Oil well drill cuttings and sunflower cake: effects on sunflower crop and soil chemical attributes.

Onshore oil well drill cuttings and sunflower cake from biodiesel production require an appropriate destination to reduce the risks of environmental contamination. The aim of this study was to evaluate the potential use of the combination of different doses of these wastes on the growth of sunflower plants ( Helianthus annus L.) and on soil chemical attributes after cultivation, making it possible to recommend safe application doses. Sunflower plants, cultivar Neon, were cultivated in a greenhouse for 80 days in Planossolo Háplico (Ultisol) as the main substrate. The design used was completely randomized, in a 6 × 6 factorial arrangement, composed of five doses of sunflower cake (2, 4, 8, 16 and 32 Mg ha ^-1 ) and five doses of drill cuttings (5, 15, 30, 45 and 60 Mg ha ^-1 ) and an experimental control using only Ultisol After cultivation, soil chemical attributes and the parameters height (H), stem diameter (D), and dry mass (DMAP) and nutrient contents in the aerial part of the plants were analyzed. Sunflower cake dose of 32 Mg ha ^-1 limited the germination of sunflower plants. In sunflower plants, the highest contents of calcium (Ca), magnesium (Mg), phosphorus (P) and potassium (K) were verified when the sunflower cake doses were associated with drill cuttings doses >45 Mg ha ^-1 . The mixture between sunflower cake and drill cuttings in the proportion of 16:45 Mg ha ^-1 , respectively, promoted higher H, D and DMAP of sunflower plants, as well as a considerable improvement in soil fertility, without causing significant increments in sodium content in the soil after cultivation. Highlights Inadequate disposal of agro-industrial wastes represents loss of raw material and energy.Drill cuttings and sunflower cake wastes enable improvements in soil fertility attributes.The combination of sunflower cake and drill cuttings contributed to sunflower growth and nutrient contents.The mixture of drill cuttings and sunflower cake has potential for use as agricultural input.