Soil Moisture Content Controls the Denitrification Loss of Urea-N From Silty Clay Soils.

Denitrification from nitrogenous fertilizer like urea is the potential source of N₂O flux from agroecosystem. Soil moisture content controls denitrification loss of mineralizable N. A lab incubation study was conducted to understand the relationship between N₂O emissions of urea-N with and without additions of nitrification inhibitor, nitrapyrin (NP) and soil moisture content under silty clay soils. During lab incubation, we measured N₂O emissions from urea-N- treatments consisting (1) control (0 kg N ha^-1), (2) 150 kg urea-N ha^-1 (3) 150 kg urea-N ha^-1 with NP, (4) 250 kg urea-N ha^-1, and (5) 250 kg urea-N ha^-1 with NP from soils incubated at 30, 60 and 90% of soil water holding capacity. Soils, amended with urea-N across three moisture regimes, were incubated in an airtight 1 L mason jars at 25°C. Headspace samples are collected on days 1, 2, 4, 5, 7, 10, 12, 16, 20, 24, 30, 35, 45, and 60 from a sampling port (with butyl rubber septum) in a jar lid, using a 30 mL syringe fitted with a 21 gauge needle. Gas samples are analyzed for N₂O concentration using a Dani Master gas chromatograph, equipped with electron capture detector. In addition, at the termination of the experiment, soils are analyzed for inorganic N (NH₄⁺-N and NO₃^-- N) contents using an automated Timberline TL2800 Ammonia analyzer. The results will predict the moisture regulation of denitrification process as influenced by N management.