Abstract
Ammonia (NH3) volatilization can reduce the efficiency of urea applied to the surface of no-till (NT) soils. Thus, the objectives of this study were to evaluate the magnitude of NH3 losses from surface-applied urea and to determine if this loss justifies the urea incorporation in soil or its substitution for other N sources under the subtropical climatic conditions of South-Central region of Paraná State, Brazil. The experiment, performed over four harvesting seasons in a clayey Hapludox followed a randomized block design with four replicates. A single dose of N (150 kg ha-1) to V5 growth stage of corn cultivated under NT system was applied and seven treatments were evaluated, including surface-applied urea, ammonium sulfate, ammonium nitrate, urea with urease inhibitor, controlled-release N source, a liquid N source, incorporated urea, and a control treatment with no N application. Ammonia volatilization was evaluated for 20 days after N application using a semi-open static system. The average cumulative NH3 loss due to the superficial application of urea was low (12.5 % of the applied N) compared to the losses observed in warmer regions of Southeastern Brazil (greater than 50 %). The greatest NH3 losses were observed in dry years (up to 25.4 % of the applied N), and losses decreased exponentially as the amount of rainfall after N application increased. Incorporated urea and alternative N sources, with the exception of controlled-release N source, decreased NH3 volatilization in comparison with surface-applied urea. Urea incorporation is advantageous for the reduction of NH3 volatilization; however, other aspects as its low operating efficiency should be considered before this practice is adopted. In the South-Central region of Paraná, the low NH3 losses from the surface-applied urea in NT system due to wet springs and mild temperatures do not justify its replacement for other N sources.
Highlights
In Brazil, the no-till (NT) system has been adopted on approximately 25 million ha and more than 12 million ha are located in the South Region (FEBRAPDP, 2008)
The second and third years had the greatest potential for nitrogen loss due to NH3 volatilization because high temperatures accelerate the enzymatic hydrolysis of urea due to an increase in urease activity, and low volumes of precipitation result in low soil moisture, which reduces NH4+ diffusion into the soil (Rodrigues & Kiehl, 1986)
Cumulative N-NH3 losses from all four years were averaged, and the results indicated that losses from surface-applied urea were equal to 12.5 % (Table 2)
Summary
In Brazil, the no-till (NT) system has been adopted on approximately 25 million ha and more than 12 million ha are located in the South Region (FEBRAPDP, 2008). Corn plays a significant role in the success of the NT system due to the significant input of straw to the soil. For no-till soils, N amendments are often applied by surface coverage fertilization, and urea is the main used source of N. N volatilization is favored by high urease activity in the surface layer of no-tilled soils (Barreto & Westerman, 1989) and the presence of straw on the soil surface, which limits contact between the soil and the fertilizer (Menguel, 1996). High soil moisture, organic matter content and CEC levels in the surface layer of NT soils are important factors increasing the buffer capacity of soil pH variation (Vieira et al, 2008) with possible effects decreasing NH3 volatilization (Ferguson et al, 1984)
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