microbiota assemblage and network architecture.

Effect of Digestate Modified with Amendments on Soil Health and Plant Biomass under Varying Experimental Durations

A digestate with amendments provides plants with available nutrients and improves the microbiological properties of treated soil. Modification of a digestate through the addition of a biochar and sulphur source is less well-known. This pot experiment aimed at comparing the short- and long-time fertilization effects of a digestate enriched with biochar, with elemental sulphur, or with a combination of both on soil health and plant biomass. The experiment was carried out with maize, cultivated twice (1st-12th week = pre-cultivation; re-sowing after shoot harvest, 13th-24th = main cultivation) in soil amended with prepared digestate. The digestate used in pre-cultivation was incubated untreated (D) and was then treated with biochar (D + B), with elemental sulphur at a low (LS) and high (HS) dose, or with a combination of both (D + B + LS and D + B + HS). An additional unamended digestate (D) was added to each soil variant before the main cultivation. The application of digestate with a high dose of elemental sulphur and biochar mediated the most significant differences in the soil. The increase (compared to the unamended soil) was of short-term type (+11% and +6% increased total nitrogen and carbon after 12 weeks), then of long-term type (+54% and +30% increased sulphur and arylsulfatase activity after 24 weeks), and later emerged in the 13th to the 24th week of the experiment (+57% and +32% non-inhibited urease, increased N-acetyl-β-D-glucosaminidase and phosphatase). No significant differences in the effect of the applied amendments on dry aboveground plant biomass were observed.

Interception of fertile soil phosphorus leaching with immobilization materials: Recent progresses, opportunities and challenges

The non-point source pollution induced by phosphorus (P) leaching from fertile soils is accelerating the eutrophication phenomena in aqueous ecosystems. Herein, to alleviate and intercept the P leaching from the fertile soils, diverse P immobilization materials (PIM) which can transform labile P into stable P via a range of physicochemical and biological interactions have been adopted and received increasing research interest. However, the remediation mechanisms of different PIMs were complex and vary with soil properties and PIM application methods. In this review, the P fraction and mobility characteristics of different fertile soils were first introduced. Then, three kinds of PIM including inorganic materials (e.g., clay minerals and red mud), organic materials (e.g., polyacrylamide), and composites (e.g., modified biochar) applied in soil P leaching interception were concluded. The key factors (i.e., soil pH, soil texture, organic matter content and variable soil moisture) influencing PIM performance and potential PIMs used for reducing soil P leaching were also introduced. Current review can favor for proposing more suitable and insightful strategies to regulate the fertile soil P and achieve the dual goals of improving the crop land quality and yield, and preventing agricultural non-point source pollution.