THE EFFECT OF CONTROLLED-RELEASE FERTILIZER OSMOCOTE ON GROWTH, YIELDAND COMPOSITION OF ONION PLANTS

In a glasshouse and field experiments, the performance of controlled-r elease fertilizer ''Osmocote'' was compared to that of a conventional soluble fertilizer at equivalent N-amounts, using onion (Allium cepa L .) as a test crop. In the glasshouse experiment, ''Osmocote 14-6-12'' and ''Osmocote 15-5-11'' (with nutrient release duration of 3 and 4 mo nths, respectively) were compared with a soluble compound fertilizer ( 12-5-15 NPK) on onion variety Stuttgarter Reisen grown from setts, and DS-79 grown from seed. Osmocote 14-6-12 improved growth and yield of the onions, and also increased the concentration of N in variety Stutt garter Reisen. Osmocote 15-5-11 was comparable to Osmocote 14-6-12 on variety DS-79 only, but reduced the concentration on NPK and Mg in the bulbs. In the field experiment, the application of Osmocote 14-6-12 r esulted in less plant mortality, but produced higher bulb yield than t he soluble fertilizer only in a situation of oversupply of N.