Row orientation affects the momentum flux in wine grapevines

The momentum flux affects the energy exchange processes and thus may indirectly affect the water balance of agricultural fields. In wine vineyards, a high momentum flux between the vine rows may augment the evaporation and transpiration fluxes, and therefore decrease the water use efficiency. On the other hand, at night, high momentum fluxes may reduce (or even prevent) the formation of dew on the vine canopy, thus decrease the potential development of fungi and related diseases. We hypothesized that the wind direction relative to the row orientation in largely-spaced narrow hedge-rows characterizing wine vineyards greatly affects the momentum flux. This, in turn affects the vineyard microclimate, and ultimately, the grape quality. The objective of our research was to assess the effect of row orientation on the momentum fluxes in wine grapevines. The research was conducted in two adjacent vineyards in the Judean foothills in Israel (31°48'38.6"N 34°50'43.6"E and 31°48'37.1"N 34°50'24.0"E) having row orientations of NE-SW and SE-NW, respectively. With a NW prevailing wind direction, the wind is typically flowing perpendicularly to the former and in parallel to the latter vineyards. In each vineyard, 10 self-made type -T fine-wire thermocouples (0.08 mm diameter) were set on a pole places in the middle of the inter row, at heights above the ground of 5, 10, 20, 40, 80, 140, 220, 250, 300, and 400 cm. In addition, 4 fast-response 2D sonic anemometers (ATMOS 22, METER group, Inc., Pullman, WA, USA) were set at 10, 40, 140, and 250 cm above the ground. The measurements were conducted at 20 Hz, using a high-frequency data-logger (CR6, Campbell Scientific, Logan, UT, USA) connected to a high-frequency multiplexer (AM25T, Campbell Scientific, Logan, UT, USA). Power-spectra analysis revealed significant differences in the size of eddies penetrating the two vineyards, and a different structure of wind and temperature profiles. The co-spectra analysis indicates a significant difference in sensible heat flux between the two vineyards. This implies that there is a potential difference between the vineyards in the latent heat flux, and thus in the vineyards water use efficiency.