Abstract
Urea applications to soil are subject to loss by ammonia (NH3) volatilization, unless incorporated. It has been proposed that this loss can be reduced by stimulating populations of soil nitrifiers by an ammonium sulfate [(NH4)2SO4] pretreatment two to four weeks before urea application. The objective of this laboratory trial was to evaluate this concept with five diverse soils, two North American Mollisols and three South American Oxisols. The soils were incubated untreated for two weeks, followed by pretreatment with 0 or 5 kg nitrogen (N) ha‐1 as (NH4)2SO4, on a soil surface area basis. After another two weeks of incubation, the soils were treated with the equivalent of 0 or 50 kg N ha‐1 as urea. Ammonia loss was estimated after trapping into phosphoric acid (H3PO4). Ammonium sulfate pretreatment reduced NH3 loss with the two Mollisols and a sandy Oxisol and increased the recovery of the urea application as mineral [ammonium (NH4 +) + nitrate (NO3 ‐)] N in these soils. Little NH3 loss was detected from the two clay Oxisols, and (NH4)2SO4pretreatment did not influence NH3 loss or recovery of urea as mineral N. An example of a cropping system where this concept may have utility is discussed.
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