Evandro Luiz Schoninger Sr.1, Lucas Peres Miachon Sr.2, Hugo Gonzalez Villalba Sr.3 and Paulo C. Ocheuze Trivelin Sr.1, (1)Stable Isotope Laboratory, CENA, University of Sao Paulo, Piracicaba, Brazil (2)Soil Science, ESALQ, University of Sao Paulo, Piracicaba, Brazil (3)Soil Science, ESALQ, Escola Superior de Agricultura, Universidad de Sao Paulo, Piracicaba, BRAZIL
This study aimed to evaluate the foliar uptake of ammonia derived from urea applied to the surface in different growing stages of maize, and to verify the correlation between the amount absorbed and leaf area. The study was carried out under field conditions in Piracicaba, State of Sao Paulo, Brazil, in the 2011/12 and 2012/13 growing seasons. We used the experimental design of randomized blocks with four replications. The treatments consisted of five times of sidedressing urea application (labeled at 12 atoms % 15N), corresponding to growth stages V4, V6, V8, V10 and V12. Urea application was performed on trays containing the same soil of the experimental area. Seven days after fertilizer application, the soil was dried and analyzed for total N content and 15N abundance. At the same occasion, plants shoots near tray was collected, dried and analyzed for total N content and 15N abundance. At each time of urea application the leaf area (LA) of the plants was also measured. Total N content and 15N abundance values from soils and plants were used to determine the percentage of N volatilized (PNV) and percentage of volatilized N that was absorbed by plants (PNA). The PNV ranged from 23 to 68% of the applied, and these differences can be related to climatic conditions. In both growing seasons, the PNA values were 3.4, 5.5, 6.2, 9.0, and 14.8% for V4, V6, V8, V10 and V12, respectively, and approximately 89% of absorbed was accumulated in the leaves and only 11% in the stalks. There was high correlation between leaf area and PNA by the leaves (r = 0.93, p≤0.01), because the leaf area is the contact surface of the plant with ammonia in the atmosphere, supporting the hypothesis that the greater leaf area reflects a greater foliar absorption of ammonia.