Xiaorong Zhao

The effects of field‐aged biochar on soil nitrogen (N) transformation differ from those of fresh biochar. The modification of predominant N turnover processes subsequently influences soil N accumulation and availability. However, the long‐term impacts of aged biochar on in situ native soil N fractionation (excluding biochar‐derived N) and the mechanisms by which microbial communities influence available N supply remain largely unexplored. An 11‐year experiment investigated the effects of different biochar application rates (0, 30, 60, and 90 Mg ha ⁻¹ ) on total native N, soil organic N (SON) fractions, total dissolved N (TDN), microbial carbon to nitrogen imbalance (MI _C/N ), and gross N mineralisation rates (G _N‐min ) in calcareous soil (0–15 and 15–30 cm) under a winter wheat‐maize rotation. The SON fractions included labile pools (ammonia‐SON and amino acid‐N), less labile pools (amino sugar‐N and hydrolysable unknown‐N), and a recalcitrant pool (acid insoluble‐N). Results demonstrated that biochar application significantly increased soil native total N (by 7%–8%) and native recalcitrant SON (by 52%–104%) in the 15–30 cm layer. Biochar also significantly increased labile SON pools (except at 30 Mg ha ⁻¹ ) and reduced less labile SON pools compared to unamended soil at both depths. During rapid crop growth stages, biochar‐amended soil showed an upward trend in TDN content and G _N‐min value in the top 15 cm. Structural equation modelling (SEM) showed that increased available N was primarily driven by accelerated turnover of labile SON influenced by biochar content, rather than by higher labile SON content. In November, biochar application significantly decreased TDN contents and MI _C/N values, indicating reduced microbial N‐mining in aged biochar soils. SEM further implied that MI _C/N played a crucial role in limiting the degradation of less labile SON over winter. In conclusion, long‐term biochar application modified soil N fractions and influenced N turnover across different growth stages by regulating soil microbial N demand. These findings underscore the potential of biochar to sustain soil fertility and support the ecological sustainability of agricultural systems, particularly when combined with soil organic carbon management.

Organic fertilizer granulation represents a promising strategy for modifying nitrogen (N) release from compost in soil. Nevertheless, there is a lack of large-scale field trials exploring its impact on tobacco production and soil N supply. This research conducted a preliminary study by employing ¹⁵N tracing technology to investigate the effects of granular compost on soil N transformation and supply; on the yield and quality of tobacco leaves; and on the distribution of granular compost-derived N among the different soil N pools and tobacco plant organs. The results revealed that the 2 cm diameter granule organic fertilizer treatment (G2) significantly increased tobacco leaf yield by 15% compared to conventional fertilization (CK). However, the 4 cm diameter granule organic fertilizer (G4) treatment resulted in a reduction in leaf yield. Notably, the quality of tobacco leaves remained unaffected compared to conventional fertilization treatment; the N content ranged from 15 to 25 g kg⁻¹, which was within the high-quality range. The results also indicated that direct N supply to the tobacco from granular compost was limited. The G2 and G4 treatments provided 2.8% and 2.2% of the N in the fertilizer to the tobacco plants, respectively, with more than 93% of the N in the tobacco plants derived from the soil. Therefore, both of these particle sizes of granular compost facilitated the absorption of soil N by tobacco plants. At the end of the growth period, the N content derived from the G4 granular fertilizer in the soil was significantly higher than that from the G2 fertilizer. This may be due to the slower nutrient release mechanism and longer release period of the G4 fertilizer compared to G2. Our results suggested that granulated compost fertilizer (both G2 and G4) has the potential to enhance soil N supply. Despite the elevated nitrogen levels observed in leaves treated with 4 cm diameter granular fertilizer, an integrated assessment of yield performance demonstrates that the 2 cm diameter granular organic fertilizer delivers superior economic benefits. However, G2 may also have a higher potential for N loss. Further investigations under field conditions are necessary to validate the applicability of granular fertilizer of different particle sizes and its specific mechanisms of impact.

Phosphorus (P) is a crucial limiting nutrient in grassland ecosystems. Microorganisms play a vital role in soil P cycling and bioavailability. Grassland grazing profoundly affects soil P cycling, while the role of microbial‐driven mechanisms in the regulation of soil P fractions by grazing intensity is yet unclear. Here, soil samples, primarily classified as calcic Chernozems, were collected from a long‐term grazing experiment with grazing intensity gradients (0.0, 1.5, 3.0, 4.5, 6.0, 7.5, 9.0 sheep ha ⁻¹ ) in a semi‐arid grassland of Inner Mongolia. Soil chemical properties, P fractions, phospholipid fatty acid (PLFA) and functional gene abundance of inorganic P (Pi) solubilisation ( pqqC ) and organic P (Po) mineralisation ( phoD ) were measured. As grazing intensity increased, soil pH increased while soil dissolved nitrogen (DN) decreased. The marked decline in soil total PLFAs resulted in a linear reduction in soil labile Po. The gradual increase in pqqC gene abundance and constant phoD gene abundance with increasing grazing intensity suggested that the Pi solubilisation processes, not Po mineralisation processes, were pivotal for soil P transformation when the soil microbial community's growth was limited. The enhanced soil Pi solubilisation reduced soil moderately labile Pi, which in turn affected soil moderately resistant Pi and labile Pi. Under grazing intensity gradients, the increased soil pH and decreased soil DN were also involved in the regulation of soil P fractions' transformations via affecting soil total PLFAs and pqqC gene abundance. Our findings underscore the importance of Pi solubilisation processes in regulating soil P cycling under long‐term grazing intensity gradients, thereby providing valuable insights for sustainable grassland management and ecosystem conservation in semi‐arid regions.

Soil salinization is a significant obstacle to agricultural development in arid and semiarid regions. While short-term experiments have demonstrated the effective improvement of saline soils through biochar amendment, the long-term efficacy in sustainably ameliorating such soils remains uncertain. Addressing this knowledge gap, this study investigated the long-term effects of biochar amendment in a field setting by applying different rates of biochar to a salt-affected soil and cultivating silage maize for three consecutive years. The comprehensive assessment includes not only maize growth but also changes in soil physical and chemical properties over the study period. The results reveal a notable elevation in maize above-ground dry matter, directly correlated to the enhanced uptake of nitrogen, phosphorous, and potassium. Additionally, biochar application improves saline soil physical properties, including reduced bulk density (1–23%), increased soil large pores (0.7–12%), and macroaggregates (24–141%), and chemical properties, including a decrease in exchangeable sodium percentage (35–48%), and an increase in soil total organic carbon (112–857%), total nitrogen (9–198%), available nitrogen (12–49%), phosphorus (141–538%) and potassium (57–895%). These improvements ultimately resulted in better maize growth. However, the amelioration effect of biochar on these soil properties gradually diminished over the three-year study. Consequently, this study suggests that biochar is a promising soil amendment that can enhance maize growth in saline soil for at least three years in a field experiment, providing valuable insights for sustainable agricultural practices in salt-affected regions.

Our objectives were to investigate whether AP affects the soil bacterial community composition and diversity in high-level available phosphorus (AP) soils. The bacterial community was analysed through high-throughput sequencing using the Illumina MiSeq platform. Fifteen soils, including barren land, cropland and greenhouse soils which were sandy loam Fluvisols, were selected from different fields in Beijing, China, with AP contents ranging from 5.03 to 391.45 mg kg⁻¹. Statistical analyses revealed high AP (>100 mg kg⁻¹) decreased alpha diversity (Shannon’s index, H’) but not beta diversity of the soil bacterial community. The sequencing of 16S rRNA genes showed that Proteobacteria, Bacteroidetes and Acidobacteria were the dominant phyla in sandy loam Fluvisols. AP, soil organic carbon (SOC) and total nitrogen (TN) had synergistic influence on the shift of the bacterial community composition. Moreover, AP was the main driving factor affecting the soil bacterial community composition compared with other environmental factors. The members of the Proteobacteria, Bacteroidetes and Actinobacteria belonging to copiotrophic taxa typically increased in relative abundance in high-P soils, while oligotrophic taxa (mainly Acidobacteria) decreased in relative abundance. Our results demonstrated that the bacterial community composition would shift from oligotrophic to copiotrophic with increasing levels of AP.

In recent years, continuous efforts have been made to understand the impact of biochar on arable soil fertility. Little is known about whether the biochar derived from municipal sewage sludge has positive impacts on urban soil. In this study, we pyrolyzed spray-dried municipal sewage sludge at 200 °C, 300 °C, 500 °C, and 700 °C for 2 h in a muffle furnace and then amended it into an urban soil to grow turf grass in pots. The outcomes demonstrated that biochar incorporation caused remarkable increases in soil organic C, black C, total N, available P, and K by 3–8, 7–25, 2–9, 10–19, and 1.4–2 times, respectively. The dry matter of turf grass increased by 43–147%, probably due to the nutritional improvement after biochar addition. The turf grass grown in biochar-added soil had 4–70% lower heavy metals than that in the control, although the soils had much higher total heavy metals, which might imply that biochar amendment reduced the bioavailability of heavy metals. Considering the cost of biochar production and its impacts on both urban soil and grass, it would be alternative to convert the spray-dried municipal sewage sludge into biochar at 200 °C for 2 h and then used as an urban soil amendment.