Effects Of Fresh And Aged Maize Straw-derived Biochars On Ammonia Oxidation And Volatilization In A Calcareous Farmland Soil

Biochar is a kind of soil conditioner.The physicochemical properties of biochar,such as high specific surface area and abundant pores make it attract a lot of attentions.Biochar has strong adsorption capacity for nitrogen in soil,and it can not only improve the bioavailability of nitrogen fertilizer,but aslo alleviate the environmental pollution caused by excessive application of nitrogen fertilizer.However,biocharexposed to the air before itapplied to the farmland,which can oxidize the outer layer of carbon ring.After biocharapplied to the farmland,it can interact with the soil,microorganisms,and the plant roots and can also cause oxidation?aging?of the biochar.Therefore,spontaneous aging,high-temperature aging and freeze-thaw cycles aging were used to artificially simulate the aging process of biochar in nature,and the effects of fresh biochar and aged biochar on ammoxidation and ammonia volatilization of calcareous farmland soil were investigated in this study.First,based on the analysis of the basic characteristics of different exogenous materials?maize-straw powder,fresh maize straw biochar,spontaneous aged maize straw biochar,high-temperature aged maize straw biochar,and freeze-thaw cycles aged maize straw biochar?,the indoor static soil incubation experiment was carried out for 85 days after adding and evenly mixing 2%,5%?in mass?of abovementioned materials into and with the soil sample,and the sterilized soil was set as a control group at the same time.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 increased0.031,0.236,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 farmland soil mainly stemmed from biotic processes.The ammonia oxidation rates of the soils amended with spontaneous aged maize straw biochar,high-temperature aged maize straw biochar,and freeze-thaw cycles aged maize straw biochar were obviously promoted compared to maize straw power and the fresh maize straw biochar.After 11 days incubation,the ammonia oxidation rates of soil sample with 2%of abovementioned aged biochar treatment were 95.4¹38.1nmol?g^-1?h^-1,112.6¹52.0 nmol?g^-1?h^-11 and 137.8¹67.8 nmol?g^-1?h^-1,and with5%ofabovementioned agedbiochartreatment are 107.7¹45.2nmol?g^-1?h^-1,137.9¹66.4 nmol?g^-1?h^-1,157.1¹87.6 nmol?g^-1?h^-1.The degree of promotion as follow:freeze-thaw cycles aged biochar>high-temperature aged biochar>spontaneous aged biochar.To explore the effects of fresh and aged maize straw biochars on ammonia?NH₃?volatilization in a typical Loess Plateau calcareous farmland soil,the indoor static soil incubation experiment was carried out for 29 days after adding and evenly mixing 2%,5%?in mass?of abovementioned materials into and with the soil sample to investigate the diurnal variation of soil NH₃ volatilization rate and the cumulative NH₃ volatilization of the soils during the whole incubation period,and the sterilized soil was set as a control group at the same time.To unravel the mechanisms that NH₃volatilization from the soil amended with different materials,the NH₄⁺-N adsorption characteristics of the materials were also studied.The results indicated that all the materials inhibited NH₃ volatilization of the farmland soil.Compared with the soil without exogenous material added,the cumulative NH₃ volatilization during the whole incubation period decreased by 30%³4%in the freeze-thaw cycles aged or high-temperature aged biochar amended soil,decreased by 17%²3%in the spontaneous aged or fresh biochar amended soil,decreased by 19%²0%in the maize-straw powder amended soil.The first 10 days after nitrogen fertilizer application was the main stage of NH₃ volatilization,which accounted for more than90%of the cumulative NH₃ volatilization.The relatively stronger NH₃volatilization inhibition abilities of freeze-thaw cyclesaged and high-temperature aged biochars were mainly attributed to their stronger abilities of ammonia oxidation promotion and NH₄⁺-N adsorption.To explore the effect of aged biochar on the ammonia oxidation of a calcareous farmland soil with dicyandiamide?DCD?,the indoor static soil incubation experiment was carried out for 85 days after adding and evenly mixing 2%,5%?in mass?of abovementioned materials into the soil sample.The results showed that after 22 days incubation,the ammonia oxidation rates of soil sample with 2%fresh biochar,spontaneous aged biochar,high-temperature aged biochar,and freeze-thaw cycles aged biochar treatment were 48.6⁸8.5 nmol?g^-1?h^-1,43.1⁹9.5 nmol?g^-1?h^-1,58.4¹12.2nmol?g^-1?h^-1,62.0¹20.3 nmo?g^-1?h^-1,5%of abovementioned biochar treatment are 44.5⁹8.2 nmol?g^-1?h^-1,48.9¹07.5 nmol?g^-1?h^-1,53.1¹19.5nmol?g^-1?h^-1,69.4¹30.4 nmol?g^-1?h^-1.And the degree of suppression of the effectiveness of DCD as follows:freeze-thaw cycles aged biochar>high-temperature aged biochar>spontaneous aged biochar.To explore the effect of fresh and aged biochar on ammonia?NH₃?volatilization of a calcareous farmland soil with DCD,the indoor static soil incubation experiment was carried out for 29 days after adding and evenly mixing 2%?5%?in mass?of abovementioned materials into the soil sample with DCD.The results showed that compared with the treatment of no DCD,soil sample with DCD can increase the cumulative amount of ammonia volatilization.The first 10 days after nitrogen fertilizer application was the main stage of NH₃ volatilization,the application of DCD had no effect on the main period of occurrence of soil ammonia volatilization.The degree of suppression of the effectiveness of DCD as follows:freeze-thaw cycles aged biochar>high-temperature aged biochar>spontaneous aged biochar.