Abnormality Analyses of Ammonia Volatilization from Nitrogen Fertilized Soils for Commercial Potato Production

Ammonia (NH₃) volatilization from agricultural soils is a common problem in commercial potato or other crop production. It is closely associated with and positively related to  NH₄⁺  concentration in the soil. Following the application of NH₄⁺  forming or containing N fertilizers, the fate of NH₄⁺  include plant uptake, volatilization, and nitrification. Therefore, NH₄⁺  concentration decreases considerably within a few days after fertilization. Typical trend in ammonia volatilization from agricultural soils is not a normal distribution. To estimate the abnormality of NH₃volatilization probability distribution, this study was conducted with four soils, three incubation temperatures (11, 20, and 29 °C), and four fertilizers (ammonium sulfate, ammonium nitrate, urea, and potassium nitrate) plus a control without fertilization under two soil water regimes (20% and 80% field capacity).  The soils evaluated include: Krome Gravelly Loam and Biscayne Marl Soil sampled from Florida and Quincy Fine Sand and Warden Silt Loam from Washington State. Based on the Jarque-Bera test, abnormality index (A) of distribution can be defined as:

A = n/6[S^2 + 1/4(K - 3)^2]  

where n is the number of observations, S is the sample skewness, and K is the sample kurtosis. A typical normal distribution has a zero value for either S or K and hence a zero value for A as well. However, the A values for this study were 1001.8 and 895.9 for 20% and 80% field capacity soil water regimes, respectively. The K value is up to 10 and skewness up to 3. This means that the probability distribution of NH₃ volatilization from N fertilized soils is positively peaked and right skewed as compared with a typical normal distribution. These results indicate that any management practices to minimize NH₃ volatilization from fertilized soils should be implemented at a very early stage after the application of ammonium containing or forming N fertilizers due to the positive kurtosis and right skewness of NH₃ volatilization.