Field Studies and Model Simulation of the First Square Event in Cotton1

Abstract

AbstractThe ability of cotton (Gossypium hirsutum L.) production models to accurately predict the first‐square event is essential for estimating square and boll production rates. A first‐square model was formulated which requires three plant character inputs: 1) mainstem node number limits for first‐square positions, 2) characterization of fist‐square distribution between the mainstem node limits, and 3) a measure of the variability of mainstem node generation times and one environmental parameter—mean daily air temperature.Observations were made in field populations of 200 plants grown in rows spaced 101.6 cm at population densities of 98,900 plants/ha. Canparison of model simulations with the field observations in which the cultivars ‘Paymaster 909,’ ‘Paymaster 303,’ and ‘Acala 3080’ were used indicated close agreement between simulated and observed cumulative first‐square curves. The firstsquare characteristics of subpopulations of plants that emerged on the same day (Day 2 or Day 4) were most accurately simulated by beginning the simulation on the day of initial emergence for the total population. This result suggested that germination and development of seedlings that emerged as late as 3 days after the earliest plants probably began simultaneously with the earliest seedlings.Sensitivity analysis was utilized for examination of the relative influence of model parameters on the firstsquare event. Raising the position limits of the first‐square node from the interval 4 and 9 to the interval 6 and 11 increased the length of the first‐squaring period from 22 to 25 days. Changing the distribution of limit squares between the node position limits by doubling the value of the binomial distribution parameter p from 0.3 to 0.6 caused the firstquaring period to increase from 20 to 23 days. Inoreasing the mean variance of mainstem‐node generation time from 0.1 to 0.4 increased the first‐squaring period from 22 to 23 days. Mean daily air temperature had the greatest effect on the first‐squaring period; a decrease in temperature from 27 to 21 C increased the length of the first‐squaring period from 15 to 35 days.