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Microplastic might affect the crop yield, nitrogen (N) use efficiency and reactive N losses from agricultural soil systems. However, evaluation of these effects in infertile soil planted with different rice cultivars is lacking. We conducted a soil column experiment to determine the influence of a typical microplastic polyethylene (PE) input into an infertile soil with 270 kg N ha−1 and planted with two rice cultivars, i.e., a common rice Nangeng 5055 (NG) and a hybrid rice Jiafengyou 6 (JFY). The results showed that JFY produced a significantly (p < 0.05) greater grain yield than NG (61.6–66.2 vs. 48.2–52.5 g pot−1) but was not influenced by PE. Overall, PE hardly changed the N use efficiency of NG and JFY. Unexpectedly, PE significantly (p < 0.05) increased the total amino acid content of NG. Compared with JFY, NG volatilized significantly (p < 0.05) more ammonia (NH3) (0.84–0.92 vs. 0.64–0.67 g N pot−1) but emitted equal nitrous oxide (N2O). PE exerted no effect on either NH3 volatilization or the N2O emission flux pattern and cumulative losses of the rice growth cycle, whether with NG or JFY. Some properties of tested soils changed after planting with different rice cultivars and incorporating with microplastic. In conclusion, the rice production, N use efficiency, NH3 volatilization and N2O emission from the N-fertilized infertile soil were pronouncedly influenced by the rice cultivar, but not the PE. However, PE influenced the grain quality of common rice and some properties of tested soils with both rice cultivars. [ABSTRACT FROM AUTHOR]

Raw biochar with high pH possibly stimulated ammonia (NH 3) volatilization in the agricultural soil. We hypothesized that the modified biochar (MBC) with low pH can synchronically decrease the NH 3 and nitrous oxide (N 2 O) losses. We performed a two-year experiment to clarify how citric acid MBC influence the NH 3 volatilization and N 2 O emission as well as the underlying mechanisms. Two typical paddy soils, i.e., Hydragric Anthrosol and Haplic Acrisol, receiving equal urea N with 240 kg ha−1 but varied rates of MBC with 0, 5, 10, and 20 t ha−1 (named Urea, Urea + MBC5, Urea + MBC10, and Urea + MBC20, respectively) were studied. The results showed that MBC-amended treatments effectively mitigated the NH 3 volatilization from Hydragric Anthrosol and Haplic Acrisol by 29.6%–57.9% and 30.5%–62.4% in 2017, and by 16.5%–21.0% and 24.5%–35.0% in 2018, respectively, compared to Urea treatment. In addition, significantly lower N 2 O emissions with averaged 38.3% and 43.1% in 2017, and 51.7% and 26.7% were recorded under Hydragric Anthrosol and Haplic Acrisol, respectively, following the MBC application (P < 0.05). Increased MBC addition performed higher efficacy on mitigating NH 3 volatilization, particularly in the first rice season, while this "dosage effect" was not found for N 2 O reduction. Lowered pH in overlying water, enhanced adsorption of NH 4 +-N and its nitrification rate likely contributed to the lower NH 3 volatilization as result of MBC addition. The nir S and nos Z gene copies were not changed by MBC, while the nir K gene copies were decreased as result of MBC amendment by 8.3%–25.2% under Hydragric Anthrosol and by 21.8%–24.9% under Haplic Acrisol. Consequent lower ratio of nir K/(nir S + nos Z) explained the mitigation effect of MBC on N 2 O emission. In conclusion, the present two-year study recommends that MBC applied at a low dosage can perform positive effect on controlling the nitrogenous gas pollutants from paddy soil. [Display omitted] • MBC addition synchronically mitigates the NH 3 volatilization and N 2 O emission. • "Dosage effect" of MBC on reducing NH 3 loss was found, but not for N 2 O emission. • Reduced pH in floodwater mainly lead to the lower NH 3 loss after MBC addition. • Lower nir K/(nir S + nos Z) explained the mitigation effect of MBC on N 2 O emission. [ABSTRACT FROM AUTHOR]

Wood vinegar (WV) was applied alone or combined with biochar (BC) to observe their efficiency on suppressing the ammonia (NH 3) volatilization from rice paddy soil. Five treatments, i.e., control (240 kg N ha−1 applied in urea), WV-5 and WV-10 (240 kg N ha−1 plus 5 and 10 t WV ha−1, respectively), and their counterparts WV-5-BC and WV-10-BC (WV-5 and WV-10 plus 7 t BC ha−1), were evaluated by a soil columns experiment. The N fertilizer was split applied as basal and two supplementary fertilizations (named BF, SF1 and SF2, respectively). The results showed that WV-5 treatment increased rice grain yield up to 11.2% compared to the control. Compared with the control, four WV-amended treatments, exhibited lower pH values of the floodwater (7.94–8.18 vs 8.47 and 7.85–7.91 vs 7.98) and the topsoil (6.52–6.76 vs 6.82 and 6.82–6.92 vs 6.99) during the BF and SF1 periods. Both WV-5 and WV-10 increased the NH 4 +-N contents of topsoil by 10.9–17.8% and 16.1–36.2% after BF and SF1, respectively, than control treatment. Additionally, the floodwater of the WV-amended treatments had higher NH 4 +-N concentration than control during the first three days after N fertilization, which can be attributed to the stimulating effect of WV on soil urease enzyme activity. WV did not effectively reduce NH 3 volatilization as hypothesized. Interestingly, four WV-amended had relatively reduced the yield-scale NH 3 volatilization by 13.6% than the control. It is suggested that WV needs to be applied with BC at a moderate rate to achieve optimum rice yield and mitigate NH 3 volatilization. Image 1 • Acidic wood vinegar (WV) and alkaline biochar (BC) were co-applied to rice paddy soil. • WV + BC reduced NH 3 volatilization while WV alone increased that. • Yield-scale NH 3 volatilization of WV + BC was reduced by 13.6%. • Soil of WV + BC had lower pH and urease activity, but higher NH 4 + content. • WV + BC is recommended to achieve higher rice yield and lower NH 3 volatilization. [ABSTRACT FROM AUTHOR]

Biochar (BC) potentially accelerates ammonia (NH 3) volatilization from rice paddy soils. In this regard, however, application the floating duckweed (FDW) to biochar-amended soil to control the NH 3 volatilization is not studied up-to-date. Therefore, the impacts of BC application with and without FDW on the NH 3 and nitrous oxide (N 2 O) emissions, NUE and rice grain yield were evaluated in a soil columns experiment. We repacked soil columns with Hydragric Anthrosol and Haplic Acrisol treated in triplicates with Urea, Urea + BC and Urea + BC + FDW. Total NH 3 losses from Hydragric Anthrosol and Haplic Acrisol were 15.2–33.2 kg N ha−1 and 19.6–39.7 kg N ha−1, respectively. Urea + BC treatment recorded 25.6–43.7% higher (p < 0.05) NH 3 losses than Urea treatment, attributing to higher pH value of floodwater. Floating duckweed decreased soil pH and therefore significantly reduced (p < 0.05) the NH 3 volatilizations from the two soils by 50.6–54.2% over Urea + BC and by 34.2–38.0% over Urea treatment. Total N 2 O emissions from Hydragric Anthrosol and Haplic Acrisol were 1.19–3.42 kg N ha−1 and 0.67–2.08 kg N ha−1, respectively. Urea + BC treatment increased N 2 O emissions by 58.8–68.7% and Urea + BC + FDW treatment further increased N 2 O emission by 187.4–210.4% over Urea treatment. Higher ammonium content of the topsoil, explained the N 2 O increases in the Urea + BC and Urea + BC + FDW treatments. Urea + BC slightly reduced the rice grain yield and NUE, while the Urea + BC + FDW promoted both rice yield and NUE. Our data indicate that co-application of FDW along with BC in paddy soil could mitigate the NH 3 volatilization and enhance the rice grain yield and NUE. • Biochar (BC) was applied alone or along with floating duckweed (FDW) to two rice paddy soils. • BC alone significantly increased NH 3 volatilizations by 25.6–43.7%. • Combination of BC and FDW could reduce the NH 3 losses by 34.2–38.0%. • Combination of BC + FDW promoted the nitrogen usage efficiency and the rice grain yield. [ABSTRACT FROM AUTHOR]

Biogas slurry (BS) and hydrothermal carbonization aqueous products (HAP), which are rich in nitrogen (N) and dissolved organic matter (DOM), can be used as organic fertilizer to substitute inorganic N fertilizer. To evaluate the effects of co-application of BS and HAP on the ammonia (NH 3) volatilization and soil DOM content in wheat growth season, we compared six treatments that substituting 50%, 75%, and 100% of urea-N with BS plus HAP at low (L) or high (H) ratio, named BCL50, BCL75, BCL100, BCH50, BCH75, BCH100, respectively. Meanwhile, urea alone treatment was set as the control (CKU). The results showed that both BCL and BCH treatments significantly mitigate the NH 3 volatilizations by 9.1%–45.6% in comparison with CKU (P < 0.05), whose effects were correlated with soil NH 4 +-N content. In addition, the decrease in soil urease activity contributed to the lower NH 3 volatilization following application of BS plus HAP. Notably, BS plus HAP applications increased the microbial byproduct- and humic acid-like substances in soil by 9.9%–74.5% and 100.7%–451.9%, respectively. Consequently, BS and HAP amended treatments significantly increased soil humification index and DOM content by 13.7%–41.2% and 38.4%–158.7%, respectively (P < 0.05). This study suggested that BS and HAP could be co-applied into agricultural soil as a potential alternative of inorganic fertilizer N, which can decrease NH 3 loss but increase soil fertility. • BS and HAP were co-applied into paddy soil to substitute urea-N with three ratios. • Urea-N substitution treatments emitted 9.1%–45.6% lower NH 3 than the control. • Decreases in soil NH 4 +-N and urease activity contributed to the lower NH 3 loss. • Co-application of BS and HAP increased soil DOM content by 38.4%–158.7%. [ABSTRACT FROM AUTHOR]

The impacts of microplastics (MPs) pollution on the nitrogen (N) cycle in soil ecosystems have attracted worldwide attention. Meanwhile, dissolved organic matter (DOM)-rich hydrochar (HBC) is being tried as an emerging soil conditioner for gaseous N reduction load to the atmosphere. However, the influence of MPs and HBC on soil DOM and ammonia (NH 3) volatilization in wheat soils remains poorly understood. In this study, a soil column experiment was established in wheat growing soils to determine the impacts of HBC, MPs (i.e., polyethylene and polyacrylonitrile), and the co-occurrence of HBC and MPs (HBC + MPs) on soil NH 3 volatilization, physicochemical properties and wheat growth. In comparison with the control (CK, without MPs or HBC), HBC, MPs, and HBC + MPs reduced cumulative NH 3 volatilization by 45.4%, 66.7–67.4% and 29.8–58.7%, respectively. Soil DOM fulvic acid-like and humic aid substance abundances of the other treatments were increased by 18.5–56.2% and 12.7–39.3%, respectively, compared to CK. Besides, soil NH 3 fluxes were positively correlated to soil NH 4 +-N concentration at basal fertilization and soil NO 3 −-N concentration at first supplementary fertilization. HBC, MPs and HBC + MPs treatments promoted soil urease activity and plant N uptake by 6.5–24.2% and 31.9–74.3%, respectively, compared to CK. This study provides an insight into the variation of NH 3 volatilization caused by anthropogenic carbon in wheat soil ecosystems. [Display omitted] • Hydrochar and microplastics reduced cumulative NH 3 volatilization in wheat soils. • Hydrochar and microplastics increased soil DOM fulvic and humic aid-like substance. • Soil NH 3 fluxes were correlated to soil inorganic nitrogen at different stages. • Hydrochar and microplastics increased soil urease activity. • Wheat nitrogen uptake was enhanced in the presence of hydrochar and microplastics. [ABSTRACT FROM AUTHOR]