Adsorbent application and nitrogen deep placement reduced ammonia emissions in wheat fields

Abstract

Increasing soil ammonium (NH₄⁺) adsorption and nitrogen (N) application depth may be beneficial for reducing ammonia (NH₃) emissions. However, there is little consensus about the combined effects of adsorbent application and N application depth on field NH₃ emissions. The study aimed to investigate the combined effects of adsorbent (humic acid-modified montmorillonite) application and N deep placement on NH₃ emissions in wheat fields. A three-year field experiment was conducted during 2020−2023. The nine treatments included the control test (CK), adsorbent applied in 0−10 cm layer (A1), adsorbent applied in 10−20 cm layer (A2), N applied in 0−10 cm layer (N1), N and adsorbent applied in 0−10 cm layer (N1A1), N applied in 0−10 cm layer and adsorbent applied in 10−20 cm layer (N1A2), N applied in 10−20 cm layer (N2), N applied in 10−20 cm layer and adsorbent applied in 0−10 cm layer (N2A1), and N and adsorbent applied in 10−20 cm layer (N2A2). Results showed that field NH₃ emissions ranged 3.88−7.76 kg N ha⁻¹ in the treatments without N application and 10.00−25.86 kg N ha⁻¹ in N-applied treatments. The greater NH₃ emissions with N application were partly attributed to the higher soil NH₄⁺ concentration, pH, and temperature and the lower volumetric water content. Adsorbent application reduced NH₃ emissions by 2.0 %−42.3 % because it increased soil adsorption of NH₄⁺. N deep placement reduced soil pH and NH₄⁺ concentration in 0−10 cm layers, and then decreased NH₃ emissions by 20.0 %−50.1 % (p < 0.05). A combination of adsorbent application and N shallow application led to similar NH₃ emissions as N deep placement, while it also led to greater wheat grain yield and biomass. NH₃ emissions were 13.5 %−51.5 % lower in N2A2 than in other N-applied treatments. Overall, adsorbent application and N deep placement reduced NH₃ emissions and improved wheat productivity, and thus is a promising practice in wheat production.