EVALUATION OF ON-FARM IRRIGATION SCHEDULING METHODS FOR POTATOES

The neutron probe, infrared thermometry and crop water stress index (C WSI), and a computer-assisted irrigation scheduling method were evalua ted in terms of their effect on tuber yield, tuber quality, and water use. The experiment was conducted during 1990 and 1998 near Othello, c entral Washington, using Russet Burbank potatoes grown in a silt loam soil. Irrigation treatments did not commence until after tuber initiat ion. In general, no differences in total number of tubers and total tu ber yield resulted from the different scheduling methods. However, the canopy temperature method showed reduction in the yield of number one tubers in 1990. The least total irrigation water was applied during t he growing season with the neutron probe method. Using CWSI values abo ve 0.5 to 1.0 (scale 0 to 10) for two consecutive days as a threshold to schedule irrigations appeared to be adequate for potatoes grown in silt loam soils. However, shortcomings of infrared thermometry suggest ed that this method may not be practical for scheduling irrigation of potatoes.