Boron fertilization enhances photosynthesis and water use efficiency in soybean at vegetative growth stage

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Abstract
Influence of boron (B) on photosynthesis and water use has not sufficiently been evaluated in soybean despite its worldwide importance as a crop. The objective of this work was to evaluate the effects of B application on photosynthesis and water use in soybean at vegetative growth stage. A pot experiment was carried out in a greenhouse. Soybean [Glycine max (L.) Merrill cv. M8644 IPRO] was grown in a clayey Oxisol previously fertilized with 4 B rates (0, 1.5, 3.0, and 6.0 mg dm−3). Net photosynthesis rate (Pn), intercellular CO2 concentration (Ci), transpiration rate (E), stomatal conductance (gs) were measured in the second trifoliate leaf of plants at the V4 growth stage. Instantaneous water use efficiency (WUEis = Pn/E) and intrinsic water use efficiency (WUEic = Pn/gs) were calculated. B application to soil increased all these variables. The most consistent increases were in Pn, WUEis, and WUEic. The critical level of hot water extractable B in soil that maximized photosynthesis and optimized water use by soybean at vegetative growth stage was calculated to be 0.38 mg dm−3.

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