Volatilização de Amônia em Solos Alagados Influenciada pela Forma de Aplicação de Ureia

Abstract

Ammonia volatilization and nitrification/denitrification are the two major N loss mechanisms in rice production. If N fertilizer is not managed appropriately, N recovery by rice plants can be low. The purpose of this study was to quantify ammonia volatilization in flooded soils influenced by the urea application method. A greenhouse study was conducted to quantify the potential of N loss via ammonia volatilization in flooded soils influenced by the urea application method. Two experiments were carried out, one in Mississippi, USA, with a thermic Vertic Haplaquepts and one in Santa Catarina, Brazil, with an Entisol Aeric soil, respectively. Ammonia was trapped in sponge sorbers impregnated with phosphoric acid and placed in PVC tubes (diameter 15 cm, length 60 cm), which were set in buckets containing a 15 cm soil layer without plants. Urea was applied at a rate of 353 mg/pot of N, equivalent to 200 kg ha -1 N, as follows: 1) a non-treated control (0 N); 2) urea applied to the surface of moist soil (80 % of field capacity) without flooding; 3) urea solubilized in deionized water and applied to the flood water; 4) prilled urea, applied to the flood water; 5) urea incorporated into mud followed by soil flooding and 6) urea applied on the surface of a dry soil followed by flooding 48 hours later. The sorbers were exchanged 1, 3, 6, 9, 13, 17, and 22 days after urea application. Water pH and ammonium concentration were determined in the flood water above the soil surface. Ammonia emission varied with the form of urea application, similarly in both soils. N losses were negligible in the control. Losses were lowest when urea was incorporated into mud followed by soil flooding and second lowest when applied to dry soil followed by flooding 48 h later (losses of, respectively, 4 and 15 % from the USA soil and 6 and 10 % from the Brazilian soil). Losses were highest when urea was applied to the flood water, be it in liquid (34 % in Mississsippi and 38 % in Santa Catarina) or in solid form (29 % in Mississsippi and 37 % in Santa Catarina), followed by urea applied to wet soil without flooding (26 % in Mississsippi and 22 % in Santa Catarina). In conclusion, to avoid excessive ammonia loss from waterlogged soils, urea should be incorporated into the mud or applied to dry soil, followed by immediate flooding in both cases.