老化玉米秸秆生物炭对碱性农田土壤氨氧化作用的影响

摘要

为探明老化(自然老化、高温老化、冻融循环老化)玉米秸秆生物炭对黄土高原碱性农田土壤氨氧化作用的影响,以玉米秸秆粉末和新鲜玉米秸秆生物炭为对照,在分析不同材料基本特性的基础上,将其按2%(质量比)与土壤充分混匀,开展为期85 d的室内静态土壤培养实验,研究土壤氨氧化速率、氨氧化细菌数量、无机氮含量和pH的动态变化.结果表明,将玉米秸秆400 ℃热解制成生物炭后,其pH增大4;与新鲜玉米秸秆生物炭相比,老化作用(自然老化、高温老化和冻融循环老化)使生物炭的pH分别降低0.30、0.50和0.99,表面羧基数量分别增加0.031、0.236和0.376 mmol·g-1,比表面积分别增大3.43、2.19和0.99 m2·g-1.室内培养实验表明,碱性农田土壤的氨氧化作用主要源自微生物氧化.土壤培养1周以后(稳定期),同一采样时间点,与玉米秸秆粉末和新鲜玉米秸秆生物炭相比,自然老化、高温老化和冻融循环老化玉米秸秆生物炭均提高了土壤的氨氧化速率(分别介于95.4~138.1、112.6~152.0和137.8~167.8 nmol·g-1·h-1)和氨氧化细菌数量(分别介于3.16×105~6.65×105、3.55×105~7.06×105和3.35×105~8.01×105g-1),促进程度表现为冻融循环老化生物炭>高温老化生物炭>自然老化生物炭.在整个培养过程中,各处理土壤NH4+-N含量随培养时间延长呈降低趋势,NO3--N和NO2--N含量呈增加趋势.该研究有助于加深理解老化玉米秸秆生物炭还田对碱性农田土壤氨氧化作用的影响,对土壤氮肥生物有效性的提高有指导意义,可为生物炭在黄土高原地区的农业工程应用提供理论借鉴.%The object of this study was to explore the effects of three types of aged maize straw-derived biochars (including spontaneous aging, high-temperature aging, and freeze-thaw cycles aging) on ammonia oxidation in a typical Loess Plateau alkaline farmland soil. The controls were maize-straw powder and fresh maize straw-derived biochar. The indoor static soil incubation experiment was carried out for 85 days after adding and evenly mixing 2% (in mass) of abovementioned materials into and with the soil sample with an aim to investigate the dynamic changes of ammonia oxidation rate, ammonia-oxidizing bacteria (AOB) amount, inorganic nitrogen content, and pH of the soils. The results showed that the pyrolysis of maize straw into biochar at the temperature of 400 ℃ increased pH by 4. Compared with the fresh maize straw-derived biochar, the pH value of the aged biochars produced from spontaneous aging, high-temperature aging, and freeze-thaw cycles aging decreased 0.30, 0.50, and 0.99, respectively, carboxyl amount increased 0.031, 0.236, and 0.376 mmol·g-1, respectively, and the specific surface area increased 3.43, 2.19, and 0.99 m2·g-1, respectively. The incubation experiment indicated that ammonia oxidation of the alkaline farmland soil mainly stemmed from biotic processes. After one-week incubation, the ammonia oxidation rates of the soils amended with spontaneous aging, high-temperature aging, and freeze-thaw cycles aging biochar were obviously promoted compared to the controls. Their ranges were 95.4~138.1, 112.6~152.0, and 137.8~167.8 nmol·g-1·h-1, respectively. AOB amounts in the soils with three different aged biochars were also markedly elevated, which were in the ranges of 3.16×105~6.65×105, 3.55×105~7.06×105, and 3.35×105~8.01×105g-1dry soil, respectively. Overall, NH4+-N in the soils decreased in the period of the incubation while NO3--N and NO2--N displayed opposite changing patterns. This study will be helpful for understanding the effects of returning aged maize straw-derived biochars back to farmland on soil ammonia oxidation, and will be meaningful for improving the effectiveness of soil nitrogen bio-availability. The study will provide a theoretical reference for the agricultural application of biochar in farmland soils of Loess Plateau.