NITROGEN, PHOSPHORUS AND POTASSIUM FERTILIZATION INTERACTIONS ON THE PHOTOSYNTHESIS OF CONTAINERIZED CITRUS NURSERY TREES

The objective of this research was to evaluate the nitrogen, phosphorus and potassium (NPK) fertilizer effect on the development of Valencia' sweet orange nursery trees budded on Rangpur lime rootstocks in a greenhouse using containers. The experiment was a complete (1/5) 5(3) factorial randomized blocks design. Treatments comprised five concentrations (g per plant) of N (1.25; 6.25; 11.25; 16.25; 21.25); K (0.42; 3.75; 6.22; 9.34; 12.45); and P (0.19; 0.89; 1.59; 2.29; 2.99). Carbon dioxide assimilation rate (A), transpiration rate (E), stomata conductance (g(s)), and internal carbon dioxide (CO2) concentration (Ci) and water use efficiency (WUE). Reducing sugar, sucrose and starch were evaluated. Response functions were adjusted and nutrient rates for maximum yield were presented. The results indicated that the high levels of N (>16.25g per plant) interferes negatively on photosynthesis. Potassium at intermediate fertilization levels (from 3.75 to 6.22g per plant) had positive effects on photosynthesis. But P had little interference on photosynthesis. Carbohydrates levels were not related to nutrients fertilized.