December 1, 2007
- Citrus sinensis,
Florida citrus trees must be irrigated to reach maximum production due to the low soil water-holding capacity of our sandy soils. Nutrients, especially nitrate-N, move rapidly through these sandy soils with drainage of excess water. In a highly urbanizing state with limited water resources, improved understanding of soil water uptake and movement is needed to optimize irrigation without leaching nutrients and impacting water quality. In a 25-month field study using mature 'Hamlin' orange (Citrus sinensis L.) trees, roots were concentrated in the top 30 cm of soil under the tree canopy (0.71 to 1.16 cm roots/cm3 soil), ETc (crop evapotranspiration) averaged 1137 mm/year, and estimated Kc (crop coefficient) ranged between 0.7 and 1.1. Day of year explained more than 88% of the variation in Kc when soil water content (?) was near field capacity. The value of Ks (soil water extraction factor) decreased steadily from 1.0 at field capacity (? = 0.072 cm3 cm-3) to approximately 0.5 at 50% available soil water depletion (? = 0.045 cm3 cm-3), where maximum soil water uptake decreased as soil water content decreased. Estimating daily plant water uptake and resulting soil water depletion based on root length density distribution under a citrus tree would provide a reasonable basis for a citrus soil water balance. It has been demonstrated that nutrient uptake is relatively rapid in citrus. However, leaching of nutrients by over-irrigation must be avoided, especially for several days after fertilizer application. Using a water balance approach, irrigation amounts can be estimated to provide adequate water for nutrient uptake and reduce leaching from over-irrigation.