Application of N-15 dilution for simultaneous estimation of nitrification and nitrate reduction in soil-water columns

Abstract

Nitrification and denitrification rates were estimated simultaneously in soil-floodwater columns of a Crowley silt loam (Typic Albaqualfs) rice soil by an¹⁵N isotopic dilution technique. Labeled NO ⁻₃ was added to the floodwater of soil-water columns, half were treated with urea fertilizer. The (NO ⁻₃ +NO ⁻₂ )−N and (NO ⁻₃ +NO ⁻₂ )−N concentrations in the floodwater were measured over time and production and reduction rates for NO ⁻₃ calculated. Nitrate reduction in the urea amended columns averaged 515 μmol N m⁻²h⁻¹ and nitrification averaged 395 μmol N m⁻²h⁻¹ over the 35–153 d incubation. The nitrification rate for 4–19 d sampling period (1,560 μmol N m⁻²h⁻¹) in the urea amended columns was almost 9 times greater than the reduction rate (175 μmol N m⁻²h⁻¹) over the same period. Without the addition of urea the NO ⁻₃ production rate averaged 32 μmol N m⁻²h⁻¹ and reduction 101 μmol N m⁻²h⁻¹.