Response of young citrus trees on selected rootstocks to nitrogen, phosphorus, and potassium fertilization

The majority of the citriculture in Brazil is located in the state of Sao Paulo, with a total production area of 700,000 ha. Trees are grafted mostly on 'Rangpur' lime (RL; Citrus limonia Osbeck) rootstock. Despite its good horticultural performance, use of other rootstocks has increased with the search for disease-tolerant varieties to improve grove productivity and longevity. Furthermore, there is a lack of information on young tree response to fertilization, and optimal nutrient requirements of different scion/rootstock combinations for maximum fruit yield. A network of field experiments was conducted to study the differential response of young sweet orange trees on selected rootstocks to nitrogen (N), phosphorus (P), and potassium (K) fertilization. The application of soil and leaf analyses to develop optimal fertilizer recommendations was evaluated. Experiments were conducted in three locations using fractional factorial design of one-half (4 x 4 x 4) type with four rates of N, P, or K calculated to be applied for five years after tree planting. Fruit yield response was evaluated during the last two years and correlated with soil and leaf analyses data. The trees on RL rootstock demonstrated increased efficiency of nutrient use and fruit production compared with those on 'Cleopatra' mandarin (CL; C. reshni hort. ex Tanaka) or 'Swingle' citrumelo SW; Poncirus trifoliata (L.) Raf. x C. x paradisi Macfad. rootstocks. The trees on SW rootstock appeared to require greater N and K rates than those on RL rootstock. Phosphorus requirement was greater for 'Natal' or 'Valencia' trees on CL than on RL rootstock. These results will become the basis for revising current fertilizer recommendation guidelines for young trees in Brazil.