Urea hydrolysis in different farmland soils as affected by long-term biochar application

Abstract

Urea is a commonly used nitrogen (N) fertilizer that contributes to world food production, and there have been increasing concerns about relatively low urea-N use efficiency. Biochar has shown the potential to mitigate N loss, but how biochar influences urea hydrolysis and the underlying mechanisms are still unclear. In this study, long-term biochar-amended upland, paddy and greenhouse soils were sampled at depths of 0–20 and 20–40 cm in Haicheng City, Northeast China. Soil N contents, urea hydrolysis rates (UHRs), and total, intracellular and extracellular urease activities were determined, as well as the total bacterial and ureolytic microbial gene abundance were quantified. The results showed that biochar increased total urease activity by 32.64–66.39% in upland soil and by 2.90–2.13-fold in paddy soil. Both intracellular and extracellular ureases contributed to the increase in total urease activity. However, in greenhouse soil, extracellular (+35.07–74.22%) and intracellular (−40.14–77.68%) urease activities responded inconsistently to biochar incorporation. Increases in ureC gene copy numbers (2.15- to 4.47-fold) in upland and greenhouse (20.93%) soil implied that biochar stimulated microorganisms capable of producing urease, and the biochar liming effect increased the soil pH (0.11–0.60 units), which optimized the ureolytic reaction, together explained the increases in urease activity. We found that the decreased soil N content was accompanied by a higher UHR in upland and greenhouse soils, suggesting that the accelerated UHR exerted a negative effect on the soil N content, possibly caused by excessive NH3 volatilization. In paddy soil, where the UHR was not increased, biochar was an effective amendment for simultaneously improving soil urease activity and N content.

Sustainable Restoration of Soil Functionality in PTE-Affected Environments: Biochar Impact on Soil Chemistry, Microbiology, Biochemistry, and Plant Growth

“…The increased URE activity observed in the amended soils, together with the reduction of total N content (Table 1), was likely indicative of a stimulation of urea hydrolysis due to biochar rather than an increased microbial content in amended soils (i.e., SMB reduced in 2.5-and 5.0-Bio; Figure 3). Such accelerated rate of URE activity in the presence of biochar was recently reported by Zhao et al [75] and could be partly responsible for the N reduction observed in the amended soils (especially 5.0-Bio; Table 1). The increased URE observed in the amended soils can also be due to an increased microbial synthesis of the enzyme stimulated by a more limited N availability in these soils [76], which in turn can be explained by NO 3 -N and NH 4 -N adsorption by biochar, as previously observed [19].…”

Maize straw is more effective than maize straw biochar at improving soil N availability and gross N transformation rate

“…First, because NH 3 volatilisation is considered the major pathway of N loss in agricultural systems resulting from N fertilizer application (Sha et al, 2019; Sun et al, 2017). More directly, our previous study conducted on the same maize biochar and soil showed that by accelerating urea hydrolysis rates and increasing soil pH (Liu et al, 2021), biochar could change the equilibrium dynamics of $$$ {{\mathrm{NH}}_4}^{+} $$$‐N dissociation, thereby stimulating NH 3 volatilisation and resulting in a lower $$$ {{\mathrm{NH}}_4}^{+} $$$‐N content in the soil (Liu et al, 2017; Zhao et al, 2022). This scenario was also illustrated by former researchers (Esfandbod et al, 2017; Yao et al, 2022) that by promoting NH 3 volatilisation, biochar reduced the availability of $$$ {{\mathrm{NH}}_4}^{+} $$$‐N, thereby delaying soil nitrification.…”

Thriving beneath olive trees: The influence of organic farming on microbial communities

“…Ureolysis was also significantly increased in the OM rhizosphere. Manure amendments are known to provide urea to the soil, that can constitute a source of nitrogen for plants due to the presence of ureolytic microorganisms [92] , [93] . Overall, our results suggest that sheep manure favor the presence of bacteria involved in beneficial processes such as improved nutrient cycling, degradation of recalcitrant pollutants and defense against soil borne pathogens.…”