By Ajia Paolillo
As the season moves from winter to spring, the irrigation requirements of citrus trees change. Typically, February through May is the drier time of year in Florida with low rainfall amounts in most areas. However, during this period, the trees are actively producing leaves and flowers, setting fruit, and pumping resources to the growing fruit during cell division and fruit enlargement. Water requirements increase during this time and enable the tree to perform these important tasks.
Citrus greening (HLB) compromises the root systems in trees. Depending on disease severity, trees can lose 50% to 80% of their root system. The remaining roots are still as efficient as those of healthy trees, there is just less of them. This makes it more challenging for the tree to take up the water it needs to grow and produce fruit. Soil types differ within Florida’s citrus-growing region, with some having a higher water-holding capacity than others. Research recommendations have suggested that regardless of soil type, irrigation should be applied to trees more frequently for less durations, reducing the amount of water applied at a given irrigation event.
The goal is to achieve a sufficient amount of available water in the soil for healthy tree growth and fruit production. Let’s look at some terms that will help growers understand what defines available water in the soil, and how to measure allowable soil water depletion to guide irrigation scheduling. Field capacity is a term used to describe the point at which all the air pockets in the soil are filled with water, and drainage through the soil profile stops. Soils reach field capacity typically after a large rain event. Field capacity is the point at which there is the most available water in that soil. In contrast, the permanent wilting point is when there is not enough available water in the soil for the tree to uptake. The drier the soil, the less available water for the trees. The depletion of available soil water is the difference between field capacity and permanent wilting point.
The amount of irrigation needed depends on the time of year, rainfall and the needs of the tree. As stated above, during February through May, rainfall is low, but the trees’ water requirements increase. The recommended guideline of available soil water depletion during these months should not be more than 25%. Once the summer rains begin around June, available soil water depletion should be 50%.
Ajia Paolillo is a University of Florida Institute of Food and Agricultural Sciences multi-county citrus agent based in Arcadia.
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