Nitrogen use efficiency,floodwater properties,and nitrogen-15 balance in transplanted lowland rice as affected by liquid urea band placement

Alternative N fertilizer management practices are needed to increase productivity and N use efficiency in lowland rice (Oryza sativa L.). In 1986 dry season, a field study using¹⁵N-labeled urea evaluated the effect of time and method of fertilizer N application on grain yield and N use efficiency. Conventional fertilizer application was compared with band placement of liquid urea and point placement of urea supergranules (USG). Grain yields were significantly higher with either band or point placement than with broadcast and incorporation or surface application. Partial pressure of NH₃ (NH₃) was significantly reduced when N was deep-placed.¹⁵N balance data show that fertilizer N applied basally and incorporated gave a total¹⁵N recovery of 52% and crop (grain + straw) recovery of 30%. Band placement of liquid urea N resulted in 82–90% total and 57–65% crop¹⁵N recovery. USG point placement gave 94% total and 70% crop¹⁵N recovery. Deep placement of second N application gave only slightly higher (98%)¹⁵N recovery compared with broadcast application (89%).