Photo by Shankar Shrestha
By Noor Ul Basar, Davie Kadyampakeni and Muhammad Adnan Shahid
As citrus trees transition into the fall season, the nutrient demand of the trees will change. Therefore, nutrient application should be adjusted accordingly.
NITROGEN
Applying nitrogen (N) beyond October through December encourages tree canopy development at the expense of fruit yield and should be avoided. Excessive application of N in the fall season may provide limited benefit because of decreasing tree demand for growth and can increase the risk of nutrient losses and damage from cold temperatures.
POTASSIUM
However, maintaining an adequate supply of other essential nutrients for HLB-affected trees remains important. During the fall, growers should consider applying the recommended portion of potassium (K)-containing fertilizer. Potassium plays an important role in several physiological processes, particularly in fruit size development, fruit quality and overall tree health.
Potassium applications should be well synchronized with tree irrigation requirements to optimize nutrient uptake and minimize potential losses as Hamlin orange, grapefruit and Satsuma mandarin trees start remobilizing resources towards fruit maturation. This is particularly important under most of Florida’s sandy soil conditions, where low nutrient-holding capacity and rapid water movement can increase the risk of nutrient losses from the root zone.
MICRONUTRIENTS
The fall season is also a good time to supplement micronutrients through foliar fertilization. Micronutrients like zinc, manganese and boron are required in small quantities, but their deficiencies are most common in HLB-affected trees. Therefore, micronutrient application should be an important consideration for the fall to correct any existing or emerging deficiency. Micronutrients should be applied via either foliar spray or ground application.
Despite their small requirements, micronutrients play critical roles in the healthy growth of citrus trees. Growers should pay attention to leaf development and environmental conditions when planning for foliar application. Sprays should target suitable foliage and provide good canopy coverage.
PROPER ANALYSIS
Finally, fertilizer decisions should be guided by proper soil and leaf nutrient analysis whenever possible. Optimum or high K in the leaf is a good indication of better fruit maturation in citrus. The application of adequate K and micronutrients plays an essential role in maintaining the tree’s nutritional status as the grove transitions through the fall season and helps achieve the right fruit size, fruit quality and a good harvest.
Noor Ul Basaris a research associate, and Davie Kadyampakeniis an associate professor, both at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center in Lake Alfred. Muhammad Adnan Shahidis an assistant professor at the UF/IFAS North Florida Research and Education Center in Quincy.
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