COMPARISON OF THREE CONTROLLED-RELEASE NITROGEN FERTILIZERS IN GREENHOUSE CROP PRODUCTION

Abstract

Controlled-release nitrogen fertilizers allow growers to reduce nitrogen loss from leaching in comparison to soluble formulations. Plant growth and nitrogen leaching during greenhouse production of Begonia × semperflorens-cultorum Hort. cv. “Brandy” (Begonia), Euphorbia pulcherrima Willd. ex Klotzch cv. “Freedom Red” (Poinsettia), Ficus benjamina L., and Nephrolepis exaltata (L.) Schott cv. “Bostoniensis” (Boston Fern) were evaluated for eight weeks using three commercial controlled-release nitrogen fertilizers in combination with phosphorus and potassium sources to maintain a 3 : 2:1 NPK ratio. Mini Polymer Coated Urea (MPCU) 41-0-0, Trikote 42-0-0, and Regalite Nitroform (RN) 38-0-0 were incorporated into the substrate at rates of 0.9 kg nitrogen (N) m−3 and 1.5 kg N m−3 prior to potting. Total soluble salts in the leachates reflected the initial leaching of salts from the substrate, some increase or maintenance of salt levels through the third week, and lower levels from the fourth through eighth weeks. The high and low rates of Trikote and the high rate of MPCU provided acceptable levels of NH4 + for production purposes through the fourth or fifth week, the low rate of MPCU provided low levels through the third week and minimal levels thereafter, while both levels of RN showed progressive decreases from the outset. NO3 − levels varied within treatments during the eight-week period, with levels suitable for production observed during the trial with MPCU and Trikote, and declining to low levels with RN. Growth indices were similar among treatments, with the exceptions of Begonia and Poinsettia, which were larger with a low rate of RN 40 days after potting (DAP). Begonia was also larger with a low rate of Trikote 40 DAP. Shoot fresh weights (SFW) of Begonia and Poinsettia were higher with a low rate of Trikote than with MPCU or RN 40 DAP, and higher for Poinsettia with low rates of both MPCU and Trikote compared to RN 57 DAP. SFW and shoot dry weights (SDW) were similar among treatments with Boston Fern and Ficus benjamina.