Biogas slurry application offers an alternative to chemical fertilizer in realizing ecologically recycling agriculture. However, the responses of soil fertility and microbial communities to long term use of biogas slurry need to be explored in different soil types and regions. We investigated the effects of repeated applications over six years on the soil properties and microbial characteristics of a fluvo-aquic soil in the North China Plain. The experiment, with equivalent nitrogen inputs, comprised: biogas slurry (BS), chemical fertilizer (CF) or substitution of half the chemical fertilizer with biogas slurry (BSCF); a control treatment had no fertilizer addition. Soil samples, at a depth of 0–20 cm, were collected for their physicochemical properties. Microbial community diversity and composition was investigated using high-throughput sequencing. Biogas slurry application treatments tended to lower the soil bulk density while increasing the water-holding capacity and the water-stable aggregate mean weight diameter. Organic carbon and available nutrient concentrations (nitrogen, potassium and phosphorus) were enhanced in all fertilization treatments relative to the control, especially in the BSCF treatment. Significant differences in microbial community composition were detected between the control and all of the fertilization treatments. BSCF resulted in the greatest diversity and most evenly balanced assemblages of both bacteria and fungi at the phylum level. There were clear associations between microbial composition and changes in soil environmental variables caused by the fertilization treatments. Bacterial community composition and alpha diversity were associated particularly with differences in soil total nitrogen, pH, and available potassium, whereas fungal communities were more related to available potassium. Half substitution of the chemical fertilizer by biogas slurry gave the greatest improvement in soil structure and nutrient availability and this was associated with greater microbial diversity and better balanced microbial communities. Our results suggest that partial substitution with biogas slurry is an alternative to complete chemical fertilizer and that it offers clear benefits for the topsoil structure and fertility in fluvo-aquic soils. It also represents a promising approach to a biogas-linked agroecosystem that restores sustainable coordination between cropping and animal husbandry under an intensive production regime.

We investigated the effects of seed burial depth and soil water content on seedling emergence and growth of Ulmus pumila var. sabulosa (sandy elm), an important native tree species distributed over the European-Asian steppe. Experimental sand burial depths in the soil were 0.5, 1.0, 1.5, 2.0 and 2.5 cm, and soil water contents were 4%, 8%, 12% and 16% of field capacity. All two-way ANOVA (five sand burial depths and four soil water contents) results showed that seed burial depths, soil water content and their interactions significantly affected all the studied plant variables. Most of the times, seedling emergence conditions were greater at the lower sand burial depths (less than 1.0 cm) than at the higher (more than 1.0 cm) seed burial depths, and at the lower water content (less than 12%) than at the higher soil water content. However, high seed burial depths (more than 1.5 cm) or low soil water content (less than 12%) reduced seedling growth or change in the root/shoot biomass ratios. In conclusion, the most suitable range of sand burial was from 0.5 to 1.0 cm soil depth and soil water content was about 12%, respectively, for the processes of seedling emergence and growth. These findings indicate that seeds of the sandy elm should be kept at rather shallow soil depths, and water should be added up to 12% of soil capacity when conducting elm planting and management. Our findings could help to create a more appropriate sandy elm cultivation and understand sparse elm woodland recruitment failures in arid and semi-arid regions.