Table 1_Impact of biochar on citrus rootstocks growth, nutrient uptake, root system architecture, and soil properties.docx

Citrus greening (Huanglongbing, HLB) continues to threaten citrus production in the United States, particularly in Florida, by impairing root growth and nutrient uptake. Concurrently, citrus producers are actively seeking alternatives to traditional chemical fertilizers, which raise concerns regarding soil sustainability. Organic amendments are widely used to improve soil organic matter (SOM) and overall soil health in agricultural systems across the United States. Among these amendments, biochar has gained attention for its potential to enhance soil fertility and plant productivity; however, questions remain regarding optimal application rates, particularly in sandy soils. Additionally, literature lacks clarity on how biochar influences citrus root system architecture across different rootstocks. This study evaluated the effects of biochar on citrus root system architecture and nutrient uptake across different rootstocks in the sandy soils. The primary objective was to determine which biochar application rate most effectively improved soil fertility and root development across different citrus rootstocks. Four citrus rootstocks (‘Sour Orange’, ‘Swingle’, ‘US-802’, and ‘US-942’) were grown for 5 months under controlled greenhouse conditions in native sandy soil amended with biochar at 0%, 10%, 20%, and 30% (v/v). The experiment followed a completely randomized design with six replications per treatment (n = 6), each consisting of a single plant per pot. Root system architectural traits were quantified using WinRHIZO™ image analysis, and soil physicochemical properties along with soil and plant tissue nutrients were evaluated at harvest. The 20% biochar treatment significantly increased root length, volume, surface area, and average diameter across all rootstocks. Plant tissue analyses showed higher macronutrient concentrations, particularly in belowground tissues. Soil moisture content, soil organic matter, pH, and cation exchange capacity increased with the biochar rate, with the highest values observed with the 30% biochar rate. Moderate biochar application effectively enhanced nutrient availability and root system architecture of citrus rootstocks, demonstrating its potential as a sustainable soil amendment to improve fertility and root growth in nutrient-limited sandy soils.