Citrus water requirements: linking irrigation scheduling and fertilizer strategies

Kelly T. Morgan, Thomas A. Obreza, Edward A. Hanlon

Abstract


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.

Keywords


Citrus sinensis; leaching; water-holding; nutrients

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283