The effect of leaf area index, solar radiation, and air temperature on photosynthesis (net CO 2 assimilation) leaf canopies of three soybean ( Glycine max L., Merr.) varieties was studied. Sections of field plots (1.16‐m 2 ) were enclosed in transparent chambers, and CO 2 assimilation rates were determined by infrared gas analysis. From a maximum of about 60 mg CO 2 2/dm 2 (ground area) .hr on July 5, the assimilation rate declined to 53 mg CO 2 /dm 2 .hr by Sept. 9. Maximum variety differences were 8 mg CO 2 /dm 2 .hr. An interaction occurred between LAI and solar radiation in their effect of photosynthesis; the critic:d LAI was 5 to 6 at 0.2 ly/min solar radiation and greater than 8 (maximum LAI attained) at 1.2 ly/min. Below LAI of four canopies showed light saturation. Optimum air temperature was 25–30 C.
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Jeffers et al. (1969) studied this question.