Ammonium fixation from urea as influenced by nitrapyrin

Abstract

During the period 1977–1979, NaNO₃, urea, and urea plus 2% (wt/wt) nitrapyrin (2‐chloro‐6‐(trimethyl)pyridine) were compared on a Matapeake silt loam (fine silty mixed mesic Typic Hapludult) . Nitrogen sources were injected as solutions into the water system at 224 kg N ha^‐1yr^‐1used for subsurface trickle irrigation of corn (Zea maysL.). Nitrogen was withheld in 1980 in order to assess residual N effects. Grain yields in 1980 for the NaNO₃, urea, and urea plus Nitrapyrin treatments were 5.10, 4.56 and 6.52 Mg ha^‐1, respectively. Corresponding ear leaf N concentrations were 17.7, 16.7 and 19.2 g kg^‐1. Significantly higher grain yield and leaf N concentrations associated with the use of nitrapyrin as a nitrification inhibitor indicated greater soil N reserves for this treatment. Non‐exchangeable (fixed) NH₄ ⁺, in soil cores taken in November 1981 averaged 54, 59 and 74 ug N g^‐1for the respective N regimes. The concentration of fixed NH₄ ⁺increased with sampling depth, averaging 54, 61 and 72 ug N g^‐1for the 0–5, 30–35, and 60–65 cm profile depths, respectively. This trend is ascribed to increasing quantities of micaceous and vermiculitic clay (<2 um) with increasing profile depth.

Key words:

• Nitrogen fixation
• Nitrification inhibitors