The effect of foliar application of humic acid on some agromorphological traits and photosynthetic pigments of Niger under drought stress

In order to investigate the effect of humic acid foliar application on drought stress effects of Niger (Guizotia abyssinica (L.F) Cass), a split plot experiment was done in a randomized complete block design with three replications at the research farm of the faculty of agriculture/Shahrekord University in 2016. The main factor consisted of four drought stress levels (60 (control), 100, 140 and 180 mm evaporation from evaporation pan) and the sub factor was including four humic acid levels (0, 2, 4 and 6 liters per hectare). The results showed that the effect of drought stress and humic acid was significant on plant height, number of lateral branches, number of head per unit area, 1000 grain weight, grain yield, biological yield, harvest index, chlorophyll, carotenoids and proline (at 1% level of probability). Drought stress caused decreasing and humic acid caused increasing in all traits except of proline. The interaction effect of drought stress and humic acid on number of head per unit area, grain yield, harvest index, proline (at 1% level of probability) and on plant height (at 5% level of probability) was significant.The maximum plant height, number of heads per unit area, grain yield and harvest index were obtained at control with six liters humic acid application per hectare, and the maximum amount of proline was observed at the treatment of 180 mm evaporation with no humic acid application. It is recommended to use 100 mm evaporation regime with 4 liters humic acid application per hectare for more economic profit.