There has been much focus on the benefits of applications of plant growth regulators like gibberellic acid and 2,4-D, and more recently oxytetracycline hydrochloride to improve the health of citrus trees infected with HLB.
Silicon also has been highlighted for its potential benefits to citrus. Mohammad Adnan Shahid, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) assistant professor, gave a presentation on the element during the Citrus Water and Nutrient Management Workshop held earlier this year at the Citrus Research and Education Center in Lake Alfred.
His presentation revealed some surprising facts about silicon, including that it is the second most abundant element in the Earth’s crust, making up nearly 26%, behind oxygen at 49%. Silicon is also in plants, ranging from 0.1% to 10% (dry weight basis).
While the element is abundant and is used in other crops, it has not been used much in Florida citrus. Shahid said that’s because it has not been researched much in the state’s signature crop. He aims to change that by working with colleagues on a few research projects out of the UF/IFAS North Florida Research and Education Center in Marianna, where he is based.
One action that moved silicon into the mainstream of specialty crop production was its categorization as a plant “beneficial substance” in 2012 by the Association of American Plant Food Control Officials. Prior to that time, all fertilizers that contained silicon listed it as a “non-plant food ingredient” on the product label. The product is also approved by the Organic Materials Review Institute.
These designations led to many new fertilizer products containing silicon hitting the market. Shahid has studied the element in other crops at previous research positions in other states. His work demonstrated silicon can have beneficial impacts on crops.
BENEFITS TO CITRUS
While more research needs to be conducted, Shahid says early observations indicate silicon can benefit citrus production.
“It can be beneficial for both fresh and processed citrus production, because it improves yield by increasing fruit size and number, and it strengthens the root system resulting in improved nutrient and water-use efficiency,” he said. “Based on our research so far and known literature, it could be most beneficial in inducing tolerance to abiotic stresses such as salinity, heat and cold, and biotic factors (pest and disease management).”
Those benefits could extend to Asian citrus psyllid (ACP) management and even improved health of HLB-infected trees. A study conducted in Columbia demonstrated that silicon applications (foliar, soil and foliar + soil) reduced ACP populations by as much as 60% compared to the control (no silicon). Shahid is currently in talks with UF/IFAS colleagues in hopes of conducting a collaborative study on ACP and HLB.
“I am highly interested in this project, since silicon also promotes root growth and strengthens the root structure,” he said. “My hypothesis is that silicon could induce the resistance to HLB or mitigate the effects of the disease by strengthening the cell walls in roots.”
In other crops, silicon applications have been proven to help plants withstand drought. In his presentation, Shahid provided examples of ornamental crops that showed a dramatic difference between the control and two rates of silicon [25 and 50 parts per million (ppm)] applied foliar, drench or in combination after receiving no water for seven days.
Other studies have shown that silicon application improves the shelf life of produce items and can significantly improve root mass in plants.
One way silicon might be most beneficial to citrus, especially in North Florida and South Georgia, is by providing improved cold tolerance. Shahid is cooperating with a grower in Perry, Florida, with on-farm trials at three sites. Part of that study is to evaluate cold protection induced by silicon applications. The trial got an excellent test during the late December freeze that sent temperatures below freezing for multiple days.
The trial is studying two rates (50 ppm and 100 ppm) applied at various frequencies. After the freeze, there were clearly visible differences in damage between silicon-treated trees and the control.
Shahid said he believes silicon has the potential to be a beneficial addition to Florida citrus fertilizer programs, but stressed more research is needed. He’s currently working with colleagues to obtain funding for further studies.
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