Ammonia volatilization from fluvo-aquic clay soil and its influencing factors during wheat growing season under different fertilization

Ammonia (NH3) volatilization is a major path of N losses from applied nitrogen fertilizers, which not only results in economic losses, but also poses risks to the environment. A field experiment was set up in Yutian county, Hebei Province, to evaluate the NH3 volatilization in fluvo-aquic clay soil under applications of different fertilizers. There were four treatments with four replicates per treatment: fresh cow manure+urea (RAW), composted cow manure+urea (COM), NPK fertilizer (NPK), and control with no N fertilizer (CK). The manures and chemical fertilizer were applied at a rate of 225 kg N·hm-2, with half mixed into the soil as basal fertilization before planting and the other half applied to the soil as a top dressing after plant emergence. A continuous air-flow enclosure method was used to monitor NH3 volatilization rates during a winter wheat growing season. The highest cumulative amount of NH3 volatilization during the wheat growing season was measured in the RAW treatment with a net loss through NH3 volatilization of 1.97% of the N applied, which was significantly higher than that in the COM and NPK treatments. Up to 80% of the total NH3 volatilization occurred after top-dressing. Soil temperature was identified as a key factor affecting NH3 volatilization during the basal fertilization period and the flux of NH3 volatilization was significantly correlated with soil moisture and NH4+-N contents after top-dressing.