Sunflower Yield vs. Water Deficits in Major Growth Periods

Abstract

ABSTRACT SUNFLOWER (hybrid 894) seed yields were mea-sured in response to the imposition of water stress in the growth periods: planting-to-bud stage, bud stage-to-last anther, and last anther-to-physiologic-maturity. Stress level was based upon degree of soil water depletion and an allowable level of leaf xylem pressure depression in mid-afternoon. Yields exhibited linear relationships to seasonal ET with slope for the upper bound function near 84.3 kg/ha-cm. On a relative scale, the upper bound slope indicated a potential yield loss of 1.3 percent per 1.0 percent decline in seasonal ET. When stress was con-centrated in the bud-to-last-anther period the relative yield decline was 3.3 times greater than the reduction in seasonal ET. Near potential seed yields are likely when root zone available water depletions are limited to 50-60 percent in the pre-bud period, 30-40 percent during flowering, and 50-60 percent in the later (after ray petal drop) seed-fill period.