Response of Cotton to Varying COz, Irrigation, and Nitrogen: Yield and Growth

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Abstract
The CO2 concentration of the atmosphere is increasing and is expected to double sometime near the middle of the next century. To determine the effects of such a CO2 increase on cotton (Gossypium hirsutum L.) growth and productivity, a series of experiments from 1983 through 1987 were conducted with open‐top CO2‐enriched field chambers at ample as well as limiting levels of water and N at Phoenix, AZ. Comparisons with open‐field plots showed that there was a significant chamber effect, amounting to a 30% average increase in growth inside, but under dry conditions in 1985, the situation was reversed. No significant effects of CO2 on harvest index, root‐shoot ratio, or lint percentage were found, so the primary effect of elevated CO2 was to produce plants that were larger. Comparing the results of 500 and 650 µmol mol−1 CO2 treatments, the increments of growth from ambient (about 350 µmol mol −1) to 500 µmol mol−1 were not significantly different from increments from 500 to 650 µmol mol−1. No statistically significant interactions were detected between CO2 level and either irrigation or nitrogen level, even when these variables were sufficiently low enough to limit growth. However, under well‐maintained water stress conditions, the growth response to CO2 tended to he somewhat larger than under normal irrigation levels. Averaging over all the data available from these experiments, seed cotton yield (lint plus seed) and above‐ground biomass were increased by 60 and 63%, respectively, by CO2 enrichmen to 650 µmol mo1−1.

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