Investigation of nitrogen, phosphor and potassium effects on yield and the population change of the mustard aphid (Lipaphis erysimi) in rape seed.

According of the importance of oil production from interior resources, the area allocated to planting canola has remarkably increased in Khuzestan province these recent years. As a result, the population of many pests such as aphids have considerably risen. The major specie of the aphids in canola fields of this province, is Lipaphis erysimi Kalt. Although, farmers tend to control it chemically, but there are many limitation of using chemical pesticides because of environmental problems, poison residual and pest resistance that they could cause. Therefore, in order to find out approaches to reduce population of this pest by using some fertilizers, an experiment was carried out in split split plot design with 3 main plot of phosphor (0,100 and 150 kg/ha super phosphate triple), 3 sub plot (0,150 and 300 kg/ha potassium sulfate) and 3 sub sub plot (0,180 and 240 kg/ha nitrate) and 4 replications in Behbahan Agricultural Research Station in 2007-2010. The measured parameters were included: The number of mustard aphid, infected stem height, percentage of infected plants, infection index and percentage of oil, nitrogen, phosphor, potassium in seed. The results showed that in first year the maximum grain yield (2834 kg/ha) has obtained under fertilizer treatment contained 150 kg of phosphor, none use of potassium, and 240 kg of nitrogen. In the second year the maximum average infection index (373) occurred under fertilizer treatment comprised of 100 kg phosphor, 150 kg potassium and none use of nitrogen, and the minimum amount of this figure (113) was obtained under condition of using 100 kg phosphor, 100 kg potassium and 180 kg nitrogen. In this case if the amount of nitrogen changed to 240 kg this index slightly raised and changed to 115. In third year the maximum grain yield (2637 kg/ha) obtained when there were used 100 kg phosphor, 300 kg potassium and 240 kg nitrogen. Thus, fertilizer formula comprised of 100 kg phosphor, 100 kg potassium and 180 kg of nitrogen recommended. Key words: Canola, Phosphor, Potassium, Nitrogen and mustard aphid