Economics of Controlled-Release Fertilizer Use on Young Citrus Trees

Abstract

Controlled-release N-P 2 O 5 -K 2 O fertilizers (CRFs) (Escote, Meister 9-month, Meister 12- month, Nutricote 360, Prokote Plus, and Sierra) and conventional, water-soluble fertilizer were applied at full, one-half, and one-fourth relative N rates to 'Valencia' orange [Citrus sinensis (L.) Osbeck) trees from planting through 6 yr of age. The full rate, which fell within the recommended range, was 5.4 Ib N/tree over 6 yr. CRFs were applied once/yr and conventional fertilizer applied 24 times in 6 yr. Fruit was harvested the third through the sixth years. Averaged across N rates, Prokote Plus, Nutricote, and Sierra produced 4-yr cumulative fruit yields of 443 to 435 Ib/tree compared with 390 Ib/tree for conventional fertilizer; Prokote Plus and Sierra also produced higher pounds-solids (pounds-solids is the term used by the Florida citrus industry to express soluble solids yield per box, per tree, or per acre, and is the basis on which a grower is paid for his fruit) yield (27.4 Ib/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 outproduced 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 plateau (the critical N rate) varied from 76% of the full N rate for conventional fertilizer (at 26.9 Ib-solids/tree) to 100% of the full N rate for Prokote Plus (34.0 Ib-solids/tree), Nutricote, and Meister. The cost of fertilizing citrus with CRFs at the full N rate was four times conventional fertilization cost, but the return was only 15% greater. The high cost of CRF products currently makes their exclusive use to produce citrus economically unfeasible.