Agronomic Effectiveness of Granular Nitrogen/Phosphorus Fertilizers Containing Elemental Sulfur with and without Ammonium Sulfate: A Review

1203 The widespread use of high-analysis, granular S-free NP fertilizers such as urea, MAP, DAP, and TSP, together with more intensifi ed cropping with higher yields, has resulted in increasing occurrences of soil S-defi ciency in many countries (Chien et al., 2009). Furthermore, a reduction in SO2 emissions to the atmosphere from industry, as required by environmental laws, has a signifi cant local eff ect on S deposition from the atmosphere to soils. For example, Sawyer et al. (2011a, 2011b) reported signifi cant maize (Zea mays L.) and alfalfa (Medicago sativa L.) yield increases in response to S applications at fi eld sites in northeastern Iowa. Grant (2013) reported signifi cant canola (Brassica napus L.) response to S fertilizers in Canada. Because pure ES is 100% S, incorporation of ES into highanalysis granular NP fertilizers will not signifi cantly reduce N and P contents of the NP fertilizers and minimize increase in transportation costs as compared with the inclusion of AS. However, AS is considered readily plant available, whereas ES is not, unless it is oxidized to SO4–S by soil microbes. Th e oxidation rate of soil incorporated ES particles increases with decreasing particle size of ES (Boswell and Friesen, 1993). For this reason, some fertilizer companies have been developing processes in which the very fi ne micronized ES particles (