It is not impossible, however, that the results were due to light stress. Soybean leaves, to a limited extent, tend to orientate their leaves toward the sun, and under conditions of strong direct winds, this may be prevented and the more reflective underside of the leaves may be intercepting the light
In another study on the Great Plains (Hagen and Skidmore 1974), under limited precipitation conditions, water-use efficiency was increased by reducing turbulent transfer by wind barriers or interspersed tall plants at least 20 cm (8 in) above the sheltered crop. The Great Plains area is characterized by high and nearly constant winds. These authors considered high wind speeds of up to 400 cm/sec (9 mph) and reported that in 1970, three weeks of warm southerly winds caused sheltered winter wheat to grow 11 cm (4 in) taller and to have 44 and 10% greater LAI's of the uppermost and all leaves, respectively than wheat in an open field. The increase in crop water-use efficiency was considered the key cause, however
Concern has been raised that windbreaks to increase water-use efficiency will impede CO2 movement under calmer air conditions. Hagen and more (1974) reject this on the basis that resistances are greater in the CO2 exchange path than in the transpiration path, and the percentage reduction in transpiration is greater than the percentage reduction in CO2 exchange. The net result would be increased water-use efficiency with decreased wind speed but with a minor effect in relatively strong winds.