Modeling the pecan nut growth and carbohydrate requirement and application of models
Abstract
The pecan nut is an important nut fruit in the USA economy, contributing more than $3.5 billion to the country's economy. The optimal time of different orchard activities like irrigation management, pesticide spray, and harvest time is difficult to identify. The growth and development of nuts as a function of heat units can be modeled to optimally time orchard activities according to a biological calendar. Our objective was to compare various nonlinear growth models and determine which best fit pecan nut development (i.e., embryo, shell, and shuck). Gompertz and Logistic functions were fitted to the pecan data. The models were fitted separately for each environment (year x location) using data collected at 4 locations in 2019 and 1 in 2020. For 2019, each location resulted in shuck and embryo development having the best fit using the Gompertz model, while the shell development was best using a logistic model. In contrast, in 2019 and 2020 with one location, Gompertz best fits embryo and logistic for shell and shuck development. This information will aid in the development of online producer tools. Pecans are reported to have alternate or masting phenomena because of irregular nut production, which is believed to be caused by carbohydrate depletion. The nonstructural carbohydrate concentration of wood and bark was determined throughout the growing season in 2019 and 2020. We found the current season shoot supports growth of the nut, while the one- year old shoot stores reserves each following year. Our result showed that there is difference in carbohydrate concentration between two years. Low starch concentration throughout the thousands of samples tested implies there could be more than two years of low production and indicate that pecan might have a masting phenomenon. Additional research was carried out to assess pecan response to varying irrigation levels. Nut size was influenced by water stress, but this response varied with cultivar. For shell hardening, the research objective was to determine how shell hardening restricts the weevil infection. The result showed that the weevil oviposits mainly in the suture where the hardness is less. Furthermore, there was a difference in the hardness of the shell among the variety. This information will be helpful in or breeder to increase tolerance or avoidance of the pest.
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- OSU Theses [15752]