Sunflower Seed Yield Estimation (T.Ha-1.Season-1) Based On SmithS (1994) Climatic Criteria

Comparatively speaking, sunflowers (Helianthus annus) perform well under drought conditions and they are therefore popular in the climatically more marginal areas of South Africa. Planted from November to December in the eastern parts and up to mid-January in the drier western parts of South Africa, good yields require an evenly distributed 400 - 600 mm rainfall during their growing season of about 120 days (Smith, 1998). Optimum growing temperatures are 18 - 25 degree Celsius, sub-optimally the range is 13 - 30 degree Celsius. Mean January temperatures should exceed 19 degree Celsius (Smith, 1998). Using Smith`s (1994) climatic criteria, yields of sunflower seeds are estimated using the effective rainfall for October to March and heat units (base 10 degree Celsius) for the same period, with modifications to yield made for soil properties and management levels. Rainfall values were derived from the 1 arc minute median monthly rainfalls generated for South Africa by Lynch (2004).