NH3 volatilization

An appreciable amount of NH3 volatilizes from soil. In some fields, up to 50% of the added ammonium-N volatilizes. In addition to the economic importance of this nitrogen loss, there is also environmental importance. In industrialized regions of the world, NH3 in the atmosphere approaches concentrations high enough to cause toxicity effects on forests. 

Soil pH buffering appears to play a major controlling role in NH3 volatilization. The potential of soil to buffer pH depends on mineralogical composition, percent base saturation, type of exchangeable cations, and CEC. An empirical formula for soil pH buffering, noted as B, is given by (Avnimelech and Laher, 1977) 

Soil pH. This is only important when the pH buffering capacity of soil is very large (B approaches zero). Generally, when initial pH is high and soil B is very low, maximum NH3 is lost (Avnimelech and Laher, 1977). 

ORGANIC MATTER, NITROGEN, PHOSPHORUS, SYNTHETIC ORGANICS 

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C. Effect-of sodium hydroxide and sodium acetate on NH3 volatility at 80°C... 

The effects of sodium acetate and sodium hydroxide on NH3 volatility at 80°C were studied by two methods. Data on the effect of sodium acetate were measured in the same apparatus used to measure the NH3-H0O data shown in Figure 1. In this case, sodium acetate was also added to the liquid phase with subsequent... 

The floodwater often has a high pH as a result of CO2 removal by photosynthe-sizing organisms, favouring NH3 volatilization. 

The removal of fertilizer N in the crop as NH4+ does not lead to acidification. Hydrolysis of urea fertilizer—by far the main form of N fertilizer used in wetland rice, together with ammonium bicarbonate in some countries—consumes 1 mol of H+ per mol of NH4+ formed (Table 7.1, Process 1). So although absorption of N as NH4+ leads to a net export of H+ from the roots to balance the resulting excess intake of cations over anions (Table 7.1, Process 5), this acidity is matched by the H+ consumed in urea hydrolysis. Likewise there is no net generation of acidity as a result of NH3 volatilization, although 1 mol of H+ is left behind per mol of NH4+ converted to NH3 (Table 7.1, Process 3). 

Figure 8.9 Profiles of urea-N, ammoniacal-N and pH with depth following broadcast application of urea on ricefield floodwater, and the corresponding rates of NH3 volatilization (calculated with the model of Rachhpal-Singh and Kirk, 1993a,b)...

Bouldin DR, Alimago BV. 1976. NH3 volatilization from IRRI paddies following broadcast applications of fertilizer nitrogen. IRRI Miscellaneous Report. Manila International Rice Research Institute. 

A special case is given by ammonia volatilization from flooded land surfaces, which involves a more complex pathway. This is because the kinetics and extent of the volatilization are affected by water quality, type of land, and biological and environmental factors. In this particular case, the rate of NH3 volatilization is mainly a function of ammonia concentration in the flooding water (Jayaweera and Mikkelsen 1991). 

Beek and Frissel (1973) Growth of nitrifier and ammonifer bacteria by Michaelis-Menten kinetics NH4 oxidation by first-order kinetics with environmental variables mineralization of proteins, sugars, cellulose, lignin, and living biomass by first-order kinetics immobilization by first-order kinetics including considerations for microbial biomass and C/N ratio NH3 volatilization by diffusion NH4 clay fixation by equilibrium model. 

Tillotson et al. (1980) Nitrification and urea hydrolysis by first-order kinetics NH3 volatilization by first-order kinetics from (NH4)2C03 formed from urea hydrolysis NH sorption by linear partition model NH and NOy plant uptake involving diffusion to roots. 

Equation B points out that the amount of acid produced during NH3 volatilization (AA) equals the difference between original NH4 ([NH4]0) minus final NH4 ([NH4]f). By rearranging Equation 8.10,... 

When plotted as 1/NH3 versus 1/NH4, Equation H would produce a straight line with slope ([H]0 + B [NH4]0)/(A W/Arb) andy intercept -B [KJKb. The equilibrium-dependent model described above was used by Avnimelech and Laher (1977) to demonstrate how pH and soil pH buffering capacity, B, control NH3 volatilization (Fig. 8A). This can also be evaluated by carrying out a sensitivity analysis on Equation G, which shows that when B approaches zero (extremely high soil pH buffering capacity), or NH4 in the system is very low, such that H° > > ([NH4]0-[NH4]r), Equation H reduces to... 

A plot of NH3 versus 1/H+ would give a straight line under constant [NH4]. Therefore, NH3 volatilization would be inversely related to H+ and directly related to NH4 (Fig. 8B). When B is large (approaches 1) (soil pH buffering capacity is... 

Explain how soil pH buffering potential controls NH3 volatilization for... 

The relative importance of various forms of N lost to the atmosphere has been shown clearly. N2 is the primary form of N lost during denitrification in salt marshes (Cartaxana and Lloyd, 1999 Smith et al, 1983). NO and N2O losses are orders of magnitude smaller by comparison. Maximal rates of N2O loss normally do not exceed 0.14 mg N m day (Smith et al, 1983). NH3 volatilization, while not a component of denitrification, is another form of gaseous N loss in salt marsh systems. It too is orders of magnitude lower than rates of N2 loss due to the fairly low sediment pH values (<8) in most marsh sediments (Koop-jakobsen, 2003 Smith et al, 1983). 

Note A.) NH3/volatile solvent inlet system. B.) assembly for pre-drying ammonia. C.) connection to reaction apparatus. Figure reproduced from Ref. 16a. 

The dominant input items were related to the application of mineral fertilizers and import of food and goods (abont 80% from total inpnt). Deposition (about 55% from abroad through transboundary air pollution) and non-symbiotic N fixation were responsible for the other 20% of input. The output was connected with N volatilization via direct NH3 volatilization and biological denitrification (33.7% from total input) and river discharge (23.2%). The sum of output was about 60% from input. 

EtOH, Et20 V. spar. sol. H2O. Mp 123°. Bp 285-286°. Reduces AgN03.NH3. Volatile in steam, EtOH and Et20. 

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