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Title: Moisture Quotients for Ammonia Volatilization from Four Soils in Potato Production Regions

Author
item LIU, G - UNIV OF FLORIDA
item LI, Y - UNIV OF FLORIDA
item Alva, Ashok

Submitted to: Journal of Water Air and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 2/1/2008
Citation: Liu, G., Y.C. Li, and A.K. Alva. 2007. Moisture quotients for ammonia volatilization from four soils in Potato production regions. Water, Air, and Soil Pollution. 183:115-127.

Interpretive Summary: A portion of nitrogen (N) fertilizer applied to the soil can be lost in gaseous form as emission of ammonia depending on the source of N fertilizer and soil factors. This form of N loss also contributes to negative effects on air quality. Therefore, minimizing ammonia emission is a desirable goal in best management of N fertilization in agriculture. To this end, a clear understanding of soil factors that affect the ammonia emission is important. This study was conducted to investigate the effects of either 80 or 20% field capacity soil water regions on ammonia emission from four soils (2 each from major potato growing regions in WA and FL) amended with 75 kg/ha N as either ammonium nitrate, ammonium sulfate, or urea. This study demonstrated that ammonia emission rate was 2 to 3 fold greater at 20% field capacity soil water content than that at 80%. To quantify the soil water effects on ammonia emission, we introduced a concept of 'moisture quotient (Q)', which is the ratio of ammonia emission at 20% vs 80% field capacity soil water content. The highest Q value (112.9) was recorded for the Krome Gravelly loam soil from Florida with pH of 7.69 (highest pH among the four soils investigated) amended with ammonium sulfate. Thus, the combination of high soil pH, low available soil water content, and ammonium form of N source were favorable for maximum rate of ammonia emission.

Technical Abstract: Ammonia (NH3) emission from nitrogen (N) fertilizers used in agriculture decreases N uptake by the crop and negatively impacts air quality. In order to better understand the factors influencing NH3 emission from agriculture, this research was conducted with four major soils used for potato production: Biscayne Marl Soil (BMS, pH 7.27), and Krome Gravelly Loam (KGL, pH 7.69) from Florida; and Quincy Fine Sand (QFS, pH 6.65), and Warden Silt Loam (WSL, pH 6.46) from Washington. Potassium nitrate, ammonium nitrate, ammonium sulfate, or urea sources were evaluated for ammonia volatilization at 75 kg N/ha rate. The soil water regime was maintained at either 20% or 80% of field capacity (FC), and incubated at 11, 20 or 29 oC. Results indicated that NH3 volatilization rate at 20% FC was 2- to 3-fold greater than at 80% FC. The cumulative volatilization loss over 28 days ranged from 0.21% of N applied as ammonium nitrate to 25.7% as ammonium sulfate. Results of this study demonstrate that NH3 volatilization was accelerated at the low soil water regime. Moisture quotient (Q) is defined as a ratio of NH3 emission rate at 20% FC to that at 80% FC both at the same temperature. The Q values of NH3 volatilization were up to 20.8 for the BMS at 20 degrees C, 112.9 for the KGL soil at 29 degrees C, 19.0 for the QFS soil at 20 degrees C, and 74.1 for the WSL soil at 29 degrees C, respectively. Thus, maintaining a near optimum soil water regime is important to minimize N loss via NH3 volatilization and to improve N uptake efficiency.