Double rows of corn (Zea mays L.) spaced at regular intervals in a soybean (Glycine max (L.) Merr.) field served as temporary windbreaks at two locations in western Minnesota. In 1969 at Dumont, Minnesota, corn windbreaks were placed between every 14 rows of soybeans (every 11.4 meters), and in 1970 at Lamberton, Minnesota, 22 rows of soybeans (17.5 meters) separated the corn windbreaks. Moisture stress was high in 1969, but moisture was adequate in 1970.Small, white evaporimeters provided estimates of potential evaporation, soybean plant potometers furnished information on potential transpiration, and the stomatal resistances of the soybean leaves were measured by a porometer and from leaf impressions. Windspeed and potential evaporation were reduced significantly over the first seven or eight soybean rows on the lee side of the windbreaks. Potential transpiration and stomatal resistance varied significantly among rows between corn windbreaks and in some cases showed cyclic trends over rows. Potential transpiration and stomatal resistance appeared to be directly related when moisture stress was low, but were inversely related when moisture stress was high.Sheltered soybean yield increases and variations over rows were largely an accumulation of the variations that occurred in the plant‐water relations during the growing season.
Crop yields and quality are frequently improved when the crop is sheltered by temporary, field wind barriers. To better understand the influence of temporary wind barriers on the microclimate, plant‐water relations, and crop yield, it is necessary to understand the effect of wind barriers on wind structure and turbulence. Several mathematical and statistical functions characterizing wind turbulence were determined for four types of wind barriers from hot‐film anemometer signals fed into a real‐time correlator with subsequent computer analysis. Wind barriers tested were double rows of corn (Zea mays L.), double rows of sunflowers (Helianthus annuus L.), a snowfence, and a solid board fence. The wind structure and turbulence parameters were always different behind the solid barrier compared to the porous barriers because the wind had to go up and over the top of the solid barrier. The porous barriers broke up the larger eddies into smaller eddies, decreased the wind velocity, and reduced the amount of energy at the lower frequencies. In general, the crop barriers gave results similar to those for snowfence for velocity but were different for energy, frequency, and scale considerations. The crop barrier leaves fluttered, causing greater energy dissipation and the generation of new distinctive frequencies. The corn and sunflowers gave similar results, although the sunflower barriers tended to be like a solid barrier because of their denser canopy.
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