Nitrogen Release Rate Differs by Fertilizer Source

Controlled-release fertilizers allow growers to reduce leachate nitrogen loss and better manage crop nutrition in comparison to water-soluble fertilizers. Nitrogen leaching and plant growth were evaluated in a container production system using a granular water-soluble (GWS) ammonium nitrate fertilizer (34-0-0), a controlled-release fertilizer (CRF) (18N-6P-12K), and a non-fertilized control (NFC). Selected plant species were grown for ten weeks using 1,485 g N per cubic meter (2.5 pounds N per cubic yard) CRF or the GWS fertilizer. Leachate pH was higher (7.0+) for the GWS and NFC treatments than the CRF (6.5 to 7.0). Total soluble salts in the leachates reflected the initial leaching of salts from the substrate, with a continued decrease in soluble salts for the GWS fertilizer and NFC treatments. With the CRF, soluble salts decreased slightly during the first five weeks, but then increased over the next five weeks. The CRF provided acceptable ammonium levels for production purposes throughout the ten-week period, while the GWS fertilizer and NFC treatments both showed progressive decreases in ammonium levels throughout the ten-week period, becoming inadequate for production. Nitrate levels varied during the ten-week period, with levels declining to insufficient amounts with the GWS fertilizer and NFC treatments, while the levels for the CRF were suitable for production throughout the study. Growth indices, fresh matter weights, and dry matter weights were higher with the CRF than with both the GWS fertilizer and NFC treatments.