Biochar prepared at different pyrolysis temperatures affects urea-nitrogen immobilization and N₂O emissions in paddy fields

Abstract

Background Food safety has become a major issue, with serious environmental pollution resulting from losses of nitrogen (N) fertilizers. N is a key element for plant growth and is often one of the most important yield-limiting nutrients in paddy soil. Urea-N immobilization is an important process for restoring the levels of soil nutrient depleted by rice production and sustaining productivity. The benefits of biochar application include improved soil fertility, altered N dynamics, and reduced nutrient leaching. However, due to high variability in the quality of biochar, the responses of N loss and rice productivity to biochar amendments, especially those prepared at different pyrolysis temperatures, are still unclear. The main objectives of the present study were to examine the effects of biochar prepared at different pyrolysis temperatures on fertilizer N immobilization in paddy soil and explore the underlying mechanisms. Methods Two biochar samples were prepared by pyrolysis of maize straw at 400 °C (B400) and 700 °C (B700), respectively. The biochar was applied to paddy soil at three rates (0, 0.7, and 2.1%, w/w), with or without N fertilization (0, 168, and 210 kg N ha–1). Pot experiments were performed to determine nitrous oxide (N2O) emissions and 15N recovery from paddy soil using a 15N tracer across the rice growing season. Results Compared with the non-biochar control, biochar significantly decreased soil bulk density while increasing soil porosity, irrespective of pyrolysis temperature and N fertilizer level. Under B400 and B700, a high biochar rate decreased N loss rate to 66.42 and 68.90%, whereas a high N level increased it to 77.21 and 76.99%, respectively. Biochar also markedly decreased N2O emissions to 1.06 (B400) and 0.75 kg ha−1 (B700); low-N treatment caused a decrease in N2O emissions under B400, but this decrease was not observed under B700. An application rate of biochar of 2.1% plus 210 kg ha−1 N fertilizer substantially decreased the N fertilizer-induced N2O emission factor under B400, whereas under B700 no significant difference was observed. Biochar combined with N fertilizer treatment decreased rice biomass and grain yield by an average of 51.55 and 23.90 g pot–1, respectively, but the yield reduction under B700 was lower than under B400. Conclusion Irrespective of pyrolysis temperature, biochar had a positive effect on residual soil 15N content, while it negatively affected the 15N recovery of rice, N2O emissions from soil, rice biomass, and grain yield in the first year. Generally, a high application rate of biochar prepared at high or low pyrolysis temperature reduced the N fertilizer-induced N2O emission factor considerably. These biochar effects were dependent on N fertilizer level, biochar application rate, and their interactions.

Short-term application of biochar increases the amount of fertilizer required to obtain potential yield and reduces marginal agronomic efficiency in high phosphorus-fixing soils

“…Therefore, immobilization and volatilization could also explain the negative effect of biochar. Similarly, Gao et al (2019) and Güereña et al (2015) found that biochar combined with mineral fertilizer decreased grain yield, and the yield reduction under biochar produced at a higher temperature (700 °C) was lower than that produced at 400 °C (Gao et al 2019). The results of the present study imply that biochar should be applied at a higher rate in high P-fixing soils to ensure its beneficial effect on yield.…”

Morphological and Physiological Characteristics of Rice Cultivars with Higher Yield and Nitrogen Use Efficiency at Various Nitrogen Rates

“…Nitrogen is one of the three major chemical fertilizers applied in rice production, and its application level, timing, and management mode significantly affect rice yield and NUE [9,[29][30][31][32]. In the current study, the responses of the three cultivars to different N rates were significantly different.…”

Long-Term Effects of Straw and Straw-Derived Biochar on Humic Substances and Aggregate-Associated Humic Substances in Brown Earth Soil

“…The ratios of alkyl C/O-alkyl C, aromatic C/aliphatic C, and hydrophobic C/hydrophilic C increased in response to BC treatment compared to SR and CK. Our findings suggested that biochar amendment could enhance the long-term storage of SOC both via macroaggregate protection and via the stability of SOC (Gao et al, 2019b).…”

“…Biochar is considered an ideal material for carbon sequestration due to its stable properties. Biochar as a soil amendment can enhance crop yield (Mahmoud et al, 2019;Ali et al, 2020), improve soil total porosity and the water-holding capacity (Gao et al, 2019b), and decrease the bio-availabilities of heavy metals and organic pollutions (He et al, 2018;Xia et al, 2019). Biochar contains high amounts of carbon and has considerable potential for increasing the SOC content.…”