Factors Affecting Release and Plant Availability of Sulfur-Coated Micronutrients
1979
Ryan, John | Prasad, J Devi
The agronomic effectiveness of S-coated micronutrients and factors influencing their dissolution were studied in the green-house and laboratory. Grain sorghum (Sorghum vulgare L.) was grown for 7 weeks on a calcareous soil incubated individually with S-coated and uncoated FeSO₄·7H₂O, MnSO₄·H₂O, and ZnSO₄·7H₂O for 0, 1, 2, 3, 5, and 8 weeks. Dry matter yield was not significantly affected, but Fe and Mn uptake decreased with time of incubation prior to cropping. Values from S-coated materials were initially higher than from uncoated materials but showed little differences after 8 weeks of incubation. Coated materials were incubated for up to 9 weeks at varying moisture contents (8–32%), temperature (8–35°C), Ca(OH)₂(1–10%) and sucrose (0.5–2 g). DTPA-extractable Fe, Mn, and Zn in treated soils decreased with incubation time and with increasing moisture, temperature and Ca(OH₂) levels while the effect of sucrose additions was variable. With continuous extraction of the granules in water and in soil by DTPA at 4-day intervals for 71 days, most of Fe, Mn, and Zn was released during the 1st month. Oxidation of the S-coatings enhanced native micronutrient availability. Unless improvement in coating materials is made, S-coated micronutrients are unlikely to have a significant impact in micronutrient fertilization.
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