Greenhouse Evaluation of Various Granular Sulfur Sources for Maize Growth.

The use of fertilizers without sulfur (S), such as urea, MAP, DAP and TSP, and the cultivation of large areas with sandy soils or low organic matter are some of the reasons for the increasing S deficiency in Brazil. The frequency of sulfur deficiency in Brazilian soils is increasing, especially in “Cerrado” region. The objective of the present study was to compare S availability of granular S fertilizers: (1) ammonium sulfate (AS), (2) blended AS and ammonium nitrate (AS+AN), (3) S-enriched MAP containing 15% S (7.5% AS-S+7.5% elemental S or ES), and (4) a new fused ammonium sulfate nitrate (fused ASN, trade name Sulf-N26). Two crops of maize were successively grown on an Oxisoil (pH 5.4) for 6-weeks each before harvest. Rates of total S applied were 0, 10, 25, 50, and 75 mg S/kg. After the first maize, the second maize was seeded without disturbing the soil pots to monitor residual S effect. The results show that dry-matter yield and S uptake by the first and second maize from S-enriched MAP were significantly lower than that from AS, blended (AS+AN) and fused ASN. The latter three S sources were not significantly different in dry-mater yield and S uptake. When dry-matter yield or S uptake was plotted against AS-S rate applied, instead of total S rate, S-enriched MAP followed the same S response curves of AS and blend (AS+AN) suggesting that only AS-S in the S-enriched MAP contributed initial and residual available S to the two maize crops. Lack of significant ES oxidation in the S-enriched MAP granules to SO₄-S was probably due to “localized” ES particles after disintegration of S-enriched MAP granules in the soil. This resulted in limited contact between soil and the dispersed ES particles that was responsible for the lack of ES oxidation.