Effect of Row Width and Nitrogen on Cotton Morphology and Canopy Microclimate

Abstract

Canopy structure is a function of cultural practices, genetics, and environment; specifically, practices affecting plant row width and soil fertility can change canopy structure. Canopy structure affects canopy microclimate. Canopy microclimate determines the rate of fruit development, pest pressure, and crop response to ambient conditions. The rank growth associated with excess N in cotton (Gossypium hirsutum L.) is associated with delay in fruit development and increased boll rot. This study was conducted to determine the effect of ultra narrow row (UNR) planting on canopy microclimate in cotton. Canopy microclimate in UNR cotton (18‐ to 25‐cm row width) and conventional (76‐ to 91‐cm row width) plantings with low N (16.8 kg ha−1 at planting only) or high N (16.8 kg ha−1 at planting and 202 kg ha−1 3 wk after bloom) fertilizer was quantified by monitoring the plant canopy temperature, relative humidity (RH), and vapor pressure deficit (VPD) every 15 min during the growing season. The study was conducted at Quincy, FL, on a Dothan sandy loam soil (fine loamy siliceous, thermic Plinthic Kandiudult) in 2000 and 2001. Plant height and nodes per plant were determined 60, 90, and 120 d after planting (DAP). A split‐plot design was used with row width as the main effect and N rate as subplot. During the hours from 0700 to 1900, temperature was 1 to 2°C higher and RH 3 to 7% lower in the conventional vs. the UNR plantings. In general, N and row width effects did not have as great an impact on canopy microclimate as did plant height. In 2001, when correlations were significant, as plant height increased to 1 m, canopy temperature during the hours of 0700 to 1900 on average decreased from 33 to 25°C, RH increased from 55 to 85%, and VPD decreased from 0.16 kPa to less than 0.08 kPa. In 2002, plants grew much faster and correlations of microclimate and plant height were not observed. Plant height under typical production conditions had more of an effect on canopy microclimate than did plant density or N treatment.