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Agronomic Evaluation of New Ureaforms for Flooded Rice¹

ABSTRACT

Rice (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.

¹ Contribution from the Agro-Economic Div. of the International Fertilizer Development Center (IFDC), Muscle Shoals, AL 35662 and the Dep. of Agronomy and Soils, Auburn Univ., Auburn, AL 36849.

² Research Associate/Greenhouse Supervisor; Division Director, IFDC respectively; Professor, Dep. of Agronomy and Soils, Auburn Univ.

Received for publication November 6, 1985.