Use of Inhibitors to Improve the Efficiency of Urea Fertilizer in Lowland Rice Field

Abstract

Attempts were made to reduce N loss from urea broadcast into the floodwater after transplanting and increase the efficient utilization of fertilizer N by flooded rice. A field experiment was conducted at the Suphanburi Rice Experiment Station in the 1991 wet season to study the effect of inhibitors; phenylphosphorodiamidate (PPD), N-(n-butyl) tjop[jps[jproctroa,ode (NBPT), lgicide terbutryn and wax-coated calcium acarbide (CaC2) , on the fate and effciency of urea applied to flooded rice (variety SPR90) grown on a Phimai soil (Fluvic Tropaquept) at the rate of 12 kg N rai
The results showed that the addition of algicide with ure maintained the floodwater pH values below 8.5 for the first three days after urea application and increased the accumulation of ammoniacal N higher than that of urea alone particularly the first five days. In the CaC2 treatment, although slight increases in floodwater pH were apparent, ammoniacal-n increased at a faster rate than the control. in contrast, single and repeated additions of NBPT with urea resulted in much lower ammoniacal-N accumulation (<50%). Application of the mixed inhibitors with urea also resulted in a similar pattern of ammoniacal -N accumulation as was obtained with the single NBPT treatment.
The maximum rate of NH3 loss (6.7 g N m-2s-1) occurred two days after urea application and decreased thereafter to a minimum after days 9. In the urea treatment, NH3 loss accounted for 20% of the applied N. Addition of algicide with urea reduced the total NH3 to a half (10.2%). In the presence of CaC2, 15% of the applied N was lost as NH3 compared with 10% from the NBPT treatment. The lowest NH3 loss to 7% and increased a maximum grain yield up to 31% (746.6 kg rai-2) when compared with the control (unamended urea).