Irrigation Levels and Potassium Doses in the Growth of Sunflower Cultivated in Soil of the Brazilian Cerrado

The chief limiting factor in sunflower (Helianthus annuus L.) development is water deficit. Besides the dearth of water, large amounts of mainly potassium (K) are essential for the favourable development and bountiful harvest of the culture. This study aimed to evaluate the growth of sunflower plants cv. SYN 042 cultivated in red Cerrado Oxisol with controlled irrigation levels and K doses. Randomized block design was selected in a 5x4 factorial scheme, administering 5 K doses (0, 40, 80, 160 and 240 mg dm-3 of K2O) and 4 different water replacement levels in the soil (75, 100, 125 and 150% of field capacity (FC)), with 4 replications. The following characteristics were evaluated: Plant height, stem diameter, Chlorophyll index, inner and outer diameters of the chapter, and dry mass of the stem. When 150% water replacement level of field capacity was utilised, it induced an increase in the plant growth as observed in terms of stem diameter, inner and outer diameters of the chapter, plant height and stem dry mass. The K added as fertiliser significantly affected the plant height, inner and outer diameters of the chapter, SPAD (direct index chlorophyll content), and stem dry mass, during the assessment performed at 60 days post emergence. The sunflower plants displayed improved development when the irrigation levels and K doses were estimated in isolation. The 150% water replacement level of field capacity provided the best results of development and growth of sunflower in Oxisol of the Cerrado.