Denitrification and NH3 volatilization are the main removal processes of nitrogen in coastal saline soils. In this incubation study, the effects of wheat straw biochar application at rates of 0, 2, 5, 10 and 15% by weight to saline soil with two salt gradients of 0 and 1‰ on denitrification and NH3 volatilization were investigated. The results show...
... Urea hydrolysis promotes NH 3 volatilization in flooded layer (Wang et al. 2012). The NH 3 volatilization was significantly correlated with the concentcing water (Pan et al. 2021) (Table 2, Fig. 6). The N loss of NH 3 volatilization is mainly concentrated in the tillering and jointing periods after applying fertilizer. ...
Salt-affected soils have poor structure and physicochemical properties, which affect soil nitrogen cycling process closely related to the environment, such as denitrification and ammonia volatilization. Biochar and polyacrylamide (PAM) have been widely used as soil amendments to improve soil physicochemical properties. However, how they affect denitrification and ammonia volatilization in saline soils is unclear. In this study, the denitrification and ammonia volatilization rates were measured in a saline soil field ameliorated with three biochar application rates (0%, 2%, and 5%, w/w) and three PAM application rates (0‰, 0.4‰, and 1‰, w/w) over 3 years. The results showed that denitrification rates decreased by 23.63–39.60% with biochar application, whereas ammonia volatilization rates increased by 9.82–25.58%. The denitrification and ammonia volatilization rates decreased by 9.87–29.08% and 11.39–19.42%, respectively, following PAM addition. However, there was no significant synergistic effect of biochar and PAM amendments on the denitrification and ammonia volatilization rates. The addition of biochar mainly reduced the denitrification rate by regulating the dissolved oxygen and electrical conductivity of overlying water and absorbing soil nitrate nitrogen. Meanwhile, biochar application increased pH and stimulated the transfer of NH4+–N from soil to overlying water, thus increasing NH3 volatilization rates. Hence, there was a tradeoff between denitrification and NH3 volatilization in the saline soils induced by biochar application. PAM reduced the denitrification rate by increasing the infiltration inorganic nitrogen and slowing the conversion of ammonium to nitrate. Moreover, PAM reduced the concentration of NH4+–N in the overlying water through absorbing soil ammonium and inhibiting urea hydrolysis, thereby decreasing NH3 volatilization rate.
Biochar amended soils reduce fertilizer N losses and suppress greenhouse gas emissions. However, biochar can increase NH3 volatilization. H2SO4-modified biochar has been studied as a means to achieve the advantages of biochar while reducing volatilization, especially under alternate wetting and drying irrigation (IAWD). In contrast to continuously flooded irrigation (ICF), IAWD is a water-saving technology that repeatedly dries and re-floods fields. A 3-year field experiment was conducted with two irrigation regimes (ICF and IAWD) as main plots and 0 (control), 20 t ha-1 biochar, and 20 t ha-1 H2SO4-modified biochar as subplots. IAWD produced 7.6-14.8% more reactive gaseous N losses (NH3 and N2O) and emitted 2.02 times N-related global warming potential (GWPN) of ICF. Biochar increased NH3 volatilization by 35.6% in the first year and decreased it by 22.4% and 24.8% in the second and third years, respectively, while H2SO4-modified biochar decreased NH3 volatilization each year. The increased NH3 volatilization was caused by the higher NH4 + concentration and pH in the floodwater and surface soil due to increasing N inputs and alkalinity from biochar. The decrease in the following two years was attributed to pH returning to the pre-treatment level and continued biochar absorption of NH4 + from the floodwater. Both biochar and H2SO4-modified biochar significantly reduced seasonal N2O emissions. H2SO4-modified biochar coupled with IAWD mitigated the initial increases in NH3 volatilization and reactive gaseous N losses in the first year, and increased grain yield, decreased reactive gaseous N losses, and GWPN compared with the IAWD without biochar throughout the three years. The use of acid-modified biochar could produce higher grain yield with lower reactive gaseous N losses and GWPN for application in the IAWD paddy systems, which benefits sustainable agricultural production. J o u r n a l P r e-p r o o f 2
NH 3 from farmland has serious impacts on human health and ecosystems. To reduce NH 3 volatilization and increase yield, biochar is applied. A field experiment was carried out to study NH 3 volatilization loss, and summer maize yield was analysed under different irrigation schemes with different amounts of biochar. Two irrigation schemes, I1 (67.5 mm) and I2 (121.5 mm), were set up according to the irrigation habits of local producers. Three biochar application rates were selected: C1 (0 t ha ⁻¹ ), C2 (20 t ha ⁻¹ ) and C3 (40 t ha ⁻¹ ). The relationship between NH 3 volatilization and influencing factors, including NH 4 ⁺ -N concentration, NO 3 ⁻ -N concentration, pH in the 0~20 cm soil layer and temperature, was investigated. The results showed that the yield significantly ( p <0.05) increased by 17.27%~46.67% after applying biochar. Compared with C1, NH 3 volatilization significantly ( p <0.05) decreased by 28.98%~31.63% in C2, while that in C3 significantly ( p <0.05) increased by 22.64%~73.87%. The effects of biochar on NH 3 volatilization were consistent under different irrigation conditions. Compared to I1, I2 not only increased the yield of summer corn but also increased the risk of NH 3 volatilization and leaching. NH 3 volatilization was positively correlated with NH 4 ⁺ -N concentration, pH and temperature, but it was negatively correlated with NO 3 ⁻ -N concentration. These results suggest that the optimal application amount of biochar for summer maize ranges from 14.59 t ha ⁻¹ to 17.19 t ha ⁻¹ in the study area.