Release rates of ammonium-nitrogen, nitrate-nitrogen, phosphorus, potassium, magnesium, iron, and manganese from seven controlled-release fertilizers

Samples of seven controlled-release fertilizers, Nutricote Total 13-13-13, Nutricote Total 18-6-8, Osmocote Plus 15-9-12, Osmocote 13-13-13, Polyon 18-6-12, Polyon 14-14-14, and Plantacote 14-8-15, were placed in leaching columns containing acid- washed sand. Samples of all leachates were analyzed weekly to determine release rates of ammonium- nitrogen (N), nitrate-N, phosphorus (P), potassium (K), magnesium (Mg), manganese (Mn), and iron (Fe). Release rates for P from all products were slower than those for NH4-N, NO3-N, and K. Release of Mg, Mn, and Fe was very poor, with less than 50% of the total amount of each of these elements ever being released from the prills for some products. Nutricote products released Fe and Mn more effectively than did Osmocote or Plantacote.