Agronomic Evaluation of New Ureaforms for Flooded Rice

Abstract

AbstractRice (Oryza sativa L.) seldom utilizes more than 20 to 40% of the applied urea. Inefficient N utilization is largely attributed to N loss through ammonia (NH3) volatilization and denitrification. Increased N efficiency can be obtained with a slow‐release fertilizer such as ureaform (UF), which is the condensation product of urea and formaldehyde. A recent development in the production process of UF utilizes paraformaldehyde (PFA) addition to urea, which produces a modified urea fertilizer containing unreacted urea and methylene urea polymers. The purpose of this study was to evaluate N uptake and yield response of flooded rice and to determine NH3 volatilization losses from applications of 15N urea, UF, and methylenediurea. The UF fertilizers evaluated had PFA additions to urea ranging from 0% (urea) to 15% (UF‐15). In a greenhouse study with flooded rice, N uptake was measured and apparent N losses were estimated from an 15N balance. Direct NH3 volatilization losses were measured in a forced‐draft volatilization system. There was an increase in N uptake and a reduction in apparent and measured N losses from the modified urea fertilizers as the proportion of PFA increased. Plant 15N uptake at maturity can be expressed by the quadriatic equation: % recovery in total plant = 18.53 + 1.10%PFA − 0.02%PFA2. Total 15N recovered ranged from 44% as urea to 64% as UF‐15. In the forced‐draft NH3 volatilization study, total NH3 losses were reduced from 55% of the applied N as urea to 34% as MDU, and as the proportion of PFA addition to urea increased, NH3 losses decreased: % of applied N volatilized = 54.74 − 1.25%PFA. Ammoniacal N concentrations in the floodwater peaked on the 1st d after fertilizer application with urea and UF but peaked on the 7th d with MDU.