Feb. 25, 2004

Fertilizer Effect on Citrus Leaf Necrosis

The Effect of Biuret and Urea Fertilizer on Citrus Leaf Necrosis
John Reid, 12, Redlands, Calif.
Finalist, Discovery Channel Young Scientist Challenge, 2003

Project background: When John's family planted 500 new orange trees on their ranch, they got a lot of confusing information about fertilization. John knew nitrogen is a critical element for citrus trees and decided to find out which types of urea nitrogen produce the best growth with the least damage. John consulted an expert, Robert Krueger, who suggested that he look at the effect of biuret, a chemical contained in the urea fertilizer he was using. John decided to compare low biuret urea (LBU) and high biuret urea (HBU) fertilizers. He predicted that medium concentrations of LBU would produce the least amount of leaf death (necrosis). He also predicted that the HBU would produce necrosis even in lower concentrations.

V. Miller

Tactics and results: John began by selecting 65 young orange trees in the family grove and marking off two branchlets from each tree. He produced six different concentrations of both LBU and HBU fertilizer and painted the different formulations on the leaves of the 130 branchlets using 10 as controls. Over the next month, he conducted three field evaluations using a necrosis and growth rate scale. His results showed that all concentrations of LBU produced more growth than equivalent HBU concentrations, except at the two lowest HBU concentrations.

John concluded that the use of a high biuret area (HBU) fertilizer at low concentrations might be a viable foliar fertilizer for young citrus trees. The added benefit of HBU fertilizer is that biuret degrades seven times more slowly than urea, reducing groundwater contamination while serving the need to advance the growth of the citrus trees.

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