Economics of controlled-release fertilizer use on young citrus trees

Controlled-release N-P2O5-K2O fertilizers (CRFs) (Escote, Meister 9-month, Meister 12- month, Nutricote 360, Prokote Plus, and Sierra) and conventiona l, water-soluble fertilizer were applied at full, one-half, and one-fourth relative N rates to 'Valencia' orange [Citrus sinensis (L.) Osbeck) trees f rom planting through 6 yr of age. The full rate, which feb within the recom mended range, was 5.4 lb N/tree over 6 yr. CRFs were applied once/yr and co nventional fertilizer applied 24 times in 6 yr. Fruit was harvested the thi rd through the sixth years. Averaged across N rates, Prokote Plus, Nutricot e, and Sierra produced 4-yr cumulative fruit yields of 443 to 435 lb/tree c ompared with 390 lb/tree for conventional fertilizer; Prokote Plus and Sier ra also produced higher pounds-solids (('pounds-solids" is the term used by the Florida citrus industry to express soluble solids yield per box, per t ree, or per acre, and is the basis on which a grower is paid for his fruit) yield (27.4 lb/tree in 4 yr) and gross dollar return ($28.58/tree in 4 yr) . Prokote Plus outproduced Escote in fruit and pounds-solids yield, and out produced Escote and Meister in dollar return. The response of pounds-solids yield to N rate was described by a quadratic plateau model. Onset of the p lateau (the critical N rate) varied from 76% of the full N rate for convent ional fertilizer (at 26.9 lb-solids/tree) to 100% of the full N rate for Pr okote Plus (34.0 lb-solids/tree), Nutricote, and Meister. The cost of ferti lizing citrus with CRFs at the full N rate was four times conventional fert ilization cost, but the return was only 15% greater. The high cost of CRF p roducts currently makes their exclusive use to produce citrus economically unfeasible.