Supplemental Irrigation For The Willamette Valley PDF Download

Some consideration has been given to the irrigation of winter wheat in the Willamette Valley of Oregon. This important crop has yielded quite well since the development and introduction of the stiff-strawed, semi-dwarf wheats, but, because of the usually dry early summers, it has been suggested that irrigation of winter wheat could probably increase the yield still further. The objective of this study was to determine the response of winter wheat to supplemental irrigation when grown under various levels of spring applied nitrogen on two important soil series. Moisture changes in the soil were followed in late spring and early summer as another phase of the study. Two winter wheat varieties were sown in October 1966 at two locations in the Willamette Valley. Each variety received supplemental nitrogen in the early spring and irrigation in late May or in June. Grain was harvested about August 1 and the yield in bushels per acre was determined. Soil moisture changes were studied at the same two locations with the use of gypsum blocks buried in the soil at different depths and at another location by soil core samples. Readings from the gypsum blocks were converted to percent moisture in the soil by a series of calculations. Based on the increase of grain yields under the various treatments, the use of nitrogen fertilizer appears to be a more practical means of increasing grain yields than does irrigation. Only a slight response to irrigation was noted. Decrease in moisture content of the soil occurred particularly in the top four feet. The largest moisture decrease occurred in the top foot, the next largest decrease was in the second foot, then the third foot, and then the fourth foot. Some moisture decrease was noted below four feet; however, the amount of decrease was small. It appears from the limited observations that soils in the Willamette Valley contain enough moisture for wheat to complete its development with little or no moisture stress.