Site-specific Management and Remote Sensing Based Plant Growth Regulator Application Decisions in Cotton.

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Title: Site-specific Management and Remote Sensing Based Plant Growth Regulator Application Decisions in Cotton.
Author: Nelson, John Randall
Advisors: Hugh A. Devine, Committee Member
Jeffrey G. White, Committee Member
Ronnie W. Heiniger, Committee Chair
Abstract: The use of plant growth regulators (PGR) on cotton (Gossypium hirsutum L.) to balance vegetative and reproductive production in the cotton plant is important to the success of crop production. The objectives of this study were: 1) to evaluate the use of color-infrared aerial imagery to model cotton growth status and prescribe variable-rate applications of plant growth regulators (PGR), 2) to examine the use of current recommendation methods in making variable-rate PGR applications by examining cotton growth, yield, and lint quality response to varying rates of PGR under different soil and environmental conditions, and 3) to determine the economic feasibility of an image-based, variable-rate PGR application system. Research was conducted in 1997, 1998, and 2005 at six on-farm sites in North Carolina. Grid sampling was done weekly during the growing season to record cotton plant parameters. Relationships between these parameters and digital pixel values were calculated using correlation and linear regression. Relationships were discovered between near infrared aerial imagery and cotton height, that were capable of modeling the variability of crop status throughout a field. Near infrared vegetation indices consistently accounted for more than 50% of the variation in cotton height in study fields. This indicates that remote sensing could be used to make variable-rate PGR application recommendations. At most of the sites, including sites in the same field on different soil series, a low rate of PGR applied one time was enough to improve lint yield and lint quality. The lack of site by PGR rate interactions indicated little opportunity to improve yield by varying rates of PGR. However, this research found that current recommendations for applying PGR were not applicable to making variable-rate PGR treatments. In 2003 image-based variable-rate PGR applications were found to be economically feasible when compared to standard uniform applications. In 2005, an optimum PGR rate derived from replicated PGR response plots increased profits over standard uniform PGR applications. However, scouting-based variable-rate PGR treatments were less profitable than the uniform treatment system.
Date: 2006-11-20
Degree: MS
Discipline: Crop Science

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