NITROGEN LEACHING AND PLANT UPTAKE FROM CONTROLLED-RELEASE FERTILIZERS

Controlled-release N fertilizers are commonly used in the production o f container-grown ornamental crops, yet the relative effects of variou s nutrient sources on N leaching are not well known. A 27-week experim ent was conducted to evaluate N leaching loss and plant growth followi ng two applications of six controlled-release N fertilizers and one so luble N fertilizer to container-grown Euonymus patens Rehd. The contro lled-release fertilizers evaluated were (noncoated) isobutylidene diur ea, oxamide, urea formaldehyde, and (coated) Osmocote, Prokote Plus, a nd sulfur-coated urea. Of the fertilizers tested, the coated fertilize rs generally out-performed the noncoated fertilizers in reducing N lea ching losses, stimulating plant growth, and increasing tissue N concen trations. Low N concentrations in the leachate of some treatments indi cated efficient nutrient use by the plant. In other treatments, low N concentrations in the leachate merely reflected incomplete N release f rom the fertilizer. A daily application of NH4NO3 resulted in a consta nt rate of N loss but was not the most effective in promoting growth. Plant growth, tissue N concentrations, and N leaching losses were all increased by doubling the fertilizer application rate from 1 kg N m-3 to 2 kg N m-3.