Submitted to: International Society of Citriculture Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/1999
Publication Date: 6/1/2000
Citation: PARAMASIVAM, S., ALVA, A.K., WHEATON, T.A., SYVERTSEN, J.P., TUCKER, D.H. CRITICAL LEAF NUTRIENT STATUS FOR OPTIMAL FRUIT PRODUCTION UNDER DIFFERING FERTILIZER MANAGEMENT PRACTICES. PROCEEDINGS OF INTERNATIONAL SOCIETY OF CITRICULTURE CONGRESS, P. 437-439. 2000. Interpretive Summary: Mineral analysis of six-month old spring flush from non-fruiting terminal provides a basis to evaluate the nutrient status of citrus trees. Six years of data were used in this study from 25+ years old Hamlin orange trees on Cleopatra Mandarin rootstock, grown with various rates and sources of nitrogen applications on a typical sandy soil. Leaf nitrogen concentrations were greater for the trees which received fertigation, as compared to those with either water soluble granular or controlled release forms of nitrogen. High yields (well over 350 boxes/acre) were obtained at nitrogen concentration ranges of 2.2 to 2.8%, or 0.09 to 0.25% of P, and 1.0 to 2.4% of K. These critical optimal concentration ranges are much broader than what have been reported in the past, thus, suggest reevaluation of the current critical concentration range recommendations.
Technical Abstract: Spring leaf nutritional standard within the optimum range for citrus trees are considered as the best indicator of successful fertilizer management practices for optimal fruit production. Six years of data from an experiment conducted in Highlands County, Florida with varying N rates (112 to 280 kg ha-1 yr-1) and fertilizer sources (water soluble granular (WSG); fertigation (FRT); and controlled release fertilizers (CRF) for 25-year-ol 'Hamlin" orange trees on Cleopatra Mandarin rootstock to develop nitrogen and irrigation best management practices (BMP), was used for this evaluation. We established relationships between relative fruit yield and leaf macro nutrient concentrations (over 500 set of data) from 6-mo-old spring flush leaves on non-fruiting twigs. Spring flush N content increased with increasing N rate and with regard to effect of N sources, the spring flush N concentration decreased in the order FRT>WSG>CRF. Other rmacro nutrients in the spring flush did not show any specific trend with increasing N rate or source. Over 98% of the yield data points were above the state average of 350 boxes ac-1 for 'Hamlin' and corresponded to leaf N content in the range of 2.2 to 2.8%. Similarly high fruit yields were observed with leaf levels of 0.09 to 0.25% of P, 1.0 to 2.4% of K, 1.0 to 3.8% of Ca and 0.3 to 0.6% of Mg. These ranges of spring flush macro nutrients concentrations which supported high yields were much wider than the previously reported optimal concentration ranges for the respective macro nutrients. This study suggests the need to reevaluate the current recommendations on the critical optimal concentration ranges.