Estimating Ammonia Volatilization From Flooded Rice Fields by Simplified Techniques

Abstract

Two simplified methods for assessing the emission of ammonia, from fertilized, flooded rice (Oryza sativa L. cv. Inga) fields without affecting the plant's environment, are described and compared with an established micrometeorological method. Method A requires a circular plot of a 25‐m radius over which wind speed and atmospheric ammonia concentrations are observed at 0.8 m above the floodwater. Method B requires measurements of ammoniacal nitrogen concentration, pH and temperature in the floodwater, and wind speed at a fixed height. Method A is the more accurate technique and requires fewer measurements. It appears that one calibration curve relating vertical flux of ammonia to these measurements can be applied in widely different environments. Method B is not only less accurate than Method A but appears to require different calibration curves to determine vertical flux for different environments. However, this method may be more useful for comparing ammonia losses from several different fertilizer treatments since only small plot areas are required for each treatment. Method B can be calibrated easily for each site by one set of simultaneous measurements on one treatment plot, using Method A.

Ammonia volatilization of urea in the out-of-season corn

“…Urease is an extracellular enzyme produced by several soil microorganisms or plant residues. Many factors affect its hydrolysis, such as: temperature, humidity, gas exchange, water evaporation rate, water content in the soil, pH, buffering capacity, cation exchange capacity and textural class (Freney et al, 1985;Hargrove, 1988;Byrnes, 2000).…”

Characteristics of ammonium uptake by rice cells in suspension culture

“…3). Based on the equation of Freney et al (1985), NH 3 , which is a permeable species across the biomembrane (Kleiner 1981), accounts for less than 0.6% of total NH4 + plus NH3 at pH 7.0 and about 1.7% at pH 7.5. Despite the presence of a larger amount of NH3 at pH 7.5 in the uptake buffer, the uptake rate at pH 7.5 was lower than that at pH 7.0, KCI at 30 mM was added to the uptake medium.…”

“…According to the equation proposed by Freney et al (1985), 99.4% of the total ammonia is in the protonated form in water at pH 7.0 at 2YC and the proportion of ionic form increases as a function of the decrease of pH. It is generally assumed that if a molecule occurs as a neutral and an ionic species, biomembranes are rather permeable toward the neutral form but much less so for ions, which usually require carriers for transport (Kleiner 1981).…”

The fate of ammonium nitrogen applied to flooded rice as affected by zeolite addition

“…Ammonium volatilization from paddy fields is a major factor of N loss (Freney et al 1985;Fillery and Velk 1986). In this case, when the fertilizer is applied at the time of plowing, the N component in the surface water is exhausted 10d later (Takamura et al 1976).…”

“…Ammonium volatilization increases when the NH4+-N concentration in the surface water is high (Freney et al 1985). The main factors related to ammonium volatilization are pH and concentration of NH4+-N in the surface water, water temperature, and wind speed.…”