Current citrus nutrient guidelines are based on studies of healthy citrus trees conducted in the pre-Huanglongbing (HLB) era and may no longer be valid for the present situation where 100% of mature citrus trees in Florida are HLB-affected. We are conducting research on different N and P rates for young/mature citrus cultivars including sweet oranges, grapefruits, and mandarins. Our project will evaluate different N and P rates. These rates will address the objective of evaluating different levels of N and P in identifying the appropriate site-specific rate of N and P for north Florida. Using fertigation and controlled release fertilizer (CRF) fertilization sources, we should be able to develop and provide site specific N and P guidelines for young and mature citrus trees of Satsuma mandarins in north Florida.