Sarah K. Del Moro
Published: 2015
Total Pages: 82
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Ammonia (NH3) volatilization and loss from nitrogen (N) fertilizer in agriculture negatively impacts crops, farm profitability, human health and surrounding ecosystems where it is deposited. A significant source of NH3 volatilization occurs from surface application of urea on sandy soils with low pH buffering capacity such as those in the semi-arid Columbia Basin region of Oregon and Washington. Ammonia volatilization can be mitigated by using alternative N fertilizers to urea. Effluent from food processing and energy production industries is also used on cropland as an efficient method to conserve water and nutrients. However, NH3 emissions from effluent application have not been quantified. The objectives of this study were to: (i) quantify NH3-N loss from urea vs. alternative N fertilizer products in a micrometeorological field study and laboratory incubation experiment, and (ii) quantify NH3 emissions from effluent applied to crops using an inverse-dispersion micrometeorological method. The fertilizers evaluated in field and laboratory trials included urea, polymer-coated urea, sulfur-coated urea, urea treated with urease inhibitor [N-(n-butyl) thiophosphoric triamide (NBPT)] and ammonium sulfate (AS). Mixed and fused N salts were also evaluated, including a blend of urea and AS and a blend of AS:ammonium nitrate (AN). A modified passive flux method was used to estimate NH3-N loss from fertilizers in the field experiment for 33 d after application. In the lab incubation trial, NH3 was collected in acid for 43 d after application. In the field trial, cumulative NH3-N loss from urea was 47% of N applied. The alternative N fertilizers reduced NH3-N loss in both the field and laboratory, with the exception of the fused urea:AS blend. The reduction of NH3-N loss ranged from 19 to 68% vs. urea in the field, and 16 to 98% vs. urea in the laboratory. In the second study, a backward Lagrangian stochastic (bLS) model was used to calculate NH3 emissions from alfalfa fields receiving effluent water (average 111 mg L−1 total Kjeldahl N content) generated from a potato processor, a dehydrated onion processor, and a cogeneration plant. An ultraviolet-differential optical absorption spectrometer (UV-DOAS) and three-dimensional sonic anemometer were used to monitor NH3 concentrations, wind speed, and temperature for 43 days downwind of the field. The average NH3-N emission rate was 1.4 kg ha−1 d−1 when effluent was applied vs. 0.5 kg ha−1 d−1 during irrigation without effluent. The greatest average NH3-N emission rate of 6.1 kg ha−1 d−1 resulted from alfalfa harvest. These studies provided insight of relative NH3 loss among a variety of alternative N fertilizers to urea. Additional N mass balance research will be required to validate the accuracy of these NH3 loss quantifications. Compared to urea, all of the alternative fertilizers significantly reduced NH3-N loss, with greatest benefit resulting from NO3p− and NH4p+ fertilizer forms (> 60% reduction vs. urea). The average NH3-N emission rate of 1.4 kg ha−1 d−1 observed during effluent application was nearly three times the rate observed from irrigation without effluent. This study confirmed the potential of alternative N fertilizers to reduce NH3 emission in agriculture in conditions favoring NH3 volatilization. This study also confirmed the need to consider NH3 loss when reusing effluent as a nutrient source for crops.
