The Cotton Simulation Model "COTTAM":Fruiting Model Calibration and Testing

Abstract

ABSTRACT ALGORITHMS contained in the simulation model COTTAM for determining the morphological development of cotton in response to environment are described. Crop growth rate is represented by a number of growing bolls called carrying capacity, and fruit shedding occurs as a function of the ratio of boll load and carrying capacity. Vegetative growth is defined as the increase in fruiting site numbers. Leaf area increases as fruiting site numbers increase. As boll load increases, vegetative growth (increase in fruiting site numbers) declines and fruit shedding increases. A root extraction zone penetrates a layered soil profile as a function of soil properties. Water stress is defined as a function of plant available water in the root extraction zone and influences vegetative growth rates and crop growth rates (carrying capacity). Fruiting algorithms were calibrated using field and greenhouse data. Numbers of fruiting sites, growing bolls, open bolls, square and boll phenological development, boll weights, leaf growth and senescence, growth of a root extraction zone, and water extraction are computed in response to daily weather data. Simulated plant development may also be influenced by plant maturity-type, plant population and row spacing, and water stress. Simulation results using COTTAM were compared to fruit numbers measured in field-grown cotton near Temple, TX, Lubbock, TX and Fresno, CA. Crops were grown at these three locations using different water application scenarios. Measured lint yields ranged from 528 to 1,583 kg ha~^ Analyses compared the timing of yield development, fruit numbers, and final yields. Simulated timing and maximum numbers of squares, growing bolls, and open bolls compared well with those measured at all three locations. At all locations, the simulated date 50% of final boll numbers were open averaged within 3 days of those measured. The standard error of estimate for simulated lint yields at all three locations was 135 kg ha~^