Managing Citrus Trees to Optimize Dry Mass and Nutrient Partitioning

Non‐bearing "Hamlin" orange trees on "Swingle citrumelo" rootstock (32 months‐old) grown on a Candler fine sand (hyperthermic, coated Typic Quartzipsamments) were harvested to estimate dry mass, nitrogen (N), phosphorus (P), and potassium (K) accumulation and partitioning into various parts of the tree. The above parameters were evaluated for trees grown under low or high fertilization rates, using either water soluble granular (WSG), controlled release formulation (CRF), or liquid fertilizer delivered through irrigation water, i.e., fertigation (FRT). Trees were irrigated using under tree sprinklers with a wetting area diameter of 3.0 m. Total dry mass per tree followed the order: CRF > FRT = WSG and FRT > CRF > WSG for the low and high fertilization rates, respectively. Effects of fertilizer source on dry mass of individual tree parts followed the above response pattern with few exceptions. Dry mass of tree parts in relation to total tree dry mass decreased in the order: trunk > branch > leaves > roots. Therefore, the woody portion of the tree represented the major proportion of tree dry mass. Total N content in trees varied from 28.4 to 50.4 g and 41.4 to 82.3 g with different fertilizer sources at the low and high fertilization rates, respectively. The tree total N content decreased in the order: CRF > FRT > WSG and FRT > CRF > WSG at the low and high fertilization rates, respectively. Nitrogen in the leaves represented the major proportion of tree N, regardless of N source or fertilization rate. Total K content of the tree was slightly lower than total N content. Effects of fertilization source on total K content was similar to that of total N content. Total P content in trees was considerably lower than that of either N or K content. Fertilization sources and rates had negligible effects on the P content.