Agronomic Effectiveness Of Granular Nitrogen/Phosphorus Fertilizers Containing Elemental Sulfur With And Without Ammonium Sulfate: A Review

Deficiency of S in soils has become a soil fertility issue worldwide because of a decrease in S deposition from air to soil due to legislation and increased crop removal. Continuous use of high-analysis nitrogen/phosphorus (NP) fertilizers lacking in S further exacerbates the S deficiency for crop production. Several newly developed granular NP fertilizers such as monoammonium phosphate (MAP), diammonium phosphate (DAP), and triple superphosphate (TSP) containing micronized elemental sulfur (ES) with/without ammonium sulfate (AS) have been marketed to farmers. It is claimed that these products can provide available SO4-S through AS and ES oxidation during the growing season. The objective of this review was to carefully examine the literature that addresses the agronomic effectiveness of the granular NPES or NP- (ES+AS) fertilizer products. The review shows that oxidation of ES particles in granular NP fertilizers is generally nil or inadequate to provide available S to seasonal (or first) crops in greenhouse studies. This is due to the negative locality effect on granular ES oxidation. In contrast, available S can be obtained from the associated AS component of the granular (ES+AS). Under field conditions, limited studies showed these granular (ES+AS) were as effective as SO4-based sources at a high single S rate, but lack of data at multiple S rates. The detailed evaluation of available data so far oft en shows that the granular NP fertilizers containing ES or (ES+AS) cannot provide available S as compared with traditional SO4-based S sources for season-long or first field crops.