A glasshouse evaluation of sulfur fertilizer sources for crops and pastures. IV. Water solubility and physical losses and sulfur and phosphorus from S-coated triple superphosphates

Abstract

Coated fertilizers must retain the coating during transport and handling, but the nutrients in the coat must be released readily in the soil to meet plant demand. Three experimental fertilizers where S is adhered to TSP granules using UNE1, UNE3 or UNE2 adhesive were compared with a commercial S coated TSP, Hifert (HF) Goldphos-10. Fertilizer S loss from the granule was measured in a rotating drum friabilator. The highest particle loss was recorded with HF, and there were no significant differences recorded between UNE1, UNE2 and UNE3. Release of S from the coated fertilizers was measured by placing the fertilizers between 500 8m nylon mesh and leaching with distilled water at 20 mL min-1 for up to 96 h. In all products there was a rapid release of S in the first 24 h and a slower release thereafter. S release was fastest from UNEl and UNE3, and the amount of Ca and P released from the granule was also highest with these two products. Granules were scanned in the electron microscope, and electron microprobe both before and after leaching. Dispersion in distilled water was also recorded. The microprobe scan confirmed the leaching data with more S remaining in the granule with HF than UNEl or UNE3. These data confirm earlier studies that the method of adhesion of S to TSP can markedly alter the agronomic performance of the fertilizer.