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Soil Science Society of America Journal Abstract -

Effect of Two Urease Inhibitors on Floodwater Ammonia Following Urea Application to Lowland Rice


This article in SSSAJ

  1. Vol. 52 No. 3, p. 856-861
    Received: Sept 21, 1987

    * Corresponding author(s):
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  1. R. J. Buresh ,
  2. S. K. De Datta,
  3. J. L. Padilla and
  4. M. I. Samson
  1. IFDC/IRRI Cooperative Project, IRRI, P.O. Box 933, Manila, Philippines



One proposed strategy for overcoming N loss by ammonia volatilization from urea applied to flooded rice (Oryza sativa L.) fields is to amend urea with a urease inhibitor. The inhibitor, in theory, would delay urea hydrolysis and thereby prevent the buildup of ammonia in the floodwater. Field studies were conducted at two locations in the Philippines to determine the effect of two urease inhibitors, phenyl phosphorodiamidate (PPD) and N-(n-butyl) thiophosphoric triamide (NBPT), on the vapor pressure of ammonia (pNH3) following application of urea to floodwater. Three rates of urea were applied two-thirds dosage at 18 d after transplanting (DT) and one-third dosage at 5 to 10 d after panicle initiation (DAPI). The amendment of urea with either PPD or NBPT retarded the disappearance of urea from floodwater and reduced the buildup of floodwater ammoniacal-N. NBPT generally matched or exceeded PPD in ability to reduce pNH3 at each N rate and timing for both locations. Whereas PPD only delayed the buildup in pNH3, particularly at higher N rates, NBPT effectively prevented a buildup in pNH3. For the 10 d following the first N application, NBPT reduced the mean pNH3 at 1400 h by 95, 96, and 98% for 23, 47, and 93 kg N ha−1, respectively, at one location. The corresponding reductions with PPD were 82, 54, and 25%, respectively. At the other location, NBPT reduced the mean pNH3 following the first N application by 97, 77, and 79% for 23, 47, and 93 kg N ha−1, respectively. The corresponding reductions with PPD were 79, 77, and 28%, respectively. The results suggested that urease inhibitors can effectively reduce ammonia loss from urea broadcast into the floodwater of rice fields.

Joint Contribution from the Agro-Economic Div., International Fertilizer Development Center (IFDC), P.O. Box 2040, Muscle Shoals, AL 35662, and the Agronomy Dep., International Rice Research Institute (IRRI), P.O. Box 933, Manila, Philippines.

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