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Orientation of Leaves of Winter Wheat Planted in North-South or East-West Rows¹

The objective of the present experiment was to determine if, and to what extent, leaves of winter wheat (Triticum aestivum L. em. Thell.), oriented in two row directions, received different amounts of light. At times distributed over two growing seasons, including fall, winter, and spring months, values of I/I_O (intensity of received direct-beam radiation to incident direct-beam radiation) were calculated from solar-noon sun angles for leaves of winter wheat (cv. ‘Osage’), planted in north-south (NS) and east-west (EW) rows. Another objective of this research was to determine leaf disposition, area, width, and length, regardless of light intensity received, for fall, winter, and spring months. In addition, climatic data were collected.

Results for the winter growth period were significant. The winter results showed that I/I_O values for leaves in NS and EW rows differed markedly during the slow-growing winter season. Furthermore, on cold, windy days, it was found that leaves in NS rows were prostrate and leaves in EW rows were erect, apparently because the plants in the EW rows were protected in the winter from the prevailing northerly winds by ridges made at planting. The leaf measurements showed that leaves in EW rows were long and narrow and leaves in NS rows were short and wide. Also, plants in NS and EW rows had most leaves pointing southerly and easterly, respectively, for all seasons; fewest leaves pointed northeasterly in both NS and EW rows. There were more living leaves in NS rows than in EW rows. The leaf measurements and I/I_O calculations showed that, during winter, the leaves in EW rows, which were generally erect and not prostrate (horizontal), were oriented in many directions and had the full range of I/I_O values (range: 0 to 1.00), while leaves in NS rows, which were often not erect, but prostrate, despite wind, had a range of values of I/I_O from 0.18 to 0.76, independent of leaf direction.

Key Words: Triticum aestivum L. em. Thell. • Leaf angle • Solar azimuth • Solar altitude • Row direction • Leaf length • Leaf width • Leaf area

² Associate professor, Kansas State Univ.

Received for publication December 23, 1981.