By Tripti Vashisth and Taylor Livingston
Florida is currently experiencing one of the most severe droughts in the past 25 years, putting HLB-affected trees under intense water stress. With Florida’s well-draining sandy soils and increased water demand in HLB-affected trees, growers are in a difficult position trying to maintain adequate tree hydration. Soil amendments, such as biochar and compost, can be effective in helping sandy soil retain water and nutrients while increasing organic matter, which is naturally very low in the citrus-growing regions of Florida.
To demonstrate the effects of these amendments in Florida grove conditions, a field trial was initiated in May 2025 on a commercial Polk County grove using 4- to 5-year-old Valencia trees grown on 100% Candler fine sand. Treatments included five biochar:compost ratios (0:100, 25:75, 50:50, 75:25 and 100:0), which totaled 4 pounds of amendments per tree with an untreated control added. For example, the 25:75 treatment was 1 pound of biochar with 3 pounds of compost. Amendments were added in May 2025, October 2025 and March 2026 with only compost added in March (no biochar). The amendments were lightly incorporated under the canopy using metal rakes.
On May 7, 2026, record-breaking temperatures reaching up to 96 degrees occurred in Central Florida during an already severe drought. Stomatal conductance, measured throughout the day, reflects how effectively a tree can uptake water and maintain gas exchange under stress. Measurements were taken at 9:30 a.m. (pre-irrigation), 12:00 p.m. (right after a 30-minute irrigation) and 2:30 p.m. (2.5 hours after irrigation). While all treatments responded to irrigation, Figure 1 shows that the 25:75, 0:100 (highest compost), and 100:0 (highest biochar) biochar:compost treatments maintained significantly higher stomatal conductance than the untreated control at 2:30 p.m. This indicates improved ability to utilize limited water, supporting sustained productivity and reducing drought stress.
Although still early in the field trial, these results provide strong evidence that soil amendments can improve water use and maintain productivity under drought and extreme heat conditions. Additional benefits, including reduced nutrient leaching and enhanced soil microbial activity, support a more holistic approach to managing abiotic stress in HLB-affected citrus.
Learn more about compost and biochar effects here.
Tripti Vashisth is an associate professor, and Taylor Livingston is a biological scientist, both at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
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