Department of Plant Sciences

Establishment of nutrient management of citrus groves for high yield and superior crop quality is a need for efficient production. Limited phosphorus (P) availability of low fertility tropical soils in Brazil impairs citrus production since adequate P supply is important in the first years after field planting. Research has demonstrated that tree growth and fruit yield in response to P fertilization vary depending on rootstock varieties. Therefore, this study evaluated P uptake and redistribution by Pêra sweet orange on Rangpur lime or Cleopatra mandarin rootstocks initially grown in nutrient solution containing either deficient (0.005 mmol/L) or suficient(1.0 mmol/L) P levels. Each of these groups of plants was later half maintained in the deficient P whereas other half was changed to the suficient P solutions both labeled with 32P (14.8 MBq per 9.0 L pot). Plants were further grown for 50 days. Based on concentrations of P in plant parts derived from solution and P remobilized in plant, we observed that, despite variations on plant growth on different rootstocks, P taken up by those on Rangpur lime was superior confirming greater efficiency of nutrient uptake of this rootstock under a non mycorrhized condition. Estimates of P remobilized from plant reserve to young leaves suggested that the process was more marked for plants on Cleopatra mandarin irrespective to P treatments. These explained the fact that leaf visual symptoms of P deficiency are more frequent on trees on Cleopatra rootstock and presented the need to fine tune P fertilization recommendations.