Effects of integrated application of phosphorus fertilizer and sewage sludge on leaf chlorophyll index and some growth characteristics of sunflower under water deficit conditions

Water deficit is one of the most important factors limiting crops production in the world and Iran. To increase the tolerance of plants to water deficit and reducing the consumption of chemical fertilizers, integrated application of organic and chemical fertilizers is recommended. Several studies have been done about the effects of phosphorus and sewage sludge on yield and quality of different crops at the world, but a report has not yet been presented about the effect of integrated application of phosphorus and sewage sludge on the growth of sunflower and determination of optimal amount of fertilizer under optimum and limited irrigation conditions. Therefore, the present study was conducted for evaluating the effect of triple superphosphate (TSP) and sewage sludge (SS) on leaf chlorophyll index (LCI) and some growth characteristics of oil sunflower under optimum and limited irrigation conditions in a clay loam soil.
The study was carried out as a split-factorial experiment based on randomized complete blocks design for two years in Agricultural Research Station of Khoy under farm conditions. Experimental factors were included year at two levels (2014 and 2015), irrigation time at two levels (irrigation after 60 and 150 mm evaporation from pan class A), SS at four levels (0, 14.2, 28.4 and 56.7 t/ha) and TSP at three levels (0, 100, 200 kg/ha). Statistical analysis of the data using MSTATC software and means comparison were performed by the Duncan test at 5% probability level.
According to the combined analysis of variances, the effect of year was significant only for plant height, BY and LAI. Water deficit decreased LCI, LAI, BY, plant height and stem diameter but application of TSP and SS increased all studied characteristics significantly compared to the control. In both optimum and limited irrigation conditions, the highest LCI, LAI, BY, plant height and stem diameter were obtained from integrated treatments which increased 40, 141, 75, 26 and 47 percent at optimum irrigation conditions and 51, 95, 114, 36 and 60 percent at limited irrigation conditions respectively compared to the control treatments.
In order to reducing the consumption of chemical fertilizers and achieving the optimum growth of sunflower, application of 200 kg TSP 56.7 tons SS under optimum and 100 kg TSP 56.7 ton of SS per hectare under limited irrigation is recommended at similar conditions.