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|Title:||Competition and Growth of Corn (Zea Mays, L.) as Functions of Population Density, Row Width, and Time (Analysis, Model, Richards)|
|Author(s):||Caldwell, Robert Martin|
|Department / Program:||Agronomy|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||This thesis (1) proposes a quantitative definition for the intensity of competition, and (2) presents the mathematical/statistical tools necessary to estimate intensity of competition as a function of population density, row width and time. The difference between the growth rate of a plant in a given plant arrangement and the growth rate of a plant in isolation is a measure of the intensity of competition per plant, ICPP.
Field experiments were performed in 1980, 1981, and 1982 to estimate ICPP for plants in different plant arrangements. Corn (Zea mays, L.) was grown in a series of five or six populations densities (square plant arrangement) and a series of seven row widths (population density constant: 50,000 plants/ha) at Urbana, Ill. Periodic harvests (8 or 11) were made to measure total shoot dry matter yield, Y. The following regression model was proposed in the analysis: (1) If PD = CPD, let PD1 = (PD - CPD), and PD2 = CPD. If RW > CRW, let RECTANGULARITY = (RW - CRW)/125; If RW < = CRW, then RECTANGULARITY = 0. Then, Y = (EL *(1-EXP(-(GL/EL) *PD1)) + GL*PD2) * (1- RECTANGULARITY) + RL*RECTANGULARITY. PD was the population density, and RW was row width. GL, EL, RL, CPD, and CRW were five fitted parameters, estimated using weighted, nonlinear regression analysis. CPD was the density in which plants were just beginning to compete. CRW was the widest row width not experiencing a yield loss due to the rectangularity of spacing. Richards function was used to model the change in the five fitted parameters over time. Plant growth rates were estimated by the model, and ICPP was calculated from the growth rates.
Intensity of competition increased with both density and row width. In 1982, ICPP for each of the row width treatments converged over the last half of the season. The relative differences among the densities for ICPP remained constant through the season.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2014-12-16|