The effects of nitrogen and water stress on allelopathic potential of sorghum forage on seed germination characteristics and primary growth safflower

To evaluate the effects of nitrogen and water stress on allelopathic potential of sorghum (Sorghum bicolor) on the seed germination traits of safflower (Carthamus tinctorius)، a factorial experiment was carried out in randomized complete design (CRD) with three replications in the greenhouse and laboratory، College of Agriculture، Shiraz University، Shiraz، Iran in 2012-13. Treatments included irrigation [Normal (I1) and water stress (I2)] and nitrogen [control (no nitrogen)، Urea (200 kg N ha-1)، Nitroxin (Azotobacter) and Nitrokara (Azospirillum and Azotobacter) inoculation per kg seeds]. Extracts were prepared from sorghum shoot resiude in 5، 10، 15 and 20 (W/V) and were applied to individual Petri dishes; distilled water was used as control treatment. Also، foliar applications of extracts were applied in treatments under the greenhouse conditions and sorghum dried residues were also mixed with the soil in amounts of 0، 5، 10، 15، and 20 g after the first irrigation. Analysis of variance showed that interaction effects of sorghum extract type and its concentration had significant effects on all traits except relative water content. Safflower germination percentage reduced with increase in concentration. 5، 10 and 15% concentrations of Nitrokara under normal irrigation had 34، 22 and 12%، effects on allelopathy index of safflower respectively. Whereas concentration of 20% extract، decreased allelopathy index by 71%. The effects antagonist on length and dry weights of roots and shoots was observed when biofertilizer treatments (Nitroxin and Nitrokara) applied. In addition، more synergist effects were obtained when urea extract was appliedt under water stress. The results of foliar application revealed a decrease in CAT and POD activities in leaves of safflower when urea was usedunder water stress conditions. However، the lowest germination rate and primary growth of safflower was abserved when urea applied under water stress conditions.