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International Journal of Agronomy
Volume 2014 (2014), Article ID 787945, 7 pages
http://dx.doi.org/10.1155/2014/787945
Research Article

Irrigated Soybean Leaf Photosynthesis in the Humid Subtropical Midsouth

Crop Production Systems Research Unit, USDA-ARS, MSA, P.O. Box 350, 141 Research Road, Stoneville, MS 38776, USA

Received 19 August 2013; Revised 20 November 2013; Accepted 10 December 2013; Published 23 January 2014

Academic Editor: Kent Burkey

Copyright © 2014 H. Arnold Bruns. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Photosynthesis (CER (μmol CO2  s−1)), stomatal conductance ( ), and intercellular [CO2] ( ) of soybean (Glycine max L. Merr.) grown using the early soybean production system (ESPS) of the midsouth were determined. Three irrigated cultivars were grown using ESPS on Bosket (Mollic Hapludalfs) and Dundee (Typic Endoaqualf) soils in 2011 and 2012 at Stoneville, MS. Single leaf CER, , and were determined at growth stages R3, R4, and R5 using decreasing photosynthetic photon flux densities (PPFD, μmol m−2 s−1) beginning at 2000 PPFD and decreasing by 250 PPFD increments to 250 PPFD. Photosynthesis changes fit a quadratic polynomial for all fixed variables and range from ~6.0 and 9.0 CER at 250 PPFD and ~22.0 to 28.0 CER at 2000 PPFD. No cultivar differences in CER, , or were noted at any growth stage or site either year. In 2012, CER, , and were lower when measured at R5 than the two previous growth stages, which was not observed in 2011. The R5 sampling in 2012 had accumulated 39 to 70 more growing degree units at 10°C base temperature (GDU 10’s) than in 2011 and were likely more mature. Increased soybean yields from ESPS appear not to result from higher leaf CER.