Effects of Biochar, Biogas Slurry, and Dicyandiamide Application on N2O Emissions from Soil in Tomato Production Under Protected Cultivation

An experiment was conducted in spring 2024 to investigate the effects of biochar, biogas slurry, and dicyandiamide (DCD) on N2O emissions from soil in protected tomato cultivation. Five treatments were applied: conventional fertilization (CK1), biogas slurry alone (CK2), biochar combined with biogas slurry (T1), DCD combined with biogas slurry (T2), and the combination of biochar, biogas slurry, and DCD (T3). The study aimed to assess the response of the soil physicochemical properties and nitrifying ammonia-oxidizing microorganisms in the tomato root zone to these treatments and to determine their impact on soil N2O emissions. The results showed that adding biochar and biogas slurry increased the soil pH, organic matter content, and levels of nitrate-N and ammonium-N, without affecting ammonia-oxidizing archaea (AOA) but inhibiting ammonia-oxidizing bacteria (AOB). The inclusion of DCD raised the soil pH and ammonium-N levels, enhanced AOA growth, did not alter organic matter content, and significantly reduced nitrate-N levels and AOB activity. Compared to CK1, treatments CK2, T1, T2, and T3 decreased the average N2O emission flux by 5.83%, 8.24%, 15.27%, and 16.16%, respectively. The application of biochar, biogas slurry, and DCD enhanced the physicochemical properties of the root zone soil and notably reduced N2O emissions in protected tomato cultivation, with T3 showing the most effective results. The biochar and biogas slurry used in this study, both derived from agricultural waste, promote sustainable agricultural development and enhance economic benefits. However, this study only considered the short-term effects of biochar, biogas slurry, and DCD, necessitating further research to explore their long-term impacts and mechanisms.