REDUCING NITROGEN LEACHING-LOSSES FROM CONTAINERIZED PLANTS - THE EFFECTIVENESS OF CONTROLLED-RELEASE FERTILIZERS

To evaluate the effectiveness of controlled-release fertilizer (CRF) for reducing nitrogen (N) leaching-losses from containerized greenhouse crops, three experiments were conducted where CRFs were applied in different ways and compared to water-soluble fertilizer (WSF). In each experiment, First Lady' marigold (Tagetes erecta L.) plants in 0.5-liter pots of a soilless growth medium were fertilized with the same amount of N from 20N-4.3P-16.6K WSF, Osmocote 14N-6.2P-11.6K CRF, or Nutricote 14N-6.2P-11.6K CRF fertilizers. The volume of irrigation water applied to all treatments was the same in each experiment. Nitrogen content , as NH4-N and NO3-N in container leachates, and plant growth were measured and used to compare WSF with CRFs incorporated in the growth medium, or as applied to the surface, in either one large application or two small doses. A single large application of CRF at planting resulted in as much or more N leaching than the regular application of WSF. Effectiveness of CRFs in limiting N leaching was greatly increased by making two smaller applications, the first at planting and the second 15 to 35 days later. More N was recovered in the leachate when CRFs were incorporated in the growth medium compared to surface application. Regardless of fertilizer type, application method, timing of application, or for each individual experiment, NO3-N was the predominant N form found in the leachate and more than one-half of the total amount of N leached during each experiment was recovered within 30 days of planting.