Calibration of a semi-open static collector for determination of ammonia volatilization from nitrogen fertilizers

Field quantification of ammonia (NH3) volatilization from applied nitrogen (N) is limited because there are no simple inexpensive methods which measure losses without interference from the measuring equipment. Five greenhouse experiments were conducted at the Center for Nuclear Energy in Agriculture, Piracicaba, Brazil in order to estimate NH3 volatilization from applied N using semi-open static collectors and the N-15 balance method. Urea, ammonium sulfate [(NH4)(2)SO4] and aqua ammonia labeled with N-15 were applied at rates from 5 to 100 mg N kg(-1) soil in pots containing 600 g of Oxisols and Ultisols (0-20 cm). Efficiency of the equipment in capturing NH3 was determined by the ratio of volatilized NH3-N from the fertilizer labeled with N-15 retained in the collector to the volatilized quantity obtained by the N-15 balance method. Efficiencies varied from less than 1% to about 50% based on the mean rate of NH3-N from the fertilizer and the mean rate of total NH3-N (fertilizer-N +soil-N) retained in the collector. The functions were adjusted by correlating all collector efficiency values with the corresponding rates of fertilizer NH3-N and total N retained in the collector regardless of soil and climatic conditions or of fertilizer application method. The models provided estimates of the efficiency of the collector for retaining NH3-N derived from fertilizer and the total NH3-N lost from the soil. The NH3-N losses were calculated based on the efficiency estimates. Losses from fertilizers were not significantly different from losses determined by the N-15 method when fertilizer N losses were greater than 0.11 mg day(-1). Total loss estimates did not differ from the losses determined by N-15 balance method for collector measured losses greater than 0.26 mg day(-1). These results showed that, if the quantity of NH3-N retained in the collector and the efficiency of the equipment are known, the collector is a simple and inexpensive device for estimating actual NH3-N losses under varying soil, climatic, and N fertilizer management conditions, without using expensive N-15-fertilizer.