comparative effect of biofertilizers with chemical fertilizers on sunflower (helianthus annuus l.) growth, yield and oil percentage in different drought stress levels

today, environment protection and safe crop production are very important. the management of soil elements by bio-fertilizers is considered as important point for sustainable agriculture. mode of action of fertilizers is very different in drought stress conditions. to evaluate biological fertilizers (agrohumic, nitroxin, superabsorbent and vermicompost) and compare them with current chemical fertilizers (n, p and k) in sunflower (helianthus annuus l.) at different drought stress levels (100% as control, 75%, 50% and 25% field capacity), a greenhouse experiment was conducted based on completely randomized design with 20 treatments and 3 replications at college of agriculture, shiraz university in 2010. results showed that drought stress effect was significant on plant height, head diameter, biological yield (by), grain yield (gy), and harvest index (hi); however, it did not affect oil percentage. highest hi was obtained at 50% f.c, also the highest grain yield and plant height were observed in bio-fertilizers and chemical fertilizer, respectively. the most grain yield achieved under control and severe drought stress conditions were found in nitroxin and superabsorbent, respectively. fertilizers had significant effect on plant height and grain yield. generally, bio-fertilizers particularly superabsorbent and vermicompost had better responses to drought stress, compared to chemical fertilizers, which was due to higher ability of them in water maintenance. according to results of this investigation, bio-fertilizers seem to be useful under limited moisture conditions to alleviate water deficit effects.