DEEP SEEPAGE UNDER NONUNIFORM SPRINKLER IRRIGATION .2. FIELD DATA

This study evaluates quantitatively the various components of an irrigation regime affecting deep percolation. The relationship between applied water and a point water balance is studied using a linear move sprinkler, irrigating a field of sugar beets (Beta vulgaris L. Var. HC11). Uniformity coefficients of about 0.60 and 0.80 are designed in length scales of 2.5 and 5.0 m. Measurements of soil water content with a surface neutron probe, evapotranspiration with infrared thermometer, and applied water with catch cans are carried out during the growing season and used to calculate deep percolation. The seasonal transpiration average is about 50 m3/ha/day (5 mm/day). Water applied in excess of the daily transpiration rate is lost as deep percolation. For a given amount of water, high irrigation uniformity is associated with a small amount of deep percolation, and low uniformity with a large amount of percolation. This effect is more pronounced on a large length scale (5 m), than on a short length scale (2.5 m). Measured uniformities and their derivations are in good agreement with theoretical prediction. © ASCE.