Evandro L. Schoninger, Stable Isotopes Laboratory, CENA/University of Sao Paulo, Piracicaba - SP, Brazil, Adilson N. Silva, Crop Science Department, ESALQ/University of Sao Paulo, Piracicaba/SP, Brazil, Lucas P. Miachon, ESALQ/University of Sao Paulo, Piracicaba - SP, Brazil and Paulo C. O. Trivelin, Laboratory of Stable Isotopes, Center for Nuclear Energy in Agriculture, University of São Paulo, Piracicaba, SP, Brazil
Plants have the ability to uptake ammonia from the atmosphere through the leaves and can partially recover the N volatilized from urea applied to the soil surface. This study aimed to evaluate foliar uptake of ammonia derived from topdressing urea application at different corn growth stages. The study was carried out under field conditions in Piracicaba, State of Sao Paulo, Brazil, in the 2011/12 season. We used the experimental design of randomized blocks with four replications. The treatments consisted of four times of topdressing urea application (labeled at 12 atoms % 15N), corresponding to growth stages V4, V6, V10 and V12. Urea application was performed on trays containing 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, 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). Urea application at V4, V6, V10 and V12 stages provided PNV values of 56, 47, 24 and 38 %, respectively. These differences, with higher values to V4 and smaller to V10 must be, mainly, due to distinct weather conditions in each application time. To PNA, we observed values of 3.5, 6.3, 10.9 and 15.1 % for V4, V6, V10 and V12 growth stages, respectively, and these values differ among themselves by LSD test. The significant correlation between LA and PNA may explain the highest ammonia uptake by plants in advanced growth stages, due to greater leaf area in older plants.