Effects of Different Tillage and Nitrogen Applications on N2O Emission and Mineral Nitrogen in Surface Water of Paddy Field

Abstract

【Objective】 Rice in southern China is traditionally grown in paddy fields and improving its fertilizer use efficiency and reducing greenhouse emissions is critical to helping achieve the mandatory goal of zero-increase in agrochemical application without compromising crop yield. This paper presents the findings of an experimental study on combined effect of tillage and nitrogen application on N2O emission and mineral N concentrations in surface water of the paddy fields. 【Method】 The experiment was conducted in a double-cropping rice field and involved four tillage treatments: zero tillage (T), micro tillage (C), rotary tillage (R), and smash ridging tillage (S). For each tillage treatment, there were two N fertilizations: conventional N application at 1 225 kg/hm2 (N1) and reducing N application to 150 kg/hm2 (N2). N2O emission and mineral N concentration in the surface water in each treatment were measured 1, 3, and 5 days after N fertilization at different growth stages of the rice. 【Result】 ① One day after N fertilization, ammonium concentration in the surface water increased rapidly to a peak one and then declined quickly. In the conventional fertilization (N1) where N was applied at both tillering and booting stage, zero-tillage increased ammonium concentration in the surface water by 4.7%~532.6%, compared to other treatments. Overall, nitrate and nitrite concentrations in the surface water of all treatments were in the range 0.08~0.20 μg/mL and less than 0.12 μg/mL, respectively. ② Reducing N application and applying it as basal fertilization and topdressing at tillering and booting stages, TN2 reduced N2O emission more than other tillage treatments. ③ N2O emission was negatively correlated to ammonium concentration in the surface water 1~5 days after N fertilization, with the correlation coefficient varying from -0.509~-0.300, depending on the timing of the fertilization. 【Conclusion】 After N fertilization, ammonium became the primary inorganic nitrogen in the surface water. Ammonium concentration of the surface water 1~5 days after the fertilization impacted N2O emissions, irrespective of the timing of the fertilization.

Keywords

• tillage method
• nitrogen rate
• inorganic nitrogen
• n2o emission
• paddy soil