15N Natural Abundance Characteristics of Ammonia Volatilization from Soils Applied by Different Types of Fertilizer

Abstract

Ammonia (NH3) volatilized from cropland significantly impacts the ecological environment and human health. The identification and quantification of atmospheric sources of NH3 from cropland are therefore important for NH3 emission reduction and air pollution control. Choosing appropriate nitrogen (N) fertilizer types is one of the key ways to reduce NH3 emissions from agricultural systems due to different N fertilizers with different emission factors. The natural abundance isotope of N (δ15N) values can well identify the source of NH3 volatilization, although there is rare research on δ15N-NH3 values volatilized when applying different types of N fertilizers. Here, we conducted an incubation experiment to study the characteristics of δ15N-NH3 values during the whole volatilization process after different N fertilizers were applied to the soil. The results show that the cumulative NH3 volatilization from urea (U), urease inhibitor fertilizer (UI), compound fertilizer (CF) and ammonium nitrate phosphate fertilizer (AP) treatment was 5.25 ± 0.00, 3.11 ± 0.00, 3.22 ± 0.19 and 1.38 ± 0.12 kg N ha−1 at the end of the 15-day incubation period, respectively. The average δ15N value of NH3 volatilized from the U, UI, CF and AP treatments was −36.02 ± 4.95, −29.08 ± 9.70, −35.18 ± 4.98 and −29.42 ± 4.33‰, respectively. Generally, the δ15N-NH3 values ranged from −41.33 to −6.30‰ during the NH3 volatilization process. The δ15N-NH3 value was lower in the U treatment than in the UI and AP treatments (p < 0.05), which suggests that N forms and the slow-release additions of different fertilizers, such as NO3−-N and urease inhibitors, can delay or slow down NH3 volatilization, resulting in relative isotopic enrichment. Therefore, the basic properties of different N fertilizers, the changes in soil NH4+-N and cumulative NH3 during the volatilization process significantly impacted the δ15N-NH3 values.