Comparison of Ammonia Volatilization from Surface Applied Fertilizer on High, Neutral, and Low pH Soils.

The fertilizer industry has developed several new nitrogen (N) products that may reduce ammonia volatilization from urea and ammonium based fertilizers.  These products include an ammonium sulfate-nitrate fused fertilizer (FUSN) and nutrisphere-N (N-N).  The objective of this study is to compare ammonia volatilization from FUSN and N-N treated fertilizer with commonly used fertilizers on different pH soils.  Fertilizer treatments were ammonium sulfate (AMS), ammonium sulfate with N-N, FUSN, urea ammonium nitrate (UAN), urea, and urea with N-N, and fertilizers were applied at a rate of 112 kg ha^-1.  Soil types were a sandy loam with a pH 8.3, a loamy sand with a pH 5.9, and a loamy sand with a pH 7.0.  Soil moisture content was adjusted to field capacity, and soil was placed in a tin (20 x 30 x 8 cm) to a depth of 5 cm.  Fertilizer was applied to the surface of the soil, and a boric acid trap was placed on the soil surface.  The tin was placed inside a 3 L Ziploc bag and sealed.  The boric acid trap was removed and replaced every 24 hours for 7 days.  Ammonia volatilization was determined by titration of the boric acid trap with 0.1 M HCl.  The 7 d total ammonia volatilization from FUSN (7.01 mg ammonium) was less than Urea (91.25 mg), but was not different from AMS (8.45 mg) and UAN (18.27 mg).  FUSN had the highest ammonia volatilization loss in the 8.3-pH soil (17.66 mg ammonium) with only 1.10 mg and 2.26 mg ammonium for the pH-6 and 7 soils, respectively.  Ammonia volatilization was lower for the urea N-N than the urea fertilizer (69.74 and 91.25 mg, respectively), but AMS and AMS N did not have different ammonia volatilization amounts.  Urea fertilizer had the lowest ammonia volatilization (26.57 mg) in the 8.3-pH soil with much higher levels in the 5.9 and 7.0-pH soils (80.60 and 102.07 mg, respectively. The lower ammonia volatilization rate in the 8.3-pH soil is a result of high calcium carbonate in the soil.  This study showed the FUSN fertilizer might be attractive to producers because it has a lower ammonia volatilization rate than urea and a higher percent N content than AMS.  Using N-N may reduce ammonia volatilization from surface applied urea.